Carnot vapour Cycle:

It is convenient to analyze the performance of steam power plants by means of idealized cycles that are theoretical approximations of real cycles. The Carnot cycle is an ideal, but non practising cycle giving maximum possible thermal efficiency for cycle operating on selected maximum and minimum temperature ranges. It is made up from four ideal processes: 1 - 2 : Evaporation of water into saturated steam within boiler at constant maximum cycle temperature T₁  (= T2)

2 - 3: Ideal (that is, constant-entropy) expansion within the steam engine or turbine that is, S₂  = S₃.

3 - 4: Partial condensation within condenser at constant minimum cycle temperature T₃ (= T₄).

4 - 1: Ideal (that is, constant-entropy) compression of wet steam within the compressor to complete

the cycle, i.e., S₄  = S₁.