Refrigeration and Liquefaction

Abstract

Refrigeration is accomplished in a thermodynamic process when the process fluid absorbs heat at temperatures below that of the environment. A process for producing refrigeration at cryogenic temperatures initially involves ambient compression of the process fluid and rejection of the heat of compression to a coolant. During the ambient temperature compression, which is normally assumed to be isothermal, the enthalpy and entropy of the process fluid decrease. The temperature of the compressed process fluid is then reduced through heat exchange with a cold fluid stream followed by an expansion. This expansion may take place either through a throttling device (isenthalpic expansion), where there is only a reduction in temperature when the Joule-Thomson coefficient is positive, or in a work-producing device (isentropic expansion), where both temperature and enthalpy decrease. At the cryogenic temperature where heat is absorbed, both the enthalpy and entropy of the process fluid increase. Before the process fluid is returned to the inlet of the compressor, it is warmed by heat exchange with the process fluid leaving the compressor.