Refrigerant
refrigerant is a compound used in a heat cycle that undergoes a phase change from a gas to a liquid and back. The two main uses of refrigerants are refrigerators/freezers and air conditioners. Cf. coolant.
The ideal refrigerant has good thermodynamic properties, is noncorrosive, and safe. The desired thermodynamic properties are a boiling point somewhat below the target temperature, a high heat of vaporization, a moderate density in liquid form, and a relatively high density in gaseous form. 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.
Corrosion properties are a matter of materials compatibility with the components used for the compressor, piping, evaporator, and condenser. Safety considerations include toxicity and flammability.
Early mechanical refrigeration systems employed sulfur dioxide gas or anhydrous ammonia, with small home refrigerators primarily using the former. Being toxic, sulfur dioxide rapidly disappeared from the market with the introduction of Freon. Ammonia is still used in some large commercial plants, well away from residential areas, where a leak will not cause widespread injuries.
Until concerns about depletion of the ozone layer arose in the 1980s, the most widely used refrigerants were the halomethanes R-12 and R-22, with R-12 being more common in automotive air conditioning and small refrigerators, and R-22 being used for residential and light commercial air conditioning, refrigerators, and freezers. Some very early systems used R-11 because its low boiling point allows low-pressure systems to be constructed, reducing the mechanical strength required for components. R-134a and certain blends are now replacing chlorinated compounds.
Use of liquified propane gas as a refrigerant is gaining favor, especially in systems designed for R-12, R-22 or R-134a.
The ideal refrigerant has good thermodynamic properties, is noncorrosive, and safe. The desired thermodynamic properties are a boiling point somewhat below the target temperature, a high heat of vaporization, a moderate density in liquid form, and a relatively high density in gaseous form. 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.
Corrosion properties are a matter of materials compatibility with the components used for the compressor, piping, evaporator, and condenser. Safety considerations include toxicity and flammability.
Early mechanical refrigeration systems employed sulfur dioxide gas or anhydrous ammonia, with small home refrigerators primarily using the former. Being toxic, sulfur dioxide rapidly disappeared from the market with the introduction of Freon. Ammonia is still used in some large commercial plants, well away from residential areas, where a leak will not cause widespread injuries.
Until concerns about depletion of the ozone layer arose in the 1980s, the most widely used refrigerants were the halomethanes R-12 and R-22, with R-12 being more common in automotive air conditioning and small refrigerators, and R-22 being used for residential and light commercial air conditioning, refrigerators, and freezers. Some very early systems used R-11 because its low boiling point allows low-pressure systems to be constructed, reducing the mechanical strength required for components. R-134a and certain blends are now replacing chlorinated compounds.
Use of liquified propane gas as a refrigerant is gaining favor, especially in systems designed for R-12, R-22 or R-134a.
posted by harbail | 2:12 AM
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