Investigations on the coupling principle of the four-stage DC linear compressor unit used in a hybrid cryocooler operating in 1–2 K

Abstract

In a hybrid cryocooler developed for operating in 1–2 K, a four-stage DC linear compressor (DCLC) unit used in a Joule-Thomson cooler (JTC) is designed to provide the extremely low suction pressure of below 3.1 kPa. An equivalent non-linear dynamic model is proposed to analyze the gas spring force within the cylinder, and the coupling principles among stages of the DCLC unit are analyzed and summarized for the optimal design. In a standalone test platform, the experimental results show that the designed four-stage DCLC unit can provide a suction pressure of 2.1 kPa, for which a total pressure ratio (TPR) of 102.5 is reached with a pressure ratio loss (PRL) of 13.4%. Furthermore, in the actual hybrid cryocooler, the acquired values of suction pressure, TPR and PRL are 1.75 kPa, 101.7 and 14.1%, respectively, which is of great significance for the hybrid cryocooler in achieving 1.8 K. The rationality and feasibility of the coupling principle are experimentally verified.