Study on the influence of distributed Joule-Thomson effect on the performance of microchannel cryocooler

Abstract

At present, the pros and cons of distributed Joule-Thomson (J-T) effect in throttling refrigeration systems have been controversial. In this paper, a microchannel J-T cryocooler is used as the prototype. The distributed J-T effect is produced by the friction loss in the throttling channel. The refrigeration performance of the cryocooler at 6.0 MPa is analyzed. Then, according to the dependence of the J-T coefficient on pressure and temperature, a fully distributed J-T effect microchannel is designed to replace the separate counterflow heat exchanger and throttling device on the high-pressure side. The characteristics are simulated and compared with the prototype. The results show that the refrigeration ability of the fully distributed J-T cryocooler is slightly inferior to that of the prototype under the same pressure drop, and excessively increasing or reducing the cross-sectional size of the channel is not conducive to cooling. However, the fully distributed J-T effect structure can effectively delay the occurrence of choked flow due to the low velocity of the fluid. Under 6.0 MPa inlet pressure, the limited mass-flow rate of fully distributed cryocooler is 7.51 g/s, and the lowest temperature can reach 147.7 K, which is significantly lower than 163.3 K that the prototype can reach in the choked state. In addition, this paper also explores the influence of distributed J-T effect on the low-pressure side, which is beneficial to precooling the high-pressure fluid more efficiently using a little distributed J-T effect. A proper part of the friction loss in the low-pressure channel helps improve the refrigeration ability. At 6.0 MPa inlet pressure, the best cooling effect is obtained when the pressure drops in the low-pressure channel account for 15.85 % of the total pressure drop.