Finite Time Thermodynamics of Brayton Refrigeration Cycle
Most of the refrigeration cycles discussed so far involve change in phase of the working fluid (refrigerant) while undergoing through different stages. However, the gas refrigeration cycle is one in which the working fluid (refrigerant) remains as gas throughout the cycle, such as Brayton refrigeration cycle and Stirling/Ericsson refrigeration cycle. The gas refrigeration cycle deviates from the reversed Carnot cycle/vapour compression refrigeration (VCR) cycle because the heat transfer to and from the gas cycle is not isothermal. In fact, the gas temperature varies considerably during heat transfer processes. Consequently, the gas refrigeration cycle has much lower coefficient of performance (COP) as compared to the VCR and reversed Carnot cycle. Also, gas refrigeration systems have a number of important applications over the vapour compression, vapour absorption, and hybrid refrigeration systems. Some of them are used to achieve very low temperature for many important applications, such as liquefaction of gases/air, aircraft cabin cooling, superconductivity-related R&D works, and other specialized applications. Among others, the Brayton refrigeration cycle is one of the important gas refrigeration cycles being used for space airconditioning applications with its unique application for aircraft cooling, liquefaction of gases, and cryogenic applications.
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