ASEN 3113Thermodynamics and Heat TransferFall 2005

ASEN 3113

Experimental Lab 1

Basic Refrigerant Training Unit (BRTU) Experimental Procedure

Assigned: Thursday, September 14, 2006

BRTU Experiment Using the Thermostatic Expansion Valve

LabVIEW:

  1. To monitor the (6) thermocouples in the system, you may use the LabVIEW program Refrigeration unit.vi accordingly. These files arelocated under: Courses H:\ITLL Documentation\ITLL Modules\Basic Refrigeration Training Unit
  2. Set all user inputs before starting the program.
  3. Startthe LabVIEW program using the right arrow button () located in the top left-hand corner of the window. Temperature values are monitored on the display graph. WARNING: Unlike other ITLL programs all the data shown in the graph is NOT written to the datafile, otherwise file size would exceed maximum limits in Excel.
  4. To write the current temperatures to file press “stop and save”. This will create a text file easily readable by many programs.

BRTU Operation:

  1. Check and double check all the valves are CLOSED(fully clockwise, and not TOO tight)
  2. Trace the flow of the refrigerant and open the proper valves. The following valves should be opened: TXV, HP1, HP4, ACO, ACI, LRI (fully counterclockwise, not TOO much).
  3. Turn Power to ON.
  4. Evaporator fan should be on LOW speed.
  5. Turn condenser fan on HIGH.
  6. Turn Compressor ON.
  7. Let the system operate till the pressures and temperatures reach equilibrium (around 10 minutes).
  8. Measure and record the following once steady state is achieved:
  9. Pressure at all 4 gages (P1, P2, P3 and P4)
  10. Atmospheric Pressure (NCAR)
  11. Thermocouple temperatures. (LabVIEW )
  12. Turn the evaporator fan to HIGH and record how long the system takes to reach equilibrium.
  13. Measure and record the following once equilibrium is achieved:
  14. Pressure at all 4 gages (P1, P2, P3 and P4)
  15. Atmospheric Pressure
  16. Thermocouple temperatures. (LabVIEW )
  17. Shut off compressor. Record head (P2) and suction (P1) pressures after 5 minutes.

Please address the following questions/tasks within your lab write up. Questions should be answered within the text of the report. Note that the following are in no particular order. Be sure to show all formulae, calculations, and relevant data.

1)Using the schematic of the Basic Refrigeration Training Unit, show the flow path of the refrigerant. Identify the changes in temperature and pressure at each of the components.

2)Construct a table with all relevant data (temperatures, pressures, refrigerant phase, enthalpies, entropy, at each component during each cycle, Please use SI units).

3)Describe what is going on at each component. What is driving the changes you see in your table?

4)Construct a T-s diagram from your table, where are the values far from ideal? Why?

5)Discuss why the entropy values before and after the expansion valve are not the same, what could you replace the expansion valve with to change this? Explain.

6)Calculate the COP of the refrigerator using enthalpy values at the various stages in the cycle. What happens to the COP in the refrigeration mode when you change the fan speed? Are these values realistic? Explain.

7)What are the irreversible processes in the refrigeration cycle?

8)What criteria are used to select a refrigerant for a particular system? Would it be wise to use water in this system?

9)Discuss the advantages and disadvantages of the refrigeration cycle with the TXV open and discuss a good application for it.