# heat exchanger

November 5, 2017 | Author: sedamyrul | Category: Heat Transfer, Heat Exchanger, Thermal Conduction, Heat, Water Heating

f...

#### Description

TABLE OF CONTENT 1.1

ABSTRACT/SUMMARY

Pages 2

1.2

INTRODUCTION

2

1.3

OBJECTIVES

3

1.4

THEORY

4

1.5

APPARATUS AND MATERIALS

7

1.6

METHODOLOGY/PROCEDURE

8

1.7

RESULTS

10

1.8

SAMPLE CALCULATION

14

1.9

DISCUSSION

17

2.0

CONCLUSIONS

18

2.1

RECOMMENDATIONS

18

2.2

REFERENCE

19

2.3

APPENDICES

19

1

ABSTRACT

Heat exchanger is a device that built for efficient heat transfer from one medium to another. There are two type of flow in double pipe heat exchanger that is counter-flow and co-current flow. Both hot and cold fluids enter the heat exchanger at the same end and move in the same direction in parallel flow (co-current). On the other hand, the hot and cold fluids enter the heat exchanger at opposite ends and flow in opposite directions in counter flow. The heat exchanger also affected by hot water temperature inlet and the flow rate variation. Hot water taken from the pump are discharge while the cold water is taken from the pipe. It has been used in all fields in our life especially, in industries field. They use the heat exchanger to treat the hot fluid stream either it product or undesired product. For this experiment we want to determine the inlet and outlet temperature of cold and hot water streams at steady state in counter-current shell and tube heat exchanger, to calculate the heat transfer and heat loss for energy balance study and also to find the LMTD and heat transfer coefficients and to perform and understanding the temperature profile and effect of flow rates on the heat transfer. The experiment is conducted using counter-current flow in shell and tube heat exchanger. The hot water flow rates (FT1) is set to fix and cold water flow rates (FT2) is varied. The experiment is repeated by varied the FT1 and fixed the FT2. The result shows the effectiveness of heat transfer at constant FT1 and FT2 is 0.05972 and 0.0593 respectively. As a conclusion, the higher the rate of heat transfer, the higher the effectiveness of heat transfer.

INTRODUCTION

Heat exchanger is an equipment built for efficient heat transfer from one medium to another. Different applications of heat exchanger require different types of hardware and configurations of heat transfer equipment. There are several types of heat exchanger such as double pipe heat exchanger, compact heat exchanger, shell and tube heat exchanger and plate and frame heat exchanger. In this experiment, shell and tube heat exchanger was the only apparatus are used. It is can be classified as parallel flow and counters flow and cross flow. For parallel flow, the hot and cold fluids are enters and exit flow in same direction. For counter flow, the hot and cold fluid flow in opposite thus the exchanger and exit exchanger 2

from opposite ends (P.Arthur., 1989). The temperature gradient or the differences in temperature facilitate this transfer of heat. Transfer of heat happens by three principle means: radiation, conduction and convection. In the use of heat exchangers radiation does take place. However, in comparison to conduction and convection, radiation does not play a major role. Conduction occurs as the heat from the higher temperature fluid passes through the solid wall. To maximize the heat transfer, the wall should be thin and made of a very conductive material.

Figure 1 - Diagram of Parallel and Counter Flow Configurations

OBJECTIVES

1. To determine the inlet and outlet temperature of cold and hot water streams at steady state in counter-current shell and tube heat exchanger. 2. To calculate the heat transfer and heat loss for energy balance study. 3. To find the LMTD and heat transfer coefficients. 4. To perform and understanding the temperature profile and effect of flow rates on the heat transfer.

3

THEORY

Heat exchangers transfer heat from one working fluid to another. For instance, steam generators, feed water heaters, re-heaters and condensers are all examples of heat exchangers found in nuclear power systems. The heat transfer rate across a heat exchanger is usually expressed in the form Q = UA ΔTLM & (1)

Where: Q& = heat transfer rate U = overall heat transfer coefficient A = heat exchanger area ΔTLm = average temperature difference between the fluids The overall heat transfer coefficient is a function of the flow geometry, fluid properties and material composition of the heat exchanger. The average temperature difference between the fluids is in general a function of the fluid properties and flow geometry as well. Heat exchanger design requires consideration of each of these factors.

Overall Heat Transfer Coefficient The overall heat transfer coefficient represents the total resistance to heat transfer from one fluid to another. The functional form of U or the product UA, may be derived for any particular geometry by performing a standard conduction analysis on the system of interest. To illustrate this, consider first a planar wall of thickness L, subject to convection on both sides.

4

Figure 2: Planar Wall Heat Exchanger The heat transfer rate from the hot fluid to the wall for a surface area defined by the length segment Δz is given by Newton’s Law of Cooling as

q=hc1AS[TH-T1]

Equation [1]

TH-T1= q/(hc1As)

Equation [2]

such that

Gives the temperature drop from the hot to cold fluid as

Equation 3a and 3b is the Overall Heat Transfer Coefficient. In actual heat exchanger design, the planar wall is seldom used. A more common design involves heat transfer across a tube wall as illustrated in Figure 2.

5

The temperature drop from the hot to cold fluid as

q =UA [TH −TC]

Equation [4]

Where

Equation [5]

Since the heat transfer area on the interior of the tubes is different from that on the exterior in cylindrical geometry, the product UA is normally used to describe heat exchanger performance. Equations 4 the heat transfer across a small length segment Δz where the hot and cold fluid temperatures can be considered constant. In reality, the hot and cold fluid temperatures change continuously along the length of the heat exchanger.

6

APPARATUS

FIGURE 3: HEAT EXCHANGER

Flow rates indicator

Temperature indicator

Temperature controller

Main switch

Concentric tube

Selector valves

Flowmeter

Control valves

Cold water inlet

Hot water inlet

Pump inlet

Storage tank

7

PROCEDURE GENERAL START-UP 1. A quick inspection was performed to make sure that equipment is in a proper working condition. 2. Closed all valves except V1and V12. 3. Hot water was filled up via water supply hose connected to valve V27. The valve closed when the tank was full. 4. The valve V28 are opened to fill up the cold water and leave the valve opened fully continues water supply. 5. The drain hose was connected to the cold water drain point. 6. The main power and heater was switch on for the hot water tank and the temperature controller was set to 500C. 7. The temperature was allowed in the water tank controller to reach the set point. 8. The equipment was ready to be run.

GENERAL SHUT-DOWN PROCEDURE 1. The heater was switch off. Waited until the hot water temperature dropped below 40˚C. 2. The pump P1 and P2 were switch off. 3. The main power was switch off. 4. All the water in the process line was drained off. The water in the hot and cold tanks was retained for the next laboratory session. 5. All the valves were closed.

8

Experiment A: Counter-Current Shell and Tube Heat Exchanger. 1. The general start-up procedures were performed in Section 6.1. 2. The valves were switched to counter-current Shell & Tube Heat Exchanger arrangement. 3. The pump P1 and P2 were switched on. 4. The valves V3 and V14 is opened and adjusted to obtain the desired flow rates for hot and cold water streams respectively. 5. The system was allowed to reach steady state for 10 minutes. 6. The FT1, FT2, TT1, TT2, TT3 and TT4 were recorded. 7. The pressure drop measurement was recorded for shell and tube-side for pressure drop studies. 8. The steps 4 t0 7 were repeated for different combinations of flow rates FT1 and FT2 as in the result sheet. 9. The pumps P1 and P2 were switched off after the completion of experiment. 10. The system was shut-down.

9

RESULT

A. Constant Hot Water Flow rates: 10 LPM TIME (min)

FT1 (LPM)

FT2 (LPM)

TT1 (0C)

TT2 (0C)

TT3 (0C)

TT4 (0C)

TT5 (0C)

DPT1 (mmH2O )

DPT2 (mmH2O)

0

10

2

37.6

28.3

46.2

49.7

50.4

93

5

10

10

2

44

29.7

47.5

49.2

50

91

5

20

10

4

39.5

30.2

46.7

49.7

50.7

88

13

30

10

6

37.5

30.7

46.1

49.0

49.9

89

58

40

10

8

36.3

31.1

45.5

48.8

49.9

86

106

50

10

10

35.8

31.4

45.6

49.1

49.8

91

193

TIME(min)

FT1 (LPM)

FT2 (LPM)

Q (W)

∆TLM (˚C)

U (W/m2. ˚C)

0

10

2

-

-

-

10

10

2

233.92

10.24

187.71

20

10

4

825.48

13.09

518.17

30

10

6

1197.5

13.36

736.51

40

10

8

1817.17

13.43

1111.81

50

10

10

2408.93

13.75

1439.56

10

B. Constant Cold Water Flow rates: 10 LPM TIME (min)

FT1 (LPM)

FT2 (LPM)

TT1 (0C)

TT2 (0C)

TT3 (0C)

TT4 (0C)

TT5 (0C)

DPT1 (mmH2O)

DPT2 (mmH2O)

0

2

10

33.9

29.2

43.3

49.5

51.5

-5

214

2

2

10

33.1

30.2

41.2

49.8

50.5

-5

216

4

4

10

33.5

30.9

44.2

49.5

50.3

-5

209

6

6

10

33.8

31.1

44.8

49.6

50.2

-3

216

8

8

10

34.9

31.0

44.8

48.9

49.9

12

215

10

10

10

35.7

31.1

46.7

50.4

51.0

26

216

Time(min)

FT1 (LPM)

FT2 (LPM)

Q (W)

∆TLM (˚C)

U (W/m2. ˚C)

0

2

10

-

-

-

10

2

10

1184.63

13.65

711.36

20

4

10

1459.40

14.61

820.79

30

6

10

1982.32

14.73

1105.81

40

8

10

2257.94

13.89

1335.73

50

10

10

2545.45

15.15

1380.58

11

Temperature Profile 60 50 40 Hot Stream

30

Cold Stream

20 10 0

Graph 1: Temperature Profile Hot Water Flow rates

Temperature Profile 60 50 40 Hot stream

30

Cold Stream 20 10 0

Graph 2: Temperature Profile Cold Water Flow rates

12

Overall Heat Transfer Coefficient (W/M2.K)

Overall Heat Transfer Coeffient vs Cold Water Flow Rate 1600 1400 1200 1000 800 600 400 200 0 0

2

4

6

8

10

12

Cold water Flow Rate (LPM)

Graph 3: Overall Heat Transfer Coefficients Vs Cold Water Flow rate Of Fixed Hot Flow rate

Overall Heat Transfer Coefficient (W/M2.K)

Overall Heat Transfer Coeffient vs Hot Water Flow Rate 1600

1400 1200 1000 800 600 400 200 0 0

2

4

6

8

10

12

Hot water Flow Rate (LPM)

Graph 4: Overall Heat Transfer Coefficients Vs Hot Water Flow rate Of Fixed Cold Flow rate

13

SAMPLE CALCULATION Constant Hot Water Flow rates = πDL x tube count

Area, A

= π (0.00775 m) (0.5 m) x 10 = 0.1217 m3 Q = mc ∆T = UA ∆TLM Taverage =

𝑇𝑖𝑛 + 𝑇𝑜𝑢𝑡 2

Find Q: (Heat transfer)

Q = Volume flow rate x density x heat capacity x difference temperature between hot in and hot out (2L/min) x (988.998 kg/m3) x (1 m3/1000 L) x (1000 W/ (1kJ/s)) x (1 min/60s) x (4.174 kJ/kg. K) x 1.7 K = 233.92W

Find ∆TLM:

Counter flow dti = temperature of inlet primary – temperature of outlet secondary dt0 = temperature of outlet primary – temperature of inlet secondary LMTD = (dt0 – dti ) / ln (dt0 / dti) dti = 49.2 – 44 = 5.2 dt0 = 47.5 – 29.7 = 17.8 LMTD = (17.8 – 5.2) / ln (17.8 / 5.2) =10.24˚C

Find U:

Q = UA ∆TLM U = 233.92W/ (0.1217 m2 x 10.24˚C) = 187.71 W/m2. ˚C

14

Find ε:

qmax = Cmin (Thot in – Tcold in) Cmin =(

𝐹 𝑡 𝑥 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 1000 𝑥 60

x Cp) / 5

= ((0.033 x 4.174) + (0.066 x 4.174) + (0.099 x 4.174) + (0.131 x 4.174) + (0.165 x 4.174)/5 =0.412 kJ/s.K Qmax= 0.412 (245.8 – 193.1) = 21712.4 W Q = (233.92 +825.48 + 1197.5 + 1817.17 +2408.93 )/5 = 1296.6 W ε = 1296.6 / 21712.4 = 0.05972

Constant Cold Water Flow rates Find Q: (Heat transfer)

Q = Volume flow rate x density x heat capacity x difference temperature between hot in and hot out = (2L/min) x (990.04 kg/m3) x (1 m3/1000 L) x (1000 W/ (1kJ/s)) x (1 min/60s) x (4.174 kJ/kg. K) x 8.6 K = 1184.63 W

Find ∆TLM:

Counter flow dti = temperature of inlet primary – temperature of outlet secondary dt0 = temperature of outlet primary – temperature of inlet secondary LMTD = (dt0 – dti ) / ln (dt0 / dti) dti = 49.8 – 33.1 = 16.7 15

dt0 = 41.2 – 30.2 = 11 LMTD = (11 – 16.7) / ln (11 / 16.7) =13.65˚C Find U:

Q = UA ∆TLM = 1184.63W/ (0.122 m2 x 13.65 ˚C) = 711.36 W/m2. ˚C

Find ε:

qmax = Cmin (Thot in – Tcold in) Cmin =(

𝐹 𝑡 𝑥 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 1000 𝑥 60

x Cp) / 5

= ((0.033 x 4.174) + (0.066 x 4.174) + (0.099 x 4.174) + (0.131 x 4.174) + (0.165 x 4.174)/5 =0.412 kJ/s.K Qmax= 0.412 (248.2 - 171) = 31806.4 W Q = (1184.63 +1459.40 + 1982.32 + 2257.94 + 2545.45 )/5 = 1885.95 W ε = 1885.95 / 31806.4 = 0.0593

16

DISCUSSIONS

In this experiment, the objectives are achieved when the experiment was carryout. First, the objective is to determine the inlet and outlet temperature of cold and hot water streams in and out at steady state in counter-current shell and tube heat exchanger. Second is to calculate the heat transfer and heat loss for energy balance study and also to find the LMTD and heat transfer coefficients. Lastly, objective of this experiment is to perform and understanding the temperature profile and effect of flow rates on the heat transfer. From the result, it shows that hot and cold water from inlet and outlet have difference temperature. Therefore, it proved that heat exchangers transfer heat from one working fluid to another. This can be applied to industries field. A heat loss at hot water streams are increase from 2 LPM until 10 LPM. The maximum heat loss energy for constant hot water is 1439.56W at 10 LPM. Also, heat loss at cold water streams are increasing from 2LPM until 10 LPM. For cold water streams the maximum heat loss energy is 1380.58 W at 10 LPM. The highest average temperature difference between the fluids for the hot water streams is 13.75 ˚C at 10 LPM. While for the cold water streams the highest average temperature difference between the fluids is 15.15˚C at 10 LPM. Increasing LPM are increased the heat transfer coefficient for hot and cold water streams. The maximum heat transfer coefficient at hot water streams is 1439.56 W/m2.˚C at 10 LPM while for cold water streams heat transfer coefficient is 1380.58 W/m2 ˚C at 10 LPM. The overall heat transfer coefficient represents the total resistance to heat transfer from one fluid to another. Generally, temperature profile hot and cold water flow rates show that hot water higher than cold water. The heat transfer is dependent on the flow rate to increase for both temperature profiles. It shows that the higher the flowrate the lower the heat transfer between the fluids.

17

CONCLUSIONS

From the result of this experiment, it shows that temperature of hot and cold water decrease and increase with higher difference of temperature inlet and outlet. It shows the counter current heat exchanger have efficient heaat transfer. Also, it proved that heat exchangers transfer heat from one working fluid to another that have been applied in our life such shower. The heat loss at hot water streams are increase from 2 LPM until 10 LPM. Heat transfer coefficient for hot and cold water streams are increase as increase LPM.

The overall heat

transfer coefficient represents the total resistance to heat transfer from one fluid to another. A temperature profile hot and cold water flow rates shows that hot water is higher than cold water. The effects of flow rate on heat transfer are increase for both temperature profiles.

RECOMMENDATION

1. Ensure that the flow rates obtained are measured accurately. 2. The temperatures should be taken at least 15 minutes after they reach the desired temperature for best results. 3. Replace the water with other materials such as hydrocarbon or refrigerant in order to expose with the different physical and properties of the fluid. 4. Make sure the parameters such as temperature, pressure or flow rates is constant before collecting the results.

18

REFERENCES

1. https://www.scribd.com/doc/23106551/Heat-Exchanger-Lab-Report 2. Arthur P.Fraas. (1989). Heat Exchanger Design. 3. SOLTEQ (n.d). Heat Exchanger Training Apparatus: Model HE 158C.Retrieved from https://www.google.com.my/url?sa=t&source=web&rct=j&ei=QZIgVe_3DI6 ZuQSVpIHYBA&url=http://www.solution.com.my/A3pdf/HE158C(A3).pdf &ved=0CBwQFjAB&usg=AFQjCNFPYOzZ8jBHin__s5NLZdfWc4orjA&sig 2=TKipDuzUCPLctNrAQD6pqA

APPENDICES

Figure 3:Heat Exchanger

19

Figure 4: Temperature and pressure reading

Figure 5: Flow rates meter of system

Physical Properties of Component

Table B1: Properties of water (saturated liquid) ˚C 21.11 26.67 30.00 31.00 32.00 32.22 34.00 34.30 34.65 35.15 35.65 35.90 36.20 36.40 37.25 47.20 48.89 50.00 51.50 54.44

CpkJ/kg . K 4.179 4.179 4.176 4.175 4.174 4.174 4.174 4.174 4.174 4.174 4.174 4.174 4.174 4.174 4.174 4.174 4.174 4.175 4.176 4.179

ῥkg/mᶟ 997.40 995.80 995.26 995.10 994.94 994.94 994.23 994.14 993.99 993.83 993.61 993.53 993.38 993.35 993.02 989.42 988.80 988.18 987.36 985.70 20

54.65 4.179 985.61 55.00 4.179 985.46 55.05 4.179 985.42 55.50 4.179 985.22 56.50 4.180 984.71 57.00 4.180 984.48 57.25 4.180 984.41 59.70 4.181 983.16 60.00 4.179 983.30 65.00 4.183 983.60 65.55 4.183 980.30 http://www4.ncsu.edu/~doster/NE400/Text/HeatExchangers/HeatExchangers.PDF

21