Read full document

Heat

Page 1 of 2
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...

Rate this document

What do you think about the quality of this document?

Share this document

Let your classmates know about this document and more at Studymode.com