Question

Ideal refrigeration cycle is:

• A. Same as Carnot cycle
• B. Same as reverse Carnot cycle
• C. Dependent on the refrigerant's properties
• D. None of these

Hint:

While actual refrigeration systems often use the Vapor Compression Refrigeration Cycle (VCR) with an expansion valve instead of an expander, the theoretical ideal reference cycle is always the Reverse Carnot Cycle.

Answer 1

The Correct Option is B

Concept: A refrigeration system operates as a heat engine running in reverse. It absorbs heat from a low-temperature reservoir and rejects it to a higher-temperature environment by consuming external work. Let us evaluate the ideal cycle types:

• Carnot Cycle: Represents the ultimate theoretical standard for a power-producing heat engine operating with maximum efficiency.

• Reverse Carnot Cycle: Reverses the direction of all thermodynamic processes in the Carnot cycle (isentropic compression, isothermal heat rejection, isentropic expansion, and isothermal heat absorption). It serves as the ideal benchmark for refrigeration systems, yielding the highest possible Coefficient of Performance ($COP$) between two operating temperatures.

Step 1: Analyze the thermodynamic efficiency limits.
The efficiency of an ideal refrigerator is defined by its Coefficient of Performance ($COP$). For a reverse Carnot refrigeration cycle, the $COP$ depends solely on the operating temperature limits: \[ COP_{\text{Carnot}} = \frac{T_{\text{L}}}{T_{\text{H}} - T_{\text{L}}} \] Because all four processes in this cycle are perfectly reversible, it provides an upper bound benchmark for an ideal refrigeration system, independent of the working fluid used. Thus, the ideal refrigeration cycle is identical to the reverse Carnot cycle.