refrigerant(redirected from Refrigerants)
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the working fluid of a refrigerating machine, which boils or expands, removing heat from an object to be cooled, and is then compressed, transfering the heat to a cooling medium, such as water or air.
Refrigerants must satisfy several requirements: they must have a low boiling temperature at pressures above atmospheric (to prevent air from leaking in), a moderate condensation pressure and temperature, a low freezing temperature and a high critical temperature, a high heat of vaporization for small specific volumes of the vapor, a low specific heat, and a high thermal conductivity. It is also desirable that they be flameproof, nontoxic, noncombustible, neutral with respect to building materials, and inert with respect to lubricants. Refrigerants may be divided into three groups according to their boiling temperature at atmospheric pressure: high-temperature (above – 10°C), medium-temperature (below – 10°C), and low-temperature (below – 50°C).
The principal refrigerants are ammonia, the Freons, and certain hydrocarbons. Ammonia is a medium-temperature refrigerant. It has the advantages of low cost and good thermophysical indexes. Its drawbacks include toxicity and the danger of explosion. Ammonia also has a destructive effect on copper and its alloys. Most Freons are nontoxic and noncombustible. They number over 50 different types and blends and include examples in all temperature groups. The most common are Freon-12, Freon-22 (medium-temperature), and Freon-13 (low-temperature). The hydrocarbons—ethane, propane, and ethylene—have a low freezing temperature but present an explosion hazard; they are used in large and intermediate-size refrigerating plants in the petroleum and gas industries. Water is used as the refrigerant in steam-jet refrigerating machines and absorption refrigerators operating on a solution of water and lithium bromide. In gas refrigerators, such gases as helium, hydrogen, nitrogen, and air usually serve as the refrigerant.
REFERENCEBogdanov, S. N., O. P. Ivanov, and A. V. Kupriianova. Kholodil’naia tekhnika: Svoistva veshchestv. Spravochnik, 2nd ed., Leningrad, 1976.
V. A. GOGOLIN