what is refrigerant?
A refrigerant is any body or substance,which acts as a cooling agent by absorbing heat from another body and substance.theoretically, any reasonably volatile substance which is liquid at the temperature desired in the evaporator can be used as a refrigerant,but in practice the choice is limited by factors such as toxicity,cos ,flammability,chemical stability etc.
there are two types of refrigerants,primary refrigerant & secondary refrigerant.
primary refrigerant:A primary refrigerant is one ,which is used in a recirculating cycle and is accompanied a change in state.during cyclic process it undergoes compression,condensation,expansion and evaporation.
secondary refrigerant: A secondary refigerant is one,which is used as heat transfer medium without a change of state but with a change in temperature.
many refrigerants have been used over the years and some of them have become obsolete and since replaced by newer refrigerants.some currently popular refrigerants are being phased out due to their damaging effect on ozone layer.conventional refrigerants are four types-
1.Inorganic 2.Azeotropes 3.Halocarbon 4.Hydrocarbon.
Ozone Depletion and Global Warming:
among these four refrigerant groups,some of the rfrigerants in the Halocarbon family have lost favour becouse of their negative impect on environmental issues.
Helocarbon refigerants contain one or more of the three halogens-chlorine,fluorine and bromine.these refrigerants are obtained by replacing one or more hydrogen atoms in a hydrocaron molecule.because of their great stability,fully halogenated compounds,such as chloflurocarbons(CFCs) persist in the atmosphere for many years and eventually diffuse into the atmosphere.the molecules of CFCs ,such as R11 and R12,contain only carbon and halogens contains contain chlorine and fluorine.
Once in the uper atmosphere,the CFC molecules break down releasing chlorine,which destroys ozone and causes Ozone Depletion.
In the lower atmosphere ,the CFC molecules absorb infrared radiation,which may contribute to the worming of the earth,this is called Global Warming.Substitution of a hudrogen atom by one or more of the halogens in a CFC molecules greatly reduces its lifelime in atmosphere and consequently its negative impect.These compounds are reffered to as hydrochlofluorocarbons(HCFCs).
So the ozone depleting refrgerants will be phased out as per decision of the Montreal protocol,an international treaty.
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