Physical Properties
The ideal refrigerant has favorable thermodynamic properties, is noncorrosive to mechanical components, and is safe (including nontoxic, nonflammable, and environmentally benign). The desired thermodynamic properties are a boiling point somewhat below the target temperature, a high heat of vaporization, a moderate density in liquid form, a relatively high density in gaseous form, and a high critical temperature. Since boiling point and gas density are affected by pressure, refrigerants may be made more suitable for a particular application by choice of operating pressure. The inert nature of many CFCs and HCFCs, while having the benefit of making them nonflammable and nontoxic, contributes to their stability in the atmosphere, and their corresponding global warming potential and ozone depletion potential. In the order of ozone depletion potential, it is generally from highest to lowest, Bromochloroflurocarbon such as Halon, CFCs then HCFCs.
Though HFCs and PFCs are non-ozone depleting, many have global warming potential that is thousands of times more than CO2. Other refrigerants such as propane and ammonia are not inert, and are flammable or toxic if released. New refrigerants have been developed that are safe to humans and to the environment, but their application has been held up by regulatory hurdles.
Read more about this topic: Refrigerant
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