| Pulsed High Magnetic Field Device is important to science research on extreme condition. The cryogenic system of Pulsed High Magnetic Field Device is consist of liquid nitrogen system, liquid 4He system, super fluid helium system, 3He system, 3He-4He dilution refrigeration system, GM refrigerator and so on.This paper designs the 100L/h helium liquefaction cycle refrigeration system based on Collins cycle. Collins helium liquefaction cycle has its self characteristic in medium-sized helium liquefaction installation, which adopts two expanders and liquid nitrogen cooling, and has four cooling levels, in which, the first level of highest temperature is liquid nitrogen cooling, the level of lowest temperature adopts throttling valve, Others are two expanders working in different temperature area.This paper designs the processes of Collins helium liquefaction cycle device, discusses the characteristics and selections of the main thermal facilities(screw compressor, helium turbo expander). Heat exchanger is the key components of the cycle, the selection, design structure parameters effect and structural optimization of which were studied.The Giaque-Hampson type coiled finned-tubes heat exchanger is chosen for the heat exchanger of helium liquefaction cycle, the thermal design method and the structure optimization method for heat exchanger are presented in order to meet the require of miner pressure drop. The effects of structure sizes on the performance are analyzed in detail. Optimization design of the geometric parameter of heat exchanger is carried out using heat-transfer volume per temperature difference regarding the volume of heat exchanger as objective function. The optimized structure parameters are presented finally.The method to design and optimize the coiled finned-tubes heat exchanger may be adapted for the same type heat exchanger.
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