비디오: Heat Transfer Efficiency Test of a Finned-tube Heat Exchanger

Testing the Heat Transfer Efficiency of a Finned-tube Heat Exchanger

Overview

Source: Michael G. Benton and Kerry M. Dooley, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA

Heat exchangers transfer heat from one fluid to another fluid. Multiple classes of heat exchangers exist to fill different needs. Some of the most common types are shell and tube exchangers and plate exchangers¹. Shell and tube heat exchangers use a system of tubes through which fluid flows¹. One set of tubes contains the liquid to be cooled or heated, while the second set contains the liquid that will either absorb heat or transmit it¹. Plate heat exchangers use a similar concept, in which plates are closely joined together with a small gap between each for liquid to flow¹. The fluid flowing between the plates alternates between hot and cold so that heat will move into or out of the necessary streams¹. These exchangers have large surface areas, so they are usually more efficient¹.

The goal for this experiment is to test the heat transfer efficiency of a finned-tube heat exchanger (Figure 1) and compare it to the theoretical efficiency of a heat exchanger without fins. The experimental data will be measured for three different flow rates of monoethylene glycol (MEG). Two different water flow rates for each MEG flow rate will be used. Using the Wilson plot method the heat transfer coefficients will be determined from the experimental data. Additionally, the Reynold's number and the amount of heat transferred will be compared for flow with and without the fins to evaluate heat transfer efficiency.

Figure 1: Finned-tube Heat Exchanger. 1) MEG outlet temperature 2) water inlet temperature 3) MEG inlet temperature 4) water outlet temperature 5) water meter 6) MEG accumulation sight glass/cylinder.

Procedure

1. Start and Flow Rate Determination

Open the charge valve located below the steam generator.
Start the unit, and allow 15 min for steam to begin forming.
Calculate the flow rate of water
1. Start a stopwatch and monitor the gauge displaying the volume of water.
2. Stop the watch after 30 s and record the total volume of water displayed on the gauge.
3. Divide the volume of water by the time to determine the volumetric flow rate.
Record the

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Results

The finned tube heat exchanger did not reach turbulent flow (Figure 2). The fins provide additional surfaces on which boundary layers form, as known through laminar and turbulent flow theory. If the fluid is not at a sufficient velocity, the fluid will not reach turbulence. The boundary layers between the fins overlap in the laminar region, so the fluid will remain laminar.

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Application and Summary

Heat exchangers are used in a variety of industries, including agriculture, chemical production, and HVAC. The goal for this experiment was to test the heat transfer efficiency of a finned-tube heat exchanger and compare it to the theoretical efficiency of a heat exchanger without fins. Experimental data was measured for three different flow rates of monoethylene glycol (MEG) and two unique water flow rates for each MEG flow rate used. The Reynold's number was determined for flow with and without the fins and was used to

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References

Types of Heat Exchangers." Types of Heat Exchangers. N.p., n.d. Web. 19 Jan. 2017.
Heat exchangers for sugar factories and distilleries." Heat exchanger for sugar and ethanol industry. N.p., n.d. Web. 19 Jan. 2017.
Biotechnology and green chemistry heat exchangers." Heat exchanger for green chemical industry. N.p., n.d. Web. 19 Jan. 2017.
Heat exchangers for heating and cooling." Heat exchangers for district heating, cooling and HVAC. N.p., n.d. Web. 19 Jan. 2017.

Tags

Heat Transfer Efficiency Finned tube Heat Exchanger Heat Exchanger Design Heat Transfer Coefficient Integration Principles Fluid Species Physical Barrier Temperature Differences Flow Area Surface Area

1. Start and Flow Rate Determination

Open the charge valve located below the steam generator.
Start the unit, and allow 15 min for steam to begin forming.
Calculate the flow rate of water
1. Start a stopwatch and monitor the gauge displaying the volume of water.
2. Stop the watch after 30 s and record the total volume of water displayed on the gauge.
3. Divide the volume of water by the time to determine the volumetric flow rate.
Record the MEG flow rate from the flow meter.
Observe the temperature from the thermocouples, and record the values.

2. Varying the flow rate and shut down

To collect data for 6 different runs, set the flow rate of water to either a high or low flow rate and run it with a high, medium, or low flow rate of MEG.
1. For reference, the previous flow rates have been used: 0.0439, 0.0881, and 0.1323 gal/sec for the low, medium, and high flow rates of MEG, respectively.
As previous, record the volumetric flow rates and temperature difference on the thermocouple for each run.
When finished, shut down the instrument.
1. Close the valves to stop the flow of steam, monoethylene glycol and water.
2. Turn off the main switch.

3. Calculations

Use Equation 1 to calculate the total heat transferred, Q, with the temperature difference read from the thermocouples (devices used to measure temperature) and the known physical dimensions of the heat exchanger (found in the user manual for the unit being operated). The temperature differences can be taken from the temperature readings of each run.
Calculate the heat transferred for each unique trial run, and use the Wilson plot method to find the heat transfer coefficients for the three MEG flow rates.
Compare the calculated heat transferred and Reynolds number to theoretical values of the heat exchanger without fins.

건너뛰기...

0:07

Overview

0:59

Principles of Heat Transfer in Heat Exchangers

4:07

Heat Exchanger Start-up

4:54

Flow Rate Variation

5:42

Calculations

6:09

Results

7:26

Applications

8:11

Summary

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