Experimental study on a two-stage large cooling capacity stirling cryocooler working below 30 K

Abstract

Developing superconducting technology and hydrogen energy system requires large cooling capacity devices working below 30 K. Two-stage Stirling cryocooler has the advantages of large cooling capacity, high efficiency, fast cool-down process, and compact configuration, etc. A two-stage Stirling cryocooler driven by crank-rod mechanism was developed and studied experimentally. The operating characteristics, including the cooling down processes, the pressure characteristics, the heat transfer characteristics of the ambient heat exchanger, and the cooling performances, are analyzed. Under 2.2 MPa charging pressure, a no-load refrigeration temperature of 15.84 K was obtained. With no heat load on the first stage, the cryocooler was capable of providing a cooling power of 138.1 W@30 K with a relative Carnot efficiency of 12.87 %, which is one of the best results of Stirling-type cryocoolers at present. Additionally, a cooling capacity of 47.4 W at 20 K with the relative Carnot efficiency of 6.44 % was achieved. During the cooling down process, an acceleration of cooling down rate of the second stage was observed, leading to a distinct acceleration phase of the declining rate of compression space’s mean pressure. It was found that the influence of the heat load on the first stage on the second stage’s cooling performance was not remarkable, and the cryocooler can provide around 131 W@30 K or 40 W@20 K cooling power on the second stage while the first stage can provide 100 W of cooling power at 75.01 K or 78.42 K, respectively. These experimental results have laid a solid foundation for a deeper understanding of the cryocooler’s operating mechanism and practical application.