Numerical simulation and experimental study of DN1250 cryopump under different thermal conditions.

A large-scale cryopump (DN1250) used in large vacuum leak detecting system was designed and its performance experimentally investigated by Beijing Institute of Spacecraft Environment Engineering. The cryopump was cooled by four closed cycle helium refrigerators. Detailed numerical analysis of the heat transfer in the first stage array was performed by using computational fluid dynamic method (CFD). Several design parameters were considered to find the effect on the temperature distribution and the cooldown time. The variation of thermal conductivity and heat capacity with temperature was taken into account. The thermal analysis method based on numerical techniques was introduced in this study, the heat transfer in the first stage array and the second stage cryopanels were carefully analysed to determine important considerations in the thermal design of the cryopump. A performance test system according to the RNEUROP standards was built to test main performance of the cryopump. The experimental results showed that the structure of first stage array which was optimized by the method could meet the requirement of the cryopump well. The temperature of the cryopanels were down to 10 K within 300 min and the result of the experiment was accordant with theoretical conclusion of the analysis. The test also showed that the pumping speed for N2 of the pump was up to 5.8×104 L/s, and the crossover value was over than 3.0×105 Pa·L.