Thermodynamics of low-temperature technology

The phenomena used for cooling gases in the region of low temperatures are described with regard to thermodynamics. They include the Thomson-Joule effect, adiabatic or polytropic expansion and the reduction of the temperature of the boiling liquid by exhausting its vapours. The practical operation and the principles of the individual liquefiers using the Linde, Claude, Kapitsa and Stirling thermodynamical cycles. The T-s diagrams of the said processes are given. The question is discussed of the cooling of superconducting magnetic systems by liquid helium. (J.B.)