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Power Engineering and Rerigeration 510 Refrigeration & Air conitoning, , , , , , 5.6.2 Desirable Properties of Refrigerants a, The ideal refrigerant should have the following properties, The boiling point should be low., Condensing pressure should not be more., Critical temperature should be high, The latent heat of vapourization should be low., Specific heat of liquid should be low., It should not have corrosive action with system materials., It should not be flammable and explosive., It should be non-toxic, Its leak should be easily detectable., 10. It should have satisfactory heat transfer coefficient,, 11. It should be easily available at low cost, [5.7 SELECTION OF REFRIGERANT FOR SPECIFIC APPLICATIONS, Selection of refrigerant is done by studying properties like thermodynamic properties, safe working properties,, physical properties. But choice of refrigerant is done mainly by considering, 1. Boiling Point:, Selected refrigerant should boil at evaporator pressure., 2. Freezing Point :, To maintain the low temperature in evaporator, it is necessary that selected refrigerant should not freeze under, evaporator temperature,, 3. Leak dete, Ideal refrigerant should not have leak tendency. Refrigerant selected have easy method of leak detection., 4, Safety:, Refrigerant selected should have safe working properties. Selected refrigerant should not have suffocation or, injury when mixed with air by leakage. It should be non-flammable, non-corrosive and should not have effect on, stored product., 5. Cost:, Selected refrigerant should satisfy the requirements of system at the same time it should be available at lower, cost easily,, ‘Ammonia is the cheapest refrigerant. R-12 is slightly cheaper than R-22., 6. Equipment type and size :, Manufacturer of refrigerant compressor pre-select the refrigerant for optimum efficiency of compressor so that, energy consumption will be less., 7. Applications :, For different applications different types of refrigerants are recommended. Few applications are, Domestic refrigerant, air conditioning plant, water cooler, window air conditioning,, automobile air conditioning, F22 Frozen food plants, food storages, display cases and for low temperature applications, ‘Ammonia and Brine | Ice plant, 5.8 CONCEPT OF GREEN HOUSE EFFECT AND GLOBAL WARMING, ‘Some of the heat absorbed by the earth from the sun is reflected back to the space thus not allowing the earth, temperature to rise above certain level. A film of gas envelopes the earth’s atmosphere. Certain gases known as, green house gases trap some of reflected heat, preventing it to reflect back to space causing increase in average, surface temperature of earth leading to Global warming, This is known as ‘Green house effect’ and the gases that trap, the heat are known as ‘Green house gases’. Thus, higher the concentration of green house gases in the atmosphere, will lead to warmer the earth surface., , Cn, , een aneene, , , , , , , , , , , , , , , , 1B4-a