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The efficiency of heat engines is high when the
Chapter 20, Problem 12DQ(choose chapter or problem)
The efficiency of heat engines is high when the temperature difference between the hot and cold reservoirs is large. Refrigerators, on the other hand, work better when the temperature difference is small. Thinking of the mechanical refrigeration cycle shown in Fig. 20.9, explain in physical terms why it takes less work to remove heat from the working substance if the two reservoirs (the inside of the refrigerator and the outside air) are at nearly the same temperature, than if the outside air is much warmer than the interior of the refrigerator.
Questions & Answers
QUESTION:
The efficiency of heat engines is high when the temperature difference between the hot and cold reservoirs is large. Refrigerators, on the other hand, work better when the temperature difference is small. Thinking of the mechanical refrigeration cycle shown in Fig. 20.9, explain in physical terms why it takes less work to remove heat from the working substance if the two reservoirs (the inside of the refrigerator and the outside air) are at nearly the same temperature, than if the outside air is much warmer than the interior of the refrigerator.
ANSWER:Solution to 12DQ Step 1 As shown in the figure, at the compressor, the evaporated coolant fluid is compressed and is supplied to the condenser coil where the heat is supplied to the outside air. The coolant fluid is then passed through the expansion valve, where the coolant will expand a