Research ArticleDenaturation Kinetics of Whey Protein Isolate Solutions andFouling Mass Distribution in a Plate Heat Exchanger

Marwa Khaldi123 Gilles Ronse12 Christophe Andreacute124

Pascal Blanpain-Avet12 Laurent Bouvier12 Thierry Six12 Saloua Bornaz5

Thomas Croguennec6 Romain Jeantet6 and Guillaume Delaplace12

1 INRA UR638 Processus aux Interfaces et Hygiene des Materiaux (PIHM) BP 20039 369 rue Jules Guesde59651 Villeneuve drsquoAscq France2Unite de Materiaux et Transformations (UMET) UMR CNRS 8207 Universite de Lille 1 59650 Villeneuve drsquoAscq France3Institut National Agronomique de Tunisie 43 avenue Charles Nicolle 1082 Tunis Mahrajene Tunisia4HEI Laboratoire de Genie des Procedes 59046 Lille France5Ecole Superieure des Industries Alimentaires de Tunis 58 avenue Alain Savary 1003 Tunis El Khadra Tunisia6INRA AGROCAMPUS OUEST UMR 1253 35042 Rennes France

Correspondence should be addressed to Marwa Khaldi marwakhaldililleinrafr

Received 23 July 2015 Revised 9 October 2015 Accepted 11 October 2015

Academic Editor Xijun Hu

Copyright copy 2015 Marwa Khaldi et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Few investigations have attempted to connect the mechanism of dairy fouling to the chemical reaction of denaturation (unfoldingand aggregation) occurring in the bulk The objective of this study is to contribute to this aspect in order to propose innovativecontrols to limit fouling deposit formation Experimental investigations have been carried out to observe the relationship betweenthe deposit mass distribution generated in plate heat exchangers (PHE) by a whey protein isolate (WPI) mainly composed of 120573-lactoglobulin (120573-Lg) and the ratio between the unfolding and aggregation rate constants Experiments using a PHE were carriedout at a pilot scale to identify the deposit distribution of a model fouling solution with different calcium contents In parallellaboratory experiments were performed to determine the unfoldingaggregation rate constants Data analysis showed that (i) 120573-Lgdenaturation is highly dependent on the calcium content (ii) for each fouling solution irrespective of the imposed temperatureprofile the deposit mass in each channel and the ratio between the unfolding and aggregation rate constants seem to be wellcorrelated This study demonstrates that both the knowledge of the thermal profile and the 120573-Lg denaturation rate constants arerequired in order to predict accurately the deposit distribution along the PHE

1 Introduction

In the dairy industry heat treatments are carried out in orderto ensure food security and to impart several functionalitiesto milk and its derivatives like thermal stability viscosity orgelation [1ndash3]

Fouling deposit formation on heat exchanger surfacesis a major industrial problem of milk processing plantswhich involves frequent cleaning of the installations therebyresulting in excessive rinsing water and harsh chemicals useA number of studies have reported the drastic economic costsof fouling Fouling and the resulting cleaning of the process

equipment account for about 80 of the total productioncosts [4] According to Tay and Yang [5] the total heatexchanger fouling costs for highly industrialized countries areabout 025 of the Gross National Product In the USA totalfouling costs have been estimated as US $ 7 billion [6]

Milk fouling deposit is complex in nature Deposit isformed by a mixture of inorganic salts (mainly calcium) andproteins (largely whey proteins) The key role played by 120573-Lghas been recognized in most milk fouling studies [7ndash9]

The fouling mechanisms are complicated and involvechemical reactions and heat and mass transfer processes[7ndash10] The deposition is a result of a number of stages

Hindawi Publishing CorporationInternational Journal of Chemical EngineeringVolume 2015 Article ID 139638 10 pageshttpdxdoiorg1011552015139638

2 International Journal of Chemical Engineering

occurring at both the bulk volume and the surface [11] asfollows

(i) unfolding and aggregation of proteins in the bulk(ii) transport of the unfolded and aggregated proteins to

the surface(iii) surface reactions resulting in incorporation of protein

into the deposit layer(iv) possible reentrainment or removal of deposit toward

the bulk

At the state of the art the possible limiting processescontrolling fouling phenomena (bulk reaction regardingthe temperature profiles surface reaction concerning theflow conditions and mass transfer of the different proteinspecies occurring in the bulk) are not clearly elucidated andambiguity on foulant precursor (unfolded andor aggregatedspecies) also exists

Belmar-Beiny et al [11] and Schreier and Fryer [12]proposed that fouling was dependent on the bulk and surfacereactions and not on the mass transfer Belmar-Beiny et al[11] using a tubular heat exchanger fouled with whey proteinconcentrate correlated the mass deposit with the volumeof fluid hot enough to produce unfolded and aggregatedproteins This result highlighted the importance of denatu-ration reactions in the bulk but does not allow concludingspecifically which protein species are dominant on foulingOn the other hand van Asselt et al [13] stated that 120573-Lgaggregates are not involved in the fouling reactions

So there is still a lack of knowledge between the chemicalreactions occurring in the bulk (unfolding and aggregation of120573-Lg for a given temperature profile) their consequences onfoulant precursor concentrations and the extent of fouling

In this study we propose to partially fill this gap byinvestigating the chemical reactions of 120573-Lg denaturationoccurring in the bulk for two WPI model fouling solutionsand their link with the fouling phenomena

The main objective of this work is to investigate whethera relationship can be established between the distribution ofthe dry fouling deposit mass in each PHE channel and the120573-Lg rate constants (computed at the mean channel temper-ature) of the model fouling solutions for various operatingconditions (processing parameters inducing various thermalprofiles)

2 Materials and Methods

21 Fouling Model Fluids Themodel fluids used in this studywere reconstituted from WPI Promilk 852FB1 supplied byIngredia (France) The composition of the powder is shownin Table 1

In each experiment 1 (ww) 120573-Lg solutions withvarious calcium concentrations were prepared by mixing10 g of WPI powder in 1 L reverse osmosis water at roomtemperature Then different quantities of a molar calciumchloride (anhydrous 96 Acros Organics Thermo FisherScientific Waltham MA USA) solution were added to the120573-Lg solution to obtain the two model fouling solutions

Table 1 Composition of WPI powder

Component Promilk 852FB1( ww)

Total proteins 801120573-Lg 660120572-lactalbuminFatLactose

133111

Minerals 29

containing respectively (i) 1 (ww) 120573-Lg and 100 ppm oftotal calcium and (ii) 1 (ww) 120573-Lg and 120 ppm of totalcalcium The pH of these fouling solutions was close to 68

Only a small range of calcium content was studiedbecause it is admitted that a very slight chemical variationresults in a large variation in the fouling formation [1415] The calcium concentration of the two model solutionswas determined by atomic absorption spectrometry with aSpectro AA 55B apparatus (Varian Palo Alto CA USA)

22 Thermal Denaturation Experiments at Constant HoldingTemperature All thermal denaturation experiments wereconducted on twelve samples of 2mL that were put instainless steel tubes (350mm length 10mm core diameter1mm wall thickness and 03 120583m surface roughness) to becloser to the actual conditions on the PHE The investigatedtemperatures was ranged from 65 to 92∘C

Before submitting samples to the desired holding tem-perature the samples were preheated at 60∘C for the rangeof desired temperatures below 80∘C and 65∘C for the rangeof desired temperatures over 80∘C in a first water bath Thechoice of this water bath temperature is not trivial The 120573-Lgdenaturation temperature is estimated at about 77∘C [16 17]

The temperature increase from the preheating tempera-ture to the desired holding temperature was performed byplacing the samples in a second water bath whose temper-ature was maintained until 20∘C higher than the holdingtemperature The second water bath was used in order toreduce the heat increase time and the denaturation levelbefore samplingThefirst sample corresponding to time zerowas taken when the sample temperature was equal to thedesired holding value

The eleven other samples were maintained during a timesufficient in a thirdwater bath taken off at different times andcooled down immediately in a beaker withmelting ice to stopfurther120573-Lg denaturationThe third water bath was fixed 2∘Chigher than the desired temperature From the second to thethird water bath the heating rate is ranged between 083 and093∘Csdotsminus1

The temperature profile in samples placed in the threewater baths was determined using a sensor connected to atemperature measurement acquisition system placed in astainless steel tube filled with water (Figure 1)

23 HPLC Analysis The soluble (native and unfolded) 120573-Lg concentration in the samples was evaluated by HPLC

International Journal of Chemical Engineering 3

0

10

20

30

40

50

60

70

80

90

7 9 11 13 15 17Time (min)

Water bath 1

Water bath2

Water bath3

Sampling

Tem

pera

ture

(∘C)

Figure 1 Imposed temperature profiles (in the three water baths) tocarry out thermal denaturation at a constant holding temperature

after precipitation of the aggregated protein at pH 46 andtheir removal by centrifugation (9000 rpm for 30min at4∘C) The chromatographic system (Waters Milford MAUSA) included a 717 Plus autosampler a 616 quadratic pumpsystem a JonesModel 7971 column oven a CLHPACE 300 AC4 separation column and the associated guard column(Advanced Chromatography Technologies Aberdeen UK)a 486 UV-visible spectrophotometer and an acquisitionsoftware (Millennium 32 Waters)

The mobile phases used in HPLC were 01 (vv)trifluoroacetic acid (99 Acros Organics Thermo FisherScientific Waltham MA USA) in Milli-Q water and 01trifluoroacetic acid in a mixture of 80 acetonitrile (HPLCgrade Thermo Fisher Scientific Waltham MA USA) and20Milli-Q water

The HPLC analyses were carried out at the followingconditions flow rate 1mLsdotminminus1 injection volume 20120583Ltemperature 40∘C elution of the proteins using a gradi-ent of acetonitrile and detection of the eluted proteins atwavelength 214 nm Analyses were repeated three times foreach standard or sample Calibration standards in the rangefrom 05 to 4 gsdotLminus1 were prepared by dissolving 120573-Lg powderin Milli-Q water For each experiment the sample concen-trations were calculated by averaging the three measuredchromatographic areas and converting this area value into a120573-Lg concentration using the HPLC calibration curve

24 Determination of the 120573-Lg Rate Constants from HPLCMeasurements The reaction model used in this study isderived from the work of Tolkach and Kulozik [18] Thedenaturation reaction concerns the transformation of solublespecies (noted 119878) into aggregates (noted119860) which is describedby the chemical equation 119878 rarr 119860 and defined in

minus119889119862119878

119889119905= 119896119899119862119899119878

(1)

where 119862119878is the soluble 120573-Lg concentration 119896

119899the denatura-

tion rate constant for a reaction order equal to 119899 and 119905 thetime

ValveTemperature probe

Pump Flowmeter

Pressure drop

Agitated tank

Heating zone

Waste

Preheating zone

F

ΔP

ΔP

FF

F

Figure 2 Schematic diagram of the experimental setup carried outfor fouling runs with the 1 (ww) WPI solutions

For each temperature the corresponding denaturationrate constant was determined from the Arrhenius plot Therelation between the denaturation kinetic rate and the heattreatment temperature is given by

ln (119896119899) = ln (1198960

119899

) minus119864119860

119877119879 (2)

where 1198960119899

is the denaturation frequency factor 119864119860the denat-

uration activation energy 119877 the universal gas constant and 119879the temperature

The value of 119899 was varied from 1 to 2 (in steps of 01) todetermine the reaction order that gives the best regressioncoefficient when plotting (119862

1198781198620119878

)1minus119899 minus 1 as a function oftime where 1198620

119878

is the initial (time zero) 120573-Lg total solubleconcentration

The slope of this linear representation is equal to 119896119899(119899 minus

1)(1198620119878

)119899minus1 and leads to the determination of 119896119899 This method

was also used by Petit et al [14] Tolkach andKulozik [18] andDannenberg and Kessler [19]

The value of 119899 = 15 reaction order was suitable forthe whole 120573-Lg denaturation reaction in the investigatedtemperature range (from 65 to 92∘C)

25 Fouling Runs and Determination of the Deposit MassDistribution Fouling experiments were carried out in a pilotplant (Figure 2)The fouling rig was composed of two distinctzones (i) a preheating zone composed of a heat exchangerwith V7 types plates (Vicarb Alfa Laval France) and 9 passes(one channel per pass) necessary to preheat the model fluidand (ii) a heating zone composed of a PHE (Vicarb modelV7 Alfa Laval France)

4 International Journal of Chemical Engineering

Table 2 Operating conditions investigated with the pilot scale experimental set mean inlet and outlet temperatures and flow rates of 120573-Lgconcentrate and hot water

Thermal profile number Total calcium content (ppm) 119879119894119901

(∘C) 119879119900119901

(∘C) 119876119901

(Lsdothminus1) 119876ℎ

(Lsdothminus1)1 100 65 85 300 3002 100 65 85 300 9003 100 65 85 300 1504 100 60 75 300 3001 120 65 85 300 3002 120 65 85 300 9003 120 65 85 300 1504 120 60 75 300 300

P10

Fouling product inlet

Foulingproduct outlet

Hot water inlet Hot water outlet

Ci channel numberPi plate number

P1

C1 C2 C3 C4 C5

Figure 3 Plate heat exchanger flow arrangement

The PHE setup consisted of 10 plates that is 5 passes(one channel per pass) of about 0074m2 projected heattransfer area per plate (0495m length and 015m width)were installed in a countercurrent configuration to optimizethe heat transfer as represented in Figure 3 The defineddesign permitted being closer to industrial heat treatmentconditions

The temperature profile inside the heat exchanger wassimulated with Sphere software (previously developed atour laboratory) temperatures in all passes of hot andcold fluids were calculated from the knowledge of fluidsrsquoinlet temperature and flow rate plate properties and heatexchanger designThe temperature profile is controlled by theheat exchanger inlet parameters product and hot fluid inlettemperatures (119879

119894119901and 119879

119894119908) and product and hot water flow

rates (resp119876119901and119876

ℎ)This was achieved with the operating

conditions indicated in Table 2 displaying the average valuesof temperatures and flow rates recorded during each heattreatment experiment

The temperature profiles displayed in Figure 4 wereobtained by Sphere simulations by employing the operatingconditions summarized in Table 2 Eight fouling runs wereconducted with WPI solutions containing two calcium con-centrations (100 and 120 ppm)

Heat exchanger plates were weighted before each heattreatment experiment After being dried in an air oven at

60

65

70

75

80

85

0 5 10 15Time (s)

12

34

Tem

pera

ture

(∘C)

Figure 4 The imposed thermal profiles in the PHE (Spheresimulations)

50∘C fouled plates were weighted at ambient temperatureand the dry deposit mass on each plate was deduced bysubtraction

The amount of fouling was also monitored by calculat-ing the fouling resistance A linear relationship was visiblebetween the average fouling resistance119877

119891 defined by (3) and

the fouling thickness assuming that the deposit layers arecovered uniformly

1

119880119892(119905)

=1

119880119892(0)

+ 119877119891 (3)

where 119880119892(0)

and 119880119892(119905)

are the overall heat transfer coefficientsat the beginning of fouling runs (ie the overall heat transfercoefficient before the occurrence of fouling) and at time 119905 (iethe overall heat transfer coefficient including the additionalcontribution of fouling)

A logarithmic mean temperature difference (LMTD)method was used to relate the heat transfer rate to theoverall heat transfer coefficient In the case of a no pure

International Journal of Chemical Engineering 5

minus12

minus10

minus8

minus6

minus4

minus2

0

Aggregation limited temperature area

Critical point

Unfolding limited temperature area

300E

minus03

295Eminus03

290E

minus03

285Eminus03

280Eminus03

275Eminus03

270E

minus03

1T (Kminus1)

ln(k

n) sim80 ∘C

Ca 100ppmCa 120ppmPetit et al (2011)

Figure 5 Arrhenius plot for the 120573-Lg denaturation of 1 (ww)WPI fouling solutions at various calcium concentrations (100 and120 ppm)

cross countercurrent flow inside the plate heat exchanger thecorrection factor 119865

119879is classically introduced

119901119862119901119901

(119879119900119901

minus 119879119894119901

) = ℎ119862119901ℎ

(119879119894ℎ

minus 119879119900ℎ

)

= 119880119892119878Δ119879LMTD119865

119879

(4)

where 119862119901119901

and 119862119901ℎ

are respectively the specific heat for theproduct and hot water

119901and

ℎare respectively the mass

flow rates for the product and hot water119879 is the temperatureand 119878 is the heat transfer area

Leuliet et al [20] gave equations for PHE using analogywith shell and tube correction factor Their method was usedfor this work to evaluate the 119865

119879factor

3 Results and Discussion

31 Arrhenius Plots for the 120573-Lg Denaturation of the ModelSolutions The Arrhenius plots for the denaturation reactionof the WPI model fouling solutions at two calcium con-centrations (100 and 120 ppm) were presented in Figure 5This figure shows the temperature influence on the 120573-Lgdenaturation kinetic rate in the range from 65 to 92∘C

Two mechanisms appear in Figure 5 separated by anArrhenius critical temperature of about 80∘C This slopechange suggests two temperature ranges below the criticaltemperature the 120573-Lg denaturation reaction is unfoldinglimited which means that the unfolding reaction is slowerthan aggregation and over 80∘C 120573-Lg denaturation is limitedby the aggregation reaction and in that case aggregation isthe slower reaction

Table 3 Denaturation parameters at the two calcium concentra-tions

Denaturationparameter 100 ppm total calcium 120 ppm total calcium

Unfoldingln(1198960unf) 1248 1172119864119860unf (kJsdotmolminus1) 3845 2712

Aggregationln(1198960agg) 863 831119864119860agg (kJsdotmolminus1) 3607 2604

These results are in agreement with Petit et al [14] Evenin the case of quasi-pure 120573-Lg model solution the criticaltemperature that splits the Arrhenius plot in two linearparts was estimated at 80∘C each temperature range beingrelated to the predominance of the unfolding or aggregationmechanisms indicating that denaturation kinetic rates variedwith temperature However this slope break is less clear in thecase of our model fouling solution probably due to its morecomplex composition (mixture of 120573-Lg and 120572-lactalbumin)

Figure 5 also shows that 120573-Lg denaturation kineticsincreased with calcium concentration Even if the exactcontribution of calcium on the denaturation of 120573-Lg is stillunclear it is speculated that calcium induces protein chargeshielding or conformational changes in 120573-Lg structure [2122] favouring both unfolding and aggregation reactionsThis result illustrates that it is essential to know the exactcontent of calcium in the fouling solutions to have a clearview of the denaturation reaction This information notcommonly evaluated nowadays in the literature is essentialto the development of accurate model of fouling based onengineering denaturation reaction

The frequency factor logarithms (ln 1198960) and activationenergies (119864

119860) obtained by fitting Arrhenius plot regression

for the unfolding and aggregation denaturation mechanism(noted resp unf and agg) are shown in Table 3

32 Fouling Mass Distribution in the PHE Figure 6 repre-sents the deposit layer formed in the first and last channelsof the PHE at respectively 65∘C (inlet temperature) and85∘C (outlet temperature) after fouling run conducted with1 (ww) WPI solution containing 100 ppm of total calciumAt the highest temperature the fouling layer is white verythick and homogeneous It clearly appears that very lowfouling is obtained in the first channel of the PHE where thebulk temperature is lower than 70∘C Fouling is not expectedto occur under 65ndash72∘C [23 24] These observations are inagreement with Foster et al [25] work which showed thatdeposit increases with temperature making fouling rougherand more adherent to hot surfaces

Figure 7 represents the fouling results obtained with 1(ww) WPI model solution containing 100 and 120 ppm oftotal calcium at different temperature profiles This figureshows that the dry deposit is not uniform and is distributeddifferently depending on the thermal profile and the calcium

6 International Journal of Chemical Engineering

Figure 6 Pictures of the deposit collected on heat exchanger surfacein the second and last channels of the PHE

concentration Indeed for the first solution at 100 ppm cal-cium the depositmass increases linearly to reach amaximumin the 5th channel whatever the imposed thermal profileHowever at 120 ppm calcium the deposit mass reached astationary value of about 260 gm2 over 74∘C (2nd channeltemperature) for the first three temperature profiles whichconsisted in a foulingmaximum limitThis increasing depositmass at low temperatures resulted from the strong increase of120573-Lg denaturation level between 65∘C (1st channel tempera-ture) and 74∘C (2nd channel temperature) temperature rangefor which the120573-Lg denaturation reaction becomes significant[17 26] The thermal profile 4 increases linearly reaching amaximum of 845 gm2 in the 5th channel

The deposit mass is negligible for the thermal profile 4at 100 and 120 ppm calcium owing to the lack of denatured120573-Lg in the bulk at such low temperatures It is suggested that120573-Lg fouled hot surfaces only when the bulk temperature washigh enough to allow 120573-Lg denaturation

Figure 8 represents the effect of the temperature profileon the total amount of deposit mass in the PHE for thetwo fouling solutions It can be observed that for the sameinlet and outlet product temperature the total deposit massvaried with the calcium concentration This is the case ofthe thermal profile 1 for which the total deposit mass goesfrom 1415 gm2 at 100 ppm calcium to 2082 gm2 at 120 ppmcalcium This was also observed for the temperature profiles3 and 4 However for the thermal profile 2 the totalamount of deposit was very close at 100 and 120 ppm calcium

This difference of fouling distributions obtained at vari-ous calcium concentrations demonstrates the major role ofthe temperature profile on 120573-Lg fouling and its distributionin the PHE

33 Effect of Thermal Profiles and Calcium Concentrationon Fouling Rate Figure 9 shows the fouling rate behaviourduring heating of the WPI solution at 100 and 120 ppmcalcium in the PHE for each thermal profile An increase inthe fouling rate with time is evident A difference between

the fouling rates can be observed for the four temperatureprofiles at 100 ppm and 120 ppm calcium

The results also show that the fouling potential of WPI inthe PHE increases with the increasing temperature Indeedfor temperature range of 65ndash85∘C fouling rate is alteredand favoured by higher amount of calcium in the modelfluid It can be noted that for the thermal profile 4 (60ndash75∘C) fouling resistance curves for calcium content of 100and 120 ppm calcium were superposed These results are notcontradictorywith the assumption ofDaufin et al [27] Xiong[28] and Simons et al [21] who asserted that calcium caninteract with the aspartic and glutamic acid carboxyl groupof the 120573-Lg and so favour the growth of the deposit bystabilizing protein aggregates This is because calcium ionsform bridges between adsorbed proteins and the proteinaggregates occurring in the bulk consequentlymodifying theprotein aggregation rate and leading to a greater cohesionbetween the protein aggregates which in turn change thedeposit structure [29] Simmons et al [30] revealed anincrease in deposition upon a Couette surface due to calciumions and a modification in the appearance of the depositfor a temperature range 75ndash90∘C In addition Pappas andRothwell [31] showed that 120573-Lg completely aggregated toform compact structures when heated with calcium from 80to 110∘C

34 Relationship between 120573-Lg Heat Denaturation Rate Con-stants and the Distribution of the Deposit Mass along the PHETo study the relationship between the chemical reaction of the120573-Lg denaturation and the deposit formation rate within thePHE the deposit mass distribution in the different channelof the PHE was plotted against 119903 = 119896unf119896agg (Figure 10) Thevalue of 119903 was calculated at the average temperature of thechannel 119896unf and 119896agg represent respectively the reaction rateconstants for the unfolding and aggregation limited zonesdeduced from the Arrhenius plots (Figure 5) for the twoWPImodel fouling solutions (at 100 and 120 ppm of calcium)

For each fouling solution it could be observed that an119878 curve (plot of the deposit mass per channel versus 119903)consolidates the fouling data whatever the imposed thermalprofile The 119878 curves could be described for all fouling runsby the following function

119872119889

= 119886 +119887 minus 119886

1 + (119888119903)119889 (5)

where 119872119889is the measured dry fouling deposit mass per

channel along the PHE and 119886 119887 119888 and 119889 are four constantsThe twomaster curves representing the deposit mass per

channel versus the ratio 119903 contained different characteristiczones

(i) an unfolding limited zone with a sharp increase of thedeposit mass per channel with 119903

(ii) an aggregation limited zone where the deposit massper channel seems to reach a limiting value

Indeed the curve of the dry deposit mass at 100 ppm calciumshowed a sharp increase at values of 119903 close to 022 (relative

International Journal of Chemical Engineering 7

0

50

100

150

200

250

300

350

1 2 3 4 5Channel number

Dep

osit

mas

s per

chan

nel (

gm

2 )

1 23 4

(a)

0

50

100

150

200

250

300

350

1 2 3 4 5Channel number

Dep

osit

mas

s per

chan

nel (

gm

2 )

1 23 4

(b)

Figure 7 Fouling mass distribution related to the projected heat transfer area per plaque in each channel of the PHE for the two foulingsolutions 1 (ww) WPI solution containing (a) 100 ppm calcium and (b) 120 ppm calcium (119894 corresponds to the thermal profile numbergiven in Figure 4 and Table 2)

0

500

1000

1500

2000

2500

3

4

1

1 2 2

3

4Tota

l dep

osit

mas

s (g

m2)

Ca 100ppmCa 120ppm

Figure 8 Total amount of the deposit mass in the PHE perunit area for 1 (ww) WPI fouling solutions at various calciumconcentrations (100 and 120 ppm) and for different temperatureprofiles (119894 corresponds to the thermal profile number given inFigure 4 and Table 2)

to the fouling beginning) then reaching a plateau at 119903 = 091For the second fouling solution (WPI solution containing120 ppm of calcium) the increase of 119903 values starts at 023 andthe maximum of the deposit mass is reached at 119903 = 067

In summary for the two fouling model solutions andthe operating conditions investigated it can be observed thata sharp increase of deposit mass occurs when 119903 is locatedbetween 022 and 089 (corresponding to bulk temperaturesranging from 65 to 805∘C) The fact that the deposit massincreases strongly when 119903 is below 1 shows that the unfoldinglimited zone controls the growth of the deposit mass Thisresult also shows that the deposit mass per channel decreases

0

50

100

150

200

250

300

0 05 1 15 2Time (h)

1234

1234

Foul

ing

resis

tanc

eRflowast100000

(m2 middot∘ C

W)

Figure 9 Fouling resistance evolution with time measured alongthe PHE Various symbols refer to various fouling runs with varyingthermal profiles and various calcium content for the 1 ww WPIsolutions (closed symbols 100 ppm calcium open symbols 120 ppmcalcium) (119894 corresponds to the thermal profile number given inFigure 4 and Table 2)

when the aggregation reaction is high enough to consumethe unfolded species under aggregates forms This result isin agreement with the previous observation of van Asseltet al [13] and consistent with the work of Blanpain-Avetet al [32] Indeed these authors conclude from fouled deposit

8 International Journal of Chemical Engineering

0

100

200

300

400

500

600

700

800

0 02 04 06 08 1 12 14

1 23 41 23 4

Aggregationlimited zone

Clog

ging

of t

he

inst

allat

ion

Unfolding limited zone

Dep

osit

mas

s per

chan

nel (

gm

2)

r = kunfkagg

Fitting model Ca 120ppmFitting model Ca 100ppm

Figure 10 Plots of the dry deposit masses per unit area versus theratio of unfolding and aggregation rate constants for the 1 wwWPI solutions (closed symbols 100 ppm calcium open symbols120 ppm calcium) (119894 corresponds to the thermal profile numbergiven in Figure 4 and Table 2)

analysis by Raman spectroscopy that protein aggregates arenot present in the deposit This result is also supportedby the recent study of Bouvier et al [33] which showedthat a correlation can be established between the unfolded120573-Lg content within the PHE and the dry deposit massdistribution

Unfortunately it was not possible to perform pilot scaleexperiments at higher values of 119903 (119903 gt 140) correspondingto the channel temperature above 844∘C because of theclogging of the installation

To ascertain validity of themaster curve independently ofthe PHE configuration further experiments were conductedat PHE consisting of 10 passes (one channel per pass) for a 1(ww) WPI model solution at 100 ppm calcium One thermalprofile (1) out of the four tested for the five channels of thePHE was imposed Figure 11 represents the deposit mass perchannel versus the ratio 119903

Also in this case the fouling mass is reasonably wellcorrelated to the ratio 119903 showing the following

(i) the importance of determining this indicator forpredicting fouling mass distribution

(ii) the robustness of the approach

4 Conclusions

Fouling experiments were performed with 1 (ww) WPIsolutions at two different calcium concentrations in order toinvestigate the effect of the operating conditions associatedwith the chemical denaturation reactivity of heat treatmentin a PHE on the deposit formation The extent of fouling

0

100

200

300

400

500

600

700

0 05 1 15

1Fitting model 10-pass PHE configuration

Dep

osit

mas

s per

chan

nel (

gm

2)

r = kunfkagg

Aggregationlimited zone limited zone

Unfolding

Figure 11 Variation of the dry deposit mass per unit area in thevarious channels with the ratio 119903 for a 10-pass PHE configuration (1corresponds to the thermal profile given in Figure 4 and Table 2)

deposit was monitored by weighing the mass of the dryfouling deposit on the plates

It was shown that

(i) 120573-Lg denaturation is a complex process with a two-step mechanism highly dependent on the calciumcontent

(ii) an increase of the calcium content in the foulingsolution induced a strong increase in the 120573-Lg denat-uration level and consequently in the fouling masswithin the PHE at high temperatures

(iii) the fouling mass distribution also depends on thethermal profiles imposed on the fouling solutions

(iv) the dry deposit mass on each pass of the PHE seemsto be correlated with 119903 = 119896unf119896agg This observationindicates that the knowledge of this parameter isimportant to predict the mass distribution of thefouling deposit

This work clearly shows that 120573-Lg competitive reactions(unfolding and aggregation) governing the growth of foulingfor a WPI solution and the identification of the heat-induceddenaturation kinetic by means of laboratory experiments areprerequisites to control fouling We encourage strongly thefouling community to develop database on these aspects tobe able to predict the distribution of fouling mass whateverthe imposed temperature profile and to mitigate fouling

International Journal of Chemical Engineering 9

Nomenclature

119886 Adjusted parameter in the nonlinear regressionusing (5)

119887 Adjusted parameter in the nonlinear regressionusing (5)

119888 Adjusted parameter in the nonlinear regressionusing (5)

Ca Calcium concentration ppm119862119878 Concentration of the total soluble 120573-Lg g Lminus1

119862119901119901 Specific heat for the product J kgminus1 Kminus1

119862119901ℎ Specific heat for the hot water J kgminus1 Kminus1

119889 Adjusted parameter in the nonlinear regressionusing (5)

119864119860 Activation energy Jmolminus1

119864119860agg 120573-Lg aggregation activation energy Jmolminus1

119864119860unf 120573-Lg unfolding activation energy Jmolminus1

119865119879 Logarithmic mean temperature difference -

119896119899 Denaturation rate constant g1minus119899 L119899minus1sminus1

1198960119899

Denaturation frequency factor g1minus119899 L119899minus1sminus1119896unf Unfolding rate constant g1minus119899 L119899minus1sminus1119896agg Aggregation rate constant g1minus119899 L119899minus1sminus1119872119889 Measured dry fouling deposit mass in a channel

along the PHE g119901 Mass flow rates for the product kg sminus1

ℎ Mass flow rates for the hot water kg sminus1

119899 Heat-induced denaturation reaction order119876119901 WPI fouling solution flow rate L hminus1

119876ℎ Hot water flow rate L hminus1

119903 Ratio between the unfolding and aggregation rateconstants -

119877 The universal gas constant equal to 8314Jmolminus1 Kminus1

119877119891 Fouling resistance m2∘ CWminus1

119878 Heat transfer area m2119879119894ℎ Hot water temperature at the PHE inlet K

119879119894119901 WPI fouling solution temperature at the PHE

inlet K119879119900ℎ Hot water temperature at the PHE outlet K

119879119900119901 Hot water temperature at the PHE outlet K

119880119892 Overall heat transfer coefficient Wmminus2 Kminus1

998779119879LMTD Logarithmic mean temperature difference K

Subscript

agg Aggregation119862119894 Channel number

ℎ Hot water119901 Product119875119894 Plate number

PHE Plate heat exchangerunf UnfoldingWPI Whey protein isolate120572-La 120572-lactalbumin120573-Lg 120573-lactoglobulin119894 Thermal profile number

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

Theauthors are indebted to the ScientificCommittee ofAgro-campus Ouest Rennes and HEI (Hautes Etudes drsquoIngenieurLille) for stimulating discussions and financial support for thePhD Thesis of the first author

References

[1] D M Mulvihill and M Donovan ldquoWhey proteins and theirthermal denaturationmdasha reviewrdquo Irish Journal of Food Scienceand Technology vol 11 no 1 pp 43ndash75 1987

[2] N Sava I Van der PlanckenWClaeys andMHendrickx ldquoThekinetics of heat-induced structural changes of 120573-lactoglobulinrdquoJournal of Dairy Science vol 88 no 5 pp 1646ndash1653 2005

[3] C Schmitt C Bovay M Rouvet S Shojaei-Rami and EKolodziejczyk ldquoWhey protein soluble aggregates from heatingwith NaCl physicochemical interfacial and foaming proper-tiesrdquo Langmuir vol 23 no 8 pp 4155ndash4166 2007

[4] B Bansal and X D Chen ldquoA critical review of milk fouling inheat exchangersrdquo Comprehensive Reviews in Food Science andFood Safety vol 5 no 2 pp 27ndash33 2006

[5] S N Tay and C Yang Assessment of the Hydro-Ball CondenserTube Cleaning System HydroBall Technics (SEA) Pte Singa-pore 2006

[6] HMMuller-SteinhagenHandbook of Heat Exchanger FoulingMitigation and Cleaning Technologies Publico PublicationsEssenGermany Institution ofChemical Engineers RugbyUK2000

[7] M Lalande and J P Tissier ldquoFouling of heat transfer surfacesrelated to 120573-lactoglobulin denaturation during heat processingof milkrdquo Biotechnology Progress vol 1 no 2 pp 131ndash139 1985

[8] P De Jong R Waalewijn and H J L J Van Der LindenldquoValidity of a kinetic fouling model for heat-treatment of wholemilkrdquo Le Lait vol 73 no 3 pp 293ndash302 1993

[9] S D Changani M T Belmar-Beiny and P J Fryer ldquoEngineer-ing and chemical factors associated with fouling and cleaning inmilk processingrdquo Experimental Thermal and Fluid Science vol14 no 4 pp 392ndash406 1997

[10] H Burton ldquoProperties of UHT-processed milkrdquo in Ultra-HighTemperature Processing of Milk and Milk Products pp 254ndash291Elsevier Applied Science Publishers 1988

[11] M T Belmar-Beiny S M Gotham W R Paterson P J Fryerand A M Pritchard ldquoThe effect of Reynolds number andfluid temperature in whey protein foulingrdquo Journal of FoodEngineering vol 19 no 2 pp 119ndash139 1993

[12] P J R Schreier and P J Fryer ldquoHeat exchanger fouling a modelstudy of the scaleup of laboratory datardquo Chemical EngineeringScience vol 50 no 8 pp 1311ndash1321 1995

[13] A J van Asselt M M M Vissers F Smit and P de Jong ldquoIn-line control of foulingrdquo in Proceedings of the Heat ExchangerFouling and CleaningmdashChallenges and Opportunities Engineer-ing Conferences International Irsee Germany June 2005

[14] J Petit A-LHerbig AMoreau andGDelaplace ldquoInfluence ofcalcium on 120573-lactoglobulin denaturation kinetics implications

10 International Journal of Chemical Engineering

in unfolding and aggregation mechanismsrdquo Journal of DairyScience vol 94 no 12 pp 5794ndash5810 2011

[15] M Khaldi P Blanpain-Avet R Guerin et al ldquoEffect of calciumcontent and flow regime on whey protein fouling and cleaningin a plate heat exchangerrdquo Journal of Food Engineering vol 147pp 68ndash78 2015

[16] B T Nielsen H Singh and J M Latham ldquoAggregation ofbovine 120573-lactoglobulins A and B on heating at 75∘Crdquo Interna-tional Dairy Journal vol 6 no 5 pp 519ndash527 1996

[17] H Lindmark-Mansson A Timgren G Alden and M Pauls-son ldquoTwo-dimensional gel electrophoresis of proteins andpeptides in bovinemilkrdquo International Dairy Journal vol 15 no2 pp 111ndash121 2005

[18] A Tolkach and U Kulozik ldquoReaction kinetic pathwayof reversible and irreversible thermal denaturation of 120573-lactoglobulinrdquo Dairy Science and Technology vol 87 no 4-5pp 301ndash315 2007

[19] F Dannenberg and H G Kessler ldquoReaction kinetics of thedenaturation of whey proteins in milkrdquo Journal of Food Sciencevol 53 no 1 pp 258ndash263 1988

[20] J C Leuliet J F Maingonnat and M Lalande ldquoThermalbehaviour of plate heat exchangers with Newtonian and non-Newtonian fluidsrdquo in Proceedings of the Congres Eurotherm 5 et1er Colloque TIFAN pp 1ndash15 Compiegne France 1988

[21] J-W F A Simons H A Kosters R W Visschers and H H Jde Jongh ldquoRole of calcium as trigger in thermal 120573-lactoglobulinaggregationrdquo Archives of Biochemistry and Biophysics vol 406no 2 pp 143ndash152 2002

[22] B T OrsquoKennedy and J S Mounsey ldquoThe dominating effect ofionic strength on the heat-induced denaturation and aggrega-tion of 120573-lactoglobulin in simulated milk ultrafiltraterdquo Interna-tional Dairy Journal vol 19 no 3 pp 123ndash128 2009

[23] M Lalande F Rene and J-P Tissier ldquoFouling and its control inheat exchangers in the dairy industryrdquo Biofouling vol 1 no 3pp 233ndash250 1989

[24] J Visser andT JM Jeurnink ldquoFouling of heat exchangers in thedairy industryrdquo ExperimentalThermal and Fluid Science vol 14no 4 pp 407ndash424 1997

[25] C L Foster M Britten and M L Green ldquoA model heat-exchange apparatus for the investigation of fouling of stainlesssteel surfaces by milk I Deposit formation at 100∘Crdquo Journal ofDairy Research vol 56 no 2 pp 201ndash209 1989

[26] P Havea H Singh and L K Creamer ldquoCharacterizationof heat-induced aggregates of 120573-lactoglobulin 120572-lactalbuminand bovine serum albumin in a whey protein concentrateenvironmentrdquo Journal of Dairy Research vol 68 no 3 pp 483ndash497 2001

[27] G Daufin J P Labbe A Quemerais et al ldquoFouling of a heatexchange surface by whey milk and model fluids an analyticalstudyrdquo Le Lait vol 67 no 3 pp 339ndash364 1987

[28] Y L Xiong ldquoInfluence of pH and ionic environment on thermalaggregation of whey proteinsrdquo Journal of Agricultural and FoodChemistry vol 40 no 3 Article ID 91-5-154 pp 380ndash384 1992

[29] T Phan-XuanDDurand TNicolai L Donato C Schmitt andL Bovetto ldquoTuning the structure of protein particles and gelswith calcium or sodium ionsrdquo Biomacromolecules vol 14 no 6pp 1980ndash1989 2013

[30] M J H Simmons P Jayaraman and P J Fryer ldquoThe effectof temperature and shear rate upon the aggregation of wheyprotein and its implications for milk foulingrdquo Journal of FoodEngineering vol 79 no 2 pp 517ndash528 2007

[31] C P Pappas and J Rothwell ldquoThe effects of heating alone or inthe presence of calcium or lactose on calcium binding to milkproteinsrdquo Food Chemistry vol 42 no 2 pp 183ndash201 1991

[32] P Blanpain-Avet A Hedoux Y Guinet et al ldquoAnalysis byRaman spectroscopy of the conformational structure of wheyproteins constituting fouling deposits during the processing ina heat exchangerrdquo Journal of Food Engineering vol 110 no 1 pp86ndash94 2012

[33] L Bouvier A Moreau G Ronse T Six J Petit and GDelaplace ldquoA CFD model as a tool to simulate 120573-lactoglobulinheat-induced denaturation and aggregation in a plate heatexchangerrdquo Journal of Food Engineering vol 136 pp 56ndash632014

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DistributedSensor Networks

International Journal of

2 International Journal of Chemical Engineering

occurring at both the bulk volume and the surface [11] asfollows

(i) unfolding and aggregation of proteins in the bulk(ii) transport of the unfolded and aggregated proteins to

the surface(iii) surface reactions resulting in incorporation of protein

into the deposit layer(iv) possible reentrainment or removal of deposit toward

the bulk

At the state of the art the possible limiting processescontrolling fouling phenomena (bulk reaction regardingthe temperature profiles surface reaction concerning theflow conditions and mass transfer of the different proteinspecies occurring in the bulk) are not clearly elucidated andambiguity on foulant precursor (unfolded andor aggregatedspecies) also exists

Belmar-Beiny et al [11] and Schreier and Fryer [12]proposed that fouling was dependent on the bulk and surfacereactions and not on the mass transfer Belmar-Beiny et al[11] using a tubular heat exchanger fouled with whey proteinconcentrate correlated the mass deposit with the volumeof fluid hot enough to produce unfolded and aggregatedproteins This result highlighted the importance of denatu-ration reactions in the bulk but does not allow concludingspecifically which protein species are dominant on foulingOn the other hand van Asselt et al [13] stated that 120573-Lgaggregates are not involved in the fouling reactions

So there is still a lack of knowledge between the chemicalreactions occurring in the bulk (unfolding and aggregation of120573-Lg for a given temperature profile) their consequences onfoulant precursor concentrations and the extent of fouling

In this study we propose to partially fill this gap byinvestigating the chemical reactions of 120573-Lg denaturationoccurring in the bulk for two WPI model fouling solutionsand their link with the fouling phenomena

The main objective of this work is to investigate whethera relationship can be established between the distribution ofthe dry fouling deposit mass in each PHE channel and the120573-Lg rate constants (computed at the mean channel temper-ature) of the model fouling solutions for various operatingconditions (processing parameters inducing various thermalprofiles)

2 Materials and Methods

21 Fouling Model Fluids Themodel fluids used in this studywere reconstituted from WPI Promilk 852FB1 supplied byIngredia (France) The composition of the powder is shownin Table 1

In each experiment 1 (ww) 120573-Lg solutions withvarious calcium concentrations were prepared by mixing10 g of WPI powder in 1 L reverse osmosis water at roomtemperature Then different quantities of a molar calciumchloride (anhydrous 96 Acros Organics Thermo FisherScientific Waltham MA USA) solution were added to the120573-Lg solution to obtain the two model fouling solutions

Table 1 Composition of WPI powder

Component Promilk 852FB1( ww)

Total proteins 801120573-Lg 660120572-lactalbuminFatLactose

133111

Minerals 29

containing respectively (i) 1 (ww) 120573-Lg and 100 ppm oftotal calcium and (ii) 1 (ww) 120573-Lg and 120 ppm of totalcalcium The pH of these fouling solutions was close to 68

Only a small range of calcium content was studiedbecause it is admitted that a very slight chemical variationresults in a large variation in the fouling formation [1415] The calcium concentration of the two model solutionswas determined by atomic absorption spectrometry with aSpectro AA 55B apparatus (Varian Palo Alto CA USA)

22 Thermal Denaturation Experiments at Constant HoldingTemperature All thermal denaturation experiments wereconducted on twelve samples of 2mL that were put instainless steel tubes (350mm length 10mm core diameter1mm wall thickness and 03 120583m surface roughness) to becloser to the actual conditions on the PHE The investigatedtemperatures was ranged from 65 to 92∘C

Before submitting samples to the desired holding tem-perature the samples were preheated at 60∘C for the rangeof desired temperatures below 80∘C and 65∘C for the rangeof desired temperatures over 80∘C in a first water bath Thechoice of this water bath temperature is not trivial The 120573-Lgdenaturation temperature is estimated at about 77∘C [16 17]

The temperature increase from the preheating tempera-ture to the desired holding temperature was performed byplacing the samples in a second water bath whose temper-ature was maintained until 20∘C higher than the holdingtemperature The second water bath was used in order toreduce the heat increase time and the denaturation levelbefore samplingThefirst sample corresponding to time zerowas taken when the sample temperature was equal to thedesired holding value

The eleven other samples were maintained during a timesufficient in a thirdwater bath taken off at different times andcooled down immediately in a beaker withmelting ice to stopfurther120573-Lg denaturationThe third water bath was fixed 2∘Chigher than the desired temperature From the second to thethird water bath the heating rate is ranged between 083 and093∘Csdotsminus1

The temperature profile in samples placed in the threewater baths was determined using a sensor connected to atemperature measurement acquisition system placed in astainless steel tube filled with water (Figure 1)

23 HPLC Analysis The soluble (native and unfolded) 120573-Lg concentration in the samples was evaluated by HPLC

International Journal of Chemical Engineering 3

0

10

20

30

40

50

60

70

80

90

7 9 11 13 15 17Time (min)

Water bath 1

Water bath2

Water bath3

Sampling

Tem

pera

ture

(∘C)

Figure 1 Imposed temperature profiles (in the three water baths) tocarry out thermal denaturation at a constant holding temperature

after precipitation of the aggregated protein at pH 46 andtheir removal by centrifugation (9000 rpm for 30min at4∘C) The chromatographic system (Waters Milford MAUSA) included a 717 Plus autosampler a 616 quadratic pumpsystem a JonesModel 7971 column oven a CLHPACE 300 AC4 separation column and the associated guard column(Advanced Chromatography Technologies Aberdeen UK)a 486 UV-visible spectrophotometer and an acquisitionsoftware (Millennium 32 Waters)

The mobile phases used in HPLC were 01 (vv)trifluoroacetic acid (99 Acros Organics Thermo FisherScientific Waltham MA USA) in Milli-Q water and 01trifluoroacetic acid in a mixture of 80 acetonitrile (HPLCgrade Thermo Fisher Scientific Waltham MA USA) and20Milli-Q water

The HPLC analyses were carried out at the followingconditions flow rate 1mLsdotminminus1 injection volume 20120583Ltemperature 40∘C elution of the proteins using a gradi-ent of acetonitrile and detection of the eluted proteins atwavelength 214 nm Analyses were repeated three times foreach standard or sample Calibration standards in the rangefrom 05 to 4 gsdotLminus1 were prepared by dissolving 120573-Lg powderin Milli-Q water For each experiment the sample concen-trations were calculated by averaging the three measuredchromatographic areas and converting this area value into a120573-Lg concentration using the HPLC calibration curve

24 Determination of the 120573-Lg Rate Constants from HPLCMeasurements The reaction model used in this study isderived from the work of Tolkach and Kulozik [18] Thedenaturation reaction concerns the transformation of solublespecies (noted 119878) into aggregates (noted119860) which is describedby the chemical equation 119878 rarr 119860 and defined in

minus119889119862119878

119889119905= 119896119899119862119899119878

(1)

where 119862119878is the soluble 120573-Lg concentration 119896

119899the denatura-

tion rate constant for a reaction order equal to 119899 and 119905 thetime

ValveTemperature probe

Pump Flowmeter

Pressure drop

Agitated tank

Heating zone

Waste

Preheating zone

F

ΔP

ΔP

FF

F

Figure 2 Schematic diagram of the experimental setup carried outfor fouling runs with the 1 (ww) WPI solutions

For each temperature the corresponding denaturationrate constant was determined from the Arrhenius plot Therelation between the denaturation kinetic rate and the heattreatment temperature is given by

ln (119896119899) = ln (1198960

119899

) minus119864119860

119877119879 (2)

where 1198960119899

is the denaturation frequency factor 119864119860the denat-

uration activation energy 119877 the universal gas constant and 119879the temperature

The value of 119899 was varied from 1 to 2 (in steps of 01) todetermine the reaction order that gives the best regressioncoefficient when plotting (119862

1198781198620119878

)1minus119899 minus 1 as a function oftime where 1198620

119878

is the initial (time zero) 120573-Lg total solubleconcentration

The slope of this linear representation is equal to 119896119899(119899 minus

1)(1198620119878

)119899minus1 and leads to the determination of 119896119899 This method

was also used by Petit et al [14] Tolkach andKulozik [18] andDannenberg and Kessler [19]

The value of 119899 = 15 reaction order was suitable forthe whole 120573-Lg denaturation reaction in the investigatedtemperature range (from 65 to 92∘C)

25 Fouling Runs and Determination of the Deposit MassDistribution Fouling experiments were carried out in a pilotplant (Figure 2)The fouling rig was composed of two distinctzones (i) a preheating zone composed of a heat exchangerwith V7 types plates (Vicarb Alfa Laval France) and 9 passes(one channel per pass) necessary to preheat the model fluidand (ii) a heating zone composed of a PHE (Vicarb modelV7 Alfa Laval France)

4 International Journal of Chemical Engineering

Table 2 Operating conditions investigated with the pilot scale experimental set mean inlet and outlet temperatures and flow rates of 120573-Lgconcentrate and hot water

Thermal profile number Total calcium content (ppm) 119879119894119901

(∘C) 119879119900119901

(∘C) 119876119901

(Lsdothminus1) 119876ℎ

(Lsdothminus1)1 100 65 85 300 3002 100 65 85 300 9003 100 65 85 300 1504 100 60 75 300 3001 120 65 85 300 3002 120 65 85 300 9003 120 65 85 300 1504 120 60 75 300 300

P10

Fouling product inlet

Foulingproduct outlet

Hot water inlet Hot water outlet

Ci channel numberPi plate number

P1

C1 C2 C3 C4 C5

Figure 3 Plate heat exchanger flow arrangement

The PHE setup consisted of 10 plates that is 5 passes(one channel per pass) of about 0074m2 projected heattransfer area per plate (0495m length and 015m width)were installed in a countercurrent configuration to optimizethe heat transfer as represented in Figure 3 The defineddesign permitted being closer to industrial heat treatmentconditions

The temperature profile inside the heat exchanger wassimulated with Sphere software (previously developed atour laboratory) temperatures in all passes of hot andcold fluids were calculated from the knowledge of fluidsrsquoinlet temperature and flow rate plate properties and heatexchanger designThe temperature profile is controlled by theheat exchanger inlet parameters product and hot fluid inlettemperatures (119879

119894119901and 119879

119894119908) and product and hot water flow

rates (resp119876119901and119876

ℎ)This was achieved with the operating

conditions indicated in Table 2 displaying the average valuesof temperatures and flow rates recorded during each heattreatment experiment

The temperature profiles displayed in Figure 4 wereobtained by Sphere simulations by employing the operatingconditions summarized in Table 2 Eight fouling runs wereconducted with WPI solutions containing two calcium con-centrations (100 and 120 ppm)

Heat exchanger plates were weighted before each heattreatment experiment After being dried in an air oven at

60

65

70

75

80

85

0 5 10 15Time (s)

12

34

Tem

pera

ture

(∘C)

Figure 4 The imposed thermal profiles in the PHE (Spheresimulations)

50∘C fouled plates were weighted at ambient temperatureand the dry deposit mass on each plate was deduced bysubtraction

The amount of fouling was also monitored by calculat-ing the fouling resistance A linear relationship was visiblebetween the average fouling resistance119877

119891 defined by (3) and

the fouling thickness assuming that the deposit layers arecovered uniformly

1

119880119892(119905)

=1

119880119892(0)

+ 119877119891 (3)

where 119880119892(0)

and 119880119892(119905)

are the overall heat transfer coefficientsat the beginning of fouling runs (ie the overall heat transfercoefficient before the occurrence of fouling) and at time 119905 (iethe overall heat transfer coefficient including the additionalcontribution of fouling)

A logarithmic mean temperature difference (LMTD)method was used to relate the heat transfer rate to theoverall heat transfer coefficient In the case of a no pure

International Journal of Chemical Engineering 5

minus12

minus10

minus8

minus6

minus4

minus2

0

Aggregation limited temperature area

Critical point

Unfolding limited temperature area

300E

minus03

295Eminus03

290E

minus03

285Eminus03

280Eminus03

275Eminus03

270E

minus03

1T (Kminus1)

ln(k

n) sim80 ∘C

Ca 100ppmCa 120ppmPetit et al (2011)

Figure 5 Arrhenius plot for the 120573-Lg denaturation of 1 (ww)WPI fouling solutions at various calcium concentrations (100 and120 ppm)

cross countercurrent flow inside the plate heat exchanger thecorrection factor 119865

119879is classically introduced

119901119862119901119901

(119879119900119901

minus 119879119894119901

) = ℎ119862119901ℎ

(119879119894ℎ

minus 119879119900ℎ

)

= 119880119892119878Δ119879LMTD119865

119879

(4)

where 119862119901119901

and 119862119901ℎ

are respectively the specific heat for theproduct and hot water

119901and

ℎare respectively the mass

flow rates for the product and hot water119879 is the temperatureand 119878 is the heat transfer area

Leuliet et al [20] gave equations for PHE using analogywith shell and tube correction factor Their method was usedfor this work to evaluate the 119865

119879factor

3 Results and Discussion

31 Arrhenius Plots for the 120573-Lg Denaturation of the ModelSolutions The Arrhenius plots for the denaturation reactionof the WPI model fouling solutions at two calcium con-centrations (100 and 120 ppm) were presented in Figure 5This figure shows the temperature influence on the 120573-Lgdenaturation kinetic rate in the range from 65 to 92∘C

Two mechanisms appear in Figure 5 separated by anArrhenius critical temperature of about 80∘C This slopechange suggests two temperature ranges below the criticaltemperature the 120573-Lg denaturation reaction is unfoldinglimited which means that the unfolding reaction is slowerthan aggregation and over 80∘C 120573-Lg denaturation is limitedby the aggregation reaction and in that case aggregation isthe slower reaction

Table 3 Denaturation parameters at the two calcium concentra-tions

Denaturationparameter 100 ppm total calcium 120 ppm total calcium

Unfoldingln(1198960unf) 1248 1172119864119860unf (kJsdotmolminus1) 3845 2712

Aggregationln(1198960agg) 863 831119864119860agg (kJsdotmolminus1) 3607 2604

These results are in agreement with Petit et al [14] Evenin the case of quasi-pure 120573-Lg model solution the criticaltemperature that splits the Arrhenius plot in two linearparts was estimated at 80∘C each temperature range beingrelated to the predominance of the unfolding or aggregationmechanisms indicating that denaturation kinetic rates variedwith temperature However this slope break is less clear in thecase of our model fouling solution probably due to its morecomplex composition (mixture of 120573-Lg and 120572-lactalbumin)

Figure 5 also shows that 120573-Lg denaturation kineticsincreased with calcium concentration Even if the exactcontribution of calcium on the denaturation of 120573-Lg is stillunclear it is speculated that calcium induces protein chargeshielding or conformational changes in 120573-Lg structure [2122] favouring both unfolding and aggregation reactionsThis result illustrates that it is essential to know the exactcontent of calcium in the fouling solutions to have a clearview of the denaturation reaction This information notcommonly evaluated nowadays in the literature is essentialto the development of accurate model of fouling based onengineering denaturation reaction

The frequency factor logarithms (ln 1198960) and activationenergies (119864

119860) obtained by fitting Arrhenius plot regression

for the unfolding and aggregation denaturation mechanism(noted resp unf and agg) are shown in Table 3

32 Fouling Mass Distribution in the PHE Figure 6 repre-sents the deposit layer formed in the first and last channelsof the PHE at respectively 65∘C (inlet temperature) and85∘C (outlet temperature) after fouling run conducted with1 (ww) WPI solution containing 100 ppm of total calciumAt the highest temperature the fouling layer is white verythick and homogeneous It clearly appears that very lowfouling is obtained in the first channel of the PHE where thebulk temperature is lower than 70∘C Fouling is not expectedto occur under 65ndash72∘C [23 24] These observations are inagreement with Foster et al [25] work which showed thatdeposit increases with temperature making fouling rougherand more adherent to hot surfaces

Figure 7 represents the fouling results obtained with 1(ww) WPI model solution containing 100 and 120 ppm oftotal calcium at different temperature profiles This figureshows that the dry deposit is not uniform and is distributeddifferently depending on the thermal profile and the calcium

6 International Journal of Chemical Engineering

Figure 6 Pictures of the deposit collected on heat exchanger surfacein the second and last channels of the PHE

concentration Indeed for the first solution at 100 ppm cal-cium the depositmass increases linearly to reach amaximumin the 5th channel whatever the imposed thermal profileHowever at 120 ppm calcium the deposit mass reached astationary value of about 260 gm2 over 74∘C (2nd channeltemperature) for the first three temperature profiles whichconsisted in a foulingmaximum limitThis increasing depositmass at low temperatures resulted from the strong increase of120573-Lg denaturation level between 65∘C (1st channel tempera-ture) and 74∘C (2nd channel temperature) temperature rangefor which the120573-Lg denaturation reaction becomes significant[17 26] The thermal profile 4 increases linearly reaching amaximum of 845 gm2 in the 5th channel

The deposit mass is negligible for the thermal profile 4at 100 and 120 ppm calcium owing to the lack of denatured120573-Lg in the bulk at such low temperatures It is suggested that120573-Lg fouled hot surfaces only when the bulk temperature washigh enough to allow 120573-Lg denaturation

Figure 8 represents the effect of the temperature profileon the total amount of deposit mass in the PHE for thetwo fouling solutions It can be observed that for the sameinlet and outlet product temperature the total deposit massvaried with the calcium concentration This is the case ofthe thermal profile 1 for which the total deposit mass goesfrom 1415 gm2 at 100 ppm calcium to 2082 gm2 at 120 ppmcalcium This was also observed for the temperature profiles3 and 4 However for the thermal profile 2 the totalamount of deposit was very close at 100 and 120 ppm calcium

This difference of fouling distributions obtained at vari-ous calcium concentrations demonstrates the major role ofthe temperature profile on 120573-Lg fouling and its distributionin the PHE

33 Effect of Thermal Profiles and Calcium Concentrationon Fouling Rate Figure 9 shows the fouling rate behaviourduring heating of the WPI solution at 100 and 120 ppmcalcium in the PHE for each thermal profile An increase inthe fouling rate with time is evident A difference between

the fouling rates can be observed for the four temperatureprofiles at 100 ppm and 120 ppm calcium

The results also show that the fouling potential of WPI inthe PHE increases with the increasing temperature Indeedfor temperature range of 65ndash85∘C fouling rate is alteredand favoured by higher amount of calcium in the modelfluid It can be noted that for the thermal profile 4 (60ndash75∘C) fouling resistance curves for calcium content of 100and 120 ppm calcium were superposed These results are notcontradictorywith the assumption ofDaufin et al [27] Xiong[28] and Simons et al [21] who asserted that calcium caninteract with the aspartic and glutamic acid carboxyl groupof the 120573-Lg and so favour the growth of the deposit bystabilizing protein aggregates This is because calcium ionsform bridges between adsorbed proteins and the proteinaggregates occurring in the bulk consequentlymodifying theprotein aggregation rate and leading to a greater cohesionbetween the protein aggregates which in turn change thedeposit structure [29] Simmons et al [30] revealed anincrease in deposition upon a Couette surface due to calciumions and a modification in the appearance of the depositfor a temperature range 75ndash90∘C In addition Pappas andRothwell [31] showed that 120573-Lg completely aggregated toform compact structures when heated with calcium from 80to 110∘C

34 Relationship between 120573-Lg Heat Denaturation Rate Con-stants and the Distribution of the Deposit Mass along the PHETo study the relationship between the chemical reaction of the120573-Lg denaturation and the deposit formation rate within thePHE the deposit mass distribution in the different channelof the PHE was plotted against 119903 = 119896unf119896agg (Figure 10) Thevalue of 119903 was calculated at the average temperature of thechannel 119896unf and 119896agg represent respectively the reaction rateconstants for the unfolding and aggregation limited zonesdeduced from the Arrhenius plots (Figure 5) for the twoWPImodel fouling solutions (at 100 and 120 ppm of calcium)

For each fouling solution it could be observed that an119878 curve (plot of the deposit mass per channel versus 119903)consolidates the fouling data whatever the imposed thermalprofile The 119878 curves could be described for all fouling runsby the following function

119872119889

= 119886 +119887 minus 119886

1 + (119888119903)119889 (5)

where 119872119889is the measured dry fouling deposit mass per

channel along the PHE and 119886 119887 119888 and 119889 are four constantsThe twomaster curves representing the deposit mass per

channel versus the ratio 119903 contained different characteristiczones

(i) an unfolding limited zone with a sharp increase of thedeposit mass per channel with 119903

(ii) an aggregation limited zone where the deposit massper channel seems to reach a limiting value

Indeed the curve of the dry deposit mass at 100 ppm calciumshowed a sharp increase at values of 119903 close to 022 (relative

International Journal of Chemical Engineering 7

0

50

100

150

200

250

300

350

1 2 3 4 5Channel number

Dep

osit

mas

s per

chan

nel (

gm

2 )

1 23 4

(a)

0

50

100

150

200

250

300

350

1 2 3 4 5Channel number

Dep

osit

mas

s per

chan

nel (

gm

2 )

1 23 4

(b)

Figure 7 Fouling mass distribution related to the projected heat transfer area per plaque in each channel of the PHE for the two foulingsolutions 1 (ww) WPI solution containing (a) 100 ppm calcium and (b) 120 ppm calcium (119894 corresponds to the thermal profile numbergiven in Figure 4 and Table 2)

0

500

1000

1500

2000

2500

3

4

1

1 2 2

3

4Tota

l dep

osit

mas

s (g

m2)

Ca 100ppmCa 120ppm

Figure 8 Total amount of the deposit mass in the PHE perunit area for 1 (ww) WPI fouling solutions at various calciumconcentrations (100 and 120 ppm) and for different temperatureprofiles (119894 corresponds to the thermal profile number given inFigure 4 and Table 2)

to the fouling beginning) then reaching a plateau at 119903 = 091For the second fouling solution (WPI solution containing120 ppm of calcium) the increase of 119903 values starts at 023 andthe maximum of the deposit mass is reached at 119903 = 067

In summary for the two fouling model solutions andthe operating conditions investigated it can be observed thata sharp increase of deposit mass occurs when 119903 is locatedbetween 022 and 089 (corresponding to bulk temperaturesranging from 65 to 805∘C) The fact that the deposit massincreases strongly when 119903 is below 1 shows that the unfoldinglimited zone controls the growth of the deposit mass Thisresult also shows that the deposit mass per channel decreases

0

50

100

150

200

250

300

0 05 1 15 2Time (h)

1234

1234

Foul

ing

resis

tanc

eRflowast100000

(m2 middot∘ C

W)

Figure 9 Fouling resistance evolution with time measured alongthe PHE Various symbols refer to various fouling runs with varyingthermal profiles and various calcium content for the 1 ww WPIsolutions (closed symbols 100 ppm calcium open symbols 120 ppmcalcium) (119894 corresponds to the thermal profile number given inFigure 4 and Table 2)

when the aggregation reaction is high enough to consumethe unfolded species under aggregates forms This result isin agreement with the previous observation of van Asseltet al [13] and consistent with the work of Blanpain-Avetet al [32] Indeed these authors conclude from fouled deposit

8 International Journal of Chemical Engineering

0

100

200

300

400

500

600

700

800

0 02 04 06 08 1 12 14

1 23 41 23 4

Aggregationlimited zone

Clog

ging

of t

he

inst

allat

ion

Unfolding limited zone

Dep

osit

mas

s per

chan

nel (

gm

2)

r = kunfkagg

Fitting model Ca 120ppmFitting model Ca 100ppm

Figure 10 Plots of the dry deposit masses per unit area versus theratio of unfolding and aggregation rate constants for the 1 wwWPI solutions (closed symbols 100 ppm calcium open symbols120 ppm calcium) (119894 corresponds to the thermal profile numbergiven in Figure 4 and Table 2)

analysis by Raman spectroscopy that protein aggregates arenot present in the deposit This result is also supportedby the recent study of Bouvier et al [33] which showedthat a correlation can be established between the unfolded120573-Lg content within the PHE and the dry deposit massdistribution

Unfortunately it was not possible to perform pilot scaleexperiments at higher values of 119903 (119903 gt 140) correspondingto the channel temperature above 844∘C because of theclogging of the installation

To ascertain validity of themaster curve independently ofthe PHE configuration further experiments were conductedat PHE consisting of 10 passes (one channel per pass) for a 1(ww) WPI model solution at 100 ppm calcium One thermalprofile (1) out of the four tested for the five channels of thePHE was imposed Figure 11 represents the deposit mass perchannel versus the ratio 119903

Also in this case the fouling mass is reasonably wellcorrelated to the ratio 119903 showing the following

(i) the importance of determining this indicator forpredicting fouling mass distribution

(ii) the robustness of the approach

4 Conclusions

Fouling experiments were performed with 1 (ww) WPIsolutions at two different calcium concentrations in order toinvestigate the effect of the operating conditions associatedwith the chemical denaturation reactivity of heat treatmentin a PHE on the deposit formation The extent of fouling

0

100

200

300

400

500

600

700

0 05 1 15

1Fitting model 10-pass PHE configuration

Dep

osit

mas

s per

chan

nel (

gm

2)

r = kunfkagg

Aggregationlimited zone limited zone

Unfolding

Figure 11 Variation of the dry deposit mass per unit area in thevarious channels with the ratio 119903 for a 10-pass PHE configuration (1corresponds to the thermal profile given in Figure 4 and Table 2)

deposit was monitored by weighing the mass of the dryfouling deposit on the plates

It was shown that

(i) 120573-Lg denaturation is a complex process with a two-step mechanism highly dependent on the calciumcontent

(ii) an increase of the calcium content in the foulingsolution induced a strong increase in the 120573-Lg denat-uration level and consequently in the fouling masswithin the PHE at high temperatures

(iii) the fouling mass distribution also depends on thethermal profiles imposed on the fouling solutions

(iv) the dry deposit mass on each pass of the PHE seemsto be correlated with 119903 = 119896unf119896agg This observationindicates that the knowledge of this parameter isimportant to predict the mass distribution of thefouling deposit

This work clearly shows that 120573-Lg competitive reactions(unfolding and aggregation) governing the growth of foulingfor a WPI solution and the identification of the heat-induceddenaturation kinetic by means of laboratory experiments areprerequisites to control fouling We encourage strongly thefouling community to develop database on these aspects tobe able to predict the distribution of fouling mass whateverthe imposed temperature profile and to mitigate fouling

International Journal of Chemical Engineering 9

Nomenclature

119886 Adjusted parameter in the nonlinear regressionusing (5)

119887 Adjusted parameter in the nonlinear regressionusing (5)

119888 Adjusted parameter in the nonlinear regressionusing (5)

Ca Calcium concentration ppm119862119878 Concentration of the total soluble 120573-Lg g Lminus1

119862119901119901 Specific heat for the product J kgminus1 Kminus1

119862119901ℎ Specific heat for the hot water J kgminus1 Kminus1

119889 Adjusted parameter in the nonlinear regressionusing (5)

119864119860 Activation energy Jmolminus1

119864119860agg 120573-Lg aggregation activation energy Jmolminus1

119864119860unf 120573-Lg unfolding activation energy Jmolminus1

119865119879 Logarithmic mean temperature difference -

119896119899 Denaturation rate constant g1minus119899 L119899minus1sminus1

1198960119899

Denaturation frequency factor g1minus119899 L119899minus1sminus1119896unf Unfolding rate constant g1minus119899 L119899minus1sminus1119896agg Aggregation rate constant g1minus119899 L119899minus1sminus1119872119889 Measured dry fouling deposit mass in a channel

along the PHE g119901 Mass flow rates for the product kg sminus1

ℎ Mass flow rates for the hot water kg sminus1

119899 Heat-induced denaturation reaction order119876119901 WPI fouling solution flow rate L hminus1

119876ℎ Hot water flow rate L hminus1

119903 Ratio between the unfolding and aggregation rateconstants -

119877 The universal gas constant equal to 8314Jmolminus1 Kminus1

119877119891 Fouling resistance m2∘ CWminus1

119878 Heat transfer area m2119879119894ℎ Hot water temperature at the PHE inlet K

119879119894119901 WPI fouling solution temperature at the PHE

inlet K119879119900ℎ Hot water temperature at the PHE outlet K

119879119900119901 Hot water temperature at the PHE outlet K

119880119892 Overall heat transfer coefficient Wmminus2 Kminus1

998779119879LMTD Logarithmic mean temperature difference K

Subscript

agg Aggregation119862119894 Channel number

ℎ Hot water119901 Product119875119894 Plate number

PHE Plate heat exchangerunf UnfoldingWPI Whey protein isolate120572-La 120572-lactalbumin120573-Lg 120573-lactoglobulin119894 Thermal profile number

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

Theauthors are indebted to the ScientificCommittee ofAgro-campus Ouest Rennes and HEI (Hautes Etudes drsquoIngenieurLille) for stimulating discussions and financial support for thePhD Thesis of the first author

References

[1] D M Mulvihill and M Donovan ldquoWhey proteins and theirthermal denaturationmdasha reviewrdquo Irish Journal of Food Scienceand Technology vol 11 no 1 pp 43ndash75 1987

[2] N Sava I Van der PlanckenWClaeys andMHendrickx ldquoThekinetics of heat-induced structural changes of 120573-lactoglobulinrdquoJournal of Dairy Science vol 88 no 5 pp 1646ndash1653 2005

[3] C Schmitt C Bovay M Rouvet S Shojaei-Rami and EKolodziejczyk ldquoWhey protein soluble aggregates from heatingwith NaCl physicochemical interfacial and foaming proper-tiesrdquo Langmuir vol 23 no 8 pp 4155ndash4166 2007

[4] B Bansal and X D Chen ldquoA critical review of milk fouling inheat exchangersrdquo Comprehensive Reviews in Food Science andFood Safety vol 5 no 2 pp 27ndash33 2006

[5] S N Tay and C Yang Assessment of the Hydro-Ball CondenserTube Cleaning System HydroBall Technics (SEA) Pte Singa-pore 2006

[6] HMMuller-SteinhagenHandbook of Heat Exchanger FoulingMitigation and Cleaning Technologies Publico PublicationsEssenGermany Institution ofChemical Engineers RugbyUK2000

[7] M Lalande and J P Tissier ldquoFouling of heat transfer surfacesrelated to 120573-lactoglobulin denaturation during heat processingof milkrdquo Biotechnology Progress vol 1 no 2 pp 131ndash139 1985

[8] P De Jong R Waalewijn and H J L J Van Der LindenldquoValidity of a kinetic fouling model for heat-treatment of wholemilkrdquo Le Lait vol 73 no 3 pp 293ndash302 1993

[9] S D Changani M T Belmar-Beiny and P J Fryer ldquoEngineer-ing and chemical factors associated with fouling and cleaning inmilk processingrdquo Experimental Thermal and Fluid Science vol14 no 4 pp 392ndash406 1997

[10] H Burton ldquoProperties of UHT-processed milkrdquo in Ultra-HighTemperature Processing of Milk and Milk Products pp 254ndash291Elsevier Applied Science Publishers 1988

[11] M T Belmar-Beiny S M Gotham W R Paterson P J Fryerand A M Pritchard ldquoThe effect of Reynolds number andfluid temperature in whey protein foulingrdquo Journal of FoodEngineering vol 19 no 2 pp 119ndash139 1993

[12] P J R Schreier and P J Fryer ldquoHeat exchanger fouling a modelstudy of the scaleup of laboratory datardquo Chemical EngineeringScience vol 50 no 8 pp 1311ndash1321 1995

[13] A J van Asselt M M M Vissers F Smit and P de Jong ldquoIn-line control of foulingrdquo in Proceedings of the Heat ExchangerFouling and CleaningmdashChallenges and Opportunities Engineer-ing Conferences International Irsee Germany June 2005

[14] J Petit A-LHerbig AMoreau andGDelaplace ldquoInfluence ofcalcium on 120573-lactoglobulin denaturation kinetics implications

10 International Journal of Chemical Engineering

in unfolding and aggregation mechanismsrdquo Journal of DairyScience vol 94 no 12 pp 5794ndash5810 2011

[15] M Khaldi P Blanpain-Avet R Guerin et al ldquoEffect of calciumcontent and flow regime on whey protein fouling and cleaningin a plate heat exchangerrdquo Journal of Food Engineering vol 147pp 68ndash78 2015

[16] B T Nielsen H Singh and J M Latham ldquoAggregation ofbovine 120573-lactoglobulins A and B on heating at 75∘Crdquo Interna-tional Dairy Journal vol 6 no 5 pp 519ndash527 1996

[17] H Lindmark-Mansson A Timgren G Alden and M Pauls-son ldquoTwo-dimensional gel electrophoresis of proteins andpeptides in bovinemilkrdquo International Dairy Journal vol 15 no2 pp 111ndash121 2005

[18] A Tolkach and U Kulozik ldquoReaction kinetic pathwayof reversible and irreversible thermal denaturation of 120573-lactoglobulinrdquo Dairy Science and Technology vol 87 no 4-5pp 301ndash315 2007

[19] F Dannenberg and H G Kessler ldquoReaction kinetics of thedenaturation of whey proteins in milkrdquo Journal of Food Sciencevol 53 no 1 pp 258ndash263 1988

[20] J C Leuliet J F Maingonnat and M Lalande ldquoThermalbehaviour of plate heat exchangers with Newtonian and non-Newtonian fluidsrdquo in Proceedings of the Congres Eurotherm 5 et1er Colloque TIFAN pp 1ndash15 Compiegne France 1988

[21] J-W F A Simons H A Kosters R W Visschers and H H Jde Jongh ldquoRole of calcium as trigger in thermal 120573-lactoglobulinaggregationrdquo Archives of Biochemistry and Biophysics vol 406no 2 pp 143ndash152 2002

[22] B T OrsquoKennedy and J S Mounsey ldquoThe dominating effect ofionic strength on the heat-induced denaturation and aggrega-tion of 120573-lactoglobulin in simulated milk ultrafiltraterdquo Interna-tional Dairy Journal vol 19 no 3 pp 123ndash128 2009

[23] M Lalande F Rene and J-P Tissier ldquoFouling and its control inheat exchangers in the dairy industryrdquo Biofouling vol 1 no 3pp 233ndash250 1989

[24] J Visser andT JM Jeurnink ldquoFouling of heat exchangers in thedairy industryrdquo ExperimentalThermal and Fluid Science vol 14no 4 pp 407ndash424 1997

[25] C L Foster M Britten and M L Green ldquoA model heat-exchange apparatus for the investigation of fouling of stainlesssteel surfaces by milk I Deposit formation at 100∘Crdquo Journal ofDairy Research vol 56 no 2 pp 201ndash209 1989

[26] P Havea H Singh and L K Creamer ldquoCharacterizationof heat-induced aggregates of 120573-lactoglobulin 120572-lactalbuminand bovine serum albumin in a whey protein concentrateenvironmentrdquo Journal of Dairy Research vol 68 no 3 pp 483ndash497 2001

[27] G Daufin J P Labbe A Quemerais et al ldquoFouling of a heatexchange surface by whey milk and model fluids an analyticalstudyrdquo Le Lait vol 67 no 3 pp 339ndash364 1987

[28] Y L Xiong ldquoInfluence of pH and ionic environment on thermalaggregation of whey proteinsrdquo Journal of Agricultural and FoodChemistry vol 40 no 3 Article ID 91-5-154 pp 380ndash384 1992

[29] T Phan-XuanDDurand TNicolai L Donato C Schmitt andL Bovetto ldquoTuning the structure of protein particles and gelswith calcium or sodium ionsrdquo Biomacromolecules vol 14 no 6pp 1980ndash1989 2013

[30] M J H Simmons P Jayaraman and P J Fryer ldquoThe effectof temperature and shear rate upon the aggregation of wheyprotein and its implications for milk foulingrdquo Journal of FoodEngineering vol 79 no 2 pp 517ndash528 2007

[31] C P Pappas and J Rothwell ldquoThe effects of heating alone or inthe presence of calcium or lactose on calcium binding to milkproteinsrdquo Food Chemistry vol 42 no 2 pp 183ndash201 1991

[32] P Blanpain-Avet A Hedoux Y Guinet et al ldquoAnalysis byRaman spectroscopy of the conformational structure of wheyproteins constituting fouling deposits during the processing ina heat exchangerrdquo Journal of Food Engineering vol 110 no 1 pp86ndash94 2012

[33] L Bouvier A Moreau G Ronse T Six J Petit and GDelaplace ldquoA CFD model as a tool to simulate 120573-lactoglobulinheat-induced denaturation and aggregation in a plate heatexchangerrdquo Journal of Food Engineering vol 136 pp 56ndash632014

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Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

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Chemical EngineeringInternational Journal of Antennas and

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Navigation and Observation

International Journal of

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DistributedSensor Networks

International Journal of

International Journal of Chemical Engineering 3

0

10

20

30

40

50

60

70

80

90

7 9 11 13 15 17Time (min)

Water bath 1

Water bath2

Water bath3

Sampling

Tem

pera

ture

(∘C)

Figure 1 Imposed temperature profiles (in the three water baths) tocarry out thermal denaturation at a constant holding temperature

after precipitation of the aggregated protein at pH 46 andtheir removal by centrifugation (9000 rpm for 30min at4∘C) The chromatographic system (Waters Milford MAUSA) included a 717 Plus autosampler a 616 quadratic pumpsystem a JonesModel 7971 column oven a CLHPACE 300 AC4 separation column and the associated guard column(Advanced Chromatography Technologies Aberdeen UK)a 486 UV-visible spectrophotometer and an acquisitionsoftware (Millennium 32 Waters)

The mobile phases used in HPLC were 01 (vv)trifluoroacetic acid (99 Acros Organics Thermo FisherScientific Waltham MA USA) in Milli-Q water and 01trifluoroacetic acid in a mixture of 80 acetonitrile (HPLCgrade Thermo Fisher Scientific Waltham MA USA) and20Milli-Q water

The HPLC analyses were carried out at the followingconditions flow rate 1mLsdotminminus1 injection volume 20120583Ltemperature 40∘C elution of the proteins using a gradi-ent of acetonitrile and detection of the eluted proteins atwavelength 214 nm Analyses were repeated three times foreach standard or sample Calibration standards in the rangefrom 05 to 4 gsdotLminus1 were prepared by dissolving 120573-Lg powderin Milli-Q water For each experiment the sample concen-trations were calculated by averaging the three measuredchromatographic areas and converting this area value into a120573-Lg concentration using the HPLC calibration curve

24 Determination of the 120573-Lg Rate Constants from HPLCMeasurements The reaction model used in this study isderived from the work of Tolkach and Kulozik [18] Thedenaturation reaction concerns the transformation of solublespecies (noted 119878) into aggregates (noted119860) which is describedby the chemical equation 119878 rarr 119860 and defined in

minus119889119862119878

119889119905= 119896119899119862119899119878

(1)

where 119862119878is the soluble 120573-Lg concentration 119896

119899the denatura-

tion rate constant for a reaction order equal to 119899 and 119905 thetime

ValveTemperature probe

Pump Flowmeter

Pressure drop

Agitated tank

Heating zone

Waste

Preheating zone

F

ΔP

ΔP

FF

F

Figure 2 Schematic diagram of the experimental setup carried outfor fouling runs with the 1 (ww) WPI solutions

For each temperature the corresponding denaturationrate constant was determined from the Arrhenius plot Therelation between the denaturation kinetic rate and the heattreatment temperature is given by

ln (119896119899) = ln (1198960

119899

) minus119864119860

119877119879 (2)

where 1198960119899

is the denaturation frequency factor 119864119860the denat-

uration activation energy 119877 the universal gas constant and 119879the temperature

The value of 119899 was varied from 1 to 2 (in steps of 01) todetermine the reaction order that gives the best regressioncoefficient when plotting (119862

1198781198620119878

)1minus119899 minus 1 as a function oftime where 1198620

119878

is the initial (time zero) 120573-Lg total solubleconcentration

The slope of this linear representation is equal to 119896119899(119899 minus

1)(1198620119878

)119899minus1 and leads to the determination of 119896119899 This method

was also used by Petit et al [14] Tolkach andKulozik [18] andDannenberg and Kessler [19]

The value of 119899 = 15 reaction order was suitable forthe whole 120573-Lg denaturation reaction in the investigatedtemperature range (from 65 to 92∘C)

25 Fouling Runs and Determination of the Deposit MassDistribution Fouling experiments were carried out in a pilotplant (Figure 2)The fouling rig was composed of two distinctzones (i) a preheating zone composed of a heat exchangerwith V7 types plates (Vicarb Alfa Laval France) and 9 passes(one channel per pass) necessary to preheat the model fluidand (ii) a heating zone composed of a PHE (Vicarb modelV7 Alfa Laval France)

4 International Journal of Chemical Engineering

Table 2 Operating conditions investigated with the pilot scale experimental set mean inlet and outlet temperatures and flow rates of 120573-Lgconcentrate and hot water

Thermal profile number Total calcium content (ppm) 119879119894119901

(∘C) 119879119900119901

(∘C) 119876119901

(Lsdothminus1) 119876ℎ

(Lsdothminus1)1 100 65 85 300 3002 100 65 85 300 9003 100 65 85 300 1504 100 60 75 300 3001 120 65 85 300 3002 120 65 85 300 9003 120 65 85 300 1504 120 60 75 300 300

P10

Fouling product inlet

Foulingproduct outlet

Hot water inlet Hot water outlet

Ci channel numberPi plate number

P1

C1 C2 C3 C4 C5

Figure 3 Plate heat exchanger flow arrangement

The PHE setup consisted of 10 plates that is 5 passes(one channel per pass) of about 0074m2 projected heattransfer area per plate (0495m length and 015m width)were installed in a countercurrent configuration to optimizethe heat transfer as represented in Figure 3 The defineddesign permitted being closer to industrial heat treatmentconditions

The temperature profile inside the heat exchanger wassimulated with Sphere software (previously developed atour laboratory) temperatures in all passes of hot andcold fluids were calculated from the knowledge of fluidsrsquoinlet temperature and flow rate plate properties and heatexchanger designThe temperature profile is controlled by theheat exchanger inlet parameters product and hot fluid inlettemperatures (119879

119894119901and 119879

119894119908) and product and hot water flow

rates (resp119876119901and119876

ℎ)This was achieved with the operating

conditions indicated in Table 2 displaying the average valuesof temperatures and flow rates recorded during each heattreatment experiment

The temperature profiles displayed in Figure 4 wereobtained by Sphere simulations by employing the operatingconditions summarized in Table 2 Eight fouling runs wereconducted with WPI solutions containing two calcium con-centrations (100 and 120 ppm)

Heat exchanger plates were weighted before each heattreatment experiment After being dried in an air oven at

60

65

70

75

80

85

0 5 10 15Time (s)

12

34

Tem

pera

ture

(∘C)

Figure 4 The imposed thermal profiles in the PHE (Spheresimulations)

50∘C fouled plates were weighted at ambient temperatureand the dry deposit mass on each plate was deduced bysubtraction

The amount of fouling was also monitored by calculat-ing the fouling resistance A linear relationship was visiblebetween the average fouling resistance119877

119891 defined by (3) and

the fouling thickness assuming that the deposit layers arecovered uniformly

1

119880119892(119905)

=1

119880119892(0)

+ 119877119891 (3)

where 119880119892(0)

and 119880119892(119905)

are the overall heat transfer coefficientsat the beginning of fouling runs (ie the overall heat transfercoefficient before the occurrence of fouling) and at time 119905 (iethe overall heat transfer coefficient including the additionalcontribution of fouling)

A logarithmic mean temperature difference (LMTD)method was used to relate the heat transfer rate to theoverall heat transfer coefficient In the case of a no pure

International Journal of Chemical Engineering 5

minus12

minus10

minus8

minus6

minus4

minus2

0

Aggregation limited temperature area

Critical point

Unfolding limited temperature area

300E

minus03

295Eminus03

290E

minus03

285Eminus03

280Eminus03

275Eminus03

270E

minus03

1T (Kminus1)

ln(k

n) sim80 ∘C

Ca 100ppmCa 120ppmPetit et al (2011)

Figure 5 Arrhenius plot for the 120573-Lg denaturation of 1 (ww)WPI fouling solutions at various calcium concentrations (100 and120 ppm)

cross countercurrent flow inside the plate heat exchanger thecorrection factor 119865

119879is classically introduced

119901119862119901119901

(119879119900119901

minus 119879119894119901

) = ℎ119862119901ℎ

(119879119894ℎ

minus 119879119900ℎ

)

= 119880119892119878Δ119879LMTD119865

119879

(4)

where 119862119901119901

and 119862119901ℎ

are respectively the specific heat for theproduct and hot water

119901and

ℎare respectively the mass

flow rates for the product and hot water119879 is the temperatureand 119878 is the heat transfer area

Leuliet et al [20] gave equations for PHE using analogywith shell and tube correction factor Their method was usedfor this work to evaluate the 119865

119879factor

3 Results and Discussion

31 Arrhenius Plots for the 120573-Lg Denaturation of the ModelSolutions The Arrhenius plots for the denaturation reactionof the WPI model fouling solutions at two calcium con-centrations (100 and 120 ppm) were presented in Figure 5This figure shows the temperature influence on the 120573-Lgdenaturation kinetic rate in the range from 65 to 92∘C

Two mechanisms appear in Figure 5 separated by anArrhenius critical temperature of about 80∘C This slopechange suggests two temperature ranges below the criticaltemperature the 120573-Lg denaturation reaction is unfoldinglimited which means that the unfolding reaction is slowerthan aggregation and over 80∘C 120573-Lg denaturation is limitedby the aggregation reaction and in that case aggregation isthe slower reaction

Table 3 Denaturation parameters at the two calcium concentra-tions

Denaturationparameter 100 ppm total calcium 120 ppm total calcium

Unfoldingln(1198960unf) 1248 1172119864119860unf (kJsdotmolminus1) 3845 2712

Aggregationln(1198960agg) 863 831119864119860agg (kJsdotmolminus1) 3607 2604

These results are in agreement with Petit et al [14] Evenin the case of quasi-pure 120573-Lg model solution the criticaltemperature that splits the Arrhenius plot in two linearparts was estimated at 80∘C each temperature range beingrelated to the predominance of the unfolding or aggregationmechanisms indicating that denaturation kinetic rates variedwith temperature However this slope break is less clear in thecase of our model fouling solution probably due to its morecomplex composition (mixture of 120573-Lg and 120572-lactalbumin)

Figure 5 also shows that 120573-Lg denaturation kineticsincreased with calcium concentration Even if the exactcontribution of calcium on the denaturation of 120573-Lg is stillunclear it is speculated that calcium induces protein chargeshielding or conformational changes in 120573-Lg structure [2122] favouring both unfolding and aggregation reactionsThis result illustrates that it is essential to know the exactcontent of calcium in the fouling solutions to have a clearview of the denaturation reaction This information notcommonly evaluated nowadays in the literature is essentialto the development of accurate model of fouling based onengineering denaturation reaction

The frequency factor logarithms (ln 1198960) and activationenergies (119864

119860) obtained by fitting Arrhenius plot regression

for the unfolding and aggregation denaturation mechanism(noted resp unf and agg) are shown in Table 3

32 Fouling Mass Distribution in the PHE Figure 6 repre-sents the deposit layer formed in the first and last channelsof the PHE at respectively 65∘C (inlet temperature) and85∘C (outlet temperature) after fouling run conducted with1 (ww) WPI solution containing 100 ppm of total calciumAt the highest temperature the fouling layer is white verythick and homogeneous It clearly appears that very lowfouling is obtained in the first channel of the PHE where thebulk temperature is lower than 70∘C Fouling is not expectedto occur under 65ndash72∘C [23 24] These observations are inagreement with Foster et al [25] work which showed thatdeposit increases with temperature making fouling rougherand more adherent to hot surfaces

Figure 7 represents the fouling results obtained with 1(ww) WPI model solution containing 100 and 120 ppm oftotal calcium at different temperature profiles This figureshows that the dry deposit is not uniform and is distributeddifferently depending on the thermal profile and the calcium

6 International Journal of Chemical Engineering

Figure 6 Pictures of the deposit collected on heat exchanger surfacein the second and last channels of the PHE

concentration Indeed for the first solution at 100 ppm cal-cium the depositmass increases linearly to reach amaximumin the 5th channel whatever the imposed thermal profileHowever at 120 ppm calcium the deposit mass reached astationary value of about 260 gm2 over 74∘C (2nd channeltemperature) for the first three temperature profiles whichconsisted in a foulingmaximum limitThis increasing depositmass at low temperatures resulted from the strong increase of120573-Lg denaturation level between 65∘C (1st channel tempera-ture) and 74∘C (2nd channel temperature) temperature rangefor which the120573-Lg denaturation reaction becomes significant[17 26] The thermal profile 4 increases linearly reaching amaximum of 845 gm2 in the 5th channel

The deposit mass is negligible for the thermal profile 4at 100 and 120 ppm calcium owing to the lack of denatured120573-Lg in the bulk at such low temperatures It is suggested that120573-Lg fouled hot surfaces only when the bulk temperature washigh enough to allow 120573-Lg denaturation

Figure 8 represents the effect of the temperature profileon the total amount of deposit mass in the PHE for thetwo fouling solutions It can be observed that for the sameinlet and outlet product temperature the total deposit massvaried with the calcium concentration This is the case ofthe thermal profile 1 for which the total deposit mass goesfrom 1415 gm2 at 100 ppm calcium to 2082 gm2 at 120 ppmcalcium This was also observed for the temperature profiles3 and 4 However for the thermal profile 2 the totalamount of deposit was very close at 100 and 120 ppm calcium

This difference of fouling distributions obtained at vari-ous calcium concentrations demonstrates the major role ofthe temperature profile on 120573-Lg fouling and its distributionin the PHE

33 Effect of Thermal Profiles and Calcium Concentrationon Fouling Rate Figure 9 shows the fouling rate behaviourduring heating of the WPI solution at 100 and 120 ppmcalcium in the PHE for each thermal profile An increase inthe fouling rate with time is evident A difference between

the fouling rates can be observed for the four temperatureprofiles at 100 ppm and 120 ppm calcium

The results also show that the fouling potential of WPI inthe PHE increases with the increasing temperature Indeedfor temperature range of 65ndash85∘C fouling rate is alteredand favoured by higher amount of calcium in the modelfluid It can be noted that for the thermal profile 4 (60ndash75∘C) fouling resistance curves for calcium content of 100and 120 ppm calcium were superposed These results are notcontradictorywith the assumption ofDaufin et al [27] Xiong[28] and Simons et al [21] who asserted that calcium caninteract with the aspartic and glutamic acid carboxyl groupof the 120573-Lg and so favour the growth of the deposit bystabilizing protein aggregates This is because calcium ionsform bridges between adsorbed proteins and the proteinaggregates occurring in the bulk consequentlymodifying theprotein aggregation rate and leading to a greater cohesionbetween the protein aggregates which in turn change thedeposit structure [29] Simmons et al [30] revealed anincrease in deposition upon a Couette surface due to calciumions and a modification in the appearance of the depositfor a temperature range 75ndash90∘C In addition Pappas andRothwell [31] showed that 120573-Lg completely aggregated toform compact structures when heated with calcium from 80to 110∘C

34 Relationship between 120573-Lg Heat Denaturation Rate Con-stants and the Distribution of the Deposit Mass along the PHETo study the relationship between the chemical reaction of the120573-Lg denaturation and the deposit formation rate within thePHE the deposit mass distribution in the different channelof the PHE was plotted against 119903 = 119896unf119896agg (Figure 10) Thevalue of 119903 was calculated at the average temperature of thechannel 119896unf and 119896agg represent respectively the reaction rateconstants for the unfolding and aggregation limited zonesdeduced from the Arrhenius plots (Figure 5) for the twoWPImodel fouling solutions (at 100 and 120 ppm of calcium)

For each fouling solution it could be observed that an119878 curve (plot of the deposit mass per channel versus 119903)consolidates the fouling data whatever the imposed thermalprofile The 119878 curves could be described for all fouling runsby the following function

119872119889

= 119886 +119887 minus 119886

1 + (119888119903)119889 (5)

where 119872119889is the measured dry fouling deposit mass per

channel along the PHE and 119886 119887 119888 and 119889 are four constantsThe twomaster curves representing the deposit mass per

channel versus the ratio 119903 contained different characteristiczones

(i) an unfolding limited zone with a sharp increase of thedeposit mass per channel with 119903

(ii) an aggregation limited zone where the deposit massper channel seems to reach a limiting value

Indeed the curve of the dry deposit mass at 100 ppm calciumshowed a sharp increase at values of 119903 close to 022 (relative

International Journal of Chemical Engineering 7

0

50

100

150

200

250

300

350

1 2 3 4 5Channel number

Dep

osit

mas

s per

chan

nel (

gm

2 )

1 23 4

(a)

0

50

100

150

200

250

300

350

1 2 3 4 5Channel number

Dep

osit

mas

s per

chan

nel (

gm

2 )

1 23 4

(b)

Figure 7 Fouling mass distribution related to the projected heat transfer area per plaque in each channel of the PHE for the two foulingsolutions 1 (ww) WPI solution containing (a) 100 ppm calcium and (b) 120 ppm calcium (119894 corresponds to the thermal profile numbergiven in Figure 4 and Table 2)

0

500

1000

1500

2000

2500

3

4

1

1 2 2

3

4Tota

l dep

osit

mas

s (g

m2)

Ca 100ppmCa 120ppm

Figure 8 Total amount of the deposit mass in the PHE perunit area for 1 (ww) WPI fouling solutions at various calciumconcentrations (100 and 120 ppm) and for different temperatureprofiles (119894 corresponds to the thermal profile number given inFigure 4 and Table 2)

to the fouling beginning) then reaching a plateau at 119903 = 091For the second fouling solution (WPI solution containing120 ppm of calcium) the increase of 119903 values starts at 023 andthe maximum of the deposit mass is reached at 119903 = 067

In summary for the two fouling model solutions andthe operating conditions investigated it can be observed thata sharp increase of deposit mass occurs when 119903 is locatedbetween 022 and 089 (corresponding to bulk temperaturesranging from 65 to 805∘C) The fact that the deposit massincreases strongly when 119903 is below 1 shows that the unfoldinglimited zone controls the growth of the deposit mass Thisresult also shows that the deposit mass per channel decreases

0

50

100

150

200

250

300

0 05 1 15 2Time (h)

1234

1234

Foul

ing

resis

tanc

eRflowast100000

(m2 middot∘ C

W)

Figure 9 Fouling resistance evolution with time measured alongthe PHE Various symbols refer to various fouling runs with varyingthermal profiles and various calcium content for the 1 ww WPIsolutions (closed symbols 100 ppm calcium open symbols 120 ppmcalcium) (119894 corresponds to the thermal profile number given inFigure 4 and Table 2)

when the aggregation reaction is high enough to consumethe unfolded species under aggregates forms This result isin agreement with the previous observation of van Asseltet al [13] and consistent with the work of Blanpain-Avetet al [32] Indeed these authors conclude from fouled deposit

8 International Journal of Chemical Engineering

0

100

200

300

400

500

600

700

800

0 02 04 06 08 1 12 14

1 23 41 23 4

Aggregationlimited zone

Clog

ging

of t

he

inst

allat

ion

Unfolding limited zone

Dep

osit

mas

s per

chan

nel (

gm

2)

r = kunfkagg

Fitting model Ca 120ppmFitting model Ca 100ppm

Figure 10 Plots of the dry deposit masses per unit area versus theratio of unfolding and aggregation rate constants for the 1 wwWPI solutions (closed symbols 100 ppm calcium open symbols120 ppm calcium) (119894 corresponds to the thermal profile numbergiven in Figure 4 and Table 2)

analysis by Raman spectroscopy that protein aggregates arenot present in the deposit This result is also supportedby the recent study of Bouvier et al [33] which showedthat a correlation can be established between the unfolded120573-Lg content within the PHE and the dry deposit massdistribution

Unfortunately it was not possible to perform pilot scaleexperiments at higher values of 119903 (119903 gt 140) correspondingto the channel temperature above 844∘C because of theclogging of the installation

To ascertain validity of themaster curve independently ofthe PHE configuration further experiments were conductedat PHE consisting of 10 passes (one channel per pass) for a 1(ww) WPI model solution at 100 ppm calcium One thermalprofile (1) out of the four tested for the five channels of thePHE was imposed Figure 11 represents the deposit mass perchannel versus the ratio 119903

Also in this case the fouling mass is reasonably wellcorrelated to the ratio 119903 showing the following

(i) the importance of determining this indicator forpredicting fouling mass distribution

(ii) the robustness of the approach

4 Conclusions

Fouling experiments were performed with 1 (ww) WPIsolutions at two different calcium concentrations in order toinvestigate the effect of the operating conditions associatedwith the chemical denaturation reactivity of heat treatmentin a PHE on the deposit formation The extent of fouling

0

100

200

300

400

500

600

700

0 05 1 15

1Fitting model 10-pass PHE configuration

Dep

osit

mas

s per

chan

nel (

gm

2)

r = kunfkagg

Aggregationlimited zone limited zone

Unfolding

Figure 11 Variation of the dry deposit mass per unit area in thevarious channels with the ratio 119903 for a 10-pass PHE configuration (1corresponds to the thermal profile given in Figure 4 and Table 2)

deposit was monitored by weighing the mass of the dryfouling deposit on the plates

It was shown that

(i) 120573-Lg denaturation is a complex process with a two-step mechanism highly dependent on the calciumcontent

(ii) an increase of the calcium content in the foulingsolution induced a strong increase in the 120573-Lg denat-uration level and consequently in the fouling masswithin the PHE at high temperatures

(iii) the fouling mass distribution also depends on thethermal profiles imposed on the fouling solutions

(iv) the dry deposit mass on each pass of the PHE seemsto be correlated with 119903 = 119896unf119896agg This observationindicates that the knowledge of this parameter isimportant to predict the mass distribution of thefouling deposit

This work clearly shows that 120573-Lg competitive reactions(unfolding and aggregation) governing the growth of foulingfor a WPI solution and the identification of the heat-induceddenaturation kinetic by means of laboratory experiments areprerequisites to control fouling We encourage strongly thefouling community to develop database on these aspects tobe able to predict the distribution of fouling mass whateverthe imposed temperature profile and to mitigate fouling

International Journal of Chemical Engineering 9

Nomenclature

119886 Adjusted parameter in the nonlinear regressionusing (5)

119887 Adjusted parameter in the nonlinear regressionusing (5)

119888 Adjusted parameter in the nonlinear regressionusing (5)

Ca Calcium concentration ppm119862119878 Concentration of the total soluble 120573-Lg g Lminus1

119862119901119901 Specific heat for the product J kgminus1 Kminus1

119862119901ℎ Specific heat for the hot water J kgminus1 Kminus1

119889 Adjusted parameter in the nonlinear regressionusing (5)

119864119860 Activation energy Jmolminus1

119864119860agg 120573-Lg aggregation activation energy Jmolminus1

119864119860unf 120573-Lg unfolding activation energy Jmolminus1

119865119879 Logarithmic mean temperature difference -

119896119899 Denaturation rate constant g1minus119899 L119899minus1sminus1

1198960119899

Denaturation frequency factor g1minus119899 L119899minus1sminus1119896unf Unfolding rate constant g1minus119899 L119899minus1sminus1119896agg Aggregation rate constant g1minus119899 L119899minus1sminus1119872119889 Measured dry fouling deposit mass in a channel

along the PHE g119901 Mass flow rates for the product kg sminus1

ℎ Mass flow rates for the hot water kg sminus1

119899 Heat-induced denaturation reaction order119876119901 WPI fouling solution flow rate L hminus1

119876ℎ Hot water flow rate L hminus1

119903 Ratio between the unfolding and aggregation rateconstants -

119877 The universal gas constant equal to 8314Jmolminus1 Kminus1

119877119891 Fouling resistance m2∘ CWminus1

119878 Heat transfer area m2119879119894ℎ Hot water temperature at the PHE inlet K

119879119894119901 WPI fouling solution temperature at the PHE

inlet K119879119900ℎ Hot water temperature at the PHE outlet K

119879119900119901 Hot water temperature at the PHE outlet K

119880119892 Overall heat transfer coefficient Wmminus2 Kminus1

998779119879LMTD Logarithmic mean temperature difference K

Subscript

agg Aggregation119862119894 Channel number

ℎ Hot water119901 Product119875119894 Plate number

PHE Plate heat exchangerunf UnfoldingWPI Whey protein isolate120572-La 120572-lactalbumin120573-Lg 120573-lactoglobulin119894 Thermal profile number

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

Theauthors are indebted to the ScientificCommittee ofAgro-campus Ouest Rennes and HEI (Hautes Etudes drsquoIngenieurLille) for stimulating discussions and financial support for thePhD Thesis of the first author

References

[1] D M Mulvihill and M Donovan ldquoWhey proteins and theirthermal denaturationmdasha reviewrdquo Irish Journal of Food Scienceand Technology vol 11 no 1 pp 43ndash75 1987

[2] N Sava I Van der PlanckenWClaeys andMHendrickx ldquoThekinetics of heat-induced structural changes of 120573-lactoglobulinrdquoJournal of Dairy Science vol 88 no 5 pp 1646ndash1653 2005

[3] C Schmitt C Bovay M Rouvet S Shojaei-Rami and EKolodziejczyk ldquoWhey protein soluble aggregates from heatingwith NaCl physicochemical interfacial and foaming proper-tiesrdquo Langmuir vol 23 no 8 pp 4155ndash4166 2007

[4] B Bansal and X D Chen ldquoA critical review of milk fouling inheat exchangersrdquo Comprehensive Reviews in Food Science andFood Safety vol 5 no 2 pp 27ndash33 2006

[5] S N Tay and C Yang Assessment of the Hydro-Ball CondenserTube Cleaning System HydroBall Technics (SEA) Pte Singa-pore 2006

[6] HMMuller-SteinhagenHandbook of Heat Exchanger FoulingMitigation and Cleaning Technologies Publico PublicationsEssenGermany Institution ofChemical Engineers RugbyUK2000

[7] M Lalande and J P Tissier ldquoFouling of heat transfer surfacesrelated to 120573-lactoglobulin denaturation during heat processingof milkrdquo Biotechnology Progress vol 1 no 2 pp 131ndash139 1985

[8] P De Jong R Waalewijn and H J L J Van Der LindenldquoValidity of a kinetic fouling model for heat-treatment of wholemilkrdquo Le Lait vol 73 no 3 pp 293ndash302 1993

[9] S D Changani M T Belmar-Beiny and P J Fryer ldquoEngineer-ing and chemical factors associated with fouling and cleaning inmilk processingrdquo Experimental Thermal and Fluid Science vol14 no 4 pp 392ndash406 1997

[10] H Burton ldquoProperties of UHT-processed milkrdquo in Ultra-HighTemperature Processing of Milk and Milk Products pp 254ndash291Elsevier Applied Science Publishers 1988

[11] M T Belmar-Beiny S M Gotham W R Paterson P J Fryerand A M Pritchard ldquoThe effect of Reynolds number andfluid temperature in whey protein foulingrdquo Journal of FoodEngineering vol 19 no 2 pp 119ndash139 1993

[12] P J R Schreier and P J Fryer ldquoHeat exchanger fouling a modelstudy of the scaleup of laboratory datardquo Chemical EngineeringScience vol 50 no 8 pp 1311ndash1321 1995

[13] A J van Asselt M M M Vissers F Smit and P de Jong ldquoIn-line control of foulingrdquo in Proceedings of the Heat ExchangerFouling and CleaningmdashChallenges and Opportunities Engineer-ing Conferences International Irsee Germany June 2005

[14] J Petit A-LHerbig AMoreau andGDelaplace ldquoInfluence ofcalcium on 120573-lactoglobulin denaturation kinetics implications

10 International Journal of Chemical Engineering

in unfolding and aggregation mechanismsrdquo Journal of DairyScience vol 94 no 12 pp 5794ndash5810 2011

[15] M Khaldi P Blanpain-Avet R Guerin et al ldquoEffect of calciumcontent and flow regime on whey protein fouling and cleaningin a plate heat exchangerrdquo Journal of Food Engineering vol 147pp 68ndash78 2015

[16] B T Nielsen H Singh and J M Latham ldquoAggregation ofbovine 120573-lactoglobulins A and B on heating at 75∘Crdquo Interna-tional Dairy Journal vol 6 no 5 pp 519ndash527 1996

[17] H Lindmark-Mansson A Timgren G Alden and M Pauls-son ldquoTwo-dimensional gel electrophoresis of proteins andpeptides in bovinemilkrdquo International Dairy Journal vol 15 no2 pp 111ndash121 2005

[18] A Tolkach and U Kulozik ldquoReaction kinetic pathwayof reversible and irreversible thermal denaturation of 120573-lactoglobulinrdquo Dairy Science and Technology vol 87 no 4-5pp 301ndash315 2007

[19] F Dannenberg and H G Kessler ldquoReaction kinetics of thedenaturation of whey proteins in milkrdquo Journal of Food Sciencevol 53 no 1 pp 258ndash263 1988

[20] J C Leuliet J F Maingonnat and M Lalande ldquoThermalbehaviour of plate heat exchangers with Newtonian and non-Newtonian fluidsrdquo in Proceedings of the Congres Eurotherm 5 et1er Colloque TIFAN pp 1ndash15 Compiegne France 1988

[21] J-W F A Simons H A Kosters R W Visschers and H H Jde Jongh ldquoRole of calcium as trigger in thermal 120573-lactoglobulinaggregationrdquo Archives of Biochemistry and Biophysics vol 406no 2 pp 143ndash152 2002

[22] B T OrsquoKennedy and J S Mounsey ldquoThe dominating effect ofionic strength on the heat-induced denaturation and aggrega-tion of 120573-lactoglobulin in simulated milk ultrafiltraterdquo Interna-tional Dairy Journal vol 19 no 3 pp 123ndash128 2009

[23] M Lalande F Rene and J-P Tissier ldquoFouling and its control inheat exchangers in the dairy industryrdquo Biofouling vol 1 no 3pp 233ndash250 1989

[24] J Visser andT JM Jeurnink ldquoFouling of heat exchangers in thedairy industryrdquo ExperimentalThermal and Fluid Science vol 14no 4 pp 407ndash424 1997

[25] C L Foster M Britten and M L Green ldquoA model heat-exchange apparatus for the investigation of fouling of stainlesssteel surfaces by milk I Deposit formation at 100∘Crdquo Journal ofDairy Research vol 56 no 2 pp 201ndash209 1989

[26] P Havea H Singh and L K Creamer ldquoCharacterizationof heat-induced aggregates of 120573-lactoglobulin 120572-lactalbuminand bovine serum albumin in a whey protein concentrateenvironmentrdquo Journal of Dairy Research vol 68 no 3 pp 483ndash497 2001

[27] G Daufin J P Labbe A Quemerais et al ldquoFouling of a heatexchange surface by whey milk and model fluids an analyticalstudyrdquo Le Lait vol 67 no 3 pp 339ndash364 1987

[28] Y L Xiong ldquoInfluence of pH and ionic environment on thermalaggregation of whey proteinsrdquo Journal of Agricultural and FoodChemistry vol 40 no 3 Article ID 91-5-154 pp 380ndash384 1992

[29] T Phan-XuanDDurand TNicolai L Donato C Schmitt andL Bovetto ldquoTuning the structure of protein particles and gelswith calcium or sodium ionsrdquo Biomacromolecules vol 14 no 6pp 1980ndash1989 2013

[30] M J H Simmons P Jayaraman and P J Fryer ldquoThe effectof temperature and shear rate upon the aggregation of wheyprotein and its implications for milk foulingrdquo Journal of FoodEngineering vol 79 no 2 pp 517ndash528 2007

[31] C P Pappas and J Rothwell ldquoThe effects of heating alone or inthe presence of calcium or lactose on calcium binding to milkproteinsrdquo Food Chemistry vol 42 no 2 pp 183ndash201 1991

[32] P Blanpain-Avet A Hedoux Y Guinet et al ldquoAnalysis byRaman spectroscopy of the conformational structure of wheyproteins constituting fouling deposits during the processing ina heat exchangerrdquo Journal of Food Engineering vol 110 no 1 pp86ndash94 2012

[33] L Bouvier A Moreau G Ronse T Six J Petit and GDelaplace ldquoA CFD model as a tool to simulate 120573-lactoglobulinheat-induced denaturation and aggregation in a plate heatexchangerrdquo Journal of Food Engineering vol 136 pp 56ndash632014

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Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

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Chemical EngineeringInternational Journal of Antennas and

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International Journal of

4 International Journal of Chemical Engineering

Table 2 Operating conditions investigated with the pilot scale experimental set mean inlet and outlet temperatures and flow rates of 120573-Lgconcentrate and hot water

Thermal profile number Total calcium content (ppm) 119879119894119901

(∘C) 119879119900119901

(∘C) 119876119901

(Lsdothminus1) 119876ℎ

(Lsdothminus1)1 100 65 85 300 3002 100 65 85 300 9003 100 65 85 300 1504 100 60 75 300 3001 120 65 85 300 3002 120 65 85 300 9003 120 65 85 300 1504 120 60 75 300 300

P10

Fouling product inlet

Foulingproduct outlet

Hot water inlet Hot water outlet

Ci channel numberPi plate number

P1

C1 C2 C3 C4 C5

Figure 3 Plate heat exchanger flow arrangement

The PHE setup consisted of 10 plates that is 5 passes(one channel per pass) of about 0074m2 projected heattransfer area per plate (0495m length and 015m width)were installed in a countercurrent configuration to optimizethe heat transfer as represented in Figure 3 The defineddesign permitted being closer to industrial heat treatmentconditions

The temperature profile inside the heat exchanger wassimulated with Sphere software (previously developed atour laboratory) temperatures in all passes of hot andcold fluids were calculated from the knowledge of fluidsrsquoinlet temperature and flow rate plate properties and heatexchanger designThe temperature profile is controlled by theheat exchanger inlet parameters product and hot fluid inlettemperatures (119879

119894119901and 119879

119894119908) and product and hot water flow

rates (resp119876119901and119876

ℎ)This was achieved with the operating

conditions indicated in Table 2 displaying the average valuesof temperatures and flow rates recorded during each heattreatment experiment

The temperature profiles displayed in Figure 4 wereobtained by Sphere simulations by employing the operatingconditions summarized in Table 2 Eight fouling runs wereconducted with WPI solutions containing two calcium con-centrations (100 and 120 ppm)

Heat exchanger plates were weighted before each heattreatment experiment After being dried in an air oven at

60

65

70

75

80

85

0 5 10 15Time (s)

12

34

Tem

pera

ture

(∘C)

Figure 4 The imposed thermal profiles in the PHE (Spheresimulations)

50∘C fouled plates were weighted at ambient temperatureand the dry deposit mass on each plate was deduced bysubtraction

The amount of fouling was also monitored by calculat-ing the fouling resistance A linear relationship was visiblebetween the average fouling resistance119877

119891 defined by (3) and

the fouling thickness assuming that the deposit layers arecovered uniformly

1

119880119892(119905)

=1

119880119892(0)

+ 119877119891 (3)

where 119880119892(0)

and 119880119892(119905)

are the overall heat transfer coefficientsat the beginning of fouling runs (ie the overall heat transfercoefficient before the occurrence of fouling) and at time 119905 (iethe overall heat transfer coefficient including the additionalcontribution of fouling)

A logarithmic mean temperature difference (LMTD)method was used to relate the heat transfer rate to theoverall heat transfer coefficient In the case of a no pure

International Journal of Chemical Engineering 5

minus12

minus10

minus8

minus6

minus4

minus2

0

Aggregation limited temperature area

Critical point

Unfolding limited temperature area

300E

minus03

295Eminus03

290E

minus03

285Eminus03

280Eminus03

275Eminus03

270E

minus03

1T (Kminus1)

ln(k

n) sim80 ∘C

Ca 100ppmCa 120ppmPetit et al (2011)

Figure 5 Arrhenius plot for the 120573-Lg denaturation of 1 (ww)WPI fouling solutions at various calcium concentrations (100 and120 ppm)

cross countercurrent flow inside the plate heat exchanger thecorrection factor 119865

119879is classically introduced

119901119862119901119901

(119879119900119901

minus 119879119894119901

) = ℎ119862119901ℎ

(119879119894ℎ

minus 119879119900ℎ

)

= 119880119892119878Δ119879LMTD119865

119879

(4)

where 119862119901119901

and 119862119901ℎ

are respectively the specific heat for theproduct and hot water

119901and

ℎare respectively the mass

flow rates for the product and hot water119879 is the temperatureand 119878 is the heat transfer area

Leuliet et al [20] gave equations for PHE using analogywith shell and tube correction factor Their method was usedfor this work to evaluate the 119865

119879factor

3 Results and Discussion

31 Arrhenius Plots for the 120573-Lg Denaturation of the ModelSolutions The Arrhenius plots for the denaturation reactionof the WPI model fouling solutions at two calcium con-centrations (100 and 120 ppm) were presented in Figure 5This figure shows the temperature influence on the 120573-Lgdenaturation kinetic rate in the range from 65 to 92∘C

Two mechanisms appear in Figure 5 separated by anArrhenius critical temperature of about 80∘C This slopechange suggests two temperature ranges below the criticaltemperature the 120573-Lg denaturation reaction is unfoldinglimited which means that the unfolding reaction is slowerthan aggregation and over 80∘C 120573-Lg denaturation is limitedby the aggregation reaction and in that case aggregation isthe slower reaction

Table 3 Denaturation parameters at the two calcium concentra-tions

Denaturationparameter 100 ppm total calcium 120 ppm total calcium

Unfoldingln(1198960unf) 1248 1172119864119860unf (kJsdotmolminus1) 3845 2712

Aggregationln(1198960agg) 863 831119864119860agg (kJsdotmolminus1) 3607 2604

These results are in agreement with Petit et al [14] Evenin the case of quasi-pure 120573-Lg model solution the criticaltemperature that splits the Arrhenius plot in two linearparts was estimated at 80∘C each temperature range beingrelated to the predominance of the unfolding or aggregationmechanisms indicating that denaturation kinetic rates variedwith temperature However this slope break is less clear in thecase of our model fouling solution probably due to its morecomplex composition (mixture of 120573-Lg and 120572-lactalbumin)

Figure 5 also shows that 120573-Lg denaturation kineticsincreased with calcium concentration Even if the exactcontribution of calcium on the denaturation of 120573-Lg is stillunclear it is speculated that calcium induces protein chargeshielding or conformational changes in 120573-Lg structure [2122] favouring both unfolding and aggregation reactionsThis result illustrates that it is essential to know the exactcontent of calcium in the fouling solutions to have a clearview of the denaturation reaction This information notcommonly evaluated nowadays in the literature is essentialto the development of accurate model of fouling based onengineering denaturation reaction

The frequency factor logarithms (ln 1198960) and activationenergies (119864

119860) obtained by fitting Arrhenius plot regression

for the unfolding and aggregation denaturation mechanism(noted resp unf and agg) are shown in Table 3

32 Fouling Mass Distribution in the PHE Figure 6 repre-sents the deposit layer formed in the first and last channelsof the PHE at respectively 65∘C (inlet temperature) and85∘C (outlet temperature) after fouling run conducted with1 (ww) WPI solution containing 100 ppm of total calciumAt the highest temperature the fouling layer is white verythick and homogeneous It clearly appears that very lowfouling is obtained in the first channel of the PHE where thebulk temperature is lower than 70∘C Fouling is not expectedto occur under 65ndash72∘C [23 24] These observations are inagreement with Foster et al [25] work which showed thatdeposit increases with temperature making fouling rougherand more adherent to hot surfaces

Figure 7 represents the fouling results obtained with 1(ww) WPI model solution containing 100 and 120 ppm oftotal calcium at different temperature profiles This figureshows that the dry deposit is not uniform and is distributeddifferently depending on the thermal profile and the calcium

6 International Journal of Chemical Engineering

Figure 6 Pictures of the deposit collected on heat exchanger surfacein the second and last channels of the PHE

concentration Indeed for the first solution at 100 ppm cal-cium the depositmass increases linearly to reach amaximumin the 5th channel whatever the imposed thermal profileHowever at 120 ppm calcium the deposit mass reached astationary value of about 260 gm2 over 74∘C (2nd channeltemperature) for the first three temperature profiles whichconsisted in a foulingmaximum limitThis increasing depositmass at low temperatures resulted from the strong increase of120573-Lg denaturation level between 65∘C (1st channel tempera-ture) and 74∘C (2nd channel temperature) temperature rangefor which the120573-Lg denaturation reaction becomes significant[17 26] The thermal profile 4 increases linearly reaching amaximum of 845 gm2 in the 5th channel

The deposit mass is negligible for the thermal profile 4at 100 and 120 ppm calcium owing to the lack of denatured120573-Lg in the bulk at such low temperatures It is suggested that120573-Lg fouled hot surfaces only when the bulk temperature washigh enough to allow 120573-Lg denaturation

Figure 8 represents the effect of the temperature profileon the total amount of deposit mass in the PHE for thetwo fouling solutions It can be observed that for the sameinlet and outlet product temperature the total deposit massvaried with the calcium concentration This is the case ofthe thermal profile 1 for which the total deposit mass goesfrom 1415 gm2 at 100 ppm calcium to 2082 gm2 at 120 ppmcalcium This was also observed for the temperature profiles3 and 4 However for the thermal profile 2 the totalamount of deposit was very close at 100 and 120 ppm calcium

This difference of fouling distributions obtained at vari-ous calcium concentrations demonstrates the major role ofthe temperature profile on 120573-Lg fouling and its distributionin the PHE

33 Effect of Thermal Profiles and Calcium Concentrationon Fouling Rate Figure 9 shows the fouling rate behaviourduring heating of the WPI solution at 100 and 120 ppmcalcium in the PHE for each thermal profile An increase inthe fouling rate with time is evident A difference between

the fouling rates can be observed for the four temperatureprofiles at 100 ppm and 120 ppm calcium

The results also show that the fouling potential of WPI inthe PHE increases with the increasing temperature Indeedfor temperature range of 65ndash85∘C fouling rate is alteredand favoured by higher amount of calcium in the modelfluid It can be noted that for the thermal profile 4 (60ndash75∘C) fouling resistance curves for calcium content of 100and 120 ppm calcium were superposed These results are notcontradictorywith the assumption ofDaufin et al [27] Xiong[28] and Simons et al [21] who asserted that calcium caninteract with the aspartic and glutamic acid carboxyl groupof the 120573-Lg and so favour the growth of the deposit bystabilizing protein aggregates This is because calcium ionsform bridges between adsorbed proteins and the proteinaggregates occurring in the bulk consequentlymodifying theprotein aggregation rate and leading to a greater cohesionbetween the protein aggregates which in turn change thedeposit structure [29] Simmons et al [30] revealed anincrease in deposition upon a Couette surface due to calciumions and a modification in the appearance of the depositfor a temperature range 75ndash90∘C In addition Pappas andRothwell [31] showed that 120573-Lg completely aggregated toform compact structures when heated with calcium from 80to 110∘C

34 Relationship between 120573-Lg Heat Denaturation Rate Con-stants and the Distribution of the Deposit Mass along the PHETo study the relationship between the chemical reaction of the120573-Lg denaturation and the deposit formation rate within thePHE the deposit mass distribution in the different channelof the PHE was plotted against 119903 = 119896unf119896agg (Figure 10) Thevalue of 119903 was calculated at the average temperature of thechannel 119896unf and 119896agg represent respectively the reaction rateconstants for the unfolding and aggregation limited zonesdeduced from the Arrhenius plots (Figure 5) for the twoWPImodel fouling solutions (at 100 and 120 ppm of calcium)

For each fouling solution it could be observed that an119878 curve (plot of the deposit mass per channel versus 119903)consolidates the fouling data whatever the imposed thermalprofile The 119878 curves could be described for all fouling runsby the following function

119872119889

= 119886 +119887 minus 119886

1 + (119888119903)119889 (5)

where 119872119889is the measured dry fouling deposit mass per

channel along the PHE and 119886 119887 119888 and 119889 are four constantsThe twomaster curves representing the deposit mass per

channel versus the ratio 119903 contained different characteristiczones

(i) an unfolding limited zone with a sharp increase of thedeposit mass per channel with 119903

(ii) an aggregation limited zone where the deposit massper channel seems to reach a limiting value

Indeed the curve of the dry deposit mass at 100 ppm calciumshowed a sharp increase at values of 119903 close to 022 (relative

International Journal of Chemical Engineering 7

0

50

100

150

200

250

300

350

1 2 3 4 5Channel number

Dep

osit

mas

s per

chan

nel (

gm

2 )

1 23 4

(a)

0

50

100

150

200

250

300

350

1 2 3 4 5Channel number

Dep

osit

mas

s per

chan

nel (

gm

2 )

1 23 4

(b)

Figure 7 Fouling mass distribution related to the projected heat transfer area per plaque in each channel of the PHE for the two foulingsolutions 1 (ww) WPI solution containing (a) 100 ppm calcium and (b) 120 ppm calcium (119894 corresponds to the thermal profile numbergiven in Figure 4 and Table 2)

0

500

1000

1500

2000

2500

3

4

1

1 2 2

3

4Tota

l dep

osit

mas

s (g

m2)

Ca 100ppmCa 120ppm

Figure 8 Total amount of the deposit mass in the PHE perunit area for 1 (ww) WPI fouling solutions at various calciumconcentrations (100 and 120 ppm) and for different temperatureprofiles (119894 corresponds to the thermal profile number given inFigure 4 and Table 2)

to the fouling beginning) then reaching a plateau at 119903 = 091For the second fouling solution (WPI solution containing120 ppm of calcium) the increase of 119903 values starts at 023 andthe maximum of the deposit mass is reached at 119903 = 067

In summary for the two fouling model solutions andthe operating conditions investigated it can be observed thata sharp increase of deposit mass occurs when 119903 is locatedbetween 022 and 089 (corresponding to bulk temperaturesranging from 65 to 805∘C) The fact that the deposit massincreases strongly when 119903 is below 1 shows that the unfoldinglimited zone controls the growth of the deposit mass Thisresult also shows that the deposit mass per channel decreases

0

50

100

150

200

250

300

0 05 1 15 2Time (h)

1234

1234

Foul

ing

resis

tanc

eRflowast100000

(m2 middot∘ C

W)

Figure 9 Fouling resistance evolution with time measured alongthe PHE Various symbols refer to various fouling runs with varyingthermal profiles and various calcium content for the 1 ww WPIsolutions (closed symbols 100 ppm calcium open symbols 120 ppmcalcium) (119894 corresponds to the thermal profile number given inFigure 4 and Table 2)

when the aggregation reaction is high enough to consumethe unfolded species under aggregates forms This result isin agreement with the previous observation of van Asseltet al [13] and consistent with the work of Blanpain-Avetet al [32] Indeed these authors conclude from fouled deposit

8 International Journal of Chemical Engineering

0

100

200

300

400

500

600

700

800

0 02 04 06 08 1 12 14

1 23 41 23 4

Aggregationlimited zone

Clog

ging

of t

he

inst

allat

ion

Unfolding limited zone

Dep

osit

mas

s per

chan

nel (

gm

2)

r = kunfkagg

Fitting model Ca 120ppmFitting model Ca 100ppm

Figure 10 Plots of the dry deposit masses per unit area versus theratio of unfolding and aggregation rate constants for the 1 wwWPI solutions (closed symbols 100 ppm calcium open symbols120 ppm calcium) (119894 corresponds to the thermal profile numbergiven in Figure 4 and Table 2)

analysis by Raman spectroscopy that protein aggregates arenot present in the deposit This result is also supportedby the recent study of Bouvier et al [33] which showedthat a correlation can be established between the unfolded120573-Lg content within the PHE and the dry deposit massdistribution

Unfortunately it was not possible to perform pilot scaleexperiments at higher values of 119903 (119903 gt 140) correspondingto the channel temperature above 844∘C because of theclogging of the installation

To ascertain validity of themaster curve independently ofthe PHE configuration further experiments were conductedat PHE consisting of 10 passes (one channel per pass) for a 1(ww) WPI model solution at 100 ppm calcium One thermalprofile (1) out of the four tested for the five channels of thePHE was imposed Figure 11 represents the deposit mass perchannel versus the ratio 119903

Also in this case the fouling mass is reasonably wellcorrelated to the ratio 119903 showing the following

(i) the importance of determining this indicator forpredicting fouling mass distribution

(ii) the robustness of the approach

4 Conclusions

Fouling experiments were performed with 1 (ww) WPIsolutions at two different calcium concentrations in order toinvestigate the effect of the operating conditions associatedwith the chemical denaturation reactivity of heat treatmentin a PHE on the deposit formation The extent of fouling

0

100

200

300

400

500

600

700

0 05 1 15

1Fitting model 10-pass PHE configuration

Dep

osit

mas

s per

chan

nel (

gm

2)

r = kunfkagg

Aggregationlimited zone limited zone

Unfolding

Figure 11 Variation of the dry deposit mass per unit area in thevarious channels with the ratio 119903 for a 10-pass PHE configuration (1corresponds to the thermal profile given in Figure 4 and Table 2)

deposit was monitored by weighing the mass of the dryfouling deposit on the plates

It was shown that

(i) 120573-Lg denaturation is a complex process with a two-step mechanism highly dependent on the calciumcontent

(ii) an increase of the calcium content in the foulingsolution induced a strong increase in the 120573-Lg denat-uration level and consequently in the fouling masswithin the PHE at high temperatures

(iii) the fouling mass distribution also depends on thethermal profiles imposed on the fouling solutions

(iv) the dry deposit mass on each pass of the PHE seemsto be correlated with 119903 = 119896unf119896agg This observationindicates that the knowledge of this parameter isimportant to predict the mass distribution of thefouling deposit

This work clearly shows that 120573-Lg competitive reactions(unfolding and aggregation) governing the growth of foulingfor a WPI solution and the identification of the heat-induceddenaturation kinetic by means of laboratory experiments areprerequisites to control fouling We encourage strongly thefouling community to develop database on these aspects tobe able to predict the distribution of fouling mass whateverthe imposed temperature profile and to mitigate fouling

International Journal of Chemical Engineering 9

Nomenclature

119886 Adjusted parameter in the nonlinear regressionusing (5)

119887 Adjusted parameter in the nonlinear regressionusing (5)

119888 Adjusted parameter in the nonlinear regressionusing (5)

Ca Calcium concentration ppm119862119878 Concentration of the total soluble 120573-Lg g Lminus1

119862119901119901 Specific heat for the product J kgminus1 Kminus1

119862119901ℎ Specific heat for the hot water J kgminus1 Kminus1

119889 Adjusted parameter in the nonlinear regressionusing (5)

119864119860 Activation energy Jmolminus1

119864119860agg 120573-Lg aggregation activation energy Jmolminus1

119864119860unf 120573-Lg unfolding activation energy Jmolminus1

119865119879 Logarithmic mean temperature difference -

119896119899 Denaturation rate constant g1minus119899 L119899minus1sminus1

1198960119899

Denaturation frequency factor g1minus119899 L119899minus1sminus1119896unf Unfolding rate constant g1minus119899 L119899minus1sminus1119896agg Aggregation rate constant g1minus119899 L119899minus1sminus1119872119889 Measured dry fouling deposit mass in a channel

along the PHE g119901 Mass flow rates for the product kg sminus1

ℎ Mass flow rates for the hot water kg sminus1

119899 Heat-induced denaturation reaction order119876119901 WPI fouling solution flow rate L hminus1

119876ℎ Hot water flow rate L hminus1

119903 Ratio between the unfolding and aggregation rateconstants -

119877 The universal gas constant equal to 8314Jmolminus1 Kminus1

119877119891 Fouling resistance m2∘ CWminus1

119878 Heat transfer area m2119879119894ℎ Hot water temperature at the PHE inlet K

119879119894119901 WPI fouling solution temperature at the PHE

inlet K119879119900ℎ Hot water temperature at the PHE outlet K

119879119900119901 Hot water temperature at the PHE outlet K

119880119892 Overall heat transfer coefficient Wmminus2 Kminus1

998779119879LMTD Logarithmic mean temperature difference K

Subscript

agg Aggregation119862119894 Channel number

ℎ Hot water119901 Product119875119894 Plate number

PHE Plate heat exchangerunf UnfoldingWPI Whey protein isolate120572-La 120572-lactalbumin120573-Lg 120573-lactoglobulin119894 Thermal profile number

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

Theauthors are indebted to the ScientificCommittee ofAgro-campus Ouest Rennes and HEI (Hautes Etudes drsquoIngenieurLille) for stimulating discussions and financial support for thePhD Thesis of the first author

References

[1] D M Mulvihill and M Donovan ldquoWhey proteins and theirthermal denaturationmdasha reviewrdquo Irish Journal of Food Scienceand Technology vol 11 no 1 pp 43ndash75 1987

[2] N Sava I Van der PlanckenWClaeys andMHendrickx ldquoThekinetics of heat-induced structural changes of 120573-lactoglobulinrdquoJournal of Dairy Science vol 88 no 5 pp 1646ndash1653 2005

[3] C Schmitt C Bovay M Rouvet S Shojaei-Rami and EKolodziejczyk ldquoWhey protein soluble aggregates from heatingwith NaCl physicochemical interfacial and foaming proper-tiesrdquo Langmuir vol 23 no 8 pp 4155ndash4166 2007

[4] B Bansal and X D Chen ldquoA critical review of milk fouling inheat exchangersrdquo Comprehensive Reviews in Food Science andFood Safety vol 5 no 2 pp 27ndash33 2006

[5] S N Tay and C Yang Assessment of the Hydro-Ball CondenserTube Cleaning System HydroBall Technics (SEA) Pte Singa-pore 2006

[6] HMMuller-SteinhagenHandbook of Heat Exchanger FoulingMitigation and Cleaning Technologies Publico PublicationsEssenGermany Institution ofChemical Engineers RugbyUK2000

[7] M Lalande and J P Tissier ldquoFouling of heat transfer surfacesrelated to 120573-lactoglobulin denaturation during heat processingof milkrdquo Biotechnology Progress vol 1 no 2 pp 131ndash139 1985

[8] P De Jong R Waalewijn and H J L J Van Der LindenldquoValidity of a kinetic fouling model for heat-treatment of wholemilkrdquo Le Lait vol 73 no 3 pp 293ndash302 1993

[9] S D Changani M T Belmar-Beiny and P J Fryer ldquoEngineer-ing and chemical factors associated with fouling and cleaning inmilk processingrdquo Experimental Thermal and Fluid Science vol14 no 4 pp 392ndash406 1997

[10] H Burton ldquoProperties of UHT-processed milkrdquo in Ultra-HighTemperature Processing of Milk and Milk Products pp 254ndash291Elsevier Applied Science Publishers 1988

[11] M T Belmar-Beiny S M Gotham W R Paterson P J Fryerand A M Pritchard ldquoThe effect of Reynolds number andfluid temperature in whey protein foulingrdquo Journal of FoodEngineering vol 19 no 2 pp 119ndash139 1993

[12] P J R Schreier and P J Fryer ldquoHeat exchanger fouling a modelstudy of the scaleup of laboratory datardquo Chemical EngineeringScience vol 50 no 8 pp 1311ndash1321 1995

[13] A J van Asselt M M M Vissers F Smit and P de Jong ldquoIn-line control of foulingrdquo in Proceedings of the Heat ExchangerFouling and CleaningmdashChallenges and Opportunities Engineer-ing Conferences International Irsee Germany June 2005

[14] J Petit A-LHerbig AMoreau andGDelaplace ldquoInfluence ofcalcium on 120573-lactoglobulin denaturation kinetics implications

10 International Journal of Chemical Engineering

in unfolding and aggregation mechanismsrdquo Journal of DairyScience vol 94 no 12 pp 5794ndash5810 2011

[15] M Khaldi P Blanpain-Avet R Guerin et al ldquoEffect of calciumcontent and flow regime on whey protein fouling and cleaningin a plate heat exchangerrdquo Journal of Food Engineering vol 147pp 68ndash78 2015

[16] B T Nielsen H Singh and J M Latham ldquoAggregation ofbovine 120573-lactoglobulins A and B on heating at 75∘Crdquo Interna-tional Dairy Journal vol 6 no 5 pp 519ndash527 1996

[17] H Lindmark-Mansson A Timgren G Alden and M Pauls-son ldquoTwo-dimensional gel electrophoresis of proteins andpeptides in bovinemilkrdquo International Dairy Journal vol 15 no2 pp 111ndash121 2005

[18] A Tolkach and U Kulozik ldquoReaction kinetic pathwayof reversible and irreversible thermal denaturation of 120573-lactoglobulinrdquo Dairy Science and Technology vol 87 no 4-5pp 301ndash315 2007

[19] F Dannenberg and H G Kessler ldquoReaction kinetics of thedenaturation of whey proteins in milkrdquo Journal of Food Sciencevol 53 no 1 pp 258ndash263 1988

[20] J C Leuliet J F Maingonnat and M Lalande ldquoThermalbehaviour of plate heat exchangers with Newtonian and non-Newtonian fluidsrdquo in Proceedings of the Congres Eurotherm 5 et1er Colloque TIFAN pp 1ndash15 Compiegne France 1988

[21] J-W F A Simons H A Kosters R W Visschers and H H Jde Jongh ldquoRole of calcium as trigger in thermal 120573-lactoglobulinaggregationrdquo Archives of Biochemistry and Biophysics vol 406no 2 pp 143ndash152 2002

[22] B T OrsquoKennedy and J S Mounsey ldquoThe dominating effect ofionic strength on the heat-induced denaturation and aggrega-tion of 120573-lactoglobulin in simulated milk ultrafiltraterdquo Interna-tional Dairy Journal vol 19 no 3 pp 123ndash128 2009

[23] M Lalande F Rene and J-P Tissier ldquoFouling and its control inheat exchangers in the dairy industryrdquo Biofouling vol 1 no 3pp 233ndash250 1989

[24] J Visser andT JM Jeurnink ldquoFouling of heat exchangers in thedairy industryrdquo ExperimentalThermal and Fluid Science vol 14no 4 pp 407ndash424 1997

[25] C L Foster M Britten and M L Green ldquoA model heat-exchange apparatus for the investigation of fouling of stainlesssteel surfaces by milk I Deposit formation at 100∘Crdquo Journal ofDairy Research vol 56 no 2 pp 201ndash209 1989

[26] P Havea H Singh and L K Creamer ldquoCharacterizationof heat-induced aggregates of 120573-lactoglobulin 120572-lactalbuminand bovine serum albumin in a whey protein concentrateenvironmentrdquo Journal of Dairy Research vol 68 no 3 pp 483ndash497 2001

[27] G Daufin J P Labbe A Quemerais et al ldquoFouling of a heatexchange surface by whey milk and model fluids an analyticalstudyrdquo Le Lait vol 67 no 3 pp 339ndash364 1987

[28] Y L Xiong ldquoInfluence of pH and ionic environment on thermalaggregation of whey proteinsrdquo Journal of Agricultural and FoodChemistry vol 40 no 3 Article ID 91-5-154 pp 380ndash384 1992

[29] T Phan-XuanDDurand TNicolai L Donato C Schmitt andL Bovetto ldquoTuning the structure of protein particles and gelswith calcium or sodium ionsrdquo Biomacromolecules vol 14 no 6pp 1980ndash1989 2013

[30] M J H Simmons P Jayaraman and P J Fryer ldquoThe effectof temperature and shear rate upon the aggregation of wheyprotein and its implications for milk foulingrdquo Journal of FoodEngineering vol 79 no 2 pp 517ndash528 2007

[31] C P Pappas and J Rothwell ldquoThe effects of heating alone or inthe presence of calcium or lactose on calcium binding to milkproteinsrdquo Food Chemistry vol 42 no 2 pp 183ndash201 1991

[32] P Blanpain-Avet A Hedoux Y Guinet et al ldquoAnalysis byRaman spectroscopy of the conformational structure of wheyproteins constituting fouling deposits during the processing ina heat exchangerrdquo Journal of Food Engineering vol 110 no 1 pp86ndash94 2012

[33] L Bouvier A Moreau G Ronse T Six J Petit and GDelaplace ldquoA CFD model as a tool to simulate 120573-lactoglobulinheat-induced denaturation and aggregation in a plate heatexchangerrdquo Journal of Food Engineering vol 136 pp 56ndash632014

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DistributedSensor Networks

International Journal of

International Journal of Chemical Engineering 5

minus12

minus10

minus8

minus6

minus4

minus2

0

Aggregation limited temperature area

Critical point

Unfolding limited temperature area

300E

minus03

295Eminus03

290E

minus03

285Eminus03

280Eminus03

275Eminus03

270E

minus03

1T (Kminus1)

ln(k

n) sim80 ∘C

Ca 100ppmCa 120ppmPetit et al (2011)

Figure 5 Arrhenius plot for the 120573-Lg denaturation of 1 (ww)WPI fouling solutions at various calcium concentrations (100 and120 ppm)

cross countercurrent flow inside the plate heat exchanger thecorrection factor 119865

119879is classically introduced

119901119862119901119901

(119879119900119901

minus 119879119894119901

) = ℎ119862119901ℎ

(119879119894ℎ

minus 119879119900ℎ

)

= 119880119892119878Δ119879LMTD119865

119879

(4)

where 119862119901119901

and 119862119901ℎ

are respectively the specific heat for theproduct and hot water

119901and

ℎare respectively the mass

flow rates for the product and hot water119879 is the temperatureand 119878 is the heat transfer area

Leuliet et al [20] gave equations for PHE using analogywith shell and tube correction factor Their method was usedfor this work to evaluate the 119865

119879factor

3 Results and Discussion

31 Arrhenius Plots for the 120573-Lg Denaturation of the ModelSolutions The Arrhenius plots for the denaturation reactionof the WPI model fouling solutions at two calcium con-centrations (100 and 120 ppm) were presented in Figure 5This figure shows the temperature influence on the 120573-Lgdenaturation kinetic rate in the range from 65 to 92∘C

Two mechanisms appear in Figure 5 separated by anArrhenius critical temperature of about 80∘C This slopechange suggests two temperature ranges below the criticaltemperature the 120573-Lg denaturation reaction is unfoldinglimited which means that the unfolding reaction is slowerthan aggregation and over 80∘C 120573-Lg denaturation is limitedby the aggregation reaction and in that case aggregation isthe slower reaction

Table 3 Denaturation parameters at the two calcium concentra-tions

Denaturationparameter 100 ppm total calcium 120 ppm total calcium

Unfoldingln(1198960unf) 1248 1172119864119860unf (kJsdotmolminus1) 3845 2712

Aggregationln(1198960agg) 863 831119864119860agg (kJsdotmolminus1) 3607 2604

These results are in agreement with Petit et al [14] Evenin the case of quasi-pure 120573-Lg model solution the criticaltemperature that splits the Arrhenius plot in two linearparts was estimated at 80∘C each temperature range beingrelated to the predominance of the unfolding or aggregationmechanisms indicating that denaturation kinetic rates variedwith temperature However this slope break is less clear in thecase of our model fouling solution probably due to its morecomplex composition (mixture of 120573-Lg and 120572-lactalbumin)

Figure 5 also shows that 120573-Lg denaturation kineticsincreased with calcium concentration Even if the exactcontribution of calcium on the denaturation of 120573-Lg is stillunclear it is speculated that calcium induces protein chargeshielding or conformational changes in 120573-Lg structure [2122] favouring both unfolding and aggregation reactionsThis result illustrates that it is essential to know the exactcontent of calcium in the fouling solutions to have a clearview of the denaturation reaction This information notcommonly evaluated nowadays in the literature is essentialto the development of accurate model of fouling based onengineering denaturation reaction

The frequency factor logarithms (ln 1198960) and activationenergies (119864

119860) obtained by fitting Arrhenius plot regression

for the unfolding and aggregation denaturation mechanism(noted resp unf and agg) are shown in Table 3

32 Fouling Mass Distribution in the PHE Figure 6 repre-sents the deposit layer formed in the first and last channelsof the PHE at respectively 65∘C (inlet temperature) and85∘C (outlet temperature) after fouling run conducted with1 (ww) WPI solution containing 100 ppm of total calciumAt the highest temperature the fouling layer is white verythick and homogeneous It clearly appears that very lowfouling is obtained in the first channel of the PHE where thebulk temperature is lower than 70∘C Fouling is not expectedto occur under 65ndash72∘C [23 24] These observations are inagreement with Foster et al [25] work which showed thatdeposit increases with temperature making fouling rougherand more adherent to hot surfaces

Figure 7 represents the fouling results obtained with 1(ww) WPI model solution containing 100 and 120 ppm oftotal calcium at different temperature profiles This figureshows that the dry deposit is not uniform and is distributeddifferently depending on the thermal profile and the calcium

6 International Journal of Chemical Engineering

Figure 6 Pictures of the deposit collected on heat exchanger surfacein the second and last channels of the PHE

concentration Indeed for the first solution at 100 ppm cal-cium the depositmass increases linearly to reach amaximumin the 5th channel whatever the imposed thermal profileHowever at 120 ppm calcium the deposit mass reached astationary value of about 260 gm2 over 74∘C (2nd channeltemperature) for the first three temperature profiles whichconsisted in a foulingmaximum limitThis increasing depositmass at low temperatures resulted from the strong increase of120573-Lg denaturation level between 65∘C (1st channel tempera-ture) and 74∘C (2nd channel temperature) temperature rangefor which the120573-Lg denaturation reaction becomes significant[17 26] The thermal profile 4 increases linearly reaching amaximum of 845 gm2 in the 5th channel

The deposit mass is negligible for the thermal profile 4at 100 and 120 ppm calcium owing to the lack of denatured120573-Lg in the bulk at such low temperatures It is suggested that120573-Lg fouled hot surfaces only when the bulk temperature washigh enough to allow 120573-Lg denaturation

Figure 8 represents the effect of the temperature profileon the total amount of deposit mass in the PHE for thetwo fouling solutions It can be observed that for the sameinlet and outlet product temperature the total deposit massvaried with the calcium concentration This is the case ofthe thermal profile 1 for which the total deposit mass goesfrom 1415 gm2 at 100 ppm calcium to 2082 gm2 at 120 ppmcalcium This was also observed for the temperature profiles3 and 4 However for the thermal profile 2 the totalamount of deposit was very close at 100 and 120 ppm calcium

This difference of fouling distributions obtained at vari-ous calcium concentrations demonstrates the major role ofthe temperature profile on 120573-Lg fouling and its distributionin the PHE

33 Effect of Thermal Profiles and Calcium Concentrationon Fouling Rate Figure 9 shows the fouling rate behaviourduring heating of the WPI solution at 100 and 120 ppmcalcium in the PHE for each thermal profile An increase inthe fouling rate with time is evident A difference between

the fouling rates can be observed for the four temperatureprofiles at 100 ppm and 120 ppm calcium

The results also show that the fouling potential of WPI inthe PHE increases with the increasing temperature Indeedfor temperature range of 65ndash85∘C fouling rate is alteredand favoured by higher amount of calcium in the modelfluid It can be noted that for the thermal profile 4 (60ndash75∘C) fouling resistance curves for calcium content of 100and 120 ppm calcium were superposed These results are notcontradictorywith the assumption ofDaufin et al [27] Xiong[28] and Simons et al [21] who asserted that calcium caninteract with the aspartic and glutamic acid carboxyl groupof the 120573-Lg and so favour the growth of the deposit bystabilizing protein aggregates This is because calcium ionsform bridges between adsorbed proteins and the proteinaggregates occurring in the bulk consequentlymodifying theprotein aggregation rate and leading to a greater cohesionbetween the protein aggregates which in turn change thedeposit structure [29] Simmons et al [30] revealed anincrease in deposition upon a Couette surface due to calciumions and a modification in the appearance of the depositfor a temperature range 75ndash90∘C In addition Pappas andRothwell [31] showed that 120573-Lg completely aggregated toform compact structures when heated with calcium from 80to 110∘C

34 Relationship between 120573-Lg Heat Denaturation Rate Con-stants and the Distribution of the Deposit Mass along the PHETo study the relationship between the chemical reaction of the120573-Lg denaturation and the deposit formation rate within thePHE the deposit mass distribution in the different channelof the PHE was plotted against 119903 = 119896unf119896agg (Figure 10) Thevalue of 119903 was calculated at the average temperature of thechannel 119896unf and 119896agg represent respectively the reaction rateconstants for the unfolding and aggregation limited zonesdeduced from the Arrhenius plots (Figure 5) for the twoWPImodel fouling solutions (at 100 and 120 ppm of calcium)

For each fouling solution it could be observed that an119878 curve (plot of the deposit mass per channel versus 119903)consolidates the fouling data whatever the imposed thermalprofile The 119878 curves could be described for all fouling runsby the following function

119872119889

= 119886 +119887 minus 119886

1 + (119888119903)119889 (5)

where 119872119889is the measured dry fouling deposit mass per

channel along the PHE and 119886 119887 119888 and 119889 are four constantsThe twomaster curves representing the deposit mass per

channel versus the ratio 119903 contained different characteristiczones

(i) an unfolding limited zone with a sharp increase of thedeposit mass per channel with 119903

(ii) an aggregation limited zone where the deposit massper channel seems to reach a limiting value

Indeed the curve of the dry deposit mass at 100 ppm calciumshowed a sharp increase at values of 119903 close to 022 (relative

International Journal of Chemical Engineering 7

0

50

100

150

200

250

300

350

1 2 3 4 5Channel number

Dep

osit

mas

s per

chan

nel (

gm

2 )

1 23 4

(a)

0

50

100

150

200

250

300

350

1 2 3 4 5Channel number

Dep

osit

mas

s per

chan

nel (

gm

2 )

1 23 4

(b)

Figure 7 Fouling mass distribution related to the projected heat transfer area per plaque in each channel of the PHE for the two foulingsolutions 1 (ww) WPI solution containing (a) 100 ppm calcium and (b) 120 ppm calcium (119894 corresponds to the thermal profile numbergiven in Figure 4 and Table 2)

0

500

1000

1500

2000

2500

3

4

1

1 2 2

3

4Tota

l dep

osit

mas

s (g

m2)

Ca 100ppmCa 120ppm

Figure 8 Total amount of the deposit mass in the PHE perunit area for 1 (ww) WPI fouling solutions at various calciumconcentrations (100 and 120 ppm) and for different temperatureprofiles (119894 corresponds to the thermal profile number given inFigure 4 and Table 2)

to the fouling beginning) then reaching a plateau at 119903 = 091For the second fouling solution (WPI solution containing120 ppm of calcium) the increase of 119903 values starts at 023 andthe maximum of the deposit mass is reached at 119903 = 067

In summary for the two fouling model solutions andthe operating conditions investigated it can be observed thata sharp increase of deposit mass occurs when 119903 is locatedbetween 022 and 089 (corresponding to bulk temperaturesranging from 65 to 805∘C) The fact that the deposit massincreases strongly when 119903 is below 1 shows that the unfoldinglimited zone controls the growth of the deposit mass Thisresult also shows that the deposit mass per channel decreases

0

50

100

150

200

250

300

0 05 1 15 2Time (h)

1234

1234

Foul

ing

resis

tanc

eRflowast100000

(m2 middot∘ C

W)

Figure 9 Fouling resistance evolution with time measured alongthe PHE Various symbols refer to various fouling runs with varyingthermal profiles and various calcium content for the 1 ww WPIsolutions (closed symbols 100 ppm calcium open symbols 120 ppmcalcium) (119894 corresponds to the thermal profile number given inFigure 4 and Table 2)

when the aggregation reaction is high enough to consumethe unfolded species under aggregates forms This result isin agreement with the previous observation of van Asseltet al [13] and consistent with the work of Blanpain-Avetet al [32] Indeed these authors conclude from fouled deposit

8 International Journal of Chemical Engineering

0

100

200

300

400

500

600

700

800

0 02 04 06 08 1 12 14

1 23 41 23 4

Aggregationlimited zone

Clog

ging

of t

he

inst

allat

ion

Unfolding limited zone

Dep

osit

mas

s per

chan

nel (

gm

2)

r = kunfkagg

Fitting model Ca 120ppmFitting model Ca 100ppm

Figure 10 Plots of the dry deposit masses per unit area versus theratio of unfolding and aggregation rate constants for the 1 wwWPI solutions (closed symbols 100 ppm calcium open symbols120 ppm calcium) (119894 corresponds to the thermal profile numbergiven in Figure 4 and Table 2)

analysis by Raman spectroscopy that protein aggregates arenot present in the deposit This result is also supportedby the recent study of Bouvier et al [33] which showedthat a correlation can be established between the unfolded120573-Lg content within the PHE and the dry deposit massdistribution

Unfortunately it was not possible to perform pilot scaleexperiments at higher values of 119903 (119903 gt 140) correspondingto the channel temperature above 844∘C because of theclogging of the installation

To ascertain validity of themaster curve independently ofthe PHE configuration further experiments were conductedat PHE consisting of 10 passes (one channel per pass) for a 1(ww) WPI model solution at 100 ppm calcium One thermalprofile (1) out of the four tested for the five channels of thePHE was imposed Figure 11 represents the deposit mass perchannel versus the ratio 119903

Also in this case the fouling mass is reasonably wellcorrelated to the ratio 119903 showing the following

(i) the importance of determining this indicator forpredicting fouling mass distribution

(ii) the robustness of the approach

4 Conclusions

Fouling experiments were performed with 1 (ww) WPIsolutions at two different calcium concentrations in order toinvestigate the effect of the operating conditions associatedwith the chemical denaturation reactivity of heat treatmentin a PHE on the deposit formation The extent of fouling

0

100

200

300

400

500

600

700

0 05 1 15

1Fitting model 10-pass PHE configuration

Dep

osit

mas

s per

chan

nel (

gm

2)

r = kunfkagg

Aggregationlimited zone limited zone

Unfolding

Figure 11 Variation of the dry deposit mass per unit area in thevarious channels with the ratio 119903 for a 10-pass PHE configuration (1corresponds to the thermal profile given in Figure 4 and Table 2)

deposit was monitored by weighing the mass of the dryfouling deposit on the plates

It was shown that

(i) 120573-Lg denaturation is a complex process with a two-step mechanism highly dependent on the calciumcontent

(ii) an increase of the calcium content in the foulingsolution induced a strong increase in the 120573-Lg denat-uration level and consequently in the fouling masswithin the PHE at high temperatures

(iii) the fouling mass distribution also depends on thethermal profiles imposed on the fouling solutions

(iv) the dry deposit mass on each pass of the PHE seemsto be correlated with 119903 = 119896unf119896agg This observationindicates that the knowledge of this parameter isimportant to predict the mass distribution of thefouling deposit

This work clearly shows that 120573-Lg competitive reactions(unfolding and aggregation) governing the growth of foulingfor a WPI solution and the identification of the heat-induceddenaturation kinetic by means of laboratory experiments areprerequisites to control fouling We encourage strongly thefouling community to develop database on these aspects tobe able to predict the distribution of fouling mass whateverthe imposed temperature profile and to mitigate fouling

International Journal of Chemical Engineering 9

Nomenclature

119886 Adjusted parameter in the nonlinear regressionusing (5)

119887 Adjusted parameter in the nonlinear regressionusing (5)

119888 Adjusted parameter in the nonlinear regressionusing (5)

Ca Calcium concentration ppm119862119878 Concentration of the total soluble 120573-Lg g Lminus1

119862119901119901 Specific heat for the product J kgminus1 Kminus1

119862119901ℎ Specific heat for the hot water J kgminus1 Kminus1

119889 Adjusted parameter in the nonlinear regressionusing (5)

119864119860 Activation energy Jmolminus1

119864119860agg 120573-Lg aggregation activation energy Jmolminus1

119864119860unf 120573-Lg unfolding activation energy Jmolminus1

119865119879 Logarithmic mean temperature difference -

119896119899 Denaturation rate constant g1minus119899 L119899minus1sminus1

1198960119899

Denaturation frequency factor g1minus119899 L119899minus1sminus1119896unf Unfolding rate constant g1minus119899 L119899minus1sminus1119896agg Aggregation rate constant g1minus119899 L119899minus1sminus1119872119889 Measured dry fouling deposit mass in a channel

along the PHE g119901 Mass flow rates for the product kg sminus1

ℎ Mass flow rates for the hot water kg sminus1

119899 Heat-induced denaturation reaction order119876119901 WPI fouling solution flow rate L hminus1

119876ℎ Hot water flow rate L hminus1

119903 Ratio between the unfolding and aggregation rateconstants -

119877 The universal gas constant equal to 8314Jmolminus1 Kminus1

119877119891 Fouling resistance m2∘ CWminus1

119878 Heat transfer area m2119879119894ℎ Hot water temperature at the PHE inlet K

119879119894119901 WPI fouling solution temperature at the PHE

inlet K119879119900ℎ Hot water temperature at the PHE outlet K

119879119900119901 Hot water temperature at the PHE outlet K

119880119892 Overall heat transfer coefficient Wmminus2 Kminus1

998779119879LMTD Logarithmic mean temperature difference K

Subscript

agg Aggregation119862119894 Channel number

ℎ Hot water119901 Product119875119894 Plate number

PHE Plate heat exchangerunf UnfoldingWPI Whey protein isolate120572-La 120572-lactalbumin120573-Lg 120573-lactoglobulin119894 Thermal profile number

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

Theauthors are indebted to the ScientificCommittee ofAgro-campus Ouest Rennes and HEI (Hautes Etudes drsquoIngenieurLille) for stimulating discussions and financial support for thePhD Thesis of the first author

References

[1] D M Mulvihill and M Donovan ldquoWhey proteins and theirthermal denaturationmdasha reviewrdquo Irish Journal of Food Scienceand Technology vol 11 no 1 pp 43ndash75 1987

[2] N Sava I Van der PlanckenWClaeys andMHendrickx ldquoThekinetics of heat-induced structural changes of 120573-lactoglobulinrdquoJournal of Dairy Science vol 88 no 5 pp 1646ndash1653 2005

[3] C Schmitt C Bovay M Rouvet S Shojaei-Rami and EKolodziejczyk ldquoWhey protein soluble aggregates from heatingwith NaCl physicochemical interfacial and foaming proper-tiesrdquo Langmuir vol 23 no 8 pp 4155ndash4166 2007

[4] B Bansal and X D Chen ldquoA critical review of milk fouling inheat exchangersrdquo Comprehensive Reviews in Food Science andFood Safety vol 5 no 2 pp 27ndash33 2006

[5] S N Tay and C Yang Assessment of the Hydro-Ball CondenserTube Cleaning System HydroBall Technics (SEA) Pte Singa-pore 2006

[6] HMMuller-SteinhagenHandbook of Heat Exchanger FoulingMitigation and Cleaning Technologies Publico PublicationsEssenGermany Institution ofChemical Engineers RugbyUK2000

[7] M Lalande and J P Tissier ldquoFouling of heat transfer surfacesrelated to 120573-lactoglobulin denaturation during heat processingof milkrdquo Biotechnology Progress vol 1 no 2 pp 131ndash139 1985

[8] P De Jong R Waalewijn and H J L J Van Der LindenldquoValidity of a kinetic fouling model for heat-treatment of wholemilkrdquo Le Lait vol 73 no 3 pp 293ndash302 1993

[9] S D Changani M T Belmar-Beiny and P J Fryer ldquoEngineer-ing and chemical factors associated with fouling and cleaning inmilk processingrdquo Experimental Thermal and Fluid Science vol14 no 4 pp 392ndash406 1997

[10] H Burton ldquoProperties of UHT-processed milkrdquo in Ultra-HighTemperature Processing of Milk and Milk Products pp 254ndash291Elsevier Applied Science Publishers 1988

[11] M T Belmar-Beiny S M Gotham W R Paterson P J Fryerand A M Pritchard ldquoThe effect of Reynolds number andfluid temperature in whey protein foulingrdquo Journal of FoodEngineering vol 19 no 2 pp 119ndash139 1993

[12] P J R Schreier and P J Fryer ldquoHeat exchanger fouling a modelstudy of the scaleup of laboratory datardquo Chemical EngineeringScience vol 50 no 8 pp 1311ndash1321 1995

[13] A J van Asselt M M M Vissers F Smit and P de Jong ldquoIn-line control of foulingrdquo in Proceedings of the Heat ExchangerFouling and CleaningmdashChallenges and Opportunities Engineer-ing Conferences International Irsee Germany June 2005

[14] J Petit A-LHerbig AMoreau andGDelaplace ldquoInfluence ofcalcium on 120573-lactoglobulin denaturation kinetics implications

10 International Journal of Chemical Engineering

in unfolding and aggregation mechanismsrdquo Journal of DairyScience vol 94 no 12 pp 5794ndash5810 2011

[15] M Khaldi P Blanpain-Avet R Guerin et al ldquoEffect of calciumcontent and flow regime on whey protein fouling and cleaningin a plate heat exchangerrdquo Journal of Food Engineering vol 147pp 68ndash78 2015

[16] B T Nielsen H Singh and J M Latham ldquoAggregation ofbovine 120573-lactoglobulins A and B on heating at 75∘Crdquo Interna-tional Dairy Journal vol 6 no 5 pp 519ndash527 1996

[17] H Lindmark-Mansson A Timgren G Alden and M Pauls-son ldquoTwo-dimensional gel electrophoresis of proteins andpeptides in bovinemilkrdquo International Dairy Journal vol 15 no2 pp 111ndash121 2005

[18] A Tolkach and U Kulozik ldquoReaction kinetic pathwayof reversible and irreversible thermal denaturation of 120573-lactoglobulinrdquo Dairy Science and Technology vol 87 no 4-5pp 301ndash315 2007

[19] F Dannenberg and H G Kessler ldquoReaction kinetics of thedenaturation of whey proteins in milkrdquo Journal of Food Sciencevol 53 no 1 pp 258ndash263 1988

[20] J C Leuliet J F Maingonnat and M Lalande ldquoThermalbehaviour of plate heat exchangers with Newtonian and non-Newtonian fluidsrdquo in Proceedings of the Congres Eurotherm 5 et1er Colloque TIFAN pp 1ndash15 Compiegne France 1988

[21] J-W F A Simons H A Kosters R W Visschers and H H Jde Jongh ldquoRole of calcium as trigger in thermal 120573-lactoglobulinaggregationrdquo Archives of Biochemistry and Biophysics vol 406no 2 pp 143ndash152 2002

[22] B T OrsquoKennedy and J S Mounsey ldquoThe dominating effect ofionic strength on the heat-induced denaturation and aggrega-tion of 120573-lactoglobulin in simulated milk ultrafiltraterdquo Interna-tional Dairy Journal vol 19 no 3 pp 123ndash128 2009

[23] M Lalande F Rene and J-P Tissier ldquoFouling and its control inheat exchangers in the dairy industryrdquo Biofouling vol 1 no 3pp 233ndash250 1989

[24] J Visser andT JM Jeurnink ldquoFouling of heat exchangers in thedairy industryrdquo ExperimentalThermal and Fluid Science vol 14no 4 pp 407ndash424 1997

[25] C L Foster M Britten and M L Green ldquoA model heat-exchange apparatus for the investigation of fouling of stainlesssteel surfaces by milk I Deposit formation at 100∘Crdquo Journal ofDairy Research vol 56 no 2 pp 201ndash209 1989

[26] P Havea H Singh and L K Creamer ldquoCharacterizationof heat-induced aggregates of 120573-lactoglobulin 120572-lactalbuminand bovine serum albumin in a whey protein concentrateenvironmentrdquo Journal of Dairy Research vol 68 no 3 pp 483ndash497 2001

[27] G Daufin J P Labbe A Quemerais et al ldquoFouling of a heatexchange surface by whey milk and model fluids an analyticalstudyrdquo Le Lait vol 67 no 3 pp 339ndash364 1987

[28] Y L Xiong ldquoInfluence of pH and ionic environment on thermalaggregation of whey proteinsrdquo Journal of Agricultural and FoodChemistry vol 40 no 3 Article ID 91-5-154 pp 380ndash384 1992

[29] T Phan-XuanDDurand TNicolai L Donato C Schmitt andL Bovetto ldquoTuning the structure of protein particles and gelswith calcium or sodium ionsrdquo Biomacromolecules vol 14 no 6pp 1980ndash1989 2013

[30] M J H Simmons P Jayaraman and P J Fryer ldquoThe effectof temperature and shear rate upon the aggregation of wheyprotein and its implications for milk foulingrdquo Journal of FoodEngineering vol 79 no 2 pp 517ndash528 2007

[31] C P Pappas and J Rothwell ldquoThe effects of heating alone or inthe presence of calcium or lactose on calcium binding to milkproteinsrdquo Food Chemistry vol 42 no 2 pp 183ndash201 1991

[32] P Blanpain-Avet A Hedoux Y Guinet et al ldquoAnalysis byRaman spectroscopy of the conformational structure of wheyproteins constituting fouling deposits during the processing ina heat exchangerrdquo Journal of Food Engineering vol 110 no 1 pp86ndash94 2012

[33] L Bouvier A Moreau G Ronse T Six J Petit and GDelaplace ldquoA CFD model as a tool to simulate 120573-lactoglobulinheat-induced denaturation and aggregation in a plate heatexchangerrdquo Journal of Food Engineering vol 136 pp 56ndash632014

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Chemical EngineeringInternational Journal of Antennas and

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DistributedSensor Networks

International Journal of

6 International Journal of Chemical Engineering

Figure 6 Pictures of the deposit collected on heat exchanger surfacein the second and last channels of the PHE

concentration Indeed for the first solution at 100 ppm cal-cium the depositmass increases linearly to reach amaximumin the 5th channel whatever the imposed thermal profileHowever at 120 ppm calcium the deposit mass reached astationary value of about 260 gm2 over 74∘C (2nd channeltemperature) for the first three temperature profiles whichconsisted in a foulingmaximum limitThis increasing depositmass at low temperatures resulted from the strong increase of120573-Lg denaturation level between 65∘C (1st channel tempera-ture) and 74∘C (2nd channel temperature) temperature rangefor which the120573-Lg denaturation reaction becomes significant[17 26] The thermal profile 4 increases linearly reaching amaximum of 845 gm2 in the 5th channel

The deposit mass is negligible for the thermal profile 4at 100 and 120 ppm calcium owing to the lack of denatured120573-Lg in the bulk at such low temperatures It is suggested that120573-Lg fouled hot surfaces only when the bulk temperature washigh enough to allow 120573-Lg denaturation

Figure 8 represents the effect of the temperature profileon the total amount of deposit mass in the PHE for thetwo fouling solutions It can be observed that for the sameinlet and outlet product temperature the total deposit massvaried with the calcium concentration This is the case ofthe thermal profile 1 for which the total deposit mass goesfrom 1415 gm2 at 100 ppm calcium to 2082 gm2 at 120 ppmcalcium This was also observed for the temperature profiles3 and 4 However for the thermal profile 2 the totalamount of deposit was very close at 100 and 120 ppm calcium

This difference of fouling distributions obtained at vari-ous calcium concentrations demonstrates the major role ofthe temperature profile on 120573-Lg fouling and its distributionin the PHE

33 Effect of Thermal Profiles and Calcium Concentrationon Fouling Rate Figure 9 shows the fouling rate behaviourduring heating of the WPI solution at 100 and 120 ppmcalcium in the PHE for each thermal profile An increase inthe fouling rate with time is evident A difference between

the fouling rates can be observed for the four temperatureprofiles at 100 ppm and 120 ppm calcium

The results also show that the fouling potential of WPI inthe PHE increases with the increasing temperature Indeedfor temperature range of 65ndash85∘C fouling rate is alteredand favoured by higher amount of calcium in the modelfluid It can be noted that for the thermal profile 4 (60ndash75∘C) fouling resistance curves for calcium content of 100and 120 ppm calcium were superposed These results are notcontradictorywith the assumption ofDaufin et al [27] Xiong[28] and Simons et al [21] who asserted that calcium caninteract with the aspartic and glutamic acid carboxyl groupof the 120573-Lg and so favour the growth of the deposit bystabilizing protein aggregates This is because calcium ionsform bridges between adsorbed proteins and the proteinaggregates occurring in the bulk consequentlymodifying theprotein aggregation rate and leading to a greater cohesionbetween the protein aggregates which in turn change thedeposit structure [29] Simmons et al [30] revealed anincrease in deposition upon a Couette surface due to calciumions and a modification in the appearance of the depositfor a temperature range 75ndash90∘C In addition Pappas andRothwell [31] showed that 120573-Lg completely aggregated toform compact structures when heated with calcium from 80to 110∘C

34 Relationship between 120573-Lg Heat Denaturation Rate Con-stants and the Distribution of the Deposit Mass along the PHETo study the relationship between the chemical reaction of the120573-Lg denaturation and the deposit formation rate within thePHE the deposit mass distribution in the different channelof the PHE was plotted against 119903 = 119896unf119896agg (Figure 10) Thevalue of 119903 was calculated at the average temperature of thechannel 119896unf and 119896agg represent respectively the reaction rateconstants for the unfolding and aggregation limited zonesdeduced from the Arrhenius plots (Figure 5) for the twoWPImodel fouling solutions (at 100 and 120 ppm of calcium)

For each fouling solution it could be observed that an119878 curve (plot of the deposit mass per channel versus 119903)consolidates the fouling data whatever the imposed thermalprofile The 119878 curves could be described for all fouling runsby the following function

119872119889

= 119886 +119887 minus 119886

1 + (119888119903)119889 (5)

where 119872119889is the measured dry fouling deposit mass per

channel along the PHE and 119886 119887 119888 and 119889 are four constantsThe twomaster curves representing the deposit mass per

channel versus the ratio 119903 contained different characteristiczones

(i) an unfolding limited zone with a sharp increase of thedeposit mass per channel with 119903

(ii) an aggregation limited zone where the deposit massper channel seems to reach a limiting value

Indeed the curve of the dry deposit mass at 100 ppm calciumshowed a sharp increase at values of 119903 close to 022 (relative

International Journal of Chemical Engineering 7

0

50

100

150

200

250

300

350

1 2 3 4 5Channel number

Dep

osit

mas

s per

chan

nel (

gm

2 )

1 23 4

(a)

0

50

100

150

200

250

300

350

1 2 3 4 5Channel number

Dep

osit

mas

s per

chan

nel (

gm

2 )

1 23 4

(b)

Figure 7 Fouling mass distribution related to the projected heat transfer area per plaque in each channel of the PHE for the two foulingsolutions 1 (ww) WPI solution containing (a) 100 ppm calcium and (b) 120 ppm calcium (119894 corresponds to the thermal profile numbergiven in Figure 4 and Table 2)

0

500

1000

1500

2000

2500

3

4

1

1 2 2

3

4Tota

l dep

osit

mas

s (g

m2)

Ca 100ppmCa 120ppm

Figure 8 Total amount of the deposit mass in the PHE perunit area for 1 (ww) WPI fouling solutions at various calciumconcentrations (100 and 120 ppm) and for different temperatureprofiles (119894 corresponds to the thermal profile number given inFigure 4 and Table 2)

to the fouling beginning) then reaching a plateau at 119903 = 091For the second fouling solution (WPI solution containing120 ppm of calcium) the increase of 119903 values starts at 023 andthe maximum of the deposit mass is reached at 119903 = 067

In summary for the two fouling model solutions andthe operating conditions investigated it can be observed thata sharp increase of deposit mass occurs when 119903 is locatedbetween 022 and 089 (corresponding to bulk temperaturesranging from 65 to 805∘C) The fact that the deposit massincreases strongly when 119903 is below 1 shows that the unfoldinglimited zone controls the growth of the deposit mass Thisresult also shows that the deposit mass per channel decreases

0

50

100

150

200

250

300

0 05 1 15 2Time (h)

1234

1234

Foul

ing

resis

tanc

eRflowast100000

(m2 middot∘ C

W)

Figure 9 Fouling resistance evolution with time measured alongthe PHE Various symbols refer to various fouling runs with varyingthermal profiles and various calcium content for the 1 ww WPIsolutions (closed symbols 100 ppm calcium open symbols 120 ppmcalcium) (119894 corresponds to the thermal profile number given inFigure 4 and Table 2)

when the aggregation reaction is high enough to consumethe unfolded species under aggregates forms This result isin agreement with the previous observation of van Asseltet al [13] and consistent with the work of Blanpain-Avetet al [32] Indeed these authors conclude from fouled deposit

8 International Journal of Chemical Engineering

0

100

200

300

400

500

600

700

800

0 02 04 06 08 1 12 14

1 23 41 23 4

Aggregationlimited zone

Clog

ging

of t

he

inst

allat

ion

Unfolding limited zone

Dep

osit

mas

s per

chan

nel (

gm

2)

r = kunfkagg

Fitting model Ca 120ppmFitting model Ca 100ppm

Figure 10 Plots of the dry deposit masses per unit area versus theratio of unfolding and aggregation rate constants for the 1 wwWPI solutions (closed symbols 100 ppm calcium open symbols120 ppm calcium) (119894 corresponds to the thermal profile numbergiven in Figure 4 and Table 2)

analysis by Raman spectroscopy that protein aggregates arenot present in the deposit This result is also supportedby the recent study of Bouvier et al [33] which showedthat a correlation can be established between the unfolded120573-Lg content within the PHE and the dry deposit massdistribution

Unfortunately it was not possible to perform pilot scaleexperiments at higher values of 119903 (119903 gt 140) correspondingto the channel temperature above 844∘C because of theclogging of the installation

To ascertain validity of themaster curve independently ofthe PHE configuration further experiments were conductedat PHE consisting of 10 passes (one channel per pass) for a 1(ww) WPI model solution at 100 ppm calcium One thermalprofile (1) out of the four tested for the five channels of thePHE was imposed Figure 11 represents the deposit mass perchannel versus the ratio 119903

Also in this case the fouling mass is reasonably wellcorrelated to the ratio 119903 showing the following

(i) the importance of determining this indicator forpredicting fouling mass distribution

(ii) the robustness of the approach

4 Conclusions

Fouling experiments were performed with 1 (ww) WPIsolutions at two different calcium concentrations in order toinvestigate the effect of the operating conditions associatedwith the chemical denaturation reactivity of heat treatmentin a PHE on the deposit formation The extent of fouling

0

100

200

300

400

500

600

700

0 05 1 15

1Fitting model 10-pass PHE configuration

Dep

osit

mas

s per

chan

nel (

gm

2)

r = kunfkagg

Aggregationlimited zone limited zone

Unfolding

Figure 11 Variation of the dry deposit mass per unit area in thevarious channels with the ratio 119903 for a 10-pass PHE configuration (1corresponds to the thermal profile given in Figure 4 and Table 2)

deposit was monitored by weighing the mass of the dryfouling deposit on the plates

It was shown that

(i) 120573-Lg denaturation is a complex process with a two-step mechanism highly dependent on the calciumcontent

(ii) an increase of the calcium content in the foulingsolution induced a strong increase in the 120573-Lg denat-uration level and consequently in the fouling masswithin the PHE at high temperatures

(iii) the fouling mass distribution also depends on thethermal profiles imposed on the fouling solutions

(iv) the dry deposit mass on each pass of the PHE seemsto be correlated with 119903 = 119896unf119896agg This observationindicates that the knowledge of this parameter isimportant to predict the mass distribution of thefouling deposit

This work clearly shows that 120573-Lg competitive reactions(unfolding and aggregation) governing the growth of foulingfor a WPI solution and the identification of the heat-induceddenaturation kinetic by means of laboratory experiments areprerequisites to control fouling We encourage strongly thefouling community to develop database on these aspects tobe able to predict the distribution of fouling mass whateverthe imposed temperature profile and to mitigate fouling

International Journal of Chemical Engineering 9

Nomenclature

119886 Adjusted parameter in the nonlinear regressionusing (5)

119887 Adjusted parameter in the nonlinear regressionusing (5)

119888 Adjusted parameter in the nonlinear regressionusing (5)

Ca Calcium concentration ppm119862119878 Concentration of the total soluble 120573-Lg g Lminus1

119862119901119901 Specific heat for the product J kgminus1 Kminus1

119862119901ℎ Specific heat for the hot water J kgminus1 Kminus1

119889 Adjusted parameter in the nonlinear regressionusing (5)

119864119860 Activation energy Jmolminus1

119864119860agg 120573-Lg aggregation activation energy Jmolminus1

119864119860unf 120573-Lg unfolding activation energy Jmolminus1

119865119879 Logarithmic mean temperature difference -

119896119899 Denaturation rate constant g1minus119899 L119899minus1sminus1

1198960119899

Denaturation frequency factor g1minus119899 L119899minus1sminus1119896unf Unfolding rate constant g1minus119899 L119899minus1sminus1119896agg Aggregation rate constant g1minus119899 L119899minus1sminus1119872119889 Measured dry fouling deposit mass in a channel

along the PHE g119901 Mass flow rates for the product kg sminus1

ℎ Mass flow rates for the hot water kg sminus1

119899 Heat-induced denaturation reaction order119876119901 WPI fouling solution flow rate L hminus1

119876ℎ Hot water flow rate L hminus1

119903 Ratio between the unfolding and aggregation rateconstants -

119877 The universal gas constant equal to 8314Jmolminus1 Kminus1

119877119891 Fouling resistance m2∘ CWminus1

119878 Heat transfer area m2119879119894ℎ Hot water temperature at the PHE inlet K

119879119894119901 WPI fouling solution temperature at the PHE

inlet K119879119900ℎ Hot water temperature at the PHE outlet K

119879119900119901 Hot water temperature at the PHE outlet K

119880119892 Overall heat transfer coefficient Wmminus2 Kminus1

998779119879LMTD Logarithmic mean temperature difference K

Subscript

agg Aggregation119862119894 Channel number

ℎ Hot water119901 Product119875119894 Plate number

PHE Plate heat exchangerunf UnfoldingWPI Whey protein isolate120572-La 120572-lactalbumin120573-Lg 120573-lactoglobulin119894 Thermal profile number

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

Theauthors are indebted to the ScientificCommittee ofAgro-campus Ouest Rennes and HEI (Hautes Etudes drsquoIngenieurLille) for stimulating discussions and financial support for thePhD Thesis of the first author

References

[1] D M Mulvihill and M Donovan ldquoWhey proteins and theirthermal denaturationmdasha reviewrdquo Irish Journal of Food Scienceand Technology vol 11 no 1 pp 43ndash75 1987

[2] N Sava I Van der PlanckenWClaeys andMHendrickx ldquoThekinetics of heat-induced structural changes of 120573-lactoglobulinrdquoJournal of Dairy Science vol 88 no 5 pp 1646ndash1653 2005

[3] C Schmitt C Bovay M Rouvet S Shojaei-Rami and EKolodziejczyk ldquoWhey protein soluble aggregates from heatingwith NaCl physicochemical interfacial and foaming proper-tiesrdquo Langmuir vol 23 no 8 pp 4155ndash4166 2007

[4] B Bansal and X D Chen ldquoA critical review of milk fouling inheat exchangersrdquo Comprehensive Reviews in Food Science andFood Safety vol 5 no 2 pp 27ndash33 2006

[5] S N Tay and C Yang Assessment of the Hydro-Ball CondenserTube Cleaning System HydroBall Technics (SEA) Pte Singa-pore 2006

[6] HMMuller-SteinhagenHandbook of Heat Exchanger FoulingMitigation and Cleaning Technologies Publico PublicationsEssenGermany Institution ofChemical Engineers RugbyUK2000

[7] M Lalande and J P Tissier ldquoFouling of heat transfer surfacesrelated to 120573-lactoglobulin denaturation during heat processingof milkrdquo Biotechnology Progress vol 1 no 2 pp 131ndash139 1985

[8] P De Jong R Waalewijn and H J L J Van Der LindenldquoValidity of a kinetic fouling model for heat-treatment of wholemilkrdquo Le Lait vol 73 no 3 pp 293ndash302 1993

[9] S D Changani M T Belmar-Beiny and P J Fryer ldquoEngineer-ing and chemical factors associated with fouling and cleaning inmilk processingrdquo Experimental Thermal and Fluid Science vol14 no 4 pp 392ndash406 1997

[10] H Burton ldquoProperties of UHT-processed milkrdquo in Ultra-HighTemperature Processing of Milk and Milk Products pp 254ndash291Elsevier Applied Science Publishers 1988

[11] M T Belmar-Beiny S M Gotham W R Paterson P J Fryerand A M Pritchard ldquoThe effect of Reynolds number andfluid temperature in whey protein foulingrdquo Journal of FoodEngineering vol 19 no 2 pp 119ndash139 1993

[12] P J R Schreier and P J Fryer ldquoHeat exchanger fouling a modelstudy of the scaleup of laboratory datardquo Chemical EngineeringScience vol 50 no 8 pp 1311ndash1321 1995

[13] A J van Asselt M M M Vissers F Smit and P de Jong ldquoIn-line control of foulingrdquo in Proceedings of the Heat ExchangerFouling and CleaningmdashChallenges and Opportunities Engineer-ing Conferences International Irsee Germany June 2005

[14] J Petit A-LHerbig AMoreau andGDelaplace ldquoInfluence ofcalcium on 120573-lactoglobulin denaturation kinetics implications

10 International Journal of Chemical Engineering

in unfolding and aggregation mechanismsrdquo Journal of DairyScience vol 94 no 12 pp 5794ndash5810 2011

[15] M Khaldi P Blanpain-Avet R Guerin et al ldquoEffect of calciumcontent and flow regime on whey protein fouling and cleaningin a plate heat exchangerrdquo Journal of Food Engineering vol 147pp 68ndash78 2015

[16] B T Nielsen H Singh and J M Latham ldquoAggregation ofbovine 120573-lactoglobulins A and B on heating at 75∘Crdquo Interna-tional Dairy Journal vol 6 no 5 pp 519ndash527 1996

[17] H Lindmark-Mansson A Timgren G Alden and M Pauls-son ldquoTwo-dimensional gel electrophoresis of proteins andpeptides in bovinemilkrdquo International Dairy Journal vol 15 no2 pp 111ndash121 2005

[18] A Tolkach and U Kulozik ldquoReaction kinetic pathwayof reversible and irreversible thermal denaturation of 120573-lactoglobulinrdquo Dairy Science and Technology vol 87 no 4-5pp 301ndash315 2007

[19] F Dannenberg and H G Kessler ldquoReaction kinetics of thedenaturation of whey proteins in milkrdquo Journal of Food Sciencevol 53 no 1 pp 258ndash263 1988

[20] J C Leuliet J F Maingonnat and M Lalande ldquoThermalbehaviour of plate heat exchangers with Newtonian and non-Newtonian fluidsrdquo in Proceedings of the Congres Eurotherm 5 et1er Colloque TIFAN pp 1ndash15 Compiegne France 1988

[21] J-W F A Simons H A Kosters R W Visschers and H H Jde Jongh ldquoRole of calcium as trigger in thermal 120573-lactoglobulinaggregationrdquo Archives of Biochemistry and Biophysics vol 406no 2 pp 143ndash152 2002

[22] B T OrsquoKennedy and J S Mounsey ldquoThe dominating effect ofionic strength on the heat-induced denaturation and aggrega-tion of 120573-lactoglobulin in simulated milk ultrafiltraterdquo Interna-tional Dairy Journal vol 19 no 3 pp 123ndash128 2009

[23] M Lalande F Rene and J-P Tissier ldquoFouling and its control inheat exchangers in the dairy industryrdquo Biofouling vol 1 no 3pp 233ndash250 1989

[24] J Visser andT JM Jeurnink ldquoFouling of heat exchangers in thedairy industryrdquo ExperimentalThermal and Fluid Science vol 14no 4 pp 407ndash424 1997

[25] C L Foster M Britten and M L Green ldquoA model heat-exchange apparatus for the investigation of fouling of stainlesssteel surfaces by milk I Deposit formation at 100∘Crdquo Journal ofDairy Research vol 56 no 2 pp 201ndash209 1989

[26] P Havea H Singh and L K Creamer ldquoCharacterizationof heat-induced aggregates of 120573-lactoglobulin 120572-lactalbuminand bovine serum albumin in a whey protein concentrateenvironmentrdquo Journal of Dairy Research vol 68 no 3 pp 483ndash497 2001

[27] G Daufin J P Labbe A Quemerais et al ldquoFouling of a heatexchange surface by whey milk and model fluids an analyticalstudyrdquo Le Lait vol 67 no 3 pp 339ndash364 1987

[28] Y L Xiong ldquoInfluence of pH and ionic environment on thermalaggregation of whey proteinsrdquo Journal of Agricultural and FoodChemistry vol 40 no 3 Article ID 91-5-154 pp 380ndash384 1992

[29] T Phan-XuanDDurand TNicolai L Donato C Schmitt andL Bovetto ldquoTuning the structure of protein particles and gelswith calcium or sodium ionsrdquo Biomacromolecules vol 14 no 6pp 1980ndash1989 2013

[30] M J H Simmons P Jayaraman and P J Fryer ldquoThe effectof temperature and shear rate upon the aggregation of wheyprotein and its implications for milk foulingrdquo Journal of FoodEngineering vol 79 no 2 pp 517ndash528 2007

[31] C P Pappas and J Rothwell ldquoThe effects of heating alone or inthe presence of calcium or lactose on calcium binding to milkproteinsrdquo Food Chemistry vol 42 no 2 pp 183ndash201 1991

[32] P Blanpain-Avet A Hedoux Y Guinet et al ldquoAnalysis byRaman spectroscopy of the conformational structure of wheyproteins constituting fouling deposits during the processing ina heat exchangerrdquo Journal of Food Engineering vol 110 no 1 pp86ndash94 2012

[33] L Bouvier A Moreau G Ronse T Six J Petit and GDelaplace ldquoA CFD model as a tool to simulate 120573-lactoglobulinheat-induced denaturation and aggregation in a plate heatexchangerrdquo Journal of Food Engineering vol 136 pp 56ndash632014

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

International Journal of Chemical Engineering 7

0

50

100

150

200

250

300

350

1 2 3 4 5Channel number

Dep

osit

mas

s per

chan

nel (

gm

2 )

1 23 4

(a)

0

50

100

150

200

250

300

350

1 2 3 4 5Channel number

Dep

osit

mas

s per

chan

nel (

gm

2 )

1 23 4

(b)

Figure 7 Fouling mass distribution related to the projected heat transfer area per plaque in each channel of the PHE for the two foulingsolutions 1 (ww) WPI solution containing (a) 100 ppm calcium and (b) 120 ppm calcium (119894 corresponds to the thermal profile numbergiven in Figure 4 and Table 2)

0

500

1000

1500

2000

2500

3

4

1

1 2 2

3

4Tota

l dep

osit

mas

s (g

m2)

Ca 100ppmCa 120ppm

Figure 8 Total amount of the deposit mass in the PHE perunit area for 1 (ww) WPI fouling solutions at various calciumconcentrations (100 and 120 ppm) and for different temperatureprofiles (119894 corresponds to the thermal profile number given inFigure 4 and Table 2)

to the fouling beginning) then reaching a plateau at 119903 = 091For the second fouling solution (WPI solution containing120 ppm of calcium) the increase of 119903 values starts at 023 andthe maximum of the deposit mass is reached at 119903 = 067

In summary for the two fouling model solutions andthe operating conditions investigated it can be observed thata sharp increase of deposit mass occurs when 119903 is locatedbetween 022 and 089 (corresponding to bulk temperaturesranging from 65 to 805∘C) The fact that the deposit massincreases strongly when 119903 is below 1 shows that the unfoldinglimited zone controls the growth of the deposit mass Thisresult also shows that the deposit mass per channel decreases

0

50

100

150

200

250

300

0 05 1 15 2Time (h)

1234

1234

Foul

ing

resis

tanc

eRflowast100000

(m2 middot∘ C

W)

Figure 9 Fouling resistance evolution with time measured alongthe PHE Various symbols refer to various fouling runs with varyingthermal profiles and various calcium content for the 1 ww WPIsolutions (closed symbols 100 ppm calcium open symbols 120 ppmcalcium) (119894 corresponds to the thermal profile number given inFigure 4 and Table 2)

when the aggregation reaction is high enough to consumethe unfolded species under aggregates forms This result isin agreement with the previous observation of van Asseltet al [13] and consistent with the work of Blanpain-Avetet al [32] Indeed these authors conclude from fouled deposit

8 International Journal of Chemical Engineering

0

100

200

300

400

500

600

700

800

0 02 04 06 08 1 12 14

1 23 41 23 4

Aggregationlimited zone

Clog

ging

of t

he

inst

allat

ion

Unfolding limited zone

Dep

osit

mas

s per

chan

nel (

gm

2)

r = kunfkagg

Fitting model Ca 120ppmFitting model Ca 100ppm

Figure 10 Plots of the dry deposit masses per unit area versus theratio of unfolding and aggregation rate constants for the 1 wwWPI solutions (closed symbols 100 ppm calcium open symbols120 ppm calcium) (119894 corresponds to the thermal profile numbergiven in Figure 4 and Table 2)

analysis by Raman spectroscopy that protein aggregates arenot present in the deposit This result is also supportedby the recent study of Bouvier et al [33] which showedthat a correlation can be established between the unfolded120573-Lg content within the PHE and the dry deposit massdistribution

Unfortunately it was not possible to perform pilot scaleexperiments at higher values of 119903 (119903 gt 140) correspondingto the channel temperature above 844∘C because of theclogging of the installation

To ascertain validity of themaster curve independently ofthe PHE configuration further experiments were conductedat PHE consisting of 10 passes (one channel per pass) for a 1(ww) WPI model solution at 100 ppm calcium One thermalprofile (1) out of the four tested for the five channels of thePHE was imposed Figure 11 represents the deposit mass perchannel versus the ratio 119903

Also in this case the fouling mass is reasonably wellcorrelated to the ratio 119903 showing the following

(i) the importance of determining this indicator forpredicting fouling mass distribution

(ii) the robustness of the approach

4 Conclusions

Fouling experiments were performed with 1 (ww) WPIsolutions at two different calcium concentrations in order toinvestigate the effect of the operating conditions associatedwith the chemical denaturation reactivity of heat treatmentin a PHE on the deposit formation The extent of fouling

0

100

200

300

400

500

600

700

0 05 1 15

1Fitting model 10-pass PHE configuration

Dep

osit

mas

s per

chan

nel (

gm

2)

r = kunfkagg

Aggregationlimited zone limited zone

Unfolding

Figure 11 Variation of the dry deposit mass per unit area in thevarious channels with the ratio 119903 for a 10-pass PHE configuration (1corresponds to the thermal profile given in Figure 4 and Table 2)

deposit was monitored by weighing the mass of the dryfouling deposit on the plates

It was shown that

(i) 120573-Lg denaturation is a complex process with a two-step mechanism highly dependent on the calciumcontent

(ii) an increase of the calcium content in the foulingsolution induced a strong increase in the 120573-Lg denat-uration level and consequently in the fouling masswithin the PHE at high temperatures

(iii) the fouling mass distribution also depends on thethermal profiles imposed on the fouling solutions

(iv) the dry deposit mass on each pass of the PHE seemsto be correlated with 119903 = 119896unf119896agg This observationindicates that the knowledge of this parameter isimportant to predict the mass distribution of thefouling deposit

This work clearly shows that 120573-Lg competitive reactions(unfolding and aggregation) governing the growth of foulingfor a WPI solution and the identification of the heat-induceddenaturation kinetic by means of laboratory experiments areprerequisites to control fouling We encourage strongly thefouling community to develop database on these aspects tobe able to predict the distribution of fouling mass whateverthe imposed temperature profile and to mitigate fouling

International Journal of Chemical Engineering 9

Nomenclature

119886 Adjusted parameter in the nonlinear regressionusing (5)

119887 Adjusted parameter in the nonlinear regressionusing (5)

119888 Adjusted parameter in the nonlinear regressionusing (5)

Ca Calcium concentration ppm119862119878 Concentration of the total soluble 120573-Lg g Lminus1

119862119901119901 Specific heat for the product J kgminus1 Kminus1

119862119901ℎ Specific heat for the hot water J kgminus1 Kminus1

119889 Adjusted parameter in the nonlinear regressionusing (5)

119864119860 Activation energy Jmolminus1

119864119860agg 120573-Lg aggregation activation energy Jmolminus1

119864119860unf 120573-Lg unfolding activation energy Jmolminus1

119865119879 Logarithmic mean temperature difference -

119896119899 Denaturation rate constant g1minus119899 L119899minus1sminus1

1198960119899

Denaturation frequency factor g1minus119899 L119899minus1sminus1119896unf Unfolding rate constant g1minus119899 L119899minus1sminus1119896agg Aggregation rate constant g1minus119899 L119899minus1sminus1119872119889 Measured dry fouling deposit mass in a channel

along the PHE g119901 Mass flow rates for the product kg sminus1

ℎ Mass flow rates for the hot water kg sminus1

119899 Heat-induced denaturation reaction order119876119901 WPI fouling solution flow rate L hminus1

119876ℎ Hot water flow rate L hminus1

119903 Ratio between the unfolding and aggregation rateconstants -

119877 The universal gas constant equal to 8314Jmolminus1 Kminus1

119877119891 Fouling resistance m2∘ CWminus1

119878 Heat transfer area m2119879119894ℎ Hot water temperature at the PHE inlet K

119879119894119901 WPI fouling solution temperature at the PHE

inlet K119879119900ℎ Hot water temperature at the PHE outlet K

119879119900119901 Hot water temperature at the PHE outlet K

119880119892 Overall heat transfer coefficient Wmminus2 Kminus1

998779119879LMTD Logarithmic mean temperature difference K

Subscript

agg Aggregation119862119894 Channel number

ℎ Hot water119901 Product119875119894 Plate number

PHE Plate heat exchangerunf UnfoldingWPI Whey protein isolate120572-La 120572-lactalbumin120573-Lg 120573-lactoglobulin119894 Thermal profile number

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

Theauthors are indebted to the ScientificCommittee ofAgro-campus Ouest Rennes and HEI (Hautes Etudes drsquoIngenieurLille) for stimulating discussions and financial support for thePhD Thesis of the first author

References

[1] D M Mulvihill and M Donovan ldquoWhey proteins and theirthermal denaturationmdasha reviewrdquo Irish Journal of Food Scienceand Technology vol 11 no 1 pp 43ndash75 1987

[2] N Sava I Van der PlanckenWClaeys andMHendrickx ldquoThekinetics of heat-induced structural changes of 120573-lactoglobulinrdquoJournal of Dairy Science vol 88 no 5 pp 1646ndash1653 2005

[3] C Schmitt C Bovay M Rouvet S Shojaei-Rami and EKolodziejczyk ldquoWhey protein soluble aggregates from heatingwith NaCl physicochemical interfacial and foaming proper-tiesrdquo Langmuir vol 23 no 8 pp 4155ndash4166 2007

[4] B Bansal and X D Chen ldquoA critical review of milk fouling inheat exchangersrdquo Comprehensive Reviews in Food Science andFood Safety vol 5 no 2 pp 27ndash33 2006

[5] S N Tay and C Yang Assessment of the Hydro-Ball CondenserTube Cleaning System HydroBall Technics (SEA) Pte Singa-pore 2006

[6] HMMuller-SteinhagenHandbook of Heat Exchanger FoulingMitigation and Cleaning Technologies Publico PublicationsEssenGermany Institution ofChemical Engineers RugbyUK2000

[7] M Lalande and J P Tissier ldquoFouling of heat transfer surfacesrelated to 120573-lactoglobulin denaturation during heat processingof milkrdquo Biotechnology Progress vol 1 no 2 pp 131ndash139 1985

[8] P De Jong R Waalewijn and H J L J Van Der LindenldquoValidity of a kinetic fouling model for heat-treatment of wholemilkrdquo Le Lait vol 73 no 3 pp 293ndash302 1993

[9] S D Changani M T Belmar-Beiny and P J Fryer ldquoEngineer-ing and chemical factors associated with fouling and cleaning inmilk processingrdquo Experimental Thermal and Fluid Science vol14 no 4 pp 392ndash406 1997

[10] H Burton ldquoProperties of UHT-processed milkrdquo in Ultra-HighTemperature Processing of Milk and Milk Products pp 254ndash291Elsevier Applied Science Publishers 1988

[11] M T Belmar-Beiny S M Gotham W R Paterson P J Fryerand A M Pritchard ldquoThe effect of Reynolds number andfluid temperature in whey protein foulingrdquo Journal of FoodEngineering vol 19 no 2 pp 119ndash139 1993

[12] P J R Schreier and P J Fryer ldquoHeat exchanger fouling a modelstudy of the scaleup of laboratory datardquo Chemical EngineeringScience vol 50 no 8 pp 1311ndash1321 1995

[13] A J van Asselt M M M Vissers F Smit and P de Jong ldquoIn-line control of foulingrdquo in Proceedings of the Heat ExchangerFouling and CleaningmdashChallenges and Opportunities Engineer-ing Conferences International Irsee Germany June 2005

[14] J Petit A-LHerbig AMoreau andGDelaplace ldquoInfluence ofcalcium on 120573-lactoglobulin denaturation kinetics implications

10 International Journal of Chemical Engineering

in unfolding and aggregation mechanismsrdquo Journal of DairyScience vol 94 no 12 pp 5794ndash5810 2011

[15] M Khaldi P Blanpain-Avet R Guerin et al ldquoEffect of calciumcontent and flow regime on whey protein fouling and cleaningin a plate heat exchangerrdquo Journal of Food Engineering vol 147pp 68ndash78 2015

[16] B T Nielsen H Singh and J M Latham ldquoAggregation ofbovine 120573-lactoglobulins A and B on heating at 75∘Crdquo Interna-tional Dairy Journal vol 6 no 5 pp 519ndash527 1996

[17] H Lindmark-Mansson A Timgren G Alden and M Pauls-son ldquoTwo-dimensional gel electrophoresis of proteins andpeptides in bovinemilkrdquo International Dairy Journal vol 15 no2 pp 111ndash121 2005

[18] A Tolkach and U Kulozik ldquoReaction kinetic pathwayof reversible and irreversible thermal denaturation of 120573-lactoglobulinrdquo Dairy Science and Technology vol 87 no 4-5pp 301ndash315 2007

[19] F Dannenberg and H G Kessler ldquoReaction kinetics of thedenaturation of whey proteins in milkrdquo Journal of Food Sciencevol 53 no 1 pp 258ndash263 1988

[20] J C Leuliet J F Maingonnat and M Lalande ldquoThermalbehaviour of plate heat exchangers with Newtonian and non-Newtonian fluidsrdquo in Proceedings of the Congres Eurotherm 5 et1er Colloque TIFAN pp 1ndash15 Compiegne France 1988

[21] J-W F A Simons H A Kosters R W Visschers and H H Jde Jongh ldquoRole of calcium as trigger in thermal 120573-lactoglobulinaggregationrdquo Archives of Biochemistry and Biophysics vol 406no 2 pp 143ndash152 2002

[22] B T OrsquoKennedy and J S Mounsey ldquoThe dominating effect ofionic strength on the heat-induced denaturation and aggrega-tion of 120573-lactoglobulin in simulated milk ultrafiltraterdquo Interna-tional Dairy Journal vol 19 no 3 pp 123ndash128 2009

[23] M Lalande F Rene and J-P Tissier ldquoFouling and its control inheat exchangers in the dairy industryrdquo Biofouling vol 1 no 3pp 233ndash250 1989

[24] J Visser andT JM Jeurnink ldquoFouling of heat exchangers in thedairy industryrdquo ExperimentalThermal and Fluid Science vol 14no 4 pp 407ndash424 1997

[25] C L Foster M Britten and M L Green ldquoA model heat-exchange apparatus for the investigation of fouling of stainlesssteel surfaces by milk I Deposit formation at 100∘Crdquo Journal ofDairy Research vol 56 no 2 pp 201ndash209 1989

[26] P Havea H Singh and L K Creamer ldquoCharacterizationof heat-induced aggregates of 120573-lactoglobulin 120572-lactalbuminand bovine serum albumin in a whey protein concentrateenvironmentrdquo Journal of Dairy Research vol 68 no 3 pp 483ndash497 2001

[27] G Daufin J P Labbe A Quemerais et al ldquoFouling of a heatexchange surface by whey milk and model fluids an analyticalstudyrdquo Le Lait vol 67 no 3 pp 339ndash364 1987

[28] Y L Xiong ldquoInfluence of pH and ionic environment on thermalaggregation of whey proteinsrdquo Journal of Agricultural and FoodChemistry vol 40 no 3 Article ID 91-5-154 pp 380ndash384 1992

[29] T Phan-XuanDDurand TNicolai L Donato C Schmitt andL Bovetto ldquoTuning the structure of protein particles and gelswith calcium or sodium ionsrdquo Biomacromolecules vol 14 no 6pp 1980ndash1989 2013

[30] M J H Simmons P Jayaraman and P J Fryer ldquoThe effectof temperature and shear rate upon the aggregation of wheyprotein and its implications for milk foulingrdquo Journal of FoodEngineering vol 79 no 2 pp 517ndash528 2007

[31] C P Pappas and J Rothwell ldquoThe effects of heating alone or inthe presence of calcium or lactose on calcium binding to milkproteinsrdquo Food Chemistry vol 42 no 2 pp 183ndash201 1991

[32] P Blanpain-Avet A Hedoux Y Guinet et al ldquoAnalysis byRaman spectroscopy of the conformational structure of wheyproteins constituting fouling deposits during the processing ina heat exchangerrdquo Journal of Food Engineering vol 110 no 1 pp86ndash94 2012

[33] L Bouvier A Moreau G Ronse T Six J Petit and GDelaplace ldquoA CFD model as a tool to simulate 120573-lactoglobulinheat-induced denaturation and aggregation in a plate heatexchangerrdquo Journal of Food Engineering vol 136 pp 56ndash632014

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

8 International Journal of Chemical Engineering

0

100

200

300

400

500

600

700

800

0 02 04 06 08 1 12 14

1 23 41 23 4

Aggregationlimited zone

Clog

ging

of t

he

inst

allat

ion

Unfolding limited zone

Dep

osit

mas

s per

chan

nel (

gm

2)

r = kunfkagg

Fitting model Ca 120ppmFitting model Ca 100ppm

Figure 10 Plots of the dry deposit masses per unit area versus theratio of unfolding and aggregation rate constants for the 1 wwWPI solutions (closed symbols 100 ppm calcium open symbols120 ppm calcium) (119894 corresponds to the thermal profile numbergiven in Figure 4 and Table 2)

analysis by Raman spectroscopy that protein aggregates arenot present in the deposit This result is also supportedby the recent study of Bouvier et al [33] which showedthat a correlation can be established between the unfolded120573-Lg content within the PHE and the dry deposit massdistribution

Unfortunately it was not possible to perform pilot scaleexperiments at higher values of 119903 (119903 gt 140) correspondingto the channel temperature above 844∘C because of theclogging of the installation

To ascertain validity of themaster curve independently ofthe PHE configuration further experiments were conductedat PHE consisting of 10 passes (one channel per pass) for a 1(ww) WPI model solution at 100 ppm calcium One thermalprofile (1) out of the four tested for the five channels of thePHE was imposed Figure 11 represents the deposit mass perchannel versus the ratio 119903

Also in this case the fouling mass is reasonably wellcorrelated to the ratio 119903 showing the following

(i) the importance of determining this indicator forpredicting fouling mass distribution

(ii) the robustness of the approach

4 Conclusions

Fouling experiments were performed with 1 (ww) WPIsolutions at two different calcium concentrations in order toinvestigate the effect of the operating conditions associatedwith the chemical denaturation reactivity of heat treatmentin a PHE on the deposit formation The extent of fouling

0

100

200

300

400

500

600

700

0 05 1 15

1Fitting model 10-pass PHE configuration

Dep

osit

mas

s per

chan

nel (

gm

2)

r = kunfkagg

Aggregationlimited zone limited zone

Unfolding

Figure 11 Variation of the dry deposit mass per unit area in thevarious channels with the ratio 119903 for a 10-pass PHE configuration (1corresponds to the thermal profile given in Figure 4 and Table 2)

deposit was monitored by weighing the mass of the dryfouling deposit on the plates

It was shown that

(i) 120573-Lg denaturation is a complex process with a two-step mechanism highly dependent on the calciumcontent

(ii) an increase of the calcium content in the foulingsolution induced a strong increase in the 120573-Lg denat-uration level and consequently in the fouling masswithin the PHE at high temperatures

(iii) the fouling mass distribution also depends on thethermal profiles imposed on the fouling solutions

(iv) the dry deposit mass on each pass of the PHE seemsto be correlated with 119903 = 119896unf119896agg This observationindicates that the knowledge of this parameter isimportant to predict the mass distribution of thefouling deposit

This work clearly shows that 120573-Lg competitive reactions(unfolding and aggregation) governing the growth of foulingfor a WPI solution and the identification of the heat-induceddenaturation kinetic by means of laboratory experiments areprerequisites to control fouling We encourage strongly thefouling community to develop database on these aspects tobe able to predict the distribution of fouling mass whateverthe imposed temperature profile and to mitigate fouling

International Journal of Chemical Engineering 9

Nomenclature

119886 Adjusted parameter in the nonlinear regressionusing (5)

119887 Adjusted parameter in the nonlinear regressionusing (5)

119888 Adjusted parameter in the nonlinear regressionusing (5)

Ca Calcium concentration ppm119862119878 Concentration of the total soluble 120573-Lg g Lminus1

119862119901119901 Specific heat for the product J kgminus1 Kminus1

119862119901ℎ Specific heat for the hot water J kgminus1 Kminus1

119889 Adjusted parameter in the nonlinear regressionusing (5)

119864119860 Activation energy Jmolminus1

119864119860agg 120573-Lg aggregation activation energy Jmolminus1

119864119860unf 120573-Lg unfolding activation energy Jmolminus1

119865119879 Logarithmic mean temperature difference -

119896119899 Denaturation rate constant g1minus119899 L119899minus1sminus1

1198960119899

Denaturation frequency factor g1minus119899 L119899minus1sminus1119896unf Unfolding rate constant g1minus119899 L119899minus1sminus1119896agg Aggregation rate constant g1minus119899 L119899minus1sminus1119872119889 Measured dry fouling deposit mass in a channel

along the PHE g119901 Mass flow rates for the product kg sminus1

ℎ Mass flow rates for the hot water kg sminus1

119899 Heat-induced denaturation reaction order119876119901 WPI fouling solution flow rate L hminus1

119876ℎ Hot water flow rate L hminus1

119903 Ratio between the unfolding and aggregation rateconstants -

119877 The universal gas constant equal to 8314Jmolminus1 Kminus1

119877119891 Fouling resistance m2∘ CWminus1

119878 Heat transfer area m2119879119894ℎ Hot water temperature at the PHE inlet K

119879119894119901 WPI fouling solution temperature at the PHE

inlet K119879119900ℎ Hot water temperature at the PHE outlet K

119879119900119901 Hot water temperature at the PHE outlet K

119880119892 Overall heat transfer coefficient Wmminus2 Kminus1

998779119879LMTD Logarithmic mean temperature difference K

Subscript

agg Aggregation119862119894 Channel number

ℎ Hot water119901 Product119875119894 Plate number

PHE Plate heat exchangerunf UnfoldingWPI Whey protein isolate120572-La 120572-lactalbumin120573-Lg 120573-lactoglobulin119894 Thermal profile number

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

Theauthors are indebted to the ScientificCommittee ofAgro-campus Ouest Rennes and HEI (Hautes Etudes drsquoIngenieurLille) for stimulating discussions and financial support for thePhD Thesis of the first author

References

[1] D M Mulvihill and M Donovan ldquoWhey proteins and theirthermal denaturationmdasha reviewrdquo Irish Journal of Food Scienceand Technology vol 11 no 1 pp 43ndash75 1987

[2] N Sava I Van der PlanckenWClaeys andMHendrickx ldquoThekinetics of heat-induced structural changes of 120573-lactoglobulinrdquoJournal of Dairy Science vol 88 no 5 pp 1646ndash1653 2005

[3] C Schmitt C Bovay M Rouvet S Shojaei-Rami and EKolodziejczyk ldquoWhey protein soluble aggregates from heatingwith NaCl physicochemical interfacial and foaming proper-tiesrdquo Langmuir vol 23 no 8 pp 4155ndash4166 2007

[4] B Bansal and X D Chen ldquoA critical review of milk fouling inheat exchangersrdquo Comprehensive Reviews in Food Science andFood Safety vol 5 no 2 pp 27ndash33 2006

[5] S N Tay and C Yang Assessment of the Hydro-Ball CondenserTube Cleaning System HydroBall Technics (SEA) Pte Singa-pore 2006

[6] HMMuller-SteinhagenHandbook of Heat Exchanger FoulingMitigation and Cleaning Technologies Publico PublicationsEssenGermany Institution ofChemical Engineers RugbyUK2000

[7] M Lalande and J P Tissier ldquoFouling of heat transfer surfacesrelated to 120573-lactoglobulin denaturation during heat processingof milkrdquo Biotechnology Progress vol 1 no 2 pp 131ndash139 1985

[8] P De Jong R Waalewijn and H J L J Van Der LindenldquoValidity of a kinetic fouling model for heat-treatment of wholemilkrdquo Le Lait vol 73 no 3 pp 293ndash302 1993

[9] S D Changani M T Belmar-Beiny and P J Fryer ldquoEngineer-ing and chemical factors associated with fouling and cleaning inmilk processingrdquo Experimental Thermal and Fluid Science vol14 no 4 pp 392ndash406 1997

[10] H Burton ldquoProperties of UHT-processed milkrdquo in Ultra-HighTemperature Processing of Milk and Milk Products pp 254ndash291Elsevier Applied Science Publishers 1988

[11] M T Belmar-Beiny S M Gotham W R Paterson P J Fryerand A M Pritchard ldquoThe effect of Reynolds number andfluid temperature in whey protein foulingrdquo Journal of FoodEngineering vol 19 no 2 pp 119ndash139 1993

[12] P J R Schreier and P J Fryer ldquoHeat exchanger fouling a modelstudy of the scaleup of laboratory datardquo Chemical EngineeringScience vol 50 no 8 pp 1311ndash1321 1995

[13] A J van Asselt M M M Vissers F Smit and P de Jong ldquoIn-line control of foulingrdquo in Proceedings of the Heat ExchangerFouling and CleaningmdashChallenges and Opportunities Engineer-ing Conferences International Irsee Germany June 2005

[14] J Petit A-LHerbig AMoreau andGDelaplace ldquoInfluence ofcalcium on 120573-lactoglobulin denaturation kinetics implications

10 International Journal of Chemical Engineering

in unfolding and aggregation mechanismsrdquo Journal of DairyScience vol 94 no 12 pp 5794ndash5810 2011

[15] M Khaldi P Blanpain-Avet R Guerin et al ldquoEffect of calciumcontent and flow regime on whey protein fouling and cleaningin a plate heat exchangerrdquo Journal of Food Engineering vol 147pp 68ndash78 2015

[16] B T Nielsen H Singh and J M Latham ldquoAggregation ofbovine 120573-lactoglobulins A and B on heating at 75∘Crdquo Interna-tional Dairy Journal vol 6 no 5 pp 519ndash527 1996

[17] H Lindmark-Mansson A Timgren G Alden and M Pauls-son ldquoTwo-dimensional gel electrophoresis of proteins andpeptides in bovinemilkrdquo International Dairy Journal vol 15 no2 pp 111ndash121 2005

[18] A Tolkach and U Kulozik ldquoReaction kinetic pathwayof reversible and irreversible thermal denaturation of 120573-lactoglobulinrdquo Dairy Science and Technology vol 87 no 4-5pp 301ndash315 2007

[19] F Dannenberg and H G Kessler ldquoReaction kinetics of thedenaturation of whey proteins in milkrdquo Journal of Food Sciencevol 53 no 1 pp 258ndash263 1988

[20] J C Leuliet J F Maingonnat and M Lalande ldquoThermalbehaviour of plate heat exchangers with Newtonian and non-Newtonian fluidsrdquo in Proceedings of the Congres Eurotherm 5 et1er Colloque TIFAN pp 1ndash15 Compiegne France 1988

[21] J-W F A Simons H A Kosters R W Visschers and H H Jde Jongh ldquoRole of calcium as trigger in thermal 120573-lactoglobulinaggregationrdquo Archives of Biochemistry and Biophysics vol 406no 2 pp 143ndash152 2002

[22] B T OrsquoKennedy and J S Mounsey ldquoThe dominating effect ofionic strength on the heat-induced denaturation and aggrega-tion of 120573-lactoglobulin in simulated milk ultrafiltraterdquo Interna-tional Dairy Journal vol 19 no 3 pp 123ndash128 2009

[23] M Lalande F Rene and J-P Tissier ldquoFouling and its control inheat exchangers in the dairy industryrdquo Biofouling vol 1 no 3pp 233ndash250 1989

[24] J Visser andT JM Jeurnink ldquoFouling of heat exchangers in thedairy industryrdquo ExperimentalThermal and Fluid Science vol 14no 4 pp 407ndash424 1997

[25] C L Foster M Britten and M L Green ldquoA model heat-exchange apparatus for the investigation of fouling of stainlesssteel surfaces by milk I Deposit formation at 100∘Crdquo Journal ofDairy Research vol 56 no 2 pp 201ndash209 1989

[26] P Havea H Singh and L K Creamer ldquoCharacterizationof heat-induced aggregates of 120573-lactoglobulin 120572-lactalbuminand bovine serum albumin in a whey protein concentrateenvironmentrdquo Journal of Dairy Research vol 68 no 3 pp 483ndash497 2001

[27] G Daufin J P Labbe A Quemerais et al ldquoFouling of a heatexchange surface by whey milk and model fluids an analyticalstudyrdquo Le Lait vol 67 no 3 pp 339ndash364 1987

[28] Y L Xiong ldquoInfluence of pH and ionic environment on thermalaggregation of whey proteinsrdquo Journal of Agricultural and FoodChemistry vol 40 no 3 Article ID 91-5-154 pp 380ndash384 1992

[29] T Phan-XuanDDurand TNicolai L Donato C Schmitt andL Bovetto ldquoTuning the structure of protein particles and gelswith calcium or sodium ionsrdquo Biomacromolecules vol 14 no 6pp 1980ndash1989 2013

[30] M J H Simmons P Jayaraman and P J Fryer ldquoThe effectof temperature and shear rate upon the aggregation of wheyprotein and its implications for milk foulingrdquo Journal of FoodEngineering vol 79 no 2 pp 517ndash528 2007

[31] C P Pappas and J Rothwell ldquoThe effects of heating alone or inthe presence of calcium or lactose on calcium binding to milkproteinsrdquo Food Chemistry vol 42 no 2 pp 183ndash201 1991

[32] P Blanpain-Avet A Hedoux Y Guinet et al ldquoAnalysis byRaman spectroscopy of the conformational structure of wheyproteins constituting fouling deposits during the processing ina heat exchangerrdquo Journal of Food Engineering vol 110 no 1 pp86ndash94 2012

[33] L Bouvier A Moreau G Ronse T Six J Petit and GDelaplace ldquoA CFD model as a tool to simulate 120573-lactoglobulinheat-induced denaturation and aggregation in a plate heatexchangerrdquo Journal of Food Engineering vol 136 pp 56ndash632014

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

International Journal of Chemical Engineering 9

Nomenclature

119886 Adjusted parameter in the nonlinear regressionusing (5)

119887 Adjusted parameter in the nonlinear regressionusing (5)

119888 Adjusted parameter in the nonlinear regressionusing (5)

Ca Calcium concentration ppm119862119878 Concentration of the total soluble 120573-Lg g Lminus1

119862119901119901 Specific heat for the product J kgminus1 Kminus1

119862119901ℎ Specific heat for the hot water J kgminus1 Kminus1

119889 Adjusted parameter in the nonlinear regressionusing (5)

119864119860 Activation energy Jmolminus1

119864119860agg 120573-Lg aggregation activation energy Jmolminus1

119864119860unf 120573-Lg unfolding activation energy Jmolminus1

119865119879 Logarithmic mean temperature difference -

119896119899 Denaturation rate constant g1minus119899 L119899minus1sminus1

1198960119899

Denaturation frequency factor g1minus119899 L119899minus1sminus1119896unf Unfolding rate constant g1minus119899 L119899minus1sminus1119896agg Aggregation rate constant g1minus119899 L119899minus1sminus1119872119889 Measured dry fouling deposit mass in a channel

along the PHE g119901 Mass flow rates for the product kg sminus1

ℎ Mass flow rates for the hot water kg sminus1

119899 Heat-induced denaturation reaction order119876119901 WPI fouling solution flow rate L hminus1

119876ℎ Hot water flow rate L hminus1

119903 Ratio between the unfolding and aggregation rateconstants -

119877 The universal gas constant equal to 8314Jmolminus1 Kminus1

119877119891 Fouling resistance m2∘ CWminus1

119878 Heat transfer area m2119879119894ℎ Hot water temperature at the PHE inlet K

119879119894119901 WPI fouling solution temperature at the PHE

inlet K119879119900ℎ Hot water temperature at the PHE outlet K

119879119900119901 Hot water temperature at the PHE outlet K

119880119892 Overall heat transfer coefficient Wmminus2 Kminus1

998779119879LMTD Logarithmic mean temperature difference K

Subscript

agg Aggregation119862119894 Channel number

ℎ Hot water119901 Product119875119894 Plate number

PHE Plate heat exchangerunf UnfoldingWPI Whey protein isolate120572-La 120572-lactalbumin120573-Lg 120573-lactoglobulin119894 Thermal profile number

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

Theauthors are indebted to the ScientificCommittee ofAgro-campus Ouest Rennes and HEI (Hautes Etudes drsquoIngenieurLille) for stimulating discussions and financial support for thePhD Thesis of the first author

References

[1] D M Mulvihill and M Donovan ldquoWhey proteins and theirthermal denaturationmdasha reviewrdquo Irish Journal of Food Scienceand Technology vol 11 no 1 pp 43ndash75 1987

[2] N Sava I Van der PlanckenWClaeys andMHendrickx ldquoThekinetics of heat-induced structural changes of 120573-lactoglobulinrdquoJournal of Dairy Science vol 88 no 5 pp 1646ndash1653 2005

[3] C Schmitt C Bovay M Rouvet S Shojaei-Rami and EKolodziejczyk ldquoWhey protein soluble aggregates from heatingwith NaCl physicochemical interfacial and foaming proper-tiesrdquo Langmuir vol 23 no 8 pp 4155ndash4166 2007

[4] B Bansal and X D Chen ldquoA critical review of milk fouling inheat exchangersrdquo Comprehensive Reviews in Food Science andFood Safety vol 5 no 2 pp 27ndash33 2006

[5] S N Tay and C Yang Assessment of the Hydro-Ball CondenserTube Cleaning System HydroBall Technics (SEA) Pte Singa-pore 2006

[6] HMMuller-SteinhagenHandbook of Heat Exchanger FoulingMitigation and Cleaning Technologies Publico PublicationsEssenGermany Institution ofChemical Engineers RugbyUK2000

[7] M Lalande and J P Tissier ldquoFouling of heat transfer surfacesrelated to 120573-lactoglobulin denaturation during heat processingof milkrdquo Biotechnology Progress vol 1 no 2 pp 131ndash139 1985

[8] P De Jong R Waalewijn and H J L J Van Der LindenldquoValidity of a kinetic fouling model for heat-treatment of wholemilkrdquo Le Lait vol 73 no 3 pp 293ndash302 1993

[9] S D Changani M T Belmar-Beiny and P J Fryer ldquoEngineer-ing and chemical factors associated with fouling and cleaning inmilk processingrdquo Experimental Thermal and Fluid Science vol14 no 4 pp 392ndash406 1997

[10] H Burton ldquoProperties of UHT-processed milkrdquo in Ultra-HighTemperature Processing of Milk and Milk Products pp 254ndash291Elsevier Applied Science Publishers 1988

[11] M T Belmar-Beiny S M Gotham W R Paterson P J Fryerand A M Pritchard ldquoThe effect of Reynolds number andfluid temperature in whey protein foulingrdquo Journal of FoodEngineering vol 19 no 2 pp 119ndash139 1993

[12] P J R Schreier and P J Fryer ldquoHeat exchanger fouling a modelstudy of the scaleup of laboratory datardquo Chemical EngineeringScience vol 50 no 8 pp 1311ndash1321 1995

[13] A J van Asselt M M M Vissers F Smit and P de Jong ldquoIn-line control of foulingrdquo in Proceedings of the Heat ExchangerFouling and CleaningmdashChallenges and Opportunities Engineer-ing Conferences International Irsee Germany June 2005

[14] J Petit A-LHerbig AMoreau andGDelaplace ldquoInfluence ofcalcium on 120573-lactoglobulin denaturation kinetics implications

10 International Journal of Chemical Engineering

in unfolding and aggregation mechanismsrdquo Journal of DairyScience vol 94 no 12 pp 5794ndash5810 2011

[15] M Khaldi P Blanpain-Avet R Guerin et al ldquoEffect of calciumcontent and flow regime on whey protein fouling and cleaningin a plate heat exchangerrdquo Journal of Food Engineering vol 147pp 68ndash78 2015

[16] B T Nielsen H Singh and J M Latham ldquoAggregation ofbovine 120573-lactoglobulins A and B on heating at 75∘Crdquo Interna-tional Dairy Journal vol 6 no 5 pp 519ndash527 1996

[17] H Lindmark-Mansson A Timgren G Alden and M Pauls-son ldquoTwo-dimensional gel electrophoresis of proteins andpeptides in bovinemilkrdquo International Dairy Journal vol 15 no2 pp 111ndash121 2005

[18] A Tolkach and U Kulozik ldquoReaction kinetic pathwayof reversible and irreversible thermal denaturation of 120573-lactoglobulinrdquo Dairy Science and Technology vol 87 no 4-5pp 301ndash315 2007

[19] F Dannenberg and H G Kessler ldquoReaction kinetics of thedenaturation of whey proteins in milkrdquo Journal of Food Sciencevol 53 no 1 pp 258ndash263 1988

[20] J C Leuliet J F Maingonnat and M Lalande ldquoThermalbehaviour of plate heat exchangers with Newtonian and non-Newtonian fluidsrdquo in Proceedings of the Congres Eurotherm 5 et1er Colloque TIFAN pp 1ndash15 Compiegne France 1988

[21] J-W F A Simons H A Kosters R W Visschers and H H Jde Jongh ldquoRole of calcium as trigger in thermal 120573-lactoglobulinaggregationrdquo Archives of Biochemistry and Biophysics vol 406no 2 pp 143ndash152 2002

[22] B T OrsquoKennedy and J S Mounsey ldquoThe dominating effect ofionic strength on the heat-induced denaturation and aggrega-tion of 120573-lactoglobulin in simulated milk ultrafiltraterdquo Interna-tional Dairy Journal vol 19 no 3 pp 123ndash128 2009

[23] M Lalande F Rene and J-P Tissier ldquoFouling and its control inheat exchangers in the dairy industryrdquo Biofouling vol 1 no 3pp 233ndash250 1989

[24] J Visser andT JM Jeurnink ldquoFouling of heat exchangers in thedairy industryrdquo ExperimentalThermal and Fluid Science vol 14no 4 pp 407ndash424 1997

[25] C L Foster M Britten and M L Green ldquoA model heat-exchange apparatus for the investigation of fouling of stainlesssteel surfaces by milk I Deposit formation at 100∘Crdquo Journal ofDairy Research vol 56 no 2 pp 201ndash209 1989

[26] P Havea H Singh and L K Creamer ldquoCharacterizationof heat-induced aggregates of 120573-lactoglobulin 120572-lactalbuminand bovine serum albumin in a whey protein concentrateenvironmentrdquo Journal of Dairy Research vol 68 no 3 pp 483ndash497 2001

[27] G Daufin J P Labbe A Quemerais et al ldquoFouling of a heatexchange surface by whey milk and model fluids an analyticalstudyrdquo Le Lait vol 67 no 3 pp 339ndash364 1987

[28] Y L Xiong ldquoInfluence of pH and ionic environment on thermalaggregation of whey proteinsrdquo Journal of Agricultural and FoodChemistry vol 40 no 3 Article ID 91-5-154 pp 380ndash384 1992

[29] T Phan-XuanDDurand TNicolai L Donato C Schmitt andL Bovetto ldquoTuning the structure of protein particles and gelswith calcium or sodium ionsrdquo Biomacromolecules vol 14 no 6pp 1980ndash1989 2013

[30] M J H Simmons P Jayaraman and P J Fryer ldquoThe effectof temperature and shear rate upon the aggregation of wheyprotein and its implications for milk foulingrdquo Journal of FoodEngineering vol 79 no 2 pp 517ndash528 2007

[31] C P Pappas and J Rothwell ldquoThe effects of heating alone or inthe presence of calcium or lactose on calcium binding to milkproteinsrdquo Food Chemistry vol 42 no 2 pp 183ndash201 1991

[32] P Blanpain-Avet A Hedoux Y Guinet et al ldquoAnalysis byRaman spectroscopy of the conformational structure of wheyproteins constituting fouling deposits during the processing ina heat exchangerrdquo Journal of Food Engineering vol 110 no 1 pp86ndash94 2012

[33] L Bouvier A Moreau G Ronse T Six J Petit and GDelaplace ldquoA CFD model as a tool to simulate 120573-lactoglobulinheat-induced denaturation and aggregation in a plate heatexchangerrdquo Journal of Food Engineering vol 136 pp 56ndash632014

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

10 International Journal of Chemical Engineering

in unfolding and aggregation mechanismsrdquo Journal of DairyScience vol 94 no 12 pp 5794ndash5810 2011

[15] M Khaldi P Blanpain-Avet R Guerin et al ldquoEffect of calciumcontent and flow regime on whey protein fouling and cleaningin a plate heat exchangerrdquo Journal of Food Engineering vol 147pp 68ndash78 2015

[16] B T Nielsen H Singh and J M Latham ldquoAggregation ofbovine 120573-lactoglobulins A and B on heating at 75∘Crdquo Interna-tional Dairy Journal vol 6 no 5 pp 519ndash527 1996

[17] H Lindmark-Mansson A Timgren G Alden and M Pauls-son ldquoTwo-dimensional gel electrophoresis of proteins andpeptides in bovinemilkrdquo International Dairy Journal vol 15 no2 pp 111ndash121 2005

[18] A Tolkach and U Kulozik ldquoReaction kinetic pathwayof reversible and irreversible thermal denaturation of 120573-lactoglobulinrdquo Dairy Science and Technology vol 87 no 4-5pp 301ndash315 2007

[19] F Dannenberg and H G Kessler ldquoReaction kinetics of thedenaturation of whey proteins in milkrdquo Journal of Food Sciencevol 53 no 1 pp 258ndash263 1988

[20] J C Leuliet J F Maingonnat and M Lalande ldquoThermalbehaviour of plate heat exchangers with Newtonian and non-Newtonian fluidsrdquo in Proceedings of the Congres Eurotherm 5 et1er Colloque TIFAN pp 1ndash15 Compiegne France 1988

[21] J-W F A Simons H A Kosters R W Visschers and H H Jde Jongh ldquoRole of calcium as trigger in thermal 120573-lactoglobulinaggregationrdquo Archives of Biochemistry and Biophysics vol 406no 2 pp 143ndash152 2002

[22] B T OrsquoKennedy and J S Mounsey ldquoThe dominating effect ofionic strength on the heat-induced denaturation and aggrega-tion of 120573-lactoglobulin in simulated milk ultrafiltraterdquo Interna-tional Dairy Journal vol 19 no 3 pp 123ndash128 2009

[23] M Lalande F Rene and J-P Tissier ldquoFouling and its control inheat exchangers in the dairy industryrdquo Biofouling vol 1 no 3pp 233ndash250 1989

[24] J Visser andT JM Jeurnink ldquoFouling of heat exchangers in thedairy industryrdquo ExperimentalThermal and Fluid Science vol 14no 4 pp 407ndash424 1997

[25] C L Foster M Britten and M L Green ldquoA model heat-exchange apparatus for the investigation of fouling of stainlesssteel surfaces by milk I Deposit formation at 100∘Crdquo Journal ofDairy Research vol 56 no 2 pp 201ndash209 1989

[26] P Havea H Singh and L K Creamer ldquoCharacterizationof heat-induced aggregates of 120573-lactoglobulin 120572-lactalbuminand bovine serum albumin in a whey protein concentrateenvironmentrdquo Journal of Dairy Research vol 68 no 3 pp 483ndash497 2001

[27] G Daufin J P Labbe A Quemerais et al ldquoFouling of a heatexchange surface by whey milk and model fluids an analyticalstudyrdquo Le Lait vol 67 no 3 pp 339ndash364 1987

[28] Y L Xiong ldquoInfluence of pH and ionic environment on thermalaggregation of whey proteinsrdquo Journal of Agricultural and FoodChemistry vol 40 no 3 Article ID 91-5-154 pp 380ndash384 1992

[29] T Phan-XuanDDurand TNicolai L Donato C Schmitt andL Bovetto ldquoTuning the structure of protein particles and gelswith calcium or sodium ionsrdquo Biomacromolecules vol 14 no 6pp 1980ndash1989 2013

[30] M J H Simmons P Jayaraman and P J Fryer ldquoThe effectof temperature and shear rate upon the aggregation of wheyprotein and its implications for milk foulingrdquo Journal of FoodEngineering vol 79 no 2 pp 517ndash528 2007

[31] C P Pappas and J Rothwell ldquoThe effects of heating alone or inthe presence of calcium or lactose on calcium binding to milkproteinsrdquo Food Chemistry vol 42 no 2 pp 183ndash201 1991

[32] P Blanpain-Avet A Hedoux Y Guinet et al ldquoAnalysis byRaman spectroscopy of the conformational structure of wheyproteins constituting fouling deposits during the processing ina heat exchangerrdquo Journal of Food Engineering vol 110 no 1 pp86ndash94 2012

[33] L Bouvier A Moreau G Ronse T Six J Petit and GDelaplace ldquoA CFD model as a tool to simulate 120573-lactoglobulinheat-induced denaturation and aggregation in a plate heatexchangerrdquo Journal of Food Engineering vol 136 pp 56ndash632014

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of