Mechanical Refrigeration (Vapor Compression Cycle)

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BODY Mechanical refrigeration based on the vapor compression cycle was first demonstrated in the 1830s and for the next century a broad range of substances were used; these included toxic compounds, such as sulfur dioxide, as well as refrigerants still in widespread use, such as ammonia. The widespread adoption of home refrigerators in the 1930s spurred the development of nonflammable and low-toxicity refrigerants, and the CFC (chlorofluorocarbon) and later HCFC refrigerants dominated this “second generation” of fluids. Refrigerants are the working fluids in refrigeration, air-conditioning, and heat-pumping systems. They absorb heat from one area, such as an air-conditioned space, and reject it into another, such as outdoors, …show more content…

There is no single setoff optimum characteristics (especially for thermodynamic properties), and often there are tradeoffs among desirable characteristics. Thus, a variety of refrigerants having a range of properties is needed to meet the requirements of various applications. A broad range of fluids has been used as refrigerants over the years, and current usage is dominated by a range of fluorinated chemicals, known as HFCs, in addition to hydrocarbons and several inorganic compounds, including ammonia and carbon dioxide …show more content…

The thermodynamic characteristics (most importantly normal boiling point, critical temperature, and heat capacity) must be matched to the application for the system to operate efficiently. Here there is no single set of optimum values, and a variety of refrigerants having a range of properties is needed to meet the requirements of various applications. Favorable transport properties (low viscosity and high thermal conductivity) have an impact on the size of the heat exchangers and thus cost of the overall system. Energy efficiency, along with the ozone depletion potential and global warming potential are key environmental criteria. Environmental impacts related to ozone depletion drove the phase out of the CFC and HCFC refrigerants. Global climate change concerns have focused attention on the HFC refrigerants. The atmospheric lifetime of a refrigerant affects both ODP and GWP; low values are associated with short atmospheric lifetimes. Here there is often a direct conflict between the need for chemical stability (within the sealed refrigeration system) and the need for chemical breakdown if a refrigerant is released to the

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