INTRODUCTION

In this experiment, the conduction in an insulated long slender brass bar like the one

in Figure 1 needed to be investigated. Assumed that the bar is of length L, a uniform hot

temperature Th is imposed on one end, and a cold temperature Tc is imposed on the other.

Also assumed, because the bar is insulated in the peripheral direction that all the heat flows

in the axial direction due to an imposed temperature differential along the bar.

Figure 1:Schematic of a Long Cylinder Insulated Bar

If a plane wall of thickness (Δx) and area (A) and thermal conductivity (k) supports a

temperature difference (ΔT) then the heat transfer rate by conduction is given by the

equation:

= k A

Figure 2: Conduction Process

The thermal conductivity k varies between different mate rials and can be a function of

temperature, but it can be treated as a constant over small temperature ranges. Because of

the enhancement of heat transfer by free electrons, thermal conductivity is analogous to

electrical conductivity and as a result, metals that are good conductors of electricity are also

good conductors of heat.

OBJECTIVE

To demonstrate the effect of flow rate variation on the performance characteristic of a

counter-flow and parallel-flow concentric tube heat exchanger

ABSTRACT

The concentric tube heat exchanger was designed in order to study the process of

heat transfer between two fluids through a solid partition. It was designed for a counter flow

arrangement and the parallel mean temperature difference method of analysis was adopted.

Water was used as fluid for the experiment. The temperature of the hot and cold water

supplied to the equipment were 60 C, respectively. The result of the experiment were⁰

tabulated and a graph of the mean temperature was drawn. The research takes into account

different type of heat exchangers.

THEORY

A heat exchanger is a piece of process equipment in which heat exchange takes place

between two fluids that enter and exit at different temperatures. The primary design objective

of the equipment may be either to remove heat from a hot fluid or to add heat to a cold fluid.

Depending upon the relative direction of fluid motion, shell-and-tube heat exchangers are

classified as parallel flow, counter flow, cross flow. In parallel flow, the hot and cold fluids

flow

in the same direction and therefore enter the exchanger on the same end and exit the

exchanger on the same end. In counter flow, the two fluids flow in opposite directions and

thus enter the exchanger and exit the exchanger from opposite ends. Cross flow heat

exchangers will not be analysed as a part of this laboratory experiment.

Figure 1 - Diagram of Parallel and Counter Flow Configurations

PROCEDURE

1. The experiment of concentric tube heat exchange is been briefed and constructed by the lecture

2. We run the different operation which is counter-flow heat exchanger operation and followed to parallel-flow heat exchanger operation

3. Firstly, the hot water inlet temperature was been set up to 60⁰C with the decade switch

4. Next,the cold water volumetric flow rate (Vc) was set to run at constant 2000 cm3/min and the hot fluid volumetric flow rate (Vh) to 1000 cm3/min

5. The pump was switch on to make fluid flow on this experiment6. All data were recorded for those temperature 7. Those temperature were labelled to hot water inlet (Tt1), hot water middle (Tt2), hot

water outlet (Tt3), cold water inlet (Tt4), cold water middle (Tt5) and cold water outlet (Tt6)

8. The experiment was repeated with hot fluid volumetric flow rate increased into the 2000cm3/min until 4000 cm3/min

9. After that, the pump was stopped and changed the experiment into parallel-flow heat exchanger operation.

10. The flow of water on the operation was controlled by used valve11. All data also were recorded for those temperature, but have a different value of the

cold water inlet (Tt6) and cold water outlet (Tt4)12. The volumetric flow rates also was set up from 1000cm3/min to 4000cm3/min13. Then, used the data that recorded to calculate the heat exchanger performance

factors14. Lastly, the result was compared the effect of changed the volumetric flow rate of the

hot fluid on each of these heat exchanger performance factors

APPARATUS

Tube heat exchange machine

Button switch for the pump

Controller of temperature readings

of Tt1, Tt2, tt3, Tt4, Tt5 and Tt6

Digital value of temperature readings

Control valve to control flow of the fluid

Meter of cold water volumetric flow rate at a constant 2000 cm3/min

Meter of hot fluid volumetric flow rate

Valve to control the volumetric flow rates

Screen of hot water inlet temperature at 60⁰C

MOHAMD FAREEZ BIN HASLIM

2014684346

DISCUSSION

Heat exchangers are devices that facilitate the exchange of heat between two fluids that are different temperatures while keeping them from mixing with each other.

In our experiment, we used the simplest type of heat exchanger that is consisting of two concentric pipes of different diameter called the double pipe heat exchanger. Two types of flow arrangement are possible in a double pipe heat exchanger:

1) Parallel flow; both the hot and cold fluids enter the heat exchanger at the same end and move in the same direction.

2) Counter flow; the hot and cold fluids enter the heat exchanger at opposite ends and flow in opposite direction.

The main point of the experiment is to discuss the effect of volumetric flow rate the hot

fluid on each of these heat exchanger performance factors. In parallel flow as we can see in

the table below, the Tc, in and Tc, out are different in theoretical value. In theoretical, the Tc,

in must be more high in temperature than the Tc, out.

Vh(cm3/min) Th, in

(oC)

Th, mid

(oC)

Th, out

(oC)

Tc, in

(oC)

Tc, mid

(oC)

Tc, out

(oC)

1,000 59.6 52.1 51.3 31.2 34.2 35.3

2,000 59.8 54.0 52.0 31.1 32.3 37.0

3,000 59.6 55.6 53.6 30.9 36.5 44.8

4,000 59.6 56.1 55.5 31.0 36.2 47.7

This can be improved in the graph,

So, it can be effect the flow rate of the flow. The efficiency also maybe affect as the value of the result taken is different. To get the efficiency, there is a calculation that has been calculated. As we can see in the graph of the efficiency versus flow rate in below, the experiment that we conducted started at 1000 until 4000 cm³/min. At the 1000 we got the efficiency of 24%. The efficiency drop from 24 to 18%. These may due from the calculation occur that involved the power emitted and power absorbed along the pipes. The efficiency increases when the flow rate is increase as shown.

The experiment continues with the counter flow or cross flow. As we can see the experimental value may be same as the theoretical value. This can be proved in the graph as below,

The inlet hot temperature is greater than the outlet hot temperature and the inlet cold temperature is lower than the outlet cold temperature. So we can say that the counter flow experiment is a success.

Vh(cm3/min) Th, in

(oC)

Th, mid

(oC)

Th, out

(oC)

Tc, in

(oC)

Tc, mid

(oC)

Tc, out

(oC)

1,000 58.1 47.3 46.5 34.4 28.4 37.7

2,000 59.6 54.1 50.4 32.2 31.3 40.8

3,000 59.2 55.5 53.0 38.0 34.5 42.6

4,000 59.5 56.6 55.0 34.0 35.8 50.3

When the experiment is started, the efficiency is in high efficiency that is in 58%. But the efficiency is drop to 23% that we can say it in high speed dropping. Then the efficiency is decreases but at 4000 cm³/min the efficiency start to increases at 44%. This also may be due to the power emitted and power absorbed that we calculated.

Errors may affect the value of the performance may causes by the machine, parallax error and surrounding error. Errors that caused by machine may of the pump. The process does not go smoothly because they have technical problem. So to overcome this problem, proper maintenance must be conduct before the experiment started. Parallax error in this experiments are when control the volume of flow rate of the system. The volume are not constant, and by using manual of human there must be error when maintain the volume flow rate. The heat losses to surroundings also may occur in this experiments, this because this process naturally conduct in this system. This rarely can be avoided because the lack of sources to maintain it.

MOHAMD FAREEZ BIN HASLIM

2014684346

CONCLUSION

As a conclusion, the objective of the experiments is to compare the effects of flow rate to the system performance. All the data collected from the experiments has been proved practically. The relationship of these parameters has been understood and all the error that may affect the experiments has been analyzed and the solution of the error has been conducted to improve.

MUHAMMAD ASRAF BIN AZMI

2014672104

DISCUSSION

Although ordinary heat exchanger may be extremely different in design and construction

such as in single phase or two phase type, however their modes of operation and

effectiveness is largely determined by the direction of the fluid flow within the exchanger. For

this experiment, the method that been used is counter flow and parallel flow in order to

determine the effect of the volumetric flow rate of the hot fluid for the performance

characteristics. The table below shows the result for these two flow:

Parallel Flow Result:

Vh

(cm3/min)

Th, in

(oC)

Th, mid

(oC)

Th, out

(oC)

Tc, in

(oC)

Tc, mid

(oC)

Tc, out

(oC)

1,000 59.6 52.1 51.3 31.2 34.2 35.3

2,000 59.8 54.0 52.0 31.1 32.3 37.0

3,000 59.6 55.6 53.6 30.9 36.5 44.8

4,000 59.6 56.1 55.5 31.0 36.2 47.7

This experiment is conducted with two parts of separated condit ions, which

are by varying the f low rates at constant temperature and by varying the

temperatures at constant f low rate. For the paral lel f low, the power absorbed

is increasing from -136.37W unti l -555.5W which means that power absorbed

more as increase the volumetric f low rate. The power emitted also increasing

due to the volumetric f low rate factor and the highest power emitted for the

paral lel at V h = 3000 cm 3 /min is 1232.39W before i t sl ight ly goes down.

These also affect the result of the power lost and the overal l heat transfer

coeff icient which is increasing too.The exit temperature in paral lel of the hot

fluid must be higherthan the entrance temperature of the cold fluid, but it does not

necessarily need to be higher thanthe exit temperature of the cold fluid.This shows that more

heat being transferred by hot water to be absorbed by cold water. This is also supported by

the data, even though in this case the exit temperature of the hot fluid is still hotter than the

exit temperature of the cold fluid.

Then, we change the parallel flow heat exchanger to the counter flow heat exchanger. The table

below shows the values of THin, THout, THmid, TCmid, TCin, and TCout.

Vh

(cm3/min)

Th, in

(oC)

Th, mid

(oC)

Th, out

(oC)

Tc, in

(oC)

Tc, mid

(oC)

Tc, out

(oC)

1,000 58.1 47.3 46.5 34.4 28.4 37.7

2,000 59.6 54.1 50.4 32.2 31.3 40.8

3,000 59.2 55.5 53.0 38.0 34.5 42.6

4,000 59.5 56.6 55.0 34.0 35.8 50.3

For the counter flow heat exchanger, the value is greater and higher than parallel as the

movement of the hot fluid and cold fluidis separated and acounter flow heat exchanger has

the hot fluid entering at one end of the heat exchanger flow path and the cold fluid entering

at the other end of the flow path. Counter flow is the most common type of liquid-liquid heat

exchanger, because it is the most efficient. The power lost, the power emitted, the efficiency

and overall heat transfer coefficient is greater and increasing than the parallel flow. The

maximum value for the power emitted in counter is 1273.47W at Vh = 3000cm3/min. Thus,

the percentage error for the power emitted is 3.23%. This shows that more heat being

transferred by hot water to be absorbed by cold water.the exit temperatureof the cold fluid

been hotter than the exit temperature of the hot fluid, the effectiveness would have been

even higher, reflecting common data in many textbooks.

The design of a parallel flow heat exchanger is advantageous when two fluids are required

to be brought to nearly the same temperature. However, there are some special cases

where a cocurrent exchanger design might still be adopted. Some of these are more uniform

temperature differences between two fluids is minimized the thermal stress throughout the

exchanger, the outlet temperature of cold fluids can approach the highest temperature of the

high fluid (the inlet temperature) and lastly, the more uniform temperature differences

produce a more uniform rate of heat transfer throughout the heat exchanger. There is slightly

error that happen in this experiment which is human error when take reading of the

exchanger. The volumetric flow sometimes dropping slightly and we need to adjust at certain

level to make sure the level of the volumetric is correct.

MUHAMMAD ASRAF BIN AZMI

2014672104

CONCLUSION

As the conclusion, this experiment was successfully done and all the objectives is achieved.

The power emitted and power absorbed are increased when we compared the effect of

changing the volumetric flow rate of the hot fluid. Besides, the power lost that we get shows

decreasing value unless the last reading give some increased value and the overall heat

transfer coefficient will increase when the volumetric flow rate of the hot fluid is increase.

Lastly, the heat transfer coefficient, the power emitted and power absorbed are influenced by

the changing of volumetric flow rate of the hot fluid.

In practical application, the counter flow configuration is preferred for its highereffectiveness.

This experiment did show that this configuration does in fact have a higher effectiveness

than the parallel flow configuration. Additionally, the counter flow configuration is also

capable of have a cold fluid exit temperature that is higher than the hot fluid exit

temperature. This was not shown experimentally, however from the data collected it is clear

that the flow rates were too high to achieve this desired result. If the experiment were

repeated with lower flow rates, it would be possible to demonstrate a situation where the exit

temperature of the cold fluid is hotter than the exit temperature of the hot fluid.

MUHAMAD FIRDAUS BIN HIPUL 2014258044

DISCUSSION

Based on our experiment of heat exchanger, the different design of system was operate which is counter-flow and parallel flow. A counter-flow heat exchanger is one direction of the flow of one of the working fluids is opposite to the direction to the flow of the other fluid. While, a parallel flow exchanger is the both fluids flow in the same direction. Figure below represents the direction of the fluid flow in the parallel and counter-flow exchanger.

The heat exchanger performance can be calculated by using the data that was recorded. In the counter-flow heat exchanger, the maximum efficiency is 58%. This happen when the volumetric flow rates at 1000 cm3/min. other, the power lost be a small value than the other condition when the volumetric flow rate at 1000 cm3/min. the logarithmic mean temperature difference is 15.89 ⁰C also the overall heat transfer coefficient (U) is -431.08 W/(m2.oC). While, when the volumetric flow rate at 4000 cm3/min, the power lost be the higher than others which is 1774.64 Watt. The relationship of the volumetric flow rates and heat exchanger is decreasing proportional. The changing of the volumetric flow rate will affected the efficiency of the heat exchanger. The advantage over the parallel flow design is the more uniform temperature difference between the two fluids minimizes the thermal stresses throughout the exchanger. Other advantage is the more uniform temperature difference produces a more uniform rate of heat transfer throughout the heat exchanger. Besides that, the outlet temperature of cold fluid can approach the highest temperature of the hot fluid (the inlet temperature).

Counter-flow heat exchanger

In parallel flow exchanger, when the volumetric flow rate at 4000 cm3/min and the efficiency will be at the higher performance that is 50%. Although, it on the higher efficiency but the power lost and the power emitted also be the one of the higher value such as 1674.97 Watt and 1119.47 Watt respectively. Then, the overall heat transfer coefficient (U) is -518.19 W/(m2.oC) and logarithmic mean temperature difference is 16 ⁰C. For the parallel flow heat exchanger, we can relate that the higher of volumetric flow rate on the system than higher of the efficiency of performance. The design of a parallel flow heat exchanger is advantageous when two fluids are required to be a brought to nearly the same temperature.

MUHAMAD FIRDAUS BIN HIPUL 2014258044

CONCLUSION

In this lab we were conduct two design of system which is counter-flow and parallel flow heat exchanger. Based on the experiment, we can determine the effect of flow rate variation on the performance characteristics of a counter-flow and parallel flow heat exchanger. In the counter-flow heat exchanger, the higher efficiency was 58% when the volumetric flow rate at the 1000 cm3/min. if the volumetric was changed to the 4000 cm3/min, the efficiency be a less performance that is 44%. The result was different for the parallel flow design. In the parallel flow, the volumetric flow rate will affected the efficiency of the system. This is because when the volumetric flow rate is increase than the efficiency or performance of the system also increases. The conclusion, whether counter-flow or parallel flow, both system have own advantages and disadvantages depends on the usage. For the future, as the engineer operate the design based on the requirement.

REFERENCE

1. Article (2015), Engineers Edge, Retrieved October 23, 2015, from

http://www.engineerisedge.com

MOHAMAD IKHWAN BIN SAMER 2014630126

DISCUSSION

Based on the objective of the experiment which is to demonstrate the effect of flow rate variation on the performance characteristic of a counter flow and parallel flow in the concentric tube heat exchanger. The variation of the flow rate can affect the performance characteristic in tube heat exchanger. The experiment involves two types of flow in the concentric tube heat exchanger which is counter flow and parallel flow. The table below show the performance characteristic on the counter flow:

Vh(cm3/min)

Power Emitted (W)

Power Absorbed

(W)

Power Lost

(W)

Efficiency

( )

(%)

DT1

(oC)

D T2

(oC)

D Tm

(oC)

U

W/(m2.oC)

1,000 568.38 -136.37 704.75 24 28.4 16 21.6 -94.23

2,000 1067.96 -196.25 1264.21 18 28.7 15 21.1 -138.82

3,000 1232.39 -462.36 1694.75 38 28.7 8.8 16.8 -470.77

4,000 1119.47 -555.5 1674.97 50 28.6 7.8 16.0 -518.19

For the lowest flow rate of 1000 /min it has the highest efficiency 58% for power transfer

as the Power Emitted is 794.36 W and Power Absorbed is -458.94 W which equate to a Power Loss of 1253.3 W . The logarithmic mean temperature difference is 15.89°C and the

overall heat transfer coefficient is -431.08W/( C°). For the highest flow rate is 4000

/min it hasan efficiency 44% for power transfer as the Power Emitted is 1232.45 W and

Power Absorbed is -542.19 W which equate to a Power loss of 1774.64 W. The logarithmic mean temperature difference is 14.29°C and the overall heat transfer coefficient is -566.3 W/(

C°). It can be said that when the flow rate increasing, the performance characteristic value

become bigger but the efficiency become lower.

For the parallel flow the table below show the performance characteristic data:

Vh(cm3/min)

Power Emitted (W)

Power Absorbed

(W)

Power Lost

(W)

Efficiency

( )

(%)

DT1

(oC)

D T2

(oC)

D Tm

(oC)

U

W/(m2.oC)

1,000 568.38 -136.37 704.75 24 28.4 16 21.6 -94.23

2,000 1067.96 -196.25 1264.21 18 28.7 15 21.1 -138.82

3,000 1232.39 -462.36 1694.75 38 28.7 8.8 16.8 -470.77

4,000 1119.47 -555.5 1674.97 50 28.6 7.8 16.0 -518.19

For the lowest flow rate of 1000 /min it an efficiency 24% for power transfer as the

Power Emitted is 568.38 W and Power Absorbed is -136.37 W which equate to a Power Loss of 704.75 W . The logarithmic mean temperature difference is 21.6°C and the overall heat

transfer coefficient is -94.23 W/( C°). For the highest flow rate is 4000 /min it has the

highest efficiency 50% for power transfer as the Power Emitted is 1119.47 W and Power Absorbed is -555.5 W which equate to a Power loss of 1674.97 W. The logarithmic mean

temperature difference is 16.0°C and the overall heat transfer coefficient is -518.19 W/(

C°). It can be said that when the flow rate increasing, the performance characteristic value

become bigger including its efficiency.

MOHAMAD IKHWAN BIN SAMER 2014630126

CONCLUSION

Based on the objective of the experiment which is to demonstrate the effect of flow rate variation on the performance characteristic of a counter flow and parallel flow in the concentric tube heat exchanger. The objective of the experiment is achieved as the performance characteristic is tabulated in the result table. As the experiment were tested on two different flow which was a counter flow and parallel flow by using a variation of flow rate and for both flow it can be said that when the flow rate increase the value of performance characteristic become bigger but it differ on it efficiency when it’s on the counter flow the efficiency decreasing and when it’s on parallel flow the efficiency increasing.

MohdKhairuddin b CheLong (2013834608)

Discussion

In this experiment, we have learnt about the flow arrangement of heat exchanger to study about the effect of flow rate variation on the performance characteristics in parallel flow and counter flow. For the parallel flow, we set the flow of hot and cold fluids in same flow direction at the start and leave same at the end. As a result, the fluid will flow in parallel in heat exchanger. While for the counter flow the hot and cold fluids start and ending with opposite direction.

For both experiment, we first set the heater to 60°C, however due to heat loss and flow rate there are slightly different from each data. In both experiment, the exit temperature must be higher than the exit temperature of the cold fluid and lesser than the temperature of the hot fluid. This can be proven by the data taken in the table. This is because of the reaction between hot and cold fluid. The heat is transferred to the cold fluid and the surrounding. That is why the exit temperature for cold fluid is higher than the entrance temperature. The energy removed from the hot fluid is the energy added to the cold fluid according to the First Law of Thermodynamics. Also, the higher the flow rate of a fluid, the lower the temperature changes in the fluid will be.

Based on the result we obtained from this experiment, we can calculate the power emitted and power absorbed from the formula given. From the calculation, the higher the volumetric flow rate, the higher the power emitted and absorbed. However, in the counter flow the value for power absorbed for 2000 and 3000cm^3/min are lower compare to 1000 cm^3/min. then the value is increased when volumetric flow rate is increased to 4000 cm^3/min. For parallel flow, the values for power emitted and absorbed increased as the volumetric flow rate keep increased.

For both experiment, we first set the heater to 60°C, however due to heat loss and flow rate there are slightly different from each data. In both experiment, the exit temperature must be higher than the exit temperature of the cold fluid and lesser than the temperature of the hot fluid. This can be proven by the data taken in the table. This is because of the reaction between hot and cold fluid. The heat is transferred to the cold fluid and the surrounding. That is why the exit temperature for cold fluid is higher than the entrance temperature. The energy removed from the hot fluid is the energy added to the cold fluid according to the First Law of Thermodynamics. Also, the higher the flow rate of a fluid, the lower the temperature changes in the fluid will be.

MohdKhairuddin b CheLong (2013834608)

Conclusion

It can be concluded that the experiment was successfully conducted but not fully acceptable when

it comes to calculation. We are able to determine the effect of flow rate variation on the

performance characteristics of parallel flow and counter flow of heat exchanger. The increasing of

volume metric will increase the value of power absorbed and power emitted. Last but not least, the

increasing value of volumetric flow rate also will affect the overall heat transfer coefficient. The heat

exchanger apparatus follows the basic laws of thermodynamics and this can be shown by the

result from conducting the experiment. In parallel flow configuration, the exit temperature of the hot

fluid is always hotter than the exit temperature of the cold fluid. This is because heat is not

spontaneously transfer from a hotter body to a colder body. Plus, the flow rate increase, the exit

temperature is also increased because it need time to transfer heat between the two fluids.

REFERENCE

1. SadikKakaç and Hongtan Liu (2002). Heat Exchangers: Selection, Rating and Thermal Design (2nd ed.). CRC Press. ISBN 0-8493-0902-6.

2. Perry, Robert H. and Green, Don W. (1984). Perry's Chemical Engineers' Handbook(6th ed.). McGraw-Hill. ISBN 0-07-049479-7.