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8/3/2019 Heat Super Final

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ABSTRACT

Generally, heat exchanger is classified according to the flow arrangement and the type of

construction. The simplest heat exchanger is one for which the hot and cold fluids move in

the same or opposite directions in a concentric tube or double- pipe construction. In the parallel- flow arrangement, the hot and cold fluids enter at the same end, flow in the same

direction, and leave at the same end. In the counter flow arrangement, the fluids enter at

opposite ends, flow in opposite directions, and leave at opposite ends.

Regarding to the experiment, the objectives are to determine the differences in

temperature between a parallel flow and a counter flow. Besides, it is also to determine the

most efficient of concentric heat exchanger in terms of flow arrangement which is either

parallel flow or counter-current flow. This experiment is based on transferring a heat at a

different temperature gradient with used concentric heat exchanger. The instrument was

attached with thermometers and flow rate meter in order to control and obtain the

temperatures of THin, THout, THmid, TCmid, TCin, and TCout and also the water flow rate (hot and

cold). The experiment is divided into 3 sections which are parallel and counter flow rate,

temperature varies and, and constant temperature with varies flow rate. Throughout the

experiment, it is found that counter flow is more efficient than parallel flow. For parallel

flow, the efficiency is at 99.81% while the overall heat transfer coefficient, U is 592.04

W/m2K at 60 °C and 704.57 W/m2K at 60 °C for counter flow rate. Meanwhile the efficiency

obtained is 99.83 %. Based on the experiment, the counter flow is more efficient than parallel

flow. Theoretically, the one should be more efficient is counter flow rather than parallel flow.

INTRODUCTION

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In general, heat exchangers are used to transfer heat from one fluid to another. It is important that

to understand the basic principles of the equipment and also know the mechanical components of

a heat exchanger in terms of on how they function and operate. Basically, a heat exchanger is a

component that allows the transfer of heat from one fluid (liquid or gas) to another fluid.

Reasons for heat transfer are to heat a cooler fluid by means of a hotter fluid, to reduce the

temperature of a hot fluid by means of a cooler fluid, to boil a liquid by means of a hotter fluid,

to condense a gaseous fluid by means of a cooler fluid, and to boil a liquid while condensing a

hotter gaseous fluid.

Several factors that must be considered in such to operate the equipment which is in order

to transfer heat, the fluids involved must be at different temperatures and they must come into

thermal contact. This is because heat can flow only from the hotter to the cooler fluid and in heat

exchanger there is no direct contact between the two fluids. Heat is being transferred from the

hot fluid to the metal isolating the two fluids and then to the cooler fluid and furthermore the

equipment has been specifically designed to operate the principles of industrial heat exchangers

in such a proper and most convenient way possible in the laboratory. Cold water supply was the

apparatus only required to operate this device. Single-phase electrical outlet and a bench top to

enable a series of simple measurements to be made by students needing an introduction to heat

exchanger design and operation. This kind of experiment can be done in short period, with

virtually no setting up operations, to accurately show the practical importance of the following

which are temperature profiles, Co-Current and counter-current flow, energy balances, long

mean temperature difference and heat transfer coefficients.

The equipment consists of insulated concentric tube exchanger with the temperature

devise are installed in both the inside and outside tubes in order to measure the fluid temperature

accurately. Hot water is fed through the inner pipe and with the cooling water in the outer

annulus in purposely to minimize losses in the system. To regulate the flow, control valves are

incorporated in each of the two streams and it can be measured using independent flow meter

installed in each line. The hot water system is very self-contained. A hot storage tank is equipped

with an immersion type heater and a adjustable temperature controller, which can maintain a

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temperature to with-in approximately 10°C. Pump was function to provide the circulation and

water returns to the storage tank via a baffle arrangement to ensure adequate mixing. A readily

identifiable valve arrangement allows simple changeover between co-current and counter-current

configurations.

OBJECTIVES

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1. For experiment (HT4-1), the objective of the experiments is to show the required of the

working principles of a concentric tube heat exchanger that operated under the parallel

flow conditions and to calculate the power emitted, power absorbed, power loss,

efficiency, logarithmic mean temperature differences and overall heat transfer coefficient.

2. In experiment (HT4-2), the objective of the experiments is to derive the working

principles of a concentric tube heat exchanger that undergo the counter flow conditions

operations using the same methods as the first experiments and also to calculated the

power emitted, power absorbed, power loss, efficiency, logarithmic mean temperature

differences and overall heat transfer coefficient.

3. In experiment (HT4-3), the objective of the experiments is to show the characteristics

performance of a concentric tube heat exchanger that have been affect by the hot water

temperature variation to calculated the temperature efficiencies of the heat exchanger for

the cold medium, hot medium and mean temperature efficiency.

4. In experiment (HT4-4), the objectives is to perform the characteristics performance of

concentric tube heat exchanger that operates under counter flow conditions when the flow

rate of variation effect the operations to calculated the power emitted, power absorbed,

power loss, efficiency, logarithmic mean temperature difference and overall heat transfer

coefficient by stabilize the Qc value and using the QH with different values.

THEORY

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Experiment of HT4-1 and HT4-2

These theories is applied for this both experiments and included of the same methods.

Power emitted = QHρHCPH (tHin - tHout)

Power absorbed = QCρHCPC (tCout - tCin)

Power loss = power emitted - power absorbed

Efficiency, η =

Log mean temperature difference, ∆tm= -

Overall heat transfer coefficient, U =

Initial Values Of Variables To Be UsedInitial values of variable to be used = 60°C

Hot Water flow rate QH = 2000cc/min

Cold water flow rate =1000cc/min

Experiment HT4-3

These theories is applied for this experiment and included of the same methods. The initial

values of variable are used as showed.

Temperature efficiency of the heat exchanger is:

a) for the cold medium

ηC= -

b) for the hot medium

ηH = - x 100

c) mean temperature efficiency

ηmean = ηC + ηH

Temperature efficiency is an indicator of the actual heat transfer taking place in the heat

exchanger as a percentage of the maximum possible heat transfer that would take place if infinite

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surface area were available. When QH ρH CpH > QC ρC CpC.so (Thot- Tcold) + ∆ T will

coverge at the hot inlet end or if QC ρC CpC > QH ρH CpH,then ∆ T will converge at cold inlet

end.

Initial Values Of Of Variable To Be Used For HT4-3

Hot water flow rate QH = 2000cc/min

Cold water flow rate Qc = 2000cc/min

Experiment of HT4-4

These theory is applied for this both experiments and included of the same methods.




Efficiency, η =

Log mean temperature difference, ∆tm= -

Overall heat transfer coefficient, U =

Initial Values Of Of Variable To Be Used For HT4-4

Controlled hot water temperature = 60°C

Cold water flow rate Qc = 2000cc/min

PROCEDURE

EXPERIMENT HT4-1

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Concentric tube heat exchanger (parallel flow arrangement)

1. The switch was switched on.

2. Water was poured into the tank located behind the equipment set up.

3. The equipment was set up into parallel flow arrangement shown on the instruction label.

4. The hot water flow rate, QH was set to 2000 cc/min, and the cold water flow rate was set

to be 1000 cc/min.

5. The temperature was released to increased until the thermometer labeled t Hin reach 60 0C.

This is the controlled hot water temperature.

6. After the tHin was reached 60 0C, the readings of thermometers labeled tHmid, tHout, tCin, tCmid,

and tCout were taken. Then, the ∆t1 and ∆t2 were calculated.

EXPERIMENT HT4-2

Concentric tube heat exchanger (counter flow arrangement)

1. Hot water from Experiment A in the tank was removed, and the tank was refilled with

cold water.

2. The equipment was set up into counter flow arrangement shown on the instruction label.

3. Hot water flow rate was set up to 2000 cc/min, while the cold water flow rate was set up

to 1000 cc/min.

4. Again, the controlled hot water temperature, which was the thermometer labeled tHin was

released to increment until it reach 60 0C.

5. Upon it reached 60 0C, the readings of thermometer labeled tHmid, tHout, tCin, tCmid, and tCout

were taken. Precaution should be taken when reading the thermometers as the labeled onthe thermometers were different for both parallel and counter flow.

6. Then, ∆t1 and ∆t2 were calculated.

EXPERIMENT HT4-3

Concentric tube heat exchanger (water temperature variation)

1. Hot water from previous experiment was removed, and the tank was refilled with cold

water.

2. This experiment was held in counter flow arrangement, so the set up will remained as

before.

3. Initial values of variables which were both the hot water flow rate, Q H and the cold water

flow rate, QC was set up to 2000 cc/min and remained constant.

4. Required hot water inlet temperature was selected by setting the decade switch on the

controller. Initially, the temperature selected was 50 0C.

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5. The thermometer was observed until it reached 50 0C, and the readings of thermometer

labeled tHmid, tHout, tCin, tCmid, and tCout were taken.

6. Steps 3 until 5 were repeated with the ascending temperature of 10 0C for every readings

taken until it reaches the maximum temperature of 80 0C. Then, ∆t1 and ∆t2 for each set

were calculated.

EXPERIMENT HT4-4

Concentric tube heat exchanger (hot water flow rate variation)

1. The tank that was filled with hot water from the previous experiment was half emptied,

and refilled with cold water so that the temperature of tHin will not exceed the controlled

hot water temperature, which was 60 0C.

2. The set up was remained in counter flow arrangement.

3. The cold water flow rate, QC was set to remain at 2000 cc/min. On the other hand, hotwater flow rate, QH was set up to 1000 cc/min. This was the manipulative variable.

4. After the temperature tHin was released to reach 60 0C, the readings of thermometer

labeled tHmid, tHout, tCin, tCmid, and tCout were taken, and ∆t1 and ∆t2 were calculated.

5. The whole steps were repeated with the ascending of QH of 1000 cc/min for each set

readings until it reach 4000 cc/min.

CALCULATION

Experiment: HT4-1


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= (2000 cm3/min) x (1 m3 / 1003 cm3) x (983 kg/m3) x (4.185kJ/Kg .K)

x (333-327) K x (1 min / 60 s)

= 823.0 W


= (1000 cm3/min) x (1 m3 / 1003 cm3) x (983 kg/m3) x (4.179 J/g .K)

x (314-302) K x (1 min / 60 s)

= 821.5 W


= (823.0-821.5) W

= 1.5 W

Efficiency, η = Power absorbed × 100

Power emitted

= (821.5/823.0) W x 100 %

= 99.81%

Log mean temperature difference, ∆tm = ∆t1 - ∆t2

Ln(∆t1/∆t2)

∆t1 = tHin - tCin

= (333 - 294) K

= 31K

∆t2 = tHout - tCout

= (326 - 313) K

= 13K

Log mean temperature difference, ∆tm = (31 – 13) / ln (31/13)

= 20.71 °C

Overall heat transfer coefficient, U = Power Absorbed

Heat transmission x ∆tm

= 821.5 W / (0.067 m2 x 20.71°C)

= 592.04 W/m2°C

9



Experiment: HT4-2



x (333-326) K x (1 min / 60 s)

= 959.89 W



x (316-302) K x (1 min / 60 s)

= 958.29 W


= (959.89 – 958.29) W

= 1.6 W


Power emitted

= (958.29 / 959.89) W x 100 %

= 99.83 %


Ln(∆t1/∆t2)

∆t1 = tHin - tCout

= (333 - 316) K

= 17K

∆t2 = tHout - tCin

= (326-302) K

= 24 K

Log mean temperature difference, ∆tm = (17-24) / ln (17/24)

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= 20.3°C



=958.29 W / (0.067 m2 x 20.3 °C)

= 704.57 W/m2.°C

Experiment: HT4-3

Calculation for 50˚C



x (323-317) K x (1 min / 60 s)

= 822.2 W



x (308-302) K x (1 min / 60 s)

= 821.4 W


= (822.2-821.4) W

= 0.8 W


Power emitted

= (821.4/822.2) W x 100 %

= 99.90 %


Ln(∆t1/∆t2)

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= (323 - 308) K

= 14 K


= (317 - 30) K

= 15 K

Log mean temperature difference, ∆tm = (14 – 15) / ln (14/15)

= 14.5°C



= 821.4 W / (0.067 m2 x 14.5°C)

= 845.5 W/m2°C

Temperature efficiencies of the heat exchanger are:

a) for the cold medium

ηC = (tCout - tCin / tHin - tCin ) x 100

= 308-302 x 100

323-302

= 28.57

b) for the hot medium

ηH = (tHin - tHout / tHin - tCin) x 100

= 323-317 x 100

323-302

= 28.57

c) mean temperature efficiency

ηmean = ηC + ηH

= 28.57 + 28.57

= 57.14

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This calculation method are used for each temperature (60°C, 70°C, 80°C) with same method of

temperature 50°C.

Experiment: HT4-4

for QH 1000 cc/min



x (333-321) K x (1 min / 60 s)

= 822.8 W



x (308-302) K x (1 min / 60 s)

= 822.8 W


= (822.8 – 822.8) W

= 0W


Power emitted

= (822.8 / 822.8) W x 100 %

= 100 %


Ln(∆t1/∆t2)


= (333 - 308) K

= 25 K


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= (321 - 308) K

= 19 K

Log mean temperature difference, ∆tm = (25 - 19) / ln (25/19)

= 21.9 °C



= 822.8 W / (0.067 m2 x 21.9 °C)

= 560.8 W/m2°C

This calculation method are used for each hot water flow rate (2000 cc/min, 3000 cc/min, 4000

cc/min)

RESULTS

Parallel Flow

Controlled Hot water Temperature = 60ºC

Hot Water Flow rate = 2000 cc/minCold Water Flow rate = 1000 cc/min

tH in tHmid (ºC) tHout (ºC) tCin (ºC) tCmid (ºC) tCout (ºC)

60 57 54 29 34 410

39 13

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∆ t1

(31ºC)

∆ t2

(13ºC)

Power

emitted,W

Power

absorbed, W

Power lost, W Efficiency % ∆ tm

(ºC)

U

W/m2

(ºC)

823 821.5 1.5 99.81 20.71 592.04

Figure 1a : Graph of Temperature for Parallel Arrangement

Counter Flow

Controlled Hot water Temperature = 60ºC

Hot Water Flow rate = 2000 cc/min

Cold Water Flow rate = 1000 cc/min

tHin (ºC) tHmid (ºC) tHout (ºC) tCin (ºC) tCmid (ºC) tCout (ºC)

60 57 53 29 33 43

∆ t1

(ºC)

∆ t2

(ºC)

17 24

15

∆ t1

∆ t2



Power emitted,

W

Power

absorbed, W

Power lost, W Efficiency % ∆ tm

(ºC)

U

W/m2 (ºC)

959.89 958.29 1.6 99.83 20.3 99.83

Figure 1b: Graph of Temperature for Counter Arrangement

Water Temperature Variation

Hot water flow rate QH = 2000 cc/min

Cold water flow rate QC = 2000 cc/min

Con Set

ºC

tHin

(ºC)

tHmid

(ºC)

tHout

(ºC)

tCin

(ºC)

tCmid

(ºC)

tCout

(ºC)

50 50 47 44 29 30 35

60 60 55 50 29 32 38

70 70 64 57 30 34 41

73 73 72 60 30 34 43

∆ t1

(ºC)

∆ t2

(ºC)

14 15

22 18

29 27

16

∆ t1

∆ t2



30 29

Con Set

ºC

Power

emitted,

W

Power

absorbed,

W

Power

lost, W

Efficiency % ∆ tm

(ºC)

U

W/m20 (ºC)

N

C

N

H

ŋmean

50 822.2 821.4 0.8 99.90 14.50 845.5 28.57 28.57 28.57

60 1371.3 1231.8 139.5 89.83 21.5 855.3 29.03 32.26 30.65

70 1785.2 1506.3 278.94 84.4 28.0 803.3 27.5 32.5 30.00

73 1785.7 1780.5 5.2 99.7 29.5 900.2 30.2 30.23 30.32

Figure1c: Graph of Temperature for Temperature Variation in Counter Arrangement Flow

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∆ t1

∆ t2

tHin

tCin

tHout

tCout

tHmid

tCmid



Flow rate Variation

Controlled hot water temperature = 60ºC

Cold water flow rate QC = 2000 cc/min

QH

Cc/min

tHin

(ºC)

tHmid

(ºC)

tHout

(ºC)

tCin

(ºC)

tCmid

(ºC)

tCout

(ºC)

1000 60 53 48 29 30 35

2000 60 51 50 29 31 38

3000 60 57 53 29 32 394000 60 57 54 29 33 40

∆ t1

(ºC)

∆ t2

(ºC)

31 13

31 12

31 14

31 14

QH

cc/min

Power

emitted,

W

Power

absorbed, W

Power lost,

W

Efficiency % ∆ tm

(ºC)

U

W/m20

(ºC)

1000 822.8 822.8 0.0 100.00 21.9 560.8

2000 1371.3 1234.2 137.1 90.00 20.2 920.2

3000 1439.8 1371.3 68.50 95.20 21.4 957.0

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4000 1646.0 1508.4 138.0 91.60 21.4 1052.7

Figure1d: Graph of Temperature for Temperature Variation in Counter Arrangement Flow

19

tHin

tCin

∆ t1

tHmid

tCmid

∆ t2

tHout

tCout



DISCUSSION

A heat exchanger is a device that efficiently transfers heat from a warmer fluid to a colder fluid.

A device which is probably all familiar with is the automobile radiator. Other applications for

heat exchanger are found in heating and air conditioning systems. All the equipment of

concentric tube heat exchanger is insulated. The hot water is fed through the inner pipe with the

cooling water in the outer annulus in order to minimize looses in the system.

For Experiment HT4-1, the tH out temperature decrease with time after hot water

temperature enter the tube but cold water out increase after the flow circulated. This happens

because of the parallel flow arrangement, where the cold and hot fluid was flow in the same

direction. The value of power absorbed is positive which means the power is being absorbing

and the efficiency became 99.81%. Efficiency value which obtained was influenced indirectly by

the power emitted from the heat transfer system where the value was higher at power emitted

rather than at power absorbed. Generally, cold water receives heat from hot water, so this

temperature and the values are possible.

A bit different in experiment HT4-2 because hot fluids flows in opposite direction to cold

one. Due to that, data obtained was different in terms of overall heat transfer coefficient same

goes with the value of efficiency. For counter flow, efficiency obtained is 99.83% which higher

than parallel flow with difference at 0.02%. However it is impossible for heat exchanger to work

at greater 100% efficiency because there are other factors that decrease efficiency such as fiction

of water inside the tube. This condition makes the amount of the heat transferred is higher

because in this case the opposite direction turn the outlet temperature of the cold fluid which may

exceed the outlet temperature of the hot fluid. We gained the value of power absorbed is positive

which means the power is being absorbing but not releasing it throughout the heat exchange

process.

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In experiment HT4-3, the objective of experiment is to demonstrate the effect of the hot

water temperature variation on the performance characteristics of a concentric tube heat

exchanger. The experiment being tested by different hot fluid temperatures inlet and using the

counter flow condition and the QC value has changed to 2000 cc/min. This condition will affect

the cold water temperature in inlet to remain the same because less heat transferred between the

two same flow rate of hot and cold water. As the experiment goes along from 70 oC to 80oC, it is

more difficult to see the temperature rises to 80oC because of the low efficiency of the heat

exchanger itself and low power of heating element.

For experiment HT4-4, it is required to control the hot water temperature as 60ºC with

2000 cc/min QC but change the QH value accordingly. Based on the calculated values, values of

power emitted and power absorbed increased with the QH. As the increase of QH it will contribute

the increasing of tHout and tCout because at that point water is absorbing the heat. Therefore,

supposedly the efficiency is declined through the QH variables because at high flow rates will

reduce the contact time for the hot and cold fluid to transfer the heat.

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CONCLUSION

Based on the Experiment HT4-1 and Experiment HT4-2 was conducted in order to

determine the most efficiency either counter or parallel. Parallel flow efficiency is 99.81 %,

power emitted is 823 W and power absorbed value is 821.5 W. The efficiency of counter flow is

99.83 % which is quite higher and more efficient rather than parallel flow. This proven from

theory which stated that counter flow is more efficient compared to parallel flow. For experiment

HT4-3, result obtained shown that when the input temperature rises contribute to rise of output

temperature though. As the temperature was set to 80 oC, it is difficult reach that temperature for

some reasons which are scaling in the pipeline and low efficiency of the heater element.

For experiment HT4-4, various of hot water flow rates being experimented and the results

obtained shown that when the value of hot water flow rate (Q H) is higher than the value of cold

water flow rate (QC), therefore the efficiency of the hot water flow rate is much higher than the

cold water flow rate. High flow rates of hot water inlet resulted of limited contact time with the

cold water. Fluctuate of the efficiency value may cause of unsuccessful result which may cause

by of some reasons which are parallax error while taking the reading of the temperatures, delay

in taking the reading, and also caused by the low power equipment used

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RECOMMENDATION

1. The eye position should be perpendicular to the meniscus and the scale and do a checking

of the heater either it is in good condition and no scaling as it can influence the result.

2. Avoid direct contact with water because it is hot also reducing taking off the cover of the

water tank because water losses might happen due to the water evaporated in the tank and

it will affect the result

3. Avoid of any leakage of the instrument, the instrument should be working properly

4. Monitor the temperature during experiment to make sure it is constant

5. Monitor the flow rates during experiment to make sure that the flow rate remains

constant.

6. Repeat the experiment at least 3 times to get accurate values and to make comparisons

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REFERENCES

1. Heat exchanger theory. (2001).Retrieved March 1,2011,from

http://en.wikipedia.org/wiki/Heat_exchanger

2. History of heat exchanger.(2000).Retrieved Feb 28, 2011,from

http://www.engineeredge.com/heat_exchanger/general.htm

3. Equipment for engineering education,concentric tube heat exchanger.(2004).Retrived

Feb 28 2011 from

http://www.fs.vsb.cz/books/GUNT/html/p3452.htm

4. Abd.Jamil.Lam (2009) Lab Manual. Concentric tube heat exchanger. Retrieved March

3,2011

5. Yunus A.Cengel (2006) Heat and Mass Transfer. Analysis of heat exchanger. Retrieved

March 8,2010.

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APPENDICES

The Diagram of Heat Exchanger

25

tHin

tCin

tCout

tHout

tHmid

tCmid



26

Tan

Pum

Flow



27

Flow

heat super final

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