An existing steady state refrigerator has been operating using the vapor-compression cycle for some months, with a C.O.P. of 3.1. Today the rate at which work is being added to the compressor is the same, but QC has decreased. Which of the following statements must be true?
A. QH must be smaller in magnitude than normal.
B. QH must be larger in magnitude than normal.
C. The compressor efficiency is lower than normal.
D. The new C.O.P must be higher.
E. None of these statements can be true.
A. Correct. Taking the refrigerator as the system, if the supplied shaftwork is the same but the heat added is lower, the heat rejected must also be lower if the system is to remain steady state.
B. Incorrect. This would violate the first law of thermodynamics. Balance the energy entering and exiting the vapor-compression cycle.
C. Incorrect. While this is one possible explanation for the change, it is not the only explanation. One of the other answers is something that *must* be true.
D. Incorrect. Reexamine Equation 5.50.
E. Incorrect. One of these statements is true.
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