Difference between Heat Engine

Heat Pump

and

Refrigerator

In this article we are going to have detailed study of difference between Heat Engine Heat Pump and Refrigerator.

Heat Engine:

Heat engine is a device which converts heat energy into mechanical work. In heat engine how much work is extracted from a given amount of heat is an important quantity.

    Q₁=W+Q₂    ⇒     W=Q₁-Q₂

Efficiency

or             

For Heat Engine,  W < Q₁  ⇒  η < 1

 

Heat Pump:

Heat pump is a device that transfers heat from a colder area to a hotter area by using mechanical/electrical energy, as in a refrigerator. Heat pumps may be used either to heat or cool. In heat pump how much heat is rejected at higher temperature is an important quantity.

Example: Room Heater

    Q₁=W+Q₂    ⇒     W=Q₁-Q₂

Efficiency(Coefficient of Performance)

or     

For Heat Pump,  Q₁ > W ⇒  η > 1

 

Refrigerator:

A refrigerator is a device which is designed to remove heat from a space that is at lower temperature than its surroundings. In refrigerator heat extracted from lower temperature is an important quantity.

    Q₁=W+Q₂    ⇒     W=Q₁-Q₂

Efficiency(Coefficient of Performance)

or 

Important: For refrigerator  T_H > T_L

⇒ β >1 , if T_H  ≤  2T_L

[ for T_H>2T_L , let T_L=5°C=278K, So 2T_L = 556K=283°C  , which is not possible.

Generally T_H and T_L difference is less than T_L, so β is always greater than 1 for refrigerator.]

[Example:-  let T_L=5°C=278K and T_H=25°C=300K , So T_H-T_L=300-278=22K<T_L(278K) ]

 

video lecture for Difference between Heat Engine Heat Pump and Refrigerator :-