Properties Of Refrigerant

The last decade has seen radical changes in the selection and use of refrigerants, mainly in response to the environmental issues of ‘holes in the ozone layer’ and ‘global warming or greenhouse effect’.

Previously there had not been much discussion about the choice of refrigerant, as the majority of applications could be met by the well known and well-tested fluids, R11, R12, R22, R502 and ammonia (R717).

The only one of these fluids to be considered environmentally friendly today is ammonia, but it is not readily suited to commercial or air-conditioning refrigeration applications because of its toxicity, flammability and attack by copper.

It will be useful to remind ourselves of the requirements for a fluid used as a refrigerant.

• A high latent heat of vaporization

• A high density of suction gas

• Non-corrosive, non-toxic and non-flammable

• Critical temperature and triple point outside the working range

• Compatibility with component materials and lubricating oil

• Reasonable working pressures (not too high, or below atmospheric pressure)

• High dielectric strength (for compressors with integral motors)

• Low cost

• Ease of leak detection

• Environmentally friendly

No single fluid has all these properties, and meets the new environmental requirements, but this chapter will show the developments that are taking place in influencing the selection and choice of a refrigerant.

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