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Refrigerants
Radical changes in the system of selection and use of refrigerants in response to environmental problems that have occurred over the past 25 years history which can be traced through the use of Refrigerant time Line (Fig. 3.1).
At the beginning of mechanical cooling air is used as the working fluid. Introduction vapour compression cycle enabled more compact and efficient systems. First, the only practical fluids were carbon dioxide and ammonia. One of the main requirements was preservation of meat on the long sea voy-30 years of New Zealand and Australia to Europe, and for ammonia was unsuitable due to its toxic nature. Carbon dioxide, although it requires a much higher pressures, was used. Methyl chloride, while toxic and very unpleasant, was used in some of the smaller systems.
Revolution came with the invention of chlorofluorocarbon (CFC) R12 on Midgley in the early 1930s.
This refrigerant and other members of the CFC family seemed to have all the useful properties. In particular, they were non-toxic, non-flammable, and with good thermodynamic properties of oil and compatibility characteristics. DCC R12, R11, R114 and R502 together with hydro chlorofluorocarbons (HCFC) R22 has become final refrigerants. They enabled the expansion of refrigerating equipment in commercial, domestic and Air conditioning sectors. Ammonia excellent thermal-dynamic properties and low cost for many industrial applications. Ecological problems of growth, development of replacements for chlorine-containing compounds.
A Summary Table (Table. 3.1) gives the basic properties of the main refrigerants used today together with their typical areas of application : low (-25 to 40C), medium (from -5 to -25C) and high (+10 to -5C) temperature.....
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