Carnot devised an ideal cycle of operation for a heat engine, called Carnot’s cycle.
Therefore, efficiency of the cycle is
A Carnot’s cycle contains the following four processes
(i) Isothermal expansion (AB)
(ii) Adiabatic expansion (BO)
(iii) Isothermal compression (CD)
(iv) Adiabatic compression (DA)
The net work done per cycle by the engine is numerically equal to the area of the loop representing the Carnot’s cycle .
After doing the calculations for different processes we can show that
[Efficiency of Carnot engine is maximum (not 1000/0) for given temperatures T1 and T2. But still Carnot engine is not a practical engine because many ideal situations have been assumed while designing this engine which can practically not be obtained.]
Refrigerator or Heat Pump
A refrigerator or heat pump is a device used for cooling things. It absorb heat from sink at lower temperature and reject a larger amount of heat to source at higher temperature.
Coefficient of performance of refrigerator is given by
where Q2 is heat absorbed from the sink, Q1 is heat rejected to source and T1 and T2 are temperatures of source and sink.
Relation between efficiency (η) and coefficient of performance (β)