# 05.4 - Refrigeration

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### OVC Intro

Refrigeration Cycle Introduction (LearnChemE.com, 3min) explains each step in an ordinary vapor compression (OVC) refrigeration cycle and the energy balance for the step. You might also enjoy the more classical introduction (USAF, 11min) representing your tax dollars at work. The musical introduction is quite impressive and several common misconceptions are addressed near the end of the video.
Comprehension Questions: Assume zero subcooling and superheating in the condenser and evaporator.
1. An OVC operates with 43 C in the condenser and -33 C in the evaporator. Why is the condenser temperature higher than than the evaporator temperature? Shouldn't it be the other way around? Explain.
2. An OVC operates with 43 C in the condenser and -33 C in the evaporator. The operating fluid is R134a. Estimate the pressures in the condenser and evaporator using the table in Appendix E-12.
3. An OVC operates with 43 C in the condenser and -33 C in the evaporator. The operating fluid is R134a. Estimate the pressures in the condenser and evaporator using the chart in Appendix E-12.
4. An OVC operates with 43 C in the condenser and -33 C in the evaporator. The operating fluid is R134a. Estimate the pressures in the condenser and evaporator using Eqn 2.47.
5. An OVC operates with 43 C in the condenser and -33 C in the evaporator. Assume the compressor of the OVC cycle is adiabatic and reversible. What two variables (P,V,T,U,H,S) determine the state at the outlet of the compressor?

How To Read the Pressure-Enthalpy (PH) Diagram for Propane (uakron.edu, 9min) A chemical process may need refrigeration to operate the condenser of a distillation column at cryogenic conditions. The process in this video operates between -100F and 80F in its refrigeration coils.
Comprehension Questions: Assume zero subcooling and superheating. (ie. The "approach temperature" is zero.)
1. Download the table of saturation properties for propane from the student supplements section of chethermo.net. Estimate the pressures and enthalpies exiting the condenser and evaporator. How do these compare to the values reported in the video?
2. Suppose the condenser outlet operated at 100 F. Estimate the condenser pressure (MPa).
3. Suppose the condenser outlet operated at 100 F. Estimate the condenser outlet enthalpy(J/g)
4. Suppose the condenser outlet operated at 100 F. Estimate the condenser inlet temperature(F)
5. Suppose the condenser outlet operated at 100 F. Estimate the condenser inlet enthalpy (J/g)