February 3, 2014

University of California, San Diego

Department of NanoEngineering

La Jolla, CA 92093

To Whom It May Concern:

As requested, this “Plate Heat Exchanger” report includes the overall heat transfer coefficient by varying hot and cold water flow rates in steady­state and batch operations.

We hope this report will satisfy the desired expectations. If you have any questions or concerns, please contact us.

Sincerely,

Group B­4 Brandon Sanchez Janet Mok bobbyjoedik@gmail.com janet.mok14@gmail.com Liliana Busanez Saman Hadavand lilianabusanez@gmail.com hada4gold@gmail.com Department of NanoEngineering, Chemical Engineering

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Plate Heat Exchangers

Lab 1 Report

Presented to the

University of California, San Diego Department of Nanoengineering

CENG 176A 3 February 2015

Prepared by: Group B­4

Lead Author Section

Janet Mok Letter of Transmittal, Abstract, Intro, Conclusion

Liliana Busanez Theory and Background

Brandon Sanchez Results and Discussion

Saman Hadavand Tech Memo and Presentation

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Abstract

The goal of the experiment was to understand the characteristics and design of a plate

heat exchanger, as well as to evaluate the effects of varying flow rates on the overall heat transfer

coefficient. The steady­state operation involved moving cold water from a source tank to a

receiving tank where the hot water stream exchanges heat with the cold water stream in the

source tank. In the batch operation, the cold water was pumped into the same tank, with constant

stirring, after exchanging heat with the hot water stream. The data and results showed that in the

steady­state operation, the overall heat transfer coefficient increased as the mass flow rates

increased. However, it was seen that in the batch operation, the overall heat transfer coefficient

decreased as the temperature difference decreased.

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Table of Contents Introduction

pp. 5

Theory Figure 1, Cocurrent Flow Figure 2. Countercurrent Flow

pp. 6

Methods pp. 9

Results Figure 3. Measured Flow Rate Figure 4. LMTD vs. time

pp. 11

Discussion pp. 13

Conclusion pp. 16

References pp. 17

Appendices Table A1. Batch data Table A2. Steady­state data Table A3. Calibration Batch Table A4. Calibration Steady­state

pp. 18

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Introduction

The Plate Heat Exchanger (PHE) Experiment uses common equipment found in heat

exchange processes used in industries such as: power, air conditioning, and biomedical

industries. The earliest development of PHEs was in response to increasingly strict requirements

from foods, particularly dairy products in the late nineteenth century. The very first patent for a

PHE was granted to the german Albrecht Dracke, who proposed in 1878 the cooling of one

liquid by another, with each flowing in a layer on opposite sides of a series of plates¹. The

growing demand for energy conservation, while using sustainable technology and preserving the

environment, has lead to high performance, compact heat exchangers with increased energy

efficiency. The PHE design is decentralized in nature, and benefits include flexible sizing of

various plates to meet batch­processing heat load demands for sustaining hygienic conditions

common in food, and pharmaceutical product processing¹.

The PHE consists of a pack of gasketed corrugated metal plates, pressed together in a

frame, which allows fluid to flow through a series of parallel flow channels and exchange heat

through the thin metal plates³. Plate heat exchangers are used for transferring heat for any

combination of gas, liquid, and two­phase streams. The gaskets prevent leakage to the outside

and directs the fluids as desired⁴. Heat is then transferred from the warm fluid via the dividing

wall to the colder fluid in a pure counter­flow arrangement, which supplements the high

effectiveness of the PHEs.

The importance of the plate heat exchanger can be seen through the various structural

advantages that it has to offer. The plate surface corrugations promotes enhanced heat transfer by

means of promoting swirl or vortex flows and increased effective heat transfer area. The heat

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transfer coefficients obtained are significantly higher than other heat exchangers for comparable

fluid conditions, which leads to a much smaller thermal size¹. Because of their high heat transfer

coefficients and true counter­flow arrangement, PHEs are able to operate under very close

approach temperature conditions which results in up to 90% heat recovery¹. Another advantage

of PHEs is due to the thin channels created between the two adjacent plates, where the volume of

fluid contained in the heat exchanger is small. Therefore, it reacts to the process condition

changes in a rather short time transient and is easier to control¹. Because plates with different

surface patterns can be combined in a single PHE, different multi­pass arrangements can be

configured which enables better optimization of operating conditions¹.

In this experiment, in order to evaluate the overall heat transfer coefficient, we analyzed

different transient heat operating conditions for plate heat exchangers at varying hot and cold

flow rates. The heat exchanger transfer coefficient from batch heat operations, and under

continuous operations was used to evaluate results that can be applied to scale­up calculations as

in industry to transfer thermal energy in between mediums. The Data logging VI was used to run

the experiment, and the flow rates and approach temperature difference were adjusted to set

operating conditions.

Background & Theory

Plate Heat Exchangers (PHE) promote well mixed flows along the plate with high

convective heat transfer coefficients that result from the inter­corrugation flow path. The plates

themselves confine fluid stream within the inter­plate flow channels. This enhances heat transfer

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and the resultant heat transfer coefficient is significantly higher for PHE than the traditional

shell­and tube heat exchangers¹.

The plate­pack in gasketed PHEs is easily disassembled and reassembled. The thin

rectangular sheet metals plates are in between gaskets, assembled in a pack, and bolted in a

frame. Heat is transferred from the hot fluid via the plate wall to the colder fluid in counter flow

arrangement. The advantage of PHE compared to other highly compact exchangers include

thermal flexible sizing of plates, easy cleaning necessary for the food industry as mentioned, and

close approach temperature pure countercurrent­flow operations (~ ) that lead to highC 1°

effectiveness of PHEs¹.

For PHE, there are three primary design flow arrangements for hot and cold fluid

arrangements that of parallel­flow, counter­flow, and multi­pass arrangement. Most common, is

cocurrent and countercurrent configurations:

Figure 1: Cocurrent Figure 2: Countercurrent

Energy moves from hot fluid to a surface by convection, through the wall by thermal

conduction, and then by convection from the surface to the cold fluid. Heat convection is forced

within a heat exchanger and it is the convective transfer that governs its performances₅⁵. The

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overall heat transfer (or rate) equation in heat exchangers is given by the energy balance across

the separating wall:

(1) C (T ) C (T ) AΔT Q = m c c hout − T c

in = m h h hin − T c

out = U LMTD

Q= Rate of heat transfer (duty), U= Overall heat transfer Coefficient, A= cross­sectionalhere,w

Area for heat transfer, = Log Mean Temperature DifferenceT Δ LMTD

The Log Mean Temperature Difference (LMTD) is used to determine the temperature

driving force for heat transfer in flow systems. LMTD is constant along the length, and used

most notably with heat exchangers.

(2)

, are the bulk temperatures, or thehere, T T ) w 1 = ( hout − T c

in T T ) 2 = ( hin − T c

out

temperature difference for countercurrent as demonstrated in Figure 2.

The overall heat transfer coefficient is determined for steady state and batch operations.

Heat losses or gains of a whole exchanger with the environment can be neglected. The steady

state operation equation to analyze the performance of the heat exchanger is

(3)C dT dx AΔT m c / = U LMTD

Overall Heat Transfer Coefficient can be estimated for different fluids as well as the type

of heat exchanger system involved (PHE). Where the heat transfer coefficient, U, for water to

water heat exchangers, can be a typical transfer coefficient of about 2000 ².W m K] [ / 2

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For the Batch Heating balance equations, the heat balance in a well­mixed tank can be

based on the cold side transfer, hot side transfer, heated by an external heat exchanger so the tank

temperature is the cold side inlet, . The process conditions and heat load are varying T cin

throughout the batch.

In batch heating, the required duty is a function of the changing batch temperature

as a function of time. where and are result of hot and cold mass flowT Δ LMTD T 1 T 2

rates, and differentiation of , in consideration to the batch heat balance. Substituting in batch T cin

heating, , to Eq.(1), the temperature time derivative cancels out. The equation for batchT Δ LMTD

as a function of time is given by:

(4)n| | ]t− l T −T (t)hin

cin

T −T (0)hin

cin = [ (K−1)ω ωc h

m(Kω −ω )h c

The constant, K, is graphed in a semi­log plot, where from the slope K can be determined to

obtain the overall heat transfer coefficient using the following to determine U:

(5)xp( ( )) K = e CpUA 1

mc −1mh

Methods

This experiment involved using a plate heat exchanger and the PHE99_MAIN.vi for both

steady­state and batch operations. Three water tanks were used to test the plate heat exchanger in

order to determine the overall heat transfer coefficient. Two cold water tanks were filled with tap

water at about near room temperature. The lengths and widths were measured for both the cold

water tanks as well as the initial water level. Both operations involved cycling hot and cold water

throughout the system until a stable temperature has been reached. The Labview program

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PHE99_MAIN.vi was used to automatically turn on the pumps and record the Hot­in, Cold­in,

Hot­out, and Cold­out temperatures measured by the thermocouples positioned in the pipes.

While the procedure to execute the experiment for each operation was similar, there were some

differences in methods and use of equipment.

For the steady­state operation, two trials were performed by keeping the hot water flow

rate constant while varying the cold water flow rates. The cold water from one tank was moved

to the other in order to produce a steady group of data during a certain time interval, in which

there were minimal temperature fluctuations from a set thermocouple temperature reading. A

“From” tank and a “To” tank were first determined from the two cold water tanks. The valves

from the Cold­out stream and Cold­in stream were opened and closed respectively depending on

the labeled tank. Lastly, the hot and cold flow rate valves were both adjusted to the desired level.

The VI was then run and both hot water and cold water pumps were turned on and the

temperature data was recorded. Once the plate heat exchanger has reached steady­state, the VI

was stopped after 60 seconds of stable data. Between each trial, the water heater had to warm the

tank up to nearly fully hot.

Similar procedures were used for the batch operation, but this operation instead would be

circulating the cold water back into the same tank it was pumped from. Only one cold water tank

would be used whose level of water was not too high or too low. The depth of the water tank

would be recorded and the Cold­out and Cold­in stream valves were adjusted accordingly. The

rest of the procedure was the same as the steady­state operation except there had to be a

motorized consistent stirring in the cold water tank to allow the water temperature to achieve

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equilibrium before passing through the heat exchanger. The flow rates for both hot and cold

water should not be adjusted so that there is as little human input as possible.

Lastly the inline flow meter was calibrated to result in a good calibration curve. Error

could increase with increasing temperatures resulting in an inaccurate reading. A temperature

was established to run the calibration, and the “From tank was set to this particular temperature.

The temperatures of both tanks were recorded as well as the initial water level in the chosen

“To” tank. The cold water pump was switched on for one minute at a certain flow rate, and then

the time elapsed and new water level was then recorded.

After the experiment was finished, the water heater was turned down to the low setting

and the labview program was closed and shut down, accordingly.The data from the steady­state

and batch operations were then used to determine the overall heat transfer coefficient for this

particular plate heat exchanger.

Results

The cold stream flow rate was measured and varied over different time intervals. A

calibration graph was developed as shown in Figure 3. The hot stream was not used for

calibration as it was assumed that information on one of the flow streams would provide

identical information on the other. A slope of 1 on the calibration curve would indicate an ideal

flow meter. A slope of 1.0792 indicates an error in the calculated flow rate of being

approximately 8% higher than the flow rate displayed by the flow meter.

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Figure 3: Cold stream calibration for calculated flow rate vs. measured flow rate

Temperature data from the batch operations were used to solve for the log­mean

temperature differences according to Eqn. 2. THIn values were averaged over the duration of the

trials due to minor fluctuations in boiler temperature. The negative values of the LMTD’s for the

trials were plotted against time as shown in Figure 4. The slopes of the curves for each trial were

extracted and used to solve for the value of K according to Eqn. 3. These K values were then

used to solve for the overall heat transfer coefficient according to Eqn. 4. These results along

with the parameters used in each equation are displayed in Table A1. The area of the heat

exchanger plate used is .0321 m2. This value is multiplied by 7 to account for the 7 plates in the

heat exchanger. Note that the flow streams were adjusted by 7.92% due to calibration.

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Figure 4: Plots of ­LMTD vs. time for batch trials

Temperature data from the steady state operation was averaged during the duration of the

trials due to minor fluctuations in temperature readings. The overall heat transfer coefficient was

determined by Eqn 1. Because Eqn. U was calculated using both hot and cold stream

information, which gives 2 values of U for each trial. This data along with temperature data is

displayed in Table A2.

Discussion

Data for the overall heat transfer coefficient was produced using flow rates that had not

been calibrated. Upon adjusting the flow rates, it was found that the overall heat transfer

coefficient increased for steady state results and decreased for batch results. These values along

with percent differences are displayed in Table A3 and A4, respectively. Noting that the flow

rate calibration is only correcting error in the flow meter readings of our data, it was found that

calibrating the mass flow rate will increase the value of U. This can be seen by analyzing Eq. 1.

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The area, temperature differences and heat capacities are the same values as before, therefore an

increase in the flow rate can only increase U. Hence, the overall heat transfer coefficient and the

mass flow rate are directly proportional for this system.

The batch results require more analysis due to the solution technique for calculating U.

When utilizing Eqn. 4, the values of the LHS are the same. The RHS has increased flow rates,

therefore the value of K decreases after calibration. When using Eqn. 5, the calculated U value is

smaller. This may be less intuitive than the steady state results because a misleading assumption

may lead one to conclude that increasing flow rates increases the heat transfer rate. The

temperature dynamics of the batch system may account for the results for increased hot and cold

inlet flow rates. A higher hot stream inlet flow rate would increase the cold stream outlet

temperature at a faster rate. This would also increase the cold stream inlet temperature at a faster

rate, which is also flowing faster into the heat exchanger. Because all streams are approaching

steady state temperatures at a faster rate, the overall heat transfer coefficient decreases as the

temperature differences between the hot and cold streams decreases.

The procedure for the flow rate calibration may have introduced error when developing

the calibration. The container used to fill the water from the cold stream hose had approximate

volume measurements and were not completely accurate. Although the volumes were

approximate on the container, our group agreed that measurement of the original water tub

intended for the procedure would introduce more error. This was concluded because the tub is

rounded and warped and doesn’t accurately represent a rectangular prism. Thus, the dimensions

of the tubs would introduce significant error in volume calculations. Calibration of the hot stream

may introduce error if the hot stream equipment contains more fouling due to high temperature

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streams. The thermal energy from the hot streams may loosen and distribute more particles

through the pipes than the cold streams, however it was assumed that the cold and hot stream

equipment was identical.

The results for U for the batch and steady state operations were not precise and ranged

from about 300 to 1900 W/m2K. The largest source of error may be from assuming that U is a

constant and not a function of temperature. This may be detrimental in calculations because

depending on the temperature of the heat exchanger plates, U may be a higher or lower value.

The values of Uc and UH for the steady state operation should theoretically be equal

values in a closed system. Sources of error are limited due to the simplicity of the system.

Temperatures read from the thermocouples may have introduced significant error because the

thermocouples were not calibrated with manual thermometer readings of the water tanks. By not

calibrating the thermocouples, temperature differences may actually be higher or lower, and will

definitely affect the values of U. The small amount of data analyzed for the steady state system

may not be enough to accurately represent the heat exchanger dynamics, and more trials would

need to be conducted to get more accurate results.

The batch operation results produced inconsistent U values of 1507, 298, 470 and 755

W/m2K. After taking a look at Table A1 and noting the differences in H2O mass for each trial, it

may be concluded that the mass of H2O that went through the system had the greatest effect on

calculating U. This can be seen by Eqn. 4, as mass of water in the denominator will affect the

value of K, which will in turn affect the calculation of U in Eqn. 5. More trials would need to be

conducted with more variance in flow rates to extract consistent K values, and hence calculate a

better value of U.

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Conclusion

In conclusion, plate heat exchangers are used throughout a wide range of industries, such

as dairy and other hygienic industries, as well as in sustainable energy conservation and

biomedical industries. The purpose of this experiment was to determine the overall heat transfer

coefficient under both the steady­state and batch operations while varying hot and cold water

flow rates. It was found that for the steady­state operation, the overall heat transfer coefficient

increased with increasing flow rates, which shows that the overall heat transfer coefficient and

the mass flow rates are directly proportional. However for the batch operation, since all the

streams were approaching steady state temperatures at a faster rate, the overall heat transfer

coefficient decreases as the temperature differences between the hot and cold streams decreases.

Furthermore, the flow rate calibration of the plate heat exchanger indicated an 8% discrepancy

between the measured flow rate and the calculated flow rate. This indicates an error in the

calibration of the flow meter.

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References [1] Wang, L; Bengt, S; Manglik, R.M., Plate Heat Exchangers: Design, Applications and Performance: Southampton: WIT, 2002. [2] Perry, R. H., Green, D. W. (Eds.): Perry's Chemical Engineers' Handbook, 7th edition, McGraw­Hill, 1997 , Section 11. [3] Pinto, M. J.; Gut, J.A.W “A Screening Method For the Optimal Selection Of Plate Heat Exchanger Configurations” Brazilian Journal of Chemical Engineering 27 May 2002: 433­439. Print. [4] Kakac, Sadik, and Hongtan Liu. Heat Exchangers Selection, Rating, and Thermal Design. Boca Raton: CRC Press, 2002. Print. [5] Martinez, I; Heat Exchangers. Webserver.dmt [Online] 1995­2015, pp1­16 http://webserver.dmt.upm.es/~isidoro/bk3/c12/Heat%20exchangers.pdf (accesssed January 28, 2015).

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Appendices

Trial THIn (K) TCIn(K) Cp (J/kg K)

Wc (kg/s)

Wh (kg/s)

Mass H2O (kg)

K U (W/m2K)

1 339.5 301.4 4184 .2045 .2052 27.63 1.0013 1507

2 334.8 293.41 4184 .2454 .0954 15.90 .9027 297.7

3 334.5 302.4 4184 .2045 .2052 8.327 1.0004 470.2

4 332.7 300.3 4184 .1363 .2045 14.76 1.104 755.2

Table A1: Batch data for determining overall heat transfer coefficient

Trial THIn (K)

TCIn(K)

THOut (K)

TCOut(K)

Wc (kg/s)

Wh (kg/s)

UH (W/m2K)

UC (W/m2K)

U % Diff.

1 327.7 292.4

317.7 307.3 .1023 .2045 1557 1159 29.3

2 335.9 291.7

323.0 310.0 .1363 .2045 1568 1761 11.6

Table A2: Steady state data for determining overall heat transfer coefficient

Overall Heat Transfer Coefficient (W/m2K)

UC UH

Trial Uncalibrated Calibrated Uncalibrated Calibrated

1 1159 1251 1557 1680

2 1761 1900 1568 1692 Table A3: Calibrated steady state values of overall heat transfer coefficient

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Overall Heat Transfer Coefficient (W/m2K)

Trial Uncalibrated Calibrated % Difference

1 1556 1507 3.2

2 300.5 297.7 .936

3 474.9 470.3 .973

4 1008 755.2 28.68 Table A4: Calibrated batch values of overall heat transfer coefficient

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TO: NanoEngineering Department Faculty FROM: Brandon Sanchez, Saman Hadavand, Janet Mok, Liliana Busanez DATE: January 30, 2015 SUBJECT: CVD We propose to design a Chemical Vapor Deposition (CVD) reactor using the

COMSOL simulation. CVD is a chemical process essential to micro­electronic device

manufacturing. In this experiment we will conduct a simulation of a CVD reactor to understand

the kinetics of silane deposition. To do this, multiple variables will be adjusted including:

temperature, wafer packing density, pressure, inlet velocity, and mole fraction of hydrogen

present in the inlet. We expect to see an increase in the rate of silane deposition as temperature

increases. Furthermore, we believe that an increase in hydrogen mole fraction and inlet velocity

will increase the rate of silane production and thus its deposition in the reactor. If you have any

concerns, please contact Saman Hadavand at (760) 884­9484.

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