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Heat

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A refrigerator is a cooling device meant to keep substances at temperatures lower than the outside temperature, as low as 2 to 3 °C.  A refrigerator works on the basic principle of heat transfer like a heat engine. While a heat engine takes in heat from a higher  temperature, expends some of it for doing work and rejects the  remaining as exhaust at a much lower temperature, a refrigerator does  quite the converse. It takes in heat from a body making it cold, has  work done upon it and rejects the heat at a much higher temperature. A heat pump as the name suggests, is a device which can pump heat in or out from an enclosure like a room. It is very similar to that of a refrigerator, the only difference being that it takes in heat from a cold reservoir like the outside air and passes it to a room at a higher, suitable temperature. It can also operate vice versa by introducing a valve where the process of cooling or heating can be adjusted. Theoretically, a refrigerator should be able to work like a heat pump. However, it has its own possibilities and limitations which shall be discussed in this essay.  A schematic diagram of a refrigerator is shown in the Appendix. The working of a refrigerator comprises of four major steps namely – evaporation, compression, condensation and expansion. A chemical called a refrigerant is used in this process to remove the heat from the refrigerator. Refrigerants must have certain specific properties – they must be easily liquefiable, they must have low specific heat capacities, they must be non-toxic, non-flammable and non-reactive with foodstuff etc. The first refrigerants used were ammonia, ether and chemo gene a mixture of petrol ether and naphtha.  However, nearly all were toxic, flammable and reactive. Thomas Midgley made a new species of compounds from fluorine called Chloro-Fluoro Carbons (CFC). They were non-toxic, non-flammable and removed large quantities of heat from the refrigerator and were ideal...