ABSTRACTFor this experiment, there are four objectives that we need to achieve. First, we want to demonstrate the working principles of a concentric tube heat exchanger operating under counter flow conditions. Second is that we want to demonstrate the working principles of a concentric tube heat exchanger operating under parallel flow conditions. Then for the third and last are that we want to demonstrate the effect of hot water temperature and flow rate variation on the performance characteristics of a concentric tube heat exchanger. The experiment was started by undergoing the start-up procedures. The instrument has been set up according to parallel flow arrangement.

1.0 INTRODUCTIONHeat exchangers are typically classified according to flow arrangement and 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.

Figure 1.0 Concentric tube heat exchangers. (a) Parallel flow (b) Counter-flowAlternatively, the fluids may move in cross flow (perpendicular to each other), as shown by the finned and unfinned tubular heat exchangers of Figure 2. The two configurations are typically differentiated by an idealization that treats fluid motion over the tubes as unmixed or mixed. In Figure 2a, the fluid is said to be unmixed because the fins inhibit motion in a direction (y) that is transverse to the main-flow direction (x). In this case the fluid temperature varies with x and y. In contrast, for the unfinned tube bundle of Figure 2b, fluid motion, hence mixing, in the transverse direction is possible, and temperature variations are primarily in the main-flow direction. Since the tube flow is unmixed, both fluids are unmixed in the finned exchanger, while one fluid is mixed and the other unmixed in the unfinned exchanger. The nature of the mixing condition can significantly influence heat exchanger performance.

Figure 2.0 Cross flow heat exchanger. (a) Finned with both fluids unmixed. (b) Unffined with one fluid mixed and the other unmixed.

2.0 OBJECTIVES

2.1 To demonstrate the working principles of a concentric tube heat exchanger operating under counter flow conditions.2.2 To demonstrate the working principles of a concentric tube heat exchanger operating under parallel flow conditions.2.3 To demonstrate the effect of hot water temperature variation on the performance characteristics of a concentric tube heat exchanger.2.4 To demonstrate the effect of flow rate variation on the performance characteristics of a concentric tube heat exchanger operating under parallel flow conditions.

3.0 APPARATUS

3.1 Concentric Tube Heat Exchanger (ARMFIELD)

4.0 PROCEDURES

4.1 General start-up procedures had been performed by the laboratory technician.4.2 The valves to counter-current concentric heat exchanger arrangement were switched on.4.3 Pumps P1 and P2 were switched on4.4 Valves V3 and V14 were opened and adjusted to obtain the desired flowrates for hot water and cold water streams, respectively.4.5 The system was allowed to reach steady state for 10 minutes4.6 FT 1, FT 2, TT 1, TT 2, TT 3 and TT 4 were recorded.4.7 The pressure drop measurements for shell-side and tube-side were recorded for pressure drop studies4.8 Steps 5.4 5.7 were repeated for different combinations of flowrate FT 1 and FT 2 as in the result sheet.4.9 Pumps P1 and P2 were switched off after the completion of experiment

5.0 RESULTS AND SAMPLE CALCULATIONS

FT 1 (LPM)FT2 (LPM)TT 1 (C)TT 2 (C)TT 3 (C)TT 4 (C)

10.02.036.030.149.049.5

10.04.033.730.648.449.0

10.06.032.629.348.549.1

10.08.032.130.048.949.7

10.010.031.930.448.149.0

Table 6.1: Data for Fixed Hot Water Flowrates at 10 LPMFT 1 (LPM)FT 2 (LPM)TT 1 (C)TT 2 (C)TT 3 (C)TT 4 (C)

2.010.031.629.847.150.0

4.010.031.630.647.449.3

6.010.031.830.848.049.2

8.010.031.929.948.349.2

10.010.032.130.449.150.1

Table 6.2: Data for Fixed Cold Water Flowrates at 10 LPM

Counter-CurrentTT1: Hot water inlet temperatureTT2: Hot water outlet temperatureTT3: Cold water inlet temperatureTT4: Cold water outlet temperatureTable 6.3: Table of Calculations for Concentric heat ExchangerFixed hot water flowrates at 10 LPMtest 1Test 2Test 3Test 4Test 5

Hot fluid (Tube) : Water

Vomunetric flowrateL/min10.010.010.010.010.0

Mass flowkg/s0.1650.1650.1650.1650.165

Inlet temperatureC3633.732.632.131.9

Outlet temperatureC30.130.629.83030.4

Heat transfer rateJ/s4064.362135.511928.851446.641033.31

Cold fluid (Shell) : water

Volumetric flowrateL/min246810

Mass flowkg/s0.0330.0660.10.1330.165

Inlet temperatureC4948.448.548.948.1

Outlet temperatureC49.54949.149.749

Heat transfer rateJ/s69.02165.65250.98445.07621.18

Temperature difference

Hot side inlet T, T13633.732.632.131.9

hot side outlet T, T230.130.629.83030.4

Cold side inlet T, T34948.448.548.948.1

Cold side outlet T, T449.54949.149.749

T log mean, Tlm-16.05-16.52-17.58-18.24-17.4

Heat lossW3995.341969.861677.871001.57412.13

Efficiency%1.77.761330.7760.12

Overall heat transfer coefficient

Total exchange aream^20.050.050.050.050.05

Overall heat transfer coefficient-5064.62-2585.36-2194.37-1586.23-1187.71

Exchanger layout

Tube11111

Shell11111

Length of tubesm0.50.50.50.50.5

Tube IDmm26.6426.6426.6426.6426.64

Tube ODmm33.433.433.433.433.4

Tube surface aream^20.050.050.050.050.05

Shell diametermm8585858585

Tube side

Cross section aream^20.0005570.0005570.0005570.0005570.000557

Mass velocity296.23296.23296.23296.23296.23

Linear velocity0.290040.290040.290040.290040.29004

Reynolds14,363.9714,363.9714,363.9714,363.9714,363.97

Prandtl3.563.563.563.563.56

Nuselt number74.0574.0574.0574.0574.05

Type of flowTurbulentTurbulentTurbulentTurbulentTurbulent

Stanton number0.001450.001450.001450.001450.00145

Heat transfer factor, jh0.003940.003940.003940.003940.00394

Tube coefficient, hi1788.991788.991788.991788.991788.99

Shell side

Cross flow area0.00480.00480.00480.00480.0048

Mass velocity6.87513.7520.83327.70834.375

Linear velocity0.00690.013810.020920.027830.03452

Equivalent diameter51.651.651.651.651.6

Reynolds443.05886.11342.551785.62215.25

Prandtl5.445.445.445.445.44

Type of flowlaminarlaminarlaminarlaminarlaminar

Nuselt number5.279.1712.7916.0719.09

Stanton number0.002190.00190.001750.001650.00158

Heat transfer factor, jh0.006810.005910.005440.005130.00491

Shell coefficient, hs62.94109.24152.35191.09226.9

Table 6.4: Table of Calculations for Concentric heat ExchangerFixed cold water flowrates at 10 LPMtest 1Test 2Test 3Test 4Test 5

Hot fluid (Tube) : Water

Vomunetric flowrate246810

Mass flow0.03290.06590.09880.13180.1647

Inlet temperature31.631.631.831.932.1

Outlet temperature29.830.630.829.930.4

Heat transfer rate247.24275.13412.491100.531168.96

Cold fluid (Shell) : water

Volumetric flowrate1010101010

Mass flow0.16590.16590.16590.16590.1659

Inlet temperature47.147.44848.349.1

Outlet temperature5049.349.249.250.1

Heat transfer rate2012.481318.52832.75624.56693.96

Temperature difference

Hot side inlet T, T131.631.631.831.932.1

hot side outlet T, T229.830.630.829.930.4

Cold side inlet T, T347.147.44848.349.1

Cold side outlet T, T45049.349.249.250.1

T log mean, Tlm-17.84-17.25-17.3-17.84-18.35

Heat loss-1765.24-1043.39-420.26475.97475

Efficiency12.2920.8749.5356.7559.34

Overall heat transfer coefficient

Total exchange area0.050.050.050.050.05

Overall heat transfer coefficient-277.17-318.99-476.87-1233.78-1274.07

Exchanger layout

Tube11111

Shell11111

Length of tubesm0.50.50.50.50.5

Tube IDmm26.6426.6426.6426.6426.64

Tube ODmm33.433.433.433.433.4

Tube surface aream^20.050.050.050.050.05

Shell diametermm8585858585

Tube side

Cross section area0.0005570.0005570.0005570.0005570.000557

Mass velocity59.066118.312177.379236.625295.691

Linear velocity0.059770.119730.17950.239460.29923

Reynolds2864.075736.868600.9811,473.7714,337.84

Prandtl3.563.563.563.563.56

Nuselt number20.3835.5349.1361.8773.94

Type of flowturbulentturbulentturbulentturbulentturbulent

Stanton number0.001990.001740.00160.001510.00145

Heat transfer factor, jh0.004660.004070.003750.003540.0034

Tube coefficient, hi492.46858.471186.931494.71786.39

Shell side

Cross flow area0.00480.00480.00480.00480.0048

Mass velocity34.5634.5634.5634.5634.56

Linear velocity0.034710.034710.034710.034710.03471

Equivalent diameter51.651.651.651.651.6

Reynolds2227.172227.172227.172227.172227.17

Prandtl5.445.445.445.445.44

Type of flowturbulentturbulentturbulentturbulentturbulent

Nuselt number19.1719.1719.1719.1719.17

Stanton number0.001580.001580.001580.001580.00158

Heat transfer factor, jh0.004910.004910.004910.004910.00491

Shell coefficient, hs228.12228.12228.12228.12228.12

Typical Chemical Data

Hot waterDensity: 988.18 kg/m3Heat capacity: 4175.00 J/kg.KThermal cond: 0.6436 W/m.KViscosity: 0.0005494 Pa.s

Cold waterDensity: 995.67 kg/m3Heat capacity: 4183.00 J/kg.KThermal cond: 0.6155 W/m.KViscosity: 0.0008007 Pa.s

Cold Water Flowrate = 2.0 LPMCounter-Current Flow (Hot water inlet at 50'C)

Hot fluid (Tube-side): WaterVolume flow : 9.70 L/minInlet temp : 51.1 oCOutlet temp : 50.0 oC

Cold fluid(Shell-Side): WaterVolume flow : 2.0 L/minInlet temp : 32.7 oCOutlet temp : 35.3 oC

Shell And Tube Heat Exchanger LayoutTube : 1Shell : 1Length of tubes : 0.5mTube ID : 26.64mmTube OD : 33.4mmTube surface area : 0.0525m2Shell diameter : 85mmCalculation of Heat transfer and heat Lost:

The Heat Transfer rate of both hot and cold water are both calculated using the heat balance equation;Heat Transfer rate for Hot Water,

Heat Transfer Rate for Cold Water,

Heat Lost Rate = Effeciency =

Calculation of Log Mean Temperature Difference :

Calculation of the Tube and Shell heat transfer Coefficients by Kerns Method :Assuming,

Heat Transfer Coefficient at Tube Side:Cross Flow Area, Mass Velocity, Linear Velocity, Renolds No, Prandtl No, Tube Side Coefficient,

Heat Transfer Coefficient at Shell Side:Cross Flow Area, Mass Velocity, Linear Velocity, Equivalent Diameter, Renolds No, Prandtl No, Nuselt No,

Stanton No, Heat Transfer Factor, Shell Side Coefficient,

Overall Heat transfer Coefficient:Total exchange area,

Overall heat transfer coefficient,

6.0 DISCUSSIONSFor this experiment, we used concentric tube heat exchanger which is one of heat exchanger types. There are four objectives that we need to investigate in order to make our experiment a success. There are two types of flow in concentric tube heat exchanger. There are counter flow and parallel flow. Counter flow is a flow where the hot and cold fluids enter at opposite ends, flow in opposite directions, and leave at opposite ends.

This configuration provides for heat transfer between the hotter portions of the two fluids at one end, as well as between the colder portions at the other. The outlet temperature of the cold fluid will be heated to the inlet temperature of cold fluid however can never exceed the inlet temperature of hot fluid as it will violate the second law of thermodynamics. Furthermore, the outlet temperature of the cold fluid may now exceed the outlet temperature of the hot fluid.Parallel flow is where the hot and cold fluids enter at the same end, flow in the same direction and leave at the same end.

Note that the outlet temperature of the cold fluid never exceeds that of the hot fluid.Theoretically for an overall heat transfer rate, the counter flow conditions is more efficient compare to the parallel flow because the value of power absorbed which is the heat transfer rate of the counter flow is higher compare to parallel flow when acting on the same operating conditions in which the value of U is kept constant. Since for this experiment, the value of U is not constant, we obtained it differently. Other than that, it should be that the Tlm of the counter flow is larger than the Tlm of the parallel flow but for this experiment, we also obtain it different from the theoretical. The efficiency of a counter flow heat exchanger is exactly due to the fact that the difference in temperature between the two fluids over the length of the heat exchanger is maximized. Therefore, the log mean temperature for a counter flow heat exchanger is larger than the log mean temperature of the parallel flow. The error that we have made in this experiment is probably because we do not wait until the temperature readings are stabilized because we do not want the temperature of the heat exchanger to exceed 60 C. It may had happened while doing counter flow operation.We can see that as the temperature increases, the value of overall heat transfer coefficient also increases except for the temperature of 60 C, there is a slightly decrease due to parallax error. This is because, as the temperature of the hot water increases, the temperature difference will be larger and thus increases the total thermal resistance between the two fluids. Notice that, the efficiencies of all the temperature variations is too large and higher compare to the mean temperature efficiency. This is because the mean 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 surface area were available. So, the efficiency should not exceed the mean temperature efficiency. Moreover, for this experiment, the mean temperature efficiency is increasing as the hot water temperature increases.Nevertheless, there are a lot of errors and mistakes that may have affected the results obtained. The very common error occurs during conducting the experiments are careless way of reading the thermometers when taking the temperatures of fluids. The eye of an observer must be parallel to the thermometer meniscus to avoid parallax error. Another mistake that may have been committed is not pressing the enter button after setting the temperatures. This has caused a minor problem when the temperature always manipulate even after setting it to the desired temperature. Besides that, the flow rates always change easily during the experiments.

7.0 CONCLUSIONAt the end of the experiment, we achieved that the parallel flow conditions is much more efficient compare to counter flow condition which is different compare to the theoretical results and when we varied the hot water temperature in parallel flow condition, we can see that as the temperature increases, the value of overall heat transfer coefficient also increases. Also the mean temperature efficiency is increasing as the hot water temperature increases. Moreover, as we varied the hot water flow rate, from low to high, the overall heat transfer coefficient, U will increase and the higher the flow rate of a fluid, the lower the temperature change in that fluid will be. Thus, it can be concluded that all of the four objectives had been reached even though there are few errors made in the experiment.

8.0 RECOMMENDATIONS

8.1 The major error in this experiment is the thermometer reading. As a suggestion, we must use the digital thermometer. This type of thermometer can give the accurate results.8.2 Position the eye level parallel to the scale when taking the thermometer readings.8.3 Carefully when to set the flow rate of hot water and cold water.8.4 Make sure the water in the tank is not over the limit.8.5 Only take the all temperature when we get absolutely the temperature needed.8.6 Make sure that the water level in the tank exceeds the heater plate.8.7 If we change the temperature in this experiment, mostly in water temperature variation experiment, we must wait for a few minute to make sure the temperature reading is constant.8.8 For flow rate variation experiment, it is difficult to control the flow rate. In some cases, if we change the hot water flow rate, it will affect the cold water flow rate. It is so difficult to get the specific flow rate for hot and cold water. As a suggestion, we should use the digital controller to get the accurate value for that flow rate.

REFERENCESChristie John Geankoplis, Transport Processes and Separation Process principle 4th Edition, Pearson Education Inc, United States, 2003Warren L. McCabe, Unit Operations of Chemical Engineering 7th Edition, McGraw-Hill Companies, Inc., 2005Yunus A. Cengel, Heat and Mass Transfer; A Practical Approach, McGraw-Hill Companies, Inc., 2006

APPENDICES