Carnot’s reversible engine
In 1824, Sadi Carnot conceived a closed reversible cycle consisting two strokes. Since that Carnot’s cycle reversible because it consists two isothermals and two adiabatic, all of which are reversible process.
Carnot’s engine is free from all the defects of practical engine, its efficiency is maximum and it is an ideal heat engine. It has three essential requisites;
Source:
The source should be at a fixed high temperature T1 from which the heat engine can draw heat. It has infinite thermal capacity and any amount of heat can be drawn from it at constant temperature T1.
Sink:
The sink should be at a fixed lower temperature T2 to which any amount of heat can be rejected. It also has infinite thermal capacity and its temperature remains constant at T2.
Working Substance:
A cylinder with non-conducting sides and conducting bottom contains the perfect gas as the working substance. A perfect non-conducting and friction-less piston is fitted into the cylinder. The working substance undergoes a complete cyclic operation.
A perfectly non-conducting stand is also provided so that the working substance can undergo adiabatic operations.