혼합냉매를 이용한 극저온 J-T 냉동기에 관한 실험적 연구

Abstract

The experimental study on the Joule-Thomson cryocooler for liquid nitrogen temperature with mixed refrigerant(MR) are described in this paper. The experiment was preformed with a single stage regular air-conditioning compressor. Mixed refrigerant was composed of 15% ㏖ of N₂, 30% ㏖ of CH₄, 30% ㏖ of C₂H6, 10% ㏖ of C₃H8 and 15% ㏖ of i-C₄H_(10). Oil mist in the MR stream could be eliminated completely through the series of oil separator and the house-made glass microfiber filter. In case of a traditional J-T refrigeration system (without bypass) with the mixed refrigerant, there occurred a fatal damage in a single stage compressor that had been designed for R22. Two main causes to this failure were considered as follows. First, the pressure ratio in the compressor was extremely increased at the beginning of the experiment. Second, the outlet temperature in compressor was higher than its limited temperature. For a stable operation of the compressor, a portion of the MR was by-passed at the inlet of the heat exchanger and transferred directly to the suction of the compressor in the modified system. The pressure ratio in J-T expansion device was gradually decreased due to condensation of the MR at low temperature. Therefore, the buffer volume at the suction was also used to increase the MR gas density in the system after the transient cool-down period. From the experiment with this modified system, the refrigeration could reach the lowest temperature of -152℃ without cooling load, and about -150℃ with 5W of cooling load.