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A refrigerant is a substance or mixture, usually a fluid, used in a heat pump and refrigeration cycle. In most cycles it undergoes phase transitions from a liquid to a gas and back again. Many working fluids have been used for such purposes. Fluorocarbons, especially chlorofluorocarbons, became commonplace in the 20th century, but they are being phased out because of their ozone depletion effects. Other common refrigerants used in various applications are ammonia, sulfur dioxide, and non-halogenated hydrocarbons such as propane.〔Siegfried Haaf, Helmut Henrici "Refrigeration Technology" in Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, 〕 The ideal refrigerant would have favorable thermodynamic properties, be noncorrosive to mechanical components, and be safe, including free from toxicity and flammability. It would not cause ozone depletion or climate change. Since different fluids have the desired traits in different degree, choice is a matter of trade-off. The desired thermodynamic properties are a boiling point somewhat below the target temperature, a high heat of vaporization, a moderate density in liquid form, a relatively high density in gaseous form, and a high critical temperature. Since boiling point and gas density are affected by pressure, refrigerants may be made more suitable for a particular application by choice of operating pressures. == Refrigerant environmental issues == The inert nature of many halons, chlorofluorocarbons (CFC) and hydrochlorofluorocarbons (HCFC), with the benefits of their being nonflammable and nontoxic, made them good choices as refrigerants, but their stability in the atmosphere and their corresponding global warming potential and ozone depletion potential raised concerns about their usage. In order from the highest to the lowest potential of ozone depletion are Bromochlorofluorocarbon, CFC then HCFC. Though HFC and PFC are non-ozone depleting, many have global warming potentials that are thousands of times greater than CO2. Some other refrigerants such as propane and ammonia are not inert, and are flammable or toxic if released. New refrigerants were developed in the early 21st century that are safer for the environment, but their application has been held up due to concerns over toxicity and flammability. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「refrigerant」の詳細全文を読む スポンサード リンク
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