Does the entropy per cycle increase, decrease, or remain the same for (a) a Carnot refrigerator, (b) a real refrigerator, and (c) a perfect refrigerator (which is, of course, impossible to build)?

1. A Carnot refrigerator
2. A real refrigerator
3. A perfect refrigerator

Entropy change is a phenomenon that quantifies how disorder or randomness has changed in a thermodynamic system. From the processes followed by given refrigerators, we can decide about the entropy.

A Carnot refrigerator is an ideal refrigerator. All processes are reversible and there is no wastage of energy due to friction and turbulence. The entropy per cycle remains the same for reversible processes.

Hence, entropy remains the same for a Carnot refrigerator.

A real refrigerator loses energy due to the friction. This is an irreversible process. Therefore, the entropy of this refrigerator increases.

A perfect refrigerator transfers heat energy from the cold reservoir to the hot reservoir. Therefore, the entropy of a perfect engine decreases, that is negative which violates the second law of thermodynamics.