Comparison Between Heat Engine, Refrigerator, And Heat Pump

heat flow in heat engine, refrigerator, heat pump
The coefficient of performance or C.O.P. is defined as the ratio of useful heating or cooling effect to work required. C.O.P. of heat engine, refrigerator, and heat pump is discussed below

Heat engine

Fig a shows a schematic diagram of the heat engine. The C.O.P. of an engine is express as its efficiency. Heat engine took Q2 amount of heat from the hot body and did work equivalent to WE. The heat supplied to sink is equal to Q1. Here the useful effect is Work done, WE., it is equal to Q2 – Q1
The C.O.P of heat engine, engine efficiency η= Work done/ Heat applied
η = WE/Q2
engine efficiency equation


Fig b shows a diagram of refrigeration. Q1 amount of heat is extracted from the cold body and deliver Q2 amount of heat to the hot body with the help of input work WR. Here Q2 = Q1 + WR. In refrigeration system the useful effect is the extraction of heat Q1, then the C.O.P of refrigeration is
COP refrigerator
- Coefficient of Performance and Relative Coefficient of Performance of Refrigeration Cycle
- Open and Closed Type of Refrigeration System – Advantages and Application

Heat pump

Fig c shows a schematic diagram of the heat pump. The heat flow is similar to the refrigerator; but in this case, the desired effect is the heat delivered Q2
Then the coefficient of performance of a heat pump is
COP heat pump
The relation between the COP of refrigerant and COP of heat pump
relation between COP of refrigeration and COP of heat pump

From the above equation we see that the C.O.P of heat pump is always greater than the unity
[ Prove the Coefficient of performance of heat pump always greater than one? ]

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