Refrigerator: Heat Engine
Almost in every house, we use the refrigerator for cooling of fish, meat, drinking water, ice cream etc and for preservation purpose. That means the machine by which lower temperature than the environment can be created and that temperature can be maintained stable is called refrigerator. How the foods can be preserved and maintained cool can be explained by its principle.
Principle: Refrigerator is considered as the inverse machine of the heat engine. The heat engine receives heat from higher temperature source and does work by a part of that heat and rejects the rest amount of heat into the heat sink at a lower temperature. On the other hand, a refrigerator receives heat from a source at a lower temperature and rejects heat into the heat sink at a higher temperature. In order to remove heat from the source at lower temperature mechanical work is to be done. A compressor in a refrigerator does this mechanical work. In this case sum of the removed heat Q1 and work, W is equal to the rejected heat Q2. In figure; the flow diagram of a refrigerator is shown. In the refrigerator used for a household purpose, Q1 is heat removed from the refrigerator by vaporization coil. W is the work done by the motor of the compressor and Q2 is the heat rejected in the air.