A hybrid 3He Joule-Thomson cryocooler designed for precooling the space dilution refrigerator

Abstract

Space sub-Kelvin refrigeration technology is an indispensable part of many deep space exploration missions. The dilution refrigerator (DR) is one of the sub-Kelvin refrigerators used in space missions. The space DR requires a closed-cycle design for a longer service life. The 3He Joule-Thomson (JT) cryocooler is an excellent choice among the space mechanical cryocoolers for precooling the space closed-cycle DR (CCDR) because it can provide a stable, vibration-free precooling environment. In this paper, the required cooling capacity of the CCDR's final precooling stage is calculated. The design goal of the 3He JT cryocooler is to obtain 3.6 mW of cooling power at or below 1.7 K. A third-stage counter-flow heat exchanger (CFHX3) is designed for the 3He JT cryocooler with an actual heat exchange efficiency higher than 99 %. A four-stage JT compression system consisting of two oil-free linear compressors is developed based on space compressors verified by many space missions of China. The JT expansion impedance consists of two orifices with diameters of 27 μm and 26 μm in series. Then, experiments are conducted on the coordination of the CFHX3, the JT expansion impedance, and the JT compression system. Hence, a hybrid 3He JT cryocooler is successfully designed, fabricated, and tested for the CCDR and obtains a no-load temperature of 1.40 K with a power consumption of 277 W. Furthermore, with a power consumption of 320 W, the 3He JT cryocooler attains a cooling power of 3.75 mW at 1.54 K with temperature fluctuation lower than ±0.02 K.