Room-Temperature Machinery

Abstract

Compressors are required in cryogenic refrigeration systems for two distinct purposes: as part of the thermodynamic cycle of a liquefier or refrigerator, and as a means of storing a gas at room temperature; sometimes these functions can be performed by the same machine. The thermodynamic necessity for a compressor has already been made clear by implication in the last chapter. It is not merely there to push the working substance round the system, but in an internal-work system to raise the pressure of the working substance to a value such that at the precooling temperature the enthalpy is smaller than that at atmospheric pressure to the extent required to give the desired performance. In an external-work system the function of the compressor is to reduce the entropy — in this role Simon referred to compressors as “entropy squeezers.”