Effects of DC flow on pulse tube cryocooler working at liquid hydrogen and liquid nitrogen temperatures

The direct current gas flow (DC flow), normally treated as a loss in the pulse tube cryocoolers (PTCs) in the past, has been found may be beneficial to the cooling performance of the PTC working at low temperatures recently. However, the reason why it can improve the cooling performance is still not clear enough. In order to reveal the working mechanism of the DC flow independently, simulation analysis and experiment verification are carried out on a two-stage Stirling type PTC without the double-inlet valve. Results indicate that in the second stage PTC working around 20 K, by introducing the DC flow with a positive direction from regenerator side to pulse tube side, the cooling performance will be improved due to the remarkable increase of the AC enthalpy flow in the pulse tube and the decrease of AC enthalpy flow in the regenerator. This is because with the help of positive DC flow, the temperature gradients in the pulse tube and the regenerator of the 20 K PTC are improved, i.e. the DC flow causes smaller heat losses in them. Nevertheless, the DC flow has no help on improving the cooling performance of the PTC working around 80 K. Simulation and experiment show consistency that with an optimized DC flow, the no-load refrigeration temperature of the second stage Stirling PTC drops 6–7 K, and the cooling capacity at 22 K increases about 1 W.