PARALLEL-FLOW PLATE HEAT EXCHANGER

Objective:

To determine the heat transfer coefficient (U) for a parallel-flow plate heat exchanger.

Theory:

The operational principle of plate heat exchanger is based on heat transfer from hot stream to cold stream, which consequently causes temperature changes in both streams.

The heat transferred from the hot to cold streams is equal to the heat received by the cold stream.

Q = mCp (TH1-TH2) = mCp (TC2-TC1)

Q = Heat transferm = Fluid massCp = Fluid heat capacityTH1 = Hot stream inlet temperatureTH2 = Hot stream outlet temperatureTC1 = Cold stream inlet temperatureTC2 = Cold stream outlet temperature

Q = UA∆Tlm U = Heat transfer coefficientA = Plate surface area∆Tlm = Log mean temperature difference, which is described by:

ΔT lm=(T H 2−TC 2 )−(T H1−TC1 )

ln [T H 2−TC 2TH 1−TC 1 ]The standard heat transfer coefficient for this experiment is between 500 - 700 W/m2.°C.

Equipment/Materials:

1. Parallel-flow plate heat exchanger2. 10L capacity plastic container3. Stop watch4. Water pump

5. Water

Procedure:

1. Switch on the heater and stirrer to heat up the fluid in the storage tank.

2. Turn hot stream pump on to recycle hot water in the tank.3. Let the water flow until the water temperature in the tank reaches

60 °C. Make sure hot stream temperature (TH2) is equal to the temperature in the tank (TH1).

4. When the temperatures are even, make preparation to record the inlet and outlet temperatures for each hot stream and cold stream simultaneously.

5. Open the cold stream valve slowly. 6. At the same time, start the stop watch and record all the related

temperatures as in procedure (4).7. Stop the stop watch when the time is up.8. Close the cold stream valve. 9. Repeat steps 3-8 for three (3) subsequent sets of data reading.

Calculate the average reading for all the data recorded.

Experiment data:

Experimental information for parallel-flow plate heat exchanger

Length of the plate 420

mm

Width of the plate 125 mm

Thickness of the plate 46 mm

Total number of plate 15 pieces

Questions:

1. Based on the recorded data, plot a graph of temperature vs. time for hot stream and cold stream.

2. Draw a temperature profile vs. plate thickness for parallel-flow plate heat exchanger.

3. Determine the overall heat transfer coefficient for this heat exchanger. Discuss why the calculated value differs from the standard value.

4. Describe the advantages of plate heat exchanger.5. Discuss all the results obtained.

References:

1. Holman, J. P., “Heat Transfer”, 8th edition, Mc Graw-Hill Inc., U.S.A, 1997.

2. Mc Cabe, W. L., Smith, J. C. & Harriot, P., “Unit Operation of Chemical Engineering”, 4th Edition, Mc Graw-Hill, 1985.

3. Geankoplis, C. J., “Transport Processes & Unit Operations”, 3rd Edition, Prentice-Hall, 1995.