Suppose that the Department of Energy develops a new reversible engine that has a coefficient of performance (COP) of 4.0 when operated as a refrigerator and a COP of 5.0 when operated as a
Heat pump. What is its thermal efficiency when operated as a heat engine doing work?
A) 80%
B) 20%
C) 25%
D) 10%
E) 45%

Question

Quizplus · Accepted Answer

The COP of a refrigerator is related to the efficiency of a heat engine by the relation COP = 1/(1 - η), where η is the efficiency. Given COP = 4 for the refrigerator, η = 1 - 1/4 = 0.75. However, for a heat engine, the efficiency is η = 1 - 1/COP_heat_pump. Given COP_heat_pump = 5, η = 1 - 1/5 = 0.20 or 20%.

Suppose That the Department of Energy Develops a New Reversible