Exergy analysis and optimization of a hybrid cryocooler operating in 1-2 K based on the two-stage Joule-Thomson expansion

Theoretical and experimental investigations on a hybrid cryocooler with the two-stage Joule-Thomson (JT) expansion operating in 1-2 K are conducted. An exergy model is carried out to analyze the irreversibility of each component and to determine the maximum exergy efficiency of the JT cycle which provides the direction for potential improvements. Important operating parameters are calculated to evaluate the exergy destructions of the components as well as the whole system. The simulation results show that the JT cycle with two-stage expansion processes has higher energy and exergy performances than the single-stage system. The experimental results indicate that with two-stage JT expansion the hybrid cryocooler achieves the cooling capacity of 56.2 mW at 2.0 K with a gross input power of 398 W, the FOM is improved from 1.54% to 1.93%, and the exergy efficiency of the JT cycle is enhanced to 48.93% from 29.77% with the single-stage JT expansion. The good agreements between simulations and experiments are observed.