Heat Engines in Thermodynamics:
A body whose temperature remains constant even when heat is gained or lost by it is called a heat reservoir. A heat engine is a mechanical device that converts heat into work.
Efficiency of a heat engine:
Efficiency of a heat engine is defined as the fraction of total heat taken from the source which is converted into work.
Refrigerators in Thermodynamics:
A mechanical device that transfers heat from a colder to a hotter place is called a refrigerator.
Coefficient of a refrigerator:
The aim of a refrigerator is to extract heat from a cold body at the expense of some external mechanical work. The externally supplied work is known as the input and the heat extracted from the cold body is called the output.
Suppose, in each complete cycle, heat received by the refrigerator from the colder body at temperature T2 = Q2
Heat delivered by the refrigerator to the surroundings at higher temperature T1 = Q1
External work done = W
From the principle of conservation of energy, we can write,
W + Q2 = Q1
or, W = Q1 – Q2
From the definition of the coefficient of performance (e) of a refrigerator, we have,
e = output/input
= Q2/ W = Q2/(Q1 – Q2)