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International Journal of Mechanical Engineering and Technology (IJMET) Volume 6, Issue 9, Sep 2015, pp. 73-93, Article ID: IJMET_06_09_008

Available online at

http://www.iaeme.com/IJMET/issues.asp?JTypeIJMET&VType=6&IType=9

ISSN Print: 0976-6340 and ISSN Online: 0976-6359

© IAEME Publication

EXPERIMENTAL AND NUMERICAL STUDY

TO ENHANCE HEAT TRANSFER ON A

HEAT EXCHANGER AL2O3/WATER

NANOFLUID USING AN AIR FLOW WITH

WATER DROPLETS

Yasameen H. Abed

M.Sc. Mechanical Engineering Department,

University of Technology, Baghdad, Iraq

Abdulhassan A.Karamallah

Professor, Mechanical Engineering Department,


Adel Mahmoud Saleh

Assistance Professor, Mechanical Engineering Department,


ABSTRACT

A experimental and numerical study has been carried out on the

enhancement of the heat exchanged on a tube and fin heat exchanger cooled

by an air flow containing water droplets by using nozzle system. A numerical

model representing the heat transfer has been presented and validated using

the experimental data. The cooling of air due to water evaporation upstream

in a channel to the exchanger (condenser fed with hot water with different

temperature) and the supplementary evaporation of droplets while impacting

or crossing the exchanger leads to enhance heat exchange. As additional to

enhance heat exchange, adding a nanoparticle (Al2O3) to the water of the heat

exchanger and studying the effect of the nanofluid with two volume

concentrations (0.5 & 2 %). All the tests were carried out with working fluid

flow rate (4, 6 and 8 L/min) and with temperature (40, 45 and 50 oC).The

results obtained maximum Nusselt number ratio (�� / ��,�� )

was (1.235) which occurred at nanofluid concentration 2% with using sprayed

air. The heat transfer coefficient ratio (�� / ��,�� ) increases when

using nanofluid and by increasing the volume concentration and the maximum

enhancement ratio was (1.45) which occurred at nanofluid concentration 2%

and with using sprayed air to cool the heat exchanger. The average Nusselt

number with Reynolds number correlated for working fluid. The numerical

Yasameen H. Abed, Abdulhassan A.Karamallah and Adel Mahmoud Saleh


analysis was based on finite volume numerical techniques to solve the

governing partial differential equations in three dimensions, using ANSYS

FLUENT commercial CFD software, to study the effect of using spray water,

air temperature and velocity, working fluid flow and temperature on the heat

transfer enhancement. The comparison between the experimental and

numerical results shows a good agreement, and the maximum error was with

maximum deviation (11%).

Key words: Enhanced, Heat Transfer, Condenser, Water Spray Air, Nanofluid

Cite this Article: Yasameen H. Abed, Abdulhassan A. Karamallah and Adel

Mahmoud Saleh, Experimental and Numerical Study to Enhance Heat

Transfer on A Heat Exchanger Al2o3/Water Nanofluid Using an Air Flow

with Water Droplets. International Journal of Mechanical Engineering and

Technology, 6(9), 2015, pp. 73-93.

http://www.iaeme.com/currentissue.asp?JType=IJMET&VType=6&IType=9

1. INTRODUCTION

Decreasing energy consumption and increasing efficiency is one of the most

important points in our area. Becoming a matter of primary importance in air

conditioning, industrial and commercial cooling applications, supermarket cooling,

blast freezing and process cooling applications, energy efficiency affects design of

chillers (and its equipment such as condensers, compressors etc.) and urges

manufacturers to develop high performance, energy-efficient, environment friendly,

and economic and long life products. The air cooled condensers (fin and tube heat

exchangers) are the most widespread category for low and average refrigeration

capacities because the cooling medium (air) is a natural and free source. However, as

air is not an efficient cooling medium, it implies high air flow and significant

exchanger area. Adding a spray of a controlled and small quantity of fine water

droplets at the air inlet seems to be a potential solution that deserves to be investigated

and analyzed, it is expects to be widely applied and several experimental and

numerical studies investigate in this realm to develop and design more efficient

system. R. Sureshkumar, et al. 2008 [1], showed experimentally that for a specific

water flow rate, the smaller nozzle at higher pressure produced more cooling than a

larger nozzle at lower pressure and they provided accurate with consistent data that

can be used for comparison with other experiments and simulations. They founded in

hot and dry conditions, a cooling up to 14 oC was attainable in both parallel and

counter flow configurations.

R. Faramarzi, et al. 2010 [2] , studied variations in net cooling capacity, total

power consumption, energy efficiency ratio (EER), and water consumption across the

tested climatic conditions, and compared the performance of the unit with the

performance of air-cooled condenser type Air Conditioner (A/C) systems. A

numerical study by K.A. Jahangeer, et al. 2011 [3], investigated the heat transfer

characteristics by using a spray water or droplets in air cooled condenser. K.T.

Chan,et al.2011[4] , used mist evaporation to improve the coefficient of performance

(COP) of air-cooled chillers with variable condensing set point temperature control.

Experimental and numerical study of the enhancement of the heat exchanged on a

tube and fin exchanger (a simple exchanger) using an air flow containing water

droplets sprayed with several varying conditions (several nozzles, set temperature

and humidity conditions, various air flows, etc.) by J. Tissot, et al. 2012, [5] and P.

Boulet et al. 2013, [6]. S.M. Peyghambarzadeh et.al. 2011, [7], studies

Experimental and Numerical Study to Enhance Heat Transfer on A Heat Exchanger

Al2o3/Water Nanofluid Using An Air Flow with Water Droplets


experimentally forced convective heat transfer in a water based nanofluid and

compared to that of pure water in an automobile radiator with Five different

concentrations of nanofluids in the range of 0, 0.1, 0.3, 0.5, 0.7, and 1 vol.%. M.M.

Heyhat et.al. 2012, [8], investigated experimentally the convective heat transfer and

friction factor of Al2O3 nanofluids with diameters of 40 nm and dispersed in distilled

water with volume concentrations of 0.1–2 vol.%, the results showed that the heat

transfer coefficient of nanofluid increased by 23% at 2 vol.% compared with that of

pure water with increasing the particle concentrations.

The present work submits an experimental work and numerical analysis in order

to study the effect of many parameters of spray conditions on air flow and on the heat

transfer characteristics of the heat exchanger. That are including: the types of fine

spray nozzles, location and directions of nozzle (either co-current or counter-current

directions of the air), and using a nanoparticles with the based fluid of the heat

exchanger which is a water.

2. THE EXPERIMANTAL PILOT

The test rig based on an instrumented air duct with a stabilized airflow in which

droplets are injected using suitable types of fine spray nozzles and the air-droplet flow

is directed in a channel toward a heat exchanger. Various characteristics (flow rate,

velocity, temperature & humidity) are determined experimentally through dedicated

measurement devices. The airflow is pre-heated at the inlet and sucked through a

square duct by a blower. A flow meter allows the measurement of the inlet flow rate.

Honeycomb grids are located after the blower in order to provide a settled and

stationary flow. The air is then entering in the channel section devoted to study the

interactions between the airflow and the droplets. Droplets are injected with a spray

nozzle and the air-droplet flow is directed toward the heat exchanger where the

finned-tube condenser is located. Hygrometers and thermocouples allow the

characterization of the air properties. Flow meter and thermocouples may also be used

for the evaluation of the heat exchanged at the exchanger by characterizing the

properties of the fluid inside the exchanger (water for the present work).

Figure 1 The pilot

Beak



The pilot experiment shown in Figure.1 in a room where the temperature and the

humidity are controlled and in Figure.2 the sketch of the pilot. Table.1 gives the

characteristics main parts of the test rig, Table.2 gives the characteristics of

condenser, and Table.3 views the used measuring apparatus. The parameters and

measurement rang is shown in Table.4.

Figure 2 The schematic diagram of experiment set up

Table 1 (characteristics of main parts of the test rig)

Parts Characteristics

1. Square duct length= (1.2)m with cross sectional area ( 0.2 x0.2 )m2

2. Cone duct length= (0.5)m with cross sectional area ( 0.2 x0.2 )m

2 and

(0.38x0.28) m2

3. Rectangular

duct width x high x length=(0.38x0.28x1.85) m

3

4. Heat exchanger width x high x length=(0.36x0.26x0.18) m3

5. Heater Power = 3 kW

6. Axial fan Model FAD25-2/ (840) m3/h ,max power =35 W

7. Honey cone width x high x thickness = (0.36 x0.26x0.005) m3

8. Heater Power = 3 kW

9. Mist pumps Diaphragm pump HF-9050 & TYP-2000

10. Thermoregulater Power=7 kW, minimum water pressure=0.2bar

11. Water pump Type KF/0 Qmax= 30L/min, H. max =24 m, r.p.m=2820min

-

1

Table.2 (Details of fin and tube condenser)

Length of tube 360 mm Fin width 18 mm

High of

condenser 250 mm No. of fins 360 / (2.15) = 167.44 ≈167

No. of tube 10 outer diameter of

tube 3′′/8 (10 mm)

Spaced fin 2 mm Tube/ thermal

conductivity 360 W /m.K

Fin thickness 0.15 mm Fin thermal

conductivity

203 W /m.K




Table 3 (Apparatuses involved in the measurement chain).

Parameter Measuring device Range of

application Resolution Accuracy

Air flow rate Air flow/ Air velocity

(Anemometer AM-4206)

0.4-25 m/s

0-50 oC

0.1 m/s

0.1 oC

± 2%

0.8 oC

Water flow rate Water flow meter (glass type

K-5012 )

2-20 L/min

35-50 oC

---- ± 2.5%

water

temperature Thermocouples type T ˗ 50

to 400

oC 0.1

oC ± (0.4% +1

oC)

Temperature

recorder

Data logger meter

( BTM- 4208SD)

Operating temp.

0-50 oC

> 85 %RH

0.1 oC ----

Humidity and

temperature

Hygrometer (humidity and

temperature meter) RS232

0 ~ 100%RH -20 -60

oC

0.1%RH

0.1 oC

±2.5%RH ±0.7

oC

Humidity /

temperature

Humidity and temperature

monitor (MHT-381SD)

10 - 90 %RH

0-50 oC

0.1%RH oC

± 4%

± 0.1 oC

Weight scale type EA 15 DEC-L 0- 15 kg ---- ± 1 g

Table.4 (Parameters and Measurement rang).

Parameters Measurement rang

Air flow rat 0.14, 0.18 & 0.22 m3/s

Air temperature 25, 30 & 35

oC

Spray water flow rate 0.6 , 1.5 & 1.7 L/h

Nozzle distance from the condenser 20,40 ,60 &80 cm

Water flow rate in tubes 4, 6, 8 L/min (240,360,480 L/h)

Water temperature in tubes of H.E 40, 45 & 50 oC

Figure.3 Diagram the Relative Humidity and Temperature of the air points placed upstream

and downstream of the heat exchanger in the plane perpendicular to flow of the air.

3. EXPERIMENTAL WORK PROCEDURE

3.1 Experimental parameters

Each experimental test was take the following parameters have been considered:

1. Ambient temperature and humidity.

36 cm

26 cm



2. Air velocity and temperature in the duct before injection.

3. Air temperature and humidity toward the heat exchanger.

4. Location of the nozzle.

5. Direction of droplets injection (co or counter-current).

6. spray water flow rate.

7. Heat exchanger water flow rate and temperatures at inlet and outlet.

3.2. The steps of experimental test

The following are the steps which must be done to complete the test:

1. Controlled the temperature and the humidity of ambient air.

2. Measured the air velocity and temperature in the duct before injection.

3. Select the location and the direction of droplets injection.

4. Measured the spray water flow rate.

5. Measured the water flow rate and the temperatures at inlet and outlet of the heat

exchanger.

6. Measured the air temperature and humidity before and after the heat exchanger.

3.3. Preparation of Al2O3 nanofluid

In general, there are two methodologies used to produce nanofluids, namely the

single-step method, where nanoparticles are produced and dispersed simultaneously

into the base fluid, and the two-step method, where the two aforementioned processes

are accomplished separately. To produce an even and stable suspension several

techniques are applied, such as use of ultrasonic equipment, pH control or addition of

stabilizers. The material of nanoparticles is chosen as Al2O3 because it is chemically

more stable and its cost is less than their metallic counterparts and also it is easily

available. Al2O3-water nanofluid is prepared by two step method. Adding a specific

grams of the Al2O3 in to the water and the mixture was mixed slowly in the sonicator

about 20 min to break up any particle aggregates and prepared two volume

concentration of nanofluid 0.5 % & 2.0 %.

Thermo physical properties of nanoparticles and base fluid (water) at 25 oC are

shown in the Table 5, and for the water-nanofluid properties are shown in the Table 6

using equations as in M.M. Heyhat 2012 [7].

Table 5 Thermophysical properties of nanoparticles and base fluid (water) at 25 oC .

Property Water Nanofluid Unit

Density ρ�=1000 ρ�=3900 kg/m3

specific heat capacity ��=4.1796 ��=0.880 kj/kg.K

thermal conductivity k�=0.6 k�=42.34 w/m.K

dynamic viscosity μ�=1.003 μ�= --- g /m.s

Nanofluid particles --- D p=30-60 nm




Table 6 (Thermophysical water-nanofluid Properties for two concentration 0.5& 2 %).

Water-Nanofluid

Properties Equation

Nanofluid volume

concentration Unit

0.5% 2.0 %

Density ρ� = (1 − φ)ρ� + φρ� 1014.5 1058 kg/m3

specific heat

capacity ��! = "(# ��)$ + (1 − ")(# ��)%

(1 − ")#% + "#$ 4.136 3.966 kj/kg.K

thermal

conductivity &! = &%(1 + 8.733") 0.626 0.705 w/m.K

dynamic viscosity +! = +%(exp / 5.989"0.278 − "4) 0.0003 0.0013 kg /m.s

3.5. Experimental Internal Convection Coefficient

To obtain heat transfer coefficient and corresponding Nusselt number, the following

procedure has been performed. According to Newton’s cooling law,

Peyghambarzadeh 2011 [7]:

Q = h78� A: (T< − T�=>>) (1)

Heat transfer rate can calculated as follows:

Q = m @ Cp (TB� − T:CD) (2)

Regarding the equality of Q in the above equations:

Nu=G = HIJK.LMN = O@ P� (QRST QUVW) LM

N XU (QYT QZ[\\) (3)

Nu=G is average Nusselt number for the whole heat exchanger , m @ is mass flow

rate which is the product of density and volume flow rate of fluid, Cp is fluid specific

heat capacity, A: is peripheral area of the tubes, k is fluid thermal conductivity

and DH is hydraulic diameter of the tube. TB� and T:CD are inlet and outlet

temperatures, T< is bulk temperature which was assumed to be the average values of

inlet and outlet temperature of the fluid moving through the heat exchanger, and T�=>> is tube wall temperature which is the mean value by two surface thermocouples,

Peyghambarzadeh 2011 [7]

4. MATHEMATICAL TREATMENT AND NUMERICAL

SIMULATION

The spray injected into the flow of air at different position in the duct. The air cooled

by evaporation of the spray takes place between the point of injection of the spray and

the heat exchanger (condenser). The first zone of the duct consists of the controlled

misted air and the second zone corresponds to the heat exchanger where the exchange

takes place between the air and the fluid circulating inside the condenser. Analysis

steps for FLUENT software package were used to develop the Computational Fluid

Dynamics (CFD) model of cooling a hot air stream by water injection using species

transport and discrete phase models of ANSYS FLUENT 14.5 and model of heat

transfer between the air-mist water and the heat exchanger. Conservation of mass

equations, energy equation and momentum equation- model RANS (Reynolds



Averaged Navier-Stokes) can express mathematically for an incompressible fluid as

Collin 2007 [9] and J. Tissot 2011[10]:

^^8_

`ρaUcd e = 0 (4)

^ ^8_

`ρaUcdTa e = ^^8_

f/ρaαD + hiPKi

4 ^Qi^8_

j (5)

^^8_

`ρaUcB Ucd e = ^^8_

f(μa + μD ) ^kcR^8_

j + ^^8_

l(μa + μD ) ^kc_^8R

m − ^^8R

lPr + pq ρakam + S�CB (6)

4.1. Numerical Simulation

The geometry used to perform the simulations corresponds to that of the rectangular

duct which is situated upstream from the exchanger of the experimental pilot.

Improved cooling through increased heat exchange and mass between the drops and

the air. Thus, several parameters are studied including the direction of injection of the

spray with respect to the flow (co-current and countercurrent) to assess the relative

influence of the increase in the exchange surface between the drops and the air and

the spatial dispersion of the spray in the air flow.

Figure 4 Computational domain includes mesh display and boundary conditions.

Figure 5 Computational domain includes mesh display for heat exchanger.

Air inlet as velocity

inlet

Air outlet as

pressure outlet

Interior domain

Wall

260

mm

360

mm

1000

mm




5. RESULTS AND DISCUSSION

5.1. Influence of distance on air cooling

Evaporation of a spray in an air flow occurs throughout its length. This evaporation

depends on the residence time of the spray and the corresponding increase humidity in

the air. We therefore sought in this section to determine the distance downstream and

upstream of injection of the spray, from which the cooling air is great. For This

distance, measures the temperature of the air are carried out on sections the vein of

experimental pilot between 20 and 80 cm downstream of the injection point spray.

The Figures (4) show the humidity and the temperature distribution of the air flow in

transverse section Z=20,40,60,80cm for nozzle type 10 and the direction of injection

of spray with the air (co- current) with inlet air temperature is 25 oC . The Figures (5)

show the humidity and the temperature distribution with counter-current flow. It seem

that the reduction temperature is not uniform over the entire cross section and is

greater at the center of the vein, in the zone where the spray is most dense. However,

this heterogeneity decreases away from the injection point. The Figures (6) & (7)

presents the evolution of the humidity and the temperature of the air in function of the

distance between the measurement surface and the injection point of the spray.

Indeed, the difference between the average temperature and the minimum temperature

decreases with increase the distance from the injection point. A co-current,

evaporation of the spray and the reduction in temperature is more important the center

of the section, because the water fraction in the air is most important. The reason for

this concentration in the injection configuration is the low spatial dispersion of drops

in space. Therefore, the cooled surface is greater and the reduction in temperature

locally less important. In the counter-current flow, the temperatures obtained the

entire section are more homogeneous and lower average than co-current in the small

distance. For the purposes of misting on a condenser that allows position nozzles near

the condenser and thus limit the drive by spray gusts of wind in the case of a

condenser placed outdoors.

(a) Humidity

Z=80 cm T amb=24.4 C RH=53.7 % T inlet= 25.0 C RH inlet=50.6 %RH min=56 % RHmax=87.6%RH med=60.6 % RH Aver=64.14%

Z=60 cm T amb=25.0 C RH=50.6% T inlet= 25.0 C RH inlet=50.1 %RH min=52.5 % RHmax=85.4 %RH med=62 % RH Aver=63.1 %

Z=40 cm T amb=24.6 C RH=48.6 % T inlet= 25.0 C RH inlet=42.1 %RH min=53.5 % RHmax=80 %RH med=57.2 % RH Aver=61.97 %

Z=20 cm T amb=25.0 C RH=42.8 % T inlet= 25.0 C RH inlet=42.4 %RH min=41.1 % RHmax=87 %RH med=42.5 % RH Aver=46.7 %

0 3 6 9 12 15 18 21 24 27 30 33 36

X

0

2

4

6

8

10

12

14

16

18

20

22

24

26

Y

35

37.5

40

42.5

45

47.5

50

52.5

55

57.5

60

62.5

65

67.5

70

72.5

75

77.5

80

85

0 3 6 9 12 15 18 21 24 27 30 33 36

X

0

2

4

6

8

10

12

14

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26

Y

0 3 6 9 12 15 18 21 24 27 30 33 36

X

0

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10

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22

24

26

Y

0 3 6 9 12 15 18 21 24 27 30 33 36

X

0

2

4

6

8

10

12

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16

18

20

22

24

26

Y

35

37.5

40

42.5

45

47.5

50

52.5

55

57.5

60

62.5

65

67.5

70

72.5

75

77.5

80

35

37.5

40

42.5

45

47.5

50

52.5

55

57.5

60

62.5

65

67.5

70

72.5

75

77.5

80

85

35

37.5

40

42.5

45

47.5

50

52.5

55

57.5

60

62.5

65

67.5

70

72.5

75

77.5

80

co-current Tinlet =25 C Nozzle=10 , spray flow=0.6 L/h, air velocity=2.4 m/s



(b) Temperature distribution

Figure 4 (a) Humidity distribution & (b) Temperature distribution in the transverse Z=20, 40,

60&80cm using nozzle type10 with a co-current (Tinlet =25 oC)

(a) Humidity distribution

counter-current Tinlet =25 C Nozzle=10 , spray flow=0.6 L/h, air velocity=2.4 m/s

Z=80 cm T amb=23.5 C RH=52.3 % T inlet= 25.0 C RH inlet= 50.6 %RH min=60.2 % RHmax=65.7 %RH med=63.2 % RH Aver=62.97 %


Z=40 cm T amb=24.8 C RH=50.9 % T inlet= 25.0 C RH inlet= 42.1 %RH min=49.4 % RHmax=66.7 %RH med=53.2 % RH Aver=54 %

Z=20 cm T amb=24.8 C RH=50.1 % T inlet= 25.0 C RH inlet= 42.0%RH min=44.2 % RHmax=84.7 %RH med=60.3 % RH Aver=62.1%

0 3 6 9 12 15 18 21 24 27 30 33 36

X

0

2

4

6

8

10

12

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16

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20

22

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26

Y

35

37.5

40

42.5

45

47.5

50

52.5

55

57.5

60

62.5

63.75

65

67.5

68.75

70

72.5

73.75

75

77.5

80

0 3 6 9 12 15 18 21 24 27 30 33 36

X

0

2

4

6

8

10

12

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18

20

22

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26

Y

35

37.5

40

42.5

45

47.5

50

52.5

55

57.5

60

61.25

62.5

65

67.5

70

72.5

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77.5

80

0 3 6 9 12 15 18 21 24 27 30 33 36

X

0

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0 3 6 9 12 15 18 21 24 27 30 33 36

X

0

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47.5

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52.5

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62.5

65

67.5

70

72.5

75

77.5

80

85

x=80 cm T amb=24.4 C RH=53.7 % T inlet= 25.0 C RH inlet=50.6 %T min=20 C T max=24.5 CT med=23.3 C T Aver=23 C

0 3 6 9 12 15 18 21 24 27 30 33 36

Z

0

3

6

9

12

15

18

21

24

Y

19

20

21

22

23

24

25

0 3 6 9 12 15 18 21 24 27 30 33 36

Z

0

3

6

9

12

15

18

21

24

Y

19

20

21

22

23

24

25

x=60 cm T amb=25.0 C RH=50.6% T inlet= 25.0 C RH inlet=50.1 %T min=21.4 C T max=24.6 CT mid=23.5 C T Aver=23.6 C

0 3 6 9 12 15 18 21 24 27 30 33 36

Z

0

2

4

6

8

10

12

14

16

18

20

22

24

26

Y

x=40 cm T amb=24.6 C RH=48.6 % T inlet= 25.0 C RH inlet=42.1 %T min=19.4 C T max=24.9 CT med=23.8 C T Aver=23.2 C

19

20

21

22

23

24

25

0 3 6 9 12 15 18 21 24 27 30 33 36

Z

0

2

4

6

8

10

12

14

16

18

20

22

24

26

Y

x=20 cm T amb=25.0 C RH=42.8 % T inlet= 25.0 C RH inlet=42.4 %T min=19.6 C T max=24.9 CT med=24.8 C TAver=24.4 C

19

20

21

22

23

24

25

co-current Tinlet =25 C Nozzle=10 , spray flow=0.6 L/h, air velocity=2.4 m/s




(b) Temperature distribution

Figure 5 (a) Humidity distribution & (b) Temperature distribution in the transverse Z=20, 4

0, 60&80cm using nozzle type 10 with a counter-current (T inlet =25 oC)

a- T air=25oC b-T air=30

oC

Figure 6 Average humidity in the transverse Z=20,40,60&80cm using nozzle type 10 with a

co & counter-current current air velocity 2.4 m/s (a)T inlet =25 oC & (b) T inlet =30

oC.

a- T air=25oC b-T air=30

oC

Figure 7 Average temperature in the transverse Z=20,40,60&80cm using nozzle type 10 with

a co & counter-current air velocity 2.4 m/s (a)T inlet =25 oC & (b) T inlet =30

oC.

x=80 cm T amb=23.5 C RH=52.3 % T inlet= 25.0 C RH inlet= 50.6 %T min=22.6 C T max=23.6 CT med=23.1 C T Aver=23.14 C

x=60 cm T amb=25.0 C RH=50.6 % T inlet= 25.0 C RH inlet= 50.0 %T min=23.2 C T max=23.9 CT mid=23.5 C T Aver=23.6 C

x=40 cm T amb=24.8 C RH=50.9 % T inlet= 25.0 C RH inlet= 42.1 %T min=21.4 C T max=24.5 CT med=23.5C T Aver=23.4 C

x=20 cm T amb=24.8 C RH=50.1 % T inlet= 25.0 C RH inlet= 42.0%T min=20.8 C T max=24.9 CT med=23.6 C TAver=23.45 C

0 3 6 9 12 15 18 21 24 27 30 33 36

Z

0

2

4

6

8

10

12

14

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18

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24

26

Y

21.4

21.8

22.1

22.4

22.6

22.8

23

23.2

23.4

23.6

24

24.4

0 3 6 9 12 15 18 21 24 27 30 33 36

Z

0

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4

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26

Y

23.2

23.3

23.4

23.5

23.6

23.7

23.8

0 3 6 9 12 15 18 21 24 27 30 33 36

Z

0

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8

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26

Y

21.4

21.8

22.2

22.6

23

23.4

23.8

24.2

0 3 6 9 12 15 18 21 24 27 30 33 36

Z

0

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26

Y

20.8

21.2

21.6

22

22.4

22.8

23.2

23.6

24

24.4

24.8

counter-current Tinlet =25 C Nozzle=10 , spray flow=0.6 L/h, air velocity=2.4 m/s



4.2. Influence of air flow on air cooling

The same measurements were performed for cooling air flow rates of 0.14, 0.187

& 0.225 m3/s corresponding to speeds of 1.5, 2.0 & 2.4 m/s. The results includes

these measurements of air velocity with the direction of injection of spray (counter-

current) where inlet air temperature is 30 oC. Comparison of the results obtained for

the airflows studied shows that the humidity increases significantly with increasing air

flow and the temperature decreasing for counter current flow, as shown in Figure (8).

In fact, increasing the velocity of the air has the effect more rapidly cause the spray

thereby reducing the residence time and dispersion of droplets in the flow. The

fraction of evaporated water is then directly reflected in diminished.

(a) Humidity distribution (b) Temperature distribution

Figure 8 Humidity and temperature distribution in the transverse Z=40 and 60 cm using

nozzle type 10 with a counter-current and inlet air temperature 30 oC for air velocity 2.4, 2.0

and 1.5 m/s.

4.3. Influence using spray system on heat exchanger

Figure (9) shows the temperature of water out of heat exchanger without and with

using spray system nozzle type 10 at Z=40 cm with a counter-current flow and air

velocity 2.4 and 1.5 m/s, for inlet air temperature 30 and 35 oC. It found that the

counter-current Tinlet =30.0 C Nozzle=10 air velocity=2.4 m/s

counter-current Tinlet =30.0 C Nozzle=10 air velocity=2.0 m/sZ=60 cm T amb=25.0 C RH=39.1 % T inlet= 30.0 C RH inlet= 32.2 %RH min=49.2 % RHmax=70.7 %RH med=58.6 % RH Aver=66.35 %

Z=40 cm T amb=25 C RH=38.6% T inlet= 30.0 C RH inlet=31.2 %RH min=42.3 % RHmax=72.4 %RH med=53.1 % RH Aver=63.8 %

Z=40 cm T amb= 25.0 C RH amb=40.3%T inlet=30.0 C RH inlet=35.1%RH min=38.7 % RH max= 68.6 %RH med=48.2 % RH Aver=50.4 %

0 3 6 9 12 15 18 21 24 27 30 33 36

X

0

2

4

6

8

10

12

14

16

18

20

22

24

26

Y

35

37.5

40

42.5

45

47.5

50

52.5

55

57.5

60

62.5

65

67.5

70

72.5

75

77.5

80

Z=60 cm T amb= 25.5 C RH amb=40.9%T inlet=30.0 C RH inlet=35.8%RH min=47.1 % RH max= 58.1 %RH med=53.7 % RH Aver=52.78 %

0 3 6 9 12 15 18 21 24 27 30 33 36

X

0

2

4

6

8

10

12

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22

24

26

Y

35

37.5

40

42.5

45

47.5

50

52.5

55

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60

62.5

65

67.5

70

72.5

75

77.5

80


0 3 6 9 12 15 18 21 24 27 30 33 36

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0

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0 3 6 9 12 15 18 21 24 27 30 33 36

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0 3 6 9 12 15 18 21 24 27 30 33 36

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0

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18

20

22

24

26

Y

Z=60 cm T amb=24.0 C RH=38 % T inlet= 30.0 C RH inlet= 27 %RH min=50 % RHmax=78.1 %RH med=62.3 % RH Aver=74.75 %

0 3 6 9 12 15 18 21 24 27 30 33 36

X

0

2

4

6

8

10

12

14

16

18

20

22

24

26

Y


35

37.5

40

42.5

45

47.5

50

52.5

55

57.5

60

62.5

65

67.5

70

72.5

75

77.5

80

35

37.5

40

42.5

45

47.5

50

52.5

55

57.5

60

62.5

65

67.5

70

72.5

75

77.5

80

35

37.5

40

42.5

45

47.5

50

52.5

55

57.5

60

62.5

65

67.5

70

72.5

75

77.5

80

35

37.5

40

42.5

45

47.5

50

52.5

55

57.5

60

62.5

65

67.5

70

72.5

75

77.5

80



Z=60 cm T amb=25.0 C RH=39.1 % T inlet= 30.0 C RH inlet= 32.2 %T min=25.7 C T max= 27.0 CT med=26.8 C T Aver=26.7C

Z=40 cm T amb=25.0 C RH=38.6% T inlet= 30.0 C RH inlet=31.2 %T min=23.6 C T max= 27.7 CT med=26.2 C T Aver=26.4 C

counter-current Tinlet =30.0 C Nozzle=10 air velocity=1.5 m/sZ=60 cm T amb=24.0 C RH=38 % T inlet= 30.0 C RH inlet= 27 %T min=24.7 C T max=26.2 CT med=25.7 C T Aver=25.6 C

Z=40 cm T amb=25.3 C RH=39.3 % T inlet= 30.0 C RH inlet= 33.1 %T min=23.8 C T max=27.6 CT med=26.5 C T Aver=26.2 C

Z=40 cm T amb= 25.0 C RH amb=40.3 %T inlet=30.0 C RH inlet=35.1 CT min=23.4 C T max= 28.1 CT med=27.3 C T Aver=26.7 C

Z=60 cm T amb= 25.5 C RH amb=40.9 %T inlet=30.0 C RH inlet=35.8 CT min=26.5 C T max= 27.5 CT med=27.2 C T Aver=27.14 C

0 3 6 9 12 15 18 21 24 27 30 33 36

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0

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26

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20

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6

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20

20.5

21

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0 3 6 9 12 15 18 21 24 27 30 33 36

X

0

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18

20

22

24

26

Y

2020.52121.52222.52323.52424.52525.525.752626.2526.526.752727.2527.52828.52929.530

0 3 6 9 12 15 18 21 24 27 30 33 36

X

0

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26

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29

29.5

30




temperature of the outlet water decreasing with reducing the flow rate and with using

spray system. The temperature of outlet water from heat exchanger decreased when

the inlet air velocity increased, the temperature gradient is dependent on the rate at

which the fluid carries the heat away, and a high velocity produces a large

temperature gradient.

(a) Inlet air temperature 30 oC

(b) Inlet air temperature 35 oC

Figure 9 Comparison the temperature of water out of heat exchanger without and with using

spray system nozzle type 10 at Z=40 with a counter-current flow and air velocity 2.4 m/s,

temperature water inlet the H.E=45 oC, inlet air temperature 30 and 35

oC.

4.4. Effect using the nanofluid flow on heat exchanger cooling

Figure (10) shows the comparison of the heat exchanger cooling performance when

using nanofluid with and without using spray system at inlet air temperature 30oC and

velocity 2.4 m/s for inlet fluid temperature 40, 45 and 50 oC. One can clearly observe

that working fluid outlet temperature has decreased with the augmentation of

nanofluid volume concentration and with used spray system. It is important to

mention that from a practical viewpoint for cooling system; at equal mass flow rate

40.5

41

41.5

42

42.5

43

43.5

44

44.5

4 6 8

tem

pe

ratu

re w

ate

r o

utl

et

th

e H

.E (

oC

)

Volume flow rate( L/min)

air velocity =1.5 m/s air velocity=1.5 m/s

air velocity= 2.4 m/s air velocity= 2.4 m/s

without using spray with using spray

40.5

41

41.5

42

42.5

43

43.5

44

44.5

4 6 8tem

pe

ratu

re w

ate

r o

utl

et

th

e H

.E (

oC

)

Volume flow rate( L/min)

air velocity=1.5 m/s air velocity=1.5 m/s

air velocity= 2.4 m/s air velocity= 2.4 m/s




the more reduction in working fluid temperature indicates a better thermal

performance of the cooling system.

(a) 40 oC (b) 45

oC

c) 50 oC

Figure 10 Comparison of the H.E cooling performance of the working fluid with and without

using spray system, inlet air temperature 30oC and air velocity 2.4 m/s for inlet working fluid

temperature in H.E 40, 45 and 50 oC.

4.5 Comparison the average temperature and relative humidity for air

before and after heat exchanger

Figure (11) shows the average temperature and relative humidity of air, with counter

flow before and after the heat exchanger without and with using mist system at Z=40

cm from injection point. When applying mist, temperature of the air decreased from

about 3 oC and the relative humidity of 38% then passed to 50% when the inlet air

temperature 30oC with velocity 2.4 and the flow rate in H.E is 8 L/min with inlet

water temperature 40o

C . Upon passing through the condenser, the temperature of the

36.5

37

37.5

38

38.5

39

4 6 8

Te

mp

. o

f w

ork

ing

flu

id o

utl

et

the

H.E

(oC

)

Vol. flow rat in H.E (L/min)

40.5

41

41.5

42

42.5

43

43.5

44

4 6 8

Te

mp

. o

f w

ork

ing

flu

id o

utl

et

the

H.E

(oC

)


45.5

46

46.5

47

47.5

48

4 6 8

Te

mp

. of

wo

rkin

g f

luid

ou

tle

t th

e H

.E (

oC

)





air increases and humidity decreases because of the heat exchange between the humid

air and the heat exchanger.

(a) Average temperature

(b) Average relative humidity

Figure 11 Average temperature and humidity of air with counter flow before and after the

heat exchanger as a function of time, without and with using misting system at Z=40 cm, inlet

air temperature Tair=30oC, inlet fluid temperature in H.E 45

oC with flow 8 L/min.

4.6. Nusselt Numbers

Figure (12) shows the heat transfer enhancement obtained due to the replacement of

water with nanofluids in the heat exchanger, which cooled by air with temperature

30oC and velocity 2.4 m/s with and without spray system. Dispersion of the

nanoparticles into the distilled water increases the thermal conductivity and viscosity

of the nanofluid, this augmentation increases with the increase in particle

concentrations. As can be seen in these figures, Nu number in all the concentrations

has increased by increase in the flow rate of the fluid and consequently Reynolds

25

27

29

31

33

35

37

39

41

43

45

0

10

20

30

40

50

60

70

80

90

10

0

11

0

12

0

Av

era

g t

em

pe

ratu

re o

f a

ir (

oC

)

after H.E after H.E

before H.E before H.E


Time ( s)

10

15

20

25

30

35

40

45

50

55

60

65

0

10

20

30

40

50

60

70

80

90

10

0

11

0

12

0

Av

era

g h

um

idit

y o

f a

ir (

% )

after H.E after H.E

before H.E before H.E


Time (s)



number and by increasing inlet fluid temperature. Figure (13) compares the results for

fluid at different inlet temperatures in order to analyze the effect of spray system on

heat transfer performance of the heat exchanger. It is clear from figures that when

using spray system, a slightly improves in Nusselt number. In general, the Nusselt

number increases as volume flow rate (or equally Reynolds number), nanofluid

volume concentration and fluid inlet temperature increase.

The enhancement in the heat transfer is explained by using Nusselt number

ratio (stu / st%,%vwxyzw {$|}~), as shown in (figure 14). It is clear that the Nusselt

number ratio increases when using nanofluid also the ratio increases by increasing the

volume concentration. The effect of using spray system on Nusselt ratio (stu / st%,%vwxyzw {$|}~) can be seen in (figure 15). The Nusselt number ratio increases

when using a sprayed air, due to decrease the temperature of air passing on the heat

exchanger the enhancement in heat transfer coefficient when using nanofluid is

attributed to the effective thermal conductivity of nanofluid solution.

(a) Without using spray (b) With using spray

Figure 12 Effect of fluid inlet temperature on Nusselt numbers for inlet air temperature 30 oC

and velocity 2.4 m/s, without and with using spray.

(a) Water (b) Nanofluid 0.5% (c) Nanofluid 2%

Figure 13 Effect of using spray system on Nusselt numbers at different inlet temperature of working fluid

in heat exchanger (inlet air temperature 30 oC and velocity 2.4 m/s), for water and nanofluid volume

concentration 0.5 and 2 %).

60

80

100

120

140

160

180

10000 20000 30000 40000

Nu

Re

Tin=50 C, ⱷ=2% Tin=45 C, ⱷ=2%

Tin=40 C, ⱷ=2% Tin=50 C, ⱷ=0.5%

Tin=45 C, ⱷ=0.5% Tin=40 C, ⱷ=0.5%

60

80

100

120

140

160

180

10000 20000 30000 40000

Nu

Re

Twin= 40 C Twin= 40 C

Twin=45 C Twin=45 C

Twin= 50 C Twin= 50 C


60

80

100

120

140

160

180

10000 20000 30000 40000

Nu

Re

T in= 40 C T in=40 C

T in=45 C T in= 45 C

T in= 50 C T in= 50 C


60

80

100

120

140

160

180

10000 20000 30000 40000

Nu

Re

T in= 40 C T in=40 C

T in=45 C T in= 45 C

T in= 50 C T in= 50 C


60

80

100

120

140

160

180

10000 20000 30000 40000

Nu

Re

Tin=50 C, ⱷ=2% Tin=45 C, ⱷ=2%

Tin=40 C, ⱷ=2% Tin=50 C, ⱷ=0.5%

Tin=45 C, ⱷ=0.5% Tin=40 C, ⱷ=0.5%




(a) Without using spray (b) With using spray

Figure 14 Effect of using nanofluid at different inlet temperature on Nusselt ratio (stu / st%,%vwxyzw {$|}~) for inlet air temperature 30

oC and velocity 2.4 m/s, without and with

using spray.

(a) 40 oC (b) 45

oC

(c) 50 oC

Figure 15 Effect of using spray system on Nusselt ratio (stu / st%,%vwxyzw {$|}~) , inlet air

temperature 30 oC and velocity 2.4 m/s and inlet fluid temperature 40, 45 and 50

oC.

0.90

0.95

1.00

1.05

1.10

1.15

1.20

1.25

1.30

2 4 6 8 10

Nu

f /

Nu

w,

wit

ho

ut

spra

y

Volume flow rate (L/min)

Tin=50 C, ⱷ=0% Tin=45 C, ⱷ=0%Tin=40 C, ⱷ=0% Tin=50 C, ⱷ=0.5%

Tin=45 C, ⱷ=0.5% Tin=40 C, ⱷ=0.5%

Tin=50 C, ⱷ=2% Tin=45 C, ⱷ=2%

Tin=40 C, ⱷ=2%

0.90

0.95

1.00

1.05

1.10

1.15

1.20

1.25

1.30

2 4 6 8 10

Nu

f/

Nu

w,

wit

ho

ut

spra

y

Volume flow rate (L/min)

Tin=50 C, ⱷ=0% Tin=45 C, ⱷ=0%Tin=40 C, ⱷ=0% Tin=50 C, ⱷ=0.5%Tin=45 C, ⱷ=0.5% Tin=40 C, ⱷ=0.5%Tin=50 C, ⱷ=2% Tin=45 C, ⱷ=2%Tin=40 C, ⱷ=2%

0.8

0.9

1.0

1.1

1.2

1.3

1.4

10000 20000 30000

Nu

f /

Nu

w,

wit

ho

ut

spra

y

Re f

water water

ⱷ=0.5 % ⱷ=0.5 %

ⱷ=2.0 % ⱷ=2.0 %

without spray with spray

0.8

0.9

1.0

1.1

1.2

1.3

1.4

10000 20000 30000

Nu

f/

Nu

w,

wit

ho

ut

spra

y

Re f

water water

ⱷ=0.5 % ⱷ=0.5 %

ⱷ=2.0 % ⱷ=2.0 %


0.8

0.9

1.0

1.1

1.2

1.3

1.4

10000 20000 30000 40000

Nu

f /

Nu

w,

wit

ho

ut

spra

y

Re f

water water

ⱷ=0.5 % ⱷ=0.5 %

ⱷ=2.0 % ⱷ=2.0 %




6. COMPARISON THE NUMERICAL AND EXPERIMENTAL

WORK

6.1. Mist Part

In this section, we will compare the experimental results with the numerical results

obtained in the same conditions. Recall that to perform these simulations, the

computer code needs input data. These data correspond mainly parameters of

instructions experiments:

• The flow rate and temperature of the air at the inlet of the duct

• The flow rate and the water temperature at the inlet of the exchanger

• The flow of mist

• The temperature of the air upstream of the exchanger.

The (figures 16) showed a good agreement between the experimental and

numerical temperature of air using nozzle type 10 in the distance Z=20,40,60&80cm

with air velocity 2.4 m/s for inlet air temperature 25,30&35 oC.

6.2. Heat Exchanger Part

The comparison between the experimental and numerical result for average Nuselt

number are shown in (figure 17) for the working fluids (water and nanofluid) without

and with the sprayed air. Notice a good agreement between the results with maximum

deviation (11%).

6.3. Comparison with the Published Work

Figure (18) Compere temperature of air for the experimental and numerical present

work with the experimental work of J.Tissot 2012 [5] using nozzle type 10 in the

distance Z=40 and 60cm and inlet air temperature 25 oC with air velocity 1.0 m/s for

counter-current and there is a good agreement.

The present heat transfer results of test facility for average inner Nusselt number

(for three inlet working fluid temperatures) are in good agreement with the empirical

correlation of Dittus –Boelter and Pak & Cho as shown in (figures 19).

(a) 25 oC (b) 30

oC

22

23

24

25

26

27

28

29

30

20 40 60 80

Av

era

ge

te

mp

. o

f a

ir f

low

( o

C )

The distance after injection ( cm)

experimental

numerical

22

23

24

25

26

27

28

29

30

20 40 60 80

Av

era

ge

te

mp

. o

f a

ir f

low

( o

C )


numerical

experimental




(c) 35 oC

Figure 16 The experimental and numerical average air temperature with using spray system

(nozzle type 10) in the distance Z=20, 40 ,60 & 80 cm and inlet air temperature 25, 30 , 35 oC with air velocity 2.4 m/s for counter-current flow.

(a) Without the sprayed air

(b) With the sprayed air

Figure 17 Comparison the experimental results of average inner Nusselt number with CFD

results for air temperature 30oC and velocity 2.4 m/s at state (a) without the sprayed air (b)

with the sprayed air

40

90

140

190

10000 20000 30000 40000

Nu

av

Re

ⱷ=2.0 %, exp.

ⱷ=0.5 %, exp.

ⱷ=0 %, exp.

ⱷ=2.0 %, nu.

40

60

80

100

120

140

160

180

200

220

10000 20000 30000 40000

Nu

av

Re

ⱷ=2.0 %, exp.

ⱷ=0.5 %, exp.

ⱷ=0 %, exp.

ⱷ=2.0 %, nu.

22

24

26

28

30

32

34

20 40 60 80

Av

era

ge

te

mp

. o

f a

ir f

low

( o

C )


experimental

numerical



Figure 18 Compere temperature of air for the experimental work of J. Tissot 2012 [ ] with the

experimental and numerical present work using nozzle type 10 in the distance Z=40 & 60

cm and inlet air temperature 25 oC with air velocity 1.0 m/s for counter-current.

(a) without the sprayed air (b) with the sprayed air

Figure 19 Comparison the experimental results of average inner Nusselt number with the

Dittus-Boelter and Pak & Cho equations inlet air temperature 30oC and velocity 2.4m/s at

state (a) without the sprayed air (b) with the sprayed air.

5. CONCLUSIONS

This study showed experimentally and numerically the influence of the cooling of

spray system and the direction of injection thereof into the air then flow toward the

heat exchanger, and in other hand showed the influence of using nanofluid at two

concentrations (0.5 and 2%) on enhance the heat transfer for the heat exchanger. The

results have clearly shown:

• It was demonstrated that the mist against the current is an advantageous

compromise compared to a co-current injection to combine a large exchange

surface and a wide dispersion of spray.

• The measurement results and for calculating distances of 20 to 80 cm are

presented and the temperatures are almost identical between the numerical and

experimental. In both the average temperature for 20, 40, 60 and 80 cm decreases

about ≈ 0.1 to 3 oC. It confirms numerically that evaporation takes place mainly

in the area of the spray back flow. We conclude that the code calculation and is

suitable for our predictive application.

21

21.2

21.4

21.6

21.8

22

22.2

22.4

22.6

40 60

Av

era

ge

te

mp

. o

f a

ir f

low

( o

C )


numerical

experimental

ex. J.Tissot 2012

40

60

80

100

120

140

160

180

200

220

10000 20000 30000 40000

Nu

av

Re

Pak and Cho

Dittus-Boelter

Present experimental data

ⱷ=2.0 %

ⱷ=0.5 %

ⱷ=0 % (water)

40

60

80

100

120

140

160

180

200

220

10000 20000 30000 40000

Nu

av

Re

Pak and ChoDittus-BoelterPresent experimental dataⱷ=2.0 %ⱷ=0.5 %ⱷ=0 % (water)




• The Nusselt number has increased by increase in the flow rate of the fluid and

consequently Reynolds number and by increasing inlet fluid temperature and by

increased nanofluid volume concentration. When using spray system, a slightly

improves in Nusselt number compered without using spray system.

• The maximum enhancement in the heat transfer explained by using Nusselt

number ratio (stu / st%,%vwxyzw {$|}~), was (1.235) which occurred at nanofluid

concentration 2% with using sprayed air.

REFERENCES

[1] R. Sureshkumar, S.R. Kale and P.L. Dhar. Heat and mass transfer processes

between a water spray and ambient air – II. Simulations, Applied Thermal

Engineering 28(2008) pp 361–371.

[2] Raminn Faramarzi, John Lutton, and Sean Gouw, Southern California Edison,

Performance comparison of evaporatively-cooled condenser versus air-cooled

condenser air conditioners. ACEEE Summer Study on Energy Efficiency in

Buildings (2010) pp 117-127.

[3] K.A. Jahangeer, Andrew A.O. Tay, Md. RaisulIslam. Numerical investigation of

transfer coefficients of an evaporatively-cooled condenser, Applied Thermal

Engineering 31(2011) pp 1655-1663.

[4] K.T. Chan, J. Yang, and F.W. Yu. Energy performance of air-cooled chiller with

water mist assisted air-cooled condensers, 12th Conference of International

Building Performance Simulation Association, Sydney, pp 14-16 November

2011.

[5] J. Tissot, P. Boulet, F. Trinquet, L. Fournaison. Experimental study on air cooling

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[6] P. Boulet, J. Tissot, F. Trinquet, L. Fournaison. Enhancement of heat exchanges

on a condenser using an air flow containing water droplets, Applied Thermal

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[7] S.M. Peyghambarzadeh, S.H. Hashemabadi, M. Seifi Jamnani and S.M. Hoseini.

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[8] M.M. Heyhat, F. Kowsary, A.M. Rashidi, S. Alem Varzane Esfehani and A.

Amrollahi. Experimental investigation of turbulent flow and convective heat

transfer characteristics of alumina water nanofluids in fully developed flow

regime, International Communications in Heat and Mass Transfer 39(2012) pp

1272–1278.

[9] A. Collin, P. Boulet, G. Parent and D. Lacroix. Numerical simulation of a water

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Thermal Sciences 46(2007) 856–868.

[10] J. Tissot, P. Boulet, F. Trinquet, L. Fournaison and H. Macchi-Tejeda. Air

cooling by evaporating droplets in the upward flow of a condenser, Int. J. Therm.

Sci, 50(2011) 2122-2131.

[11] Ashish Kumar, Dr. Ajeet Kumar Rai and Vivek Sachan, an Experimental Study

of Heat Transfer in A Corrugated Plate Heat Exchanger. International Journal of

Mechanical Engineering and Technology, 5(9), 2014, pp. 286-292.

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