Which of the following statements is true for a steady-state reversible heat engine that operates with TC = 300 K and TH = 800 K?
A. The efficiency is less than 50%.
B. The operating fluid has to be an ideal gas.
C. The operating fluid has to undergo a phase change in at least one step.
D. QH is larger in magnitude than Wnet, and they are opposite in sign.
E. None of the above is true.
A. Incorrect. The efficiency is 62.5% when calculated using Equation 4.125.
B. Incorrect. The process fluid could be any substance, even solids or people.
C. Incorrect. The process fluid could be a gas such as neon that does not change phase between these temperatures.
D. Correct. For any temperatures other than TC = 0 K or TH = ? the efficiency will be less than 1 (prove this to yourself using Equation 4.125) and QH will be greater than Wnet. But heat entering will have a different sign than work exiting.
E. Incorrect. One of these statements is true.
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