Study on a 20 K two-stage thermally-coupled pulse tube cooler with independent ambient displacers

Pulse tube cooler has the advantages of higher reliability and longer MTTF compared to Stirling cooler due to the elimination of moving components at the cold end. Pulse tube cooler working at liquid hydrogen temperatures has already become a strong candidate in sensor cooling, high-temperature superconductivity, etc. However, the efficiency of the pulse tube cooler at liquid hydrogen temperatures remains relatively low. In this paper, a two-stage thermally-coupled Stirling-type pulse tube cooler working at liquid hydrogen temperatures is designed and simulated. The first and second stage use independent ambient displacers as phase shifters. The simulation results show that the pulse tube cooler can reach a higher relative Carnot efficiency due to the improvement of the phase distribution of the whole system by using independent displacers. Meanwhile, the influence of factors such as average pressure and operating frequency on the system performance is also discussed.