Thermal Performance of a 4 K High-frequency Pulse Tube Cryocooler with Different Working Fluids

The high-frequency pulse tube cryocooler (HPTC) represents a promising miniature cryocooling technology due to its compact structure and the absence of low-temperature moving components. However, limited to the non-ideal gas effect of ⁴He, the HPTC is hard to obtain high cooling performance in the liquid helium temperature range. ³He as the working fluid can effectively improve the cooling performance of the HPTC, but the high cost hinders its wide application. In consideration of both cooling performance and cost-effectiveness, this paper explores the feasibility of utilizing ³He-⁴He mixtures as the working fluid for HPTCs. Firstly, the experimental results of a developed HPTC based ⁴He are reported. With a total power consumption of 575 W, the lowest temperature of 3.26 K was observed. And the measured cooling power at 4.2 K was 20.8 mW. Then the theoretical utmost efficiency of the cryocooler was calculated in terms of the thermophysical properties of the working fluids, using ³He-⁴He mixtures with different compositions as the working fluids. The whole machine modeling of the HPTC was further carried out, and the influence of the working fluids with different components on the structural parameters such as double-inlet and inertance tube, and operating parameters such as pressure and frequency were analyzed. The calculated results show that the cooling power is expected to be increased to 36 mW and 53 mW if the equimolar ³He-⁴He mixture and pure ³He are used, respectively.