The hot-gas bypass control can effectively eliminate the harm of high pressure on auto-refrigerating cascade system

but it is useless for the regulation of mixed refrigerant composition.The four kinds of pressure and composition adjustment method with two bypass was put forward in connection with the characteristics of higher condensing pressure and exhaust temperature of three-stage auto-refrigerating cascade cycle.The condensing pressure was changed in regular fluctuations and the solenoid valve was opened and closed frequently for the hot-gas bypass regulation

and the refrigeration system was stable after 70 min.The cold lost seriously for vapor outlet bypass adjustment of phase separator Ⅱ

and the cold of refrigerant was discharged to the reservoir through the bypass line.The performance of the refrigeration system was very close to the vapor outlet bypass adjustment of phase separator Ⅰ and two phase separators

and the refrigeration cycle was stable after 30 min.The vapor outlet bypass adjustment of phase separator Ⅰ and two phase separators were the better pressure and composition regulation method of auto-refrigerating cascade cycle according to the study of the operating conditions of compressor and evaporator.