Refrigeration Cycle: Summary

The answers to the ConcepTests are given below and will open in a separate window. 
Key points from this module:
  • The same cycle can be a refrigerator or a heat pump. The objective of a refrigerator is to remove heat at low temperature. More heat is removed than work is added (the coefficient of performance is greater than one). The heat discarded at high temperature is greater than the work added, so a heat pump can potentially be an efficient way to heat a structure.
  • The low temperature in a refrigeration cycle is obtained by feeding a high pressure liquid to a throttle. When the pressure drops in the throttle, some of the liquid evaporates and since the throttle is adiabatic, the temperature drops.
  • The coefficient of performance (COP), which is greater than one, indicates how efficient a refrigeration cycle is.
From studying this module, you should now be able to:
  • Determine the phases present at different points in the cycle.
  • Do energy balances for each part of a refrigeration cycle.
  • Calculate the coefficient of performance (COP) for a refrigeration cycle using the first and second laws.
  • Predict how the COP changes as conditions in the refrigeration cycle change.
  • Sketch the OVC refrigeration cycle on a T-S and a P-H diagram.
  • Explain the purpose of the compressor, condenser, throttle valve, and evaporator in an OVC cycle.

Prepared by John L. Falconer, Department of Chemical and Biological Engineering, University of Colorado Boulder