Optimization of the working fluid in a Joule–Thomson cold stage

Vibration-free miniature Joule–Thomson (JT) coolers are of interest for cooling a wide variety of devices, including low-noise amplifiers, semiconducting and superconducting electronics, and small optical detectors used in space applications. For cooling such devices, coolers are needed which have operating temperatures within a wide temperature range of 2–250 K. In this paper, the optimization of the working fluid in JT cold stages is described that operate at different temperatures within that range. For each temperature, the most suitable working fluid is selected on the basis of the coefficient of performance of the cold stage, which is defined as the ratio of the gross cooling power to the change in Gibbs free energy of the fluid during compression. In addition, a figure of merit of the heat exchange in the counter-flow heat exchanger is evaluated that depends only on the properties of the working fluid.