Carnot Vapor Compression Systems:

 The compression is imagined here to take place in two stages: isentropic compression up to state 2 & isothermal compression from state 2 to 3 as illustrated in below described Figure (b).

(a) Schematic Representation of a Carnot  Vapour Compression System   (b) T-S Diagram

In a heat exchanger the working medium is condensed providing saturated liquid at state four. The isentropic expansion from state 4 to state 5 provides the refrigeration effect, the area under line 5-1.

Comparing figs.(1) and (2), we may illustrate that the Carnot vapour compression cycle provides a greater refrigeration effect than the vapour compression cycle.

The COP of a Carnot vapour compression cycle is explained as following:

Here, T₁ is the temperature at which heat is discarded in the condenser and T₂ is the temperature that maintained in the evaporator. This might be illustrated that the refrigeration system functioning on the Carnot vapour compression cycle has the highest COP.