Thermodynamics

choice of refrigerant depends on the situation at hand. Of these, refrigerantssuch as R-11, R-12, R-22, R-134a, and R-502 account for over 90 percent ofthe market in the United States.Ethyl ether was the first commercially used refrigerant in vapor-compressionsystems in 1850, followed by ammonia, carbon dioxide, methyl chloride,sulphur dioxide, butane, ethane, propane, isobutane, gasoline, and chlorofluorocarbons,among others.The industrial and heavy-commercial sectors were very satisfied withammonia, and still are, although ammonia is toxic. The advantages ofammonia over other refrigerants are its low cost, higher COPs (and thuslower energy cost), more favorable thermodynamic and transport propertiesand thus higher heat transfer coefficients (requires smaller and lower-costheat exchangers), greater detectability in the event of a leak, and no effecton the ozone layer. The major drawback of ammonia is its toxicity, whichmakes it unsuitable for domestic use. Ammonia is predominantly used infood refrigeration facilities such as the cooling of fresh fruits, vegetables,meat, and fish; refrigeration of beverages and dairy products such as beer,wine, milk, and cheese; freezing of ice cream and other foods; ice production;and low-temperature refrigeration in the pharmaceutical and otherprocess industries.It is remarkable that the early refrigerants used in the light-commercial andhousehold sectors such as sulfur dioxide, ethyl chloride, and methyl chloridewere highly toxic. The widespread publicity of a few instances of leaks thatresulted in serious illnesses and death in the 1920s caused a public cry to banor limit the use of these refrigerants, creating a need for the development of asafe refrigerant for household use. At the request of Frigidaire Corporation,General Motors’ research laboratory developed R-21, the first member of theCFC family of refrigerants, within three days in 1928. Of several CFCs developed,the research team settled on R-12 as the refrigerant most suitable forcommercial use and gave the CFC family the trade name “Freon.” Commercialproduction of R-11 and R-12 was started in 1931 by a company jointly formedby General Motors and E. I. du Pont de Nemours and Co., Inc. The versatilityand low cost of CFCs made them the refrigerants of choice. CFCs werealso widely used in aerosols, foam insulations, and the electronic industry assolvents to clean computer chips.R-11 is used primarily in large-capacity water chillers serving airconditioningsystems in buildings. R-12 is used in domestic refrigeratorsand freezers, as well as automotive air conditioners. R-22 is used in windowair conditioners, heat pumps, air conditioners of commercial buildings, andlarge industrial refrigeration systems, and offers strong competition toammonia. R-502 (a blend of R-115 and R-22) is the dominant refrigerantused in commercial refrigeration systems such as those in supermarketsbecause it allows low temperatures at evaporators while operating at singlestagecompression.The ozone crisis has caused a major stir in the refrigeration and airconditioningindustry and has triggered a critical look at the refrigerants inuse. It was realized in the mid-1970s that CFCs allow more ultraviolet radiationinto the earth’s atmosphere by destroying the protective ozone layerand thus contributing to the greenhouse effect that causes global warming.As a result, the use of some CFCs is banned by international treaties. FullyChapter 11 | 617