A two-stage Stirling cryocooler capable of providing more than 100 W cooling power at 30 K

Abstract

Regenerative cryocoolers with large cooling capacity at 30 K have a promising prospect in the fields of superconducting technology and gas liquefaction. Compared with other types of cryocoolers, Stirling cryocoolers have the advantages of high cooling capacity, high efficiency, fast cool-down process and compact configuration. A two-stage Stirling cryocooler with large cooling capacity driven by the crank-rod mechanism is developed based on the Sage simulation results, and the preliminary experimental results are presented. Firstly, the pressure characteristics under different working conditions are investigated. The amplitude of the pressure and the pressure ratio at the compression chamber increases as the charging pressure increases. Increasing the refrigeration temperature of the second stage results in the decrease of the pressure amplitude, and the decreasing rate increases as the heat load on the first stage increases. Then, the performance of the ambient heat exchanger is studied. As the charging pressure increases from 2.2 to 2.6 MPa, the heat rejected from the ambient heat exchanger increases from 7.57 to 9.19 kW when there are no heat loads at the two stages of the cryocooler. The heat rejected from the ambient heat exchanger increases by 400 W with every increase of 0.1 MPa of charging pressure. With the increase of the refrigeration temperature of the second stage, the heat rejected from the ambient heat exchanger decreases, and the decreasing rate increases as the heat load on the first stage increases. Furthermore, the influence of the variation of the charging pressure and heat loads at the two stages on the cooling performance is introduced. The temperature of the second-stage cold end heat exchanger drops to 30 K at a nearly constant cooling rate after the startup of the cryocooler. As the charging pressure increases from 2.2 to 2.6 MPa, the cooling rate increases from 16.59 to 19.46 K/min, and the cooling rate increases by about 0.72 K/min for every increase in pressure of 0.1 MPa. Under the charging pressure of 2.6 MPa, the second stage of the cryocooler reaches a no-load refrigeration temperature of 19.83 K, while the temperature of the first stage is 71.2 K. The no-load refrigeration temperature has a weak relationship with the charging pressure. As the charging pressure increases, the increasing rate of cooling capacity and COP with the refrigeration temperature increases. The cryocooler is capable of providing 110 W cooling power at 30 K with a relative Carnot efficiency of 10.96%. This is the best result ever reported in China. What is more, it is found that the cooling power at the two stages has little influence on the cooling performance of each other, which means the cooling power from the first stage can be applied in the pre-cooling process with little influence on the second stage. These results lay a solid foundation for future applications and performance improvement of the cryocooler.