Numerical simulation of the second stage regenerator in a 4K GM cryocooler

In a 4K Gifford-McMahon (GM) cryocooler, the performance of the second stage is strongly dependent on the efficiency of the second stage regenerator. In order to improve the efficiency of the second stage regenerator, the internal dynamic parameters are analyzed by numerical simulation. It is found that the performance of a 4K GM cryocooler can be improved by shifting the temperature profile in the second stage regenerator to a higher level. The temperature profile in the second stage regenerator with an artificially reduced heat capacity of the regenerator material at the warm end is analyzed. Based on the simulation results, a novel and simple way, which is to replace the regenerator material at the warm end with a material having a lower heat capacity, is proposed. By reducing the heat capacity to 20 % of lead, the P-V power is increased by 7.9 W at the first stage and 1.8 W at the second stage. Correspondingly, the cooling capacity is increased by 9.0 W at the first stage and 0.13 W at the second stage. However, if the heat capacity is further reduced to 10 % of lead, the effect is reduced. The P-V power is increased by only 1.9 W at the first stage and 0.1 W at the second stage. The enthalpy flux from the regenerator is increased by 0.7 W at the first stage and 0.1 W at the second stage. Accordingly, the cooling capacity is increased by only 2.2 W at the first stage and 0.01 W at the second stage. The simulation results will be reported in this paper.