Which of the following statements are true, regarding reverse Carnot cycle? (heat pump and refrigeration)

Question

BlackTom AI · Accepted Answer

The question asks which statements are true regarding the reverse Carnot cycle (heat pump and refrigeration).
The two candidate statements are:
- a. Heat can be transferred from cold source to hot source with heat pump.
- c. Heat can be transferred from hot source to cold source with refrigerator cycle.
First, recall what a reverse Carnot cycle does: it uses work input to drive heat transfer from a colder reservoir to a warmer reservoir, effectively cooling the cold side and heating the hot side in a heat pump configuration. In a refrigeration cycle, the device extracts heat from the refrigerated space (the cold reservoir) and rejects it to the ambient (the hot reservoir), again moving heat from cold to hot, but with the cold side being the interior being cooled. In both reverse Carnot configurations, the natural direction of spontaneous heat transfer is from hot to cold, but the cycle uses work to reverse that and move heat from cold to hot.

Analyzing option a: This aligns with the heat pump function. By applying work, the refrigerator/heat pump transfers internal heat from the cold reservoir to the hot reservoir, resulting in heating of the hot side. Therefore option a is true.

Analyzing option c: The statement says heat can be transferred from hot source to cold source with refrigerator cycle. In a refrigeration cycle, the operating principle is to remove heat from the cold space and reject heat to the hot surroundings, i.e., heat flows from cold to hot when driven by the cycle, but the net effect is cooling the cold space and warming the hot reservoir. The phrase suggests heat transfer in the natural, unreversed direction during the cycle, which is not the defining direction of a reverse Carnot refrigerator; moreover, the cycle uses work to move heat against its natural direction. As stated, this option mischaracterizes the refrigerator cycle, so it is false.

If the intent is to evaluate strictly by standard thermodynamics, only option a is true and option c is false.

BH20A0720 Engineering Thermodynamics - Blended teaching 2.9.2024-15.12.2024 Quiz 6

Which of the following statements are true, regarding reverse Carnot cycle? (heat pump and refrigeration)

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