Study On The Non-uniformity Of Regenerator Temperature In A Pulse Tube Cryocooler Working At Liquid Nitrogen Temperatures

With the development of high-temperature superconductivity technology,the demand for efficient and reliable low-temperature refrigeration equipment is also increasing.High capacity pulse tube cryocoolers have promising prospect in high temperature superconductivity cooling because of their compact structure,low vibration,high reliability and long working life.However,the non-uniformity of regenerator temperature in the high capacity pulse tube cryocooler has become one of the main problems impairing the efficiency and hindering the commercialization.In order to optimize the non-uniformity of regenerator temperature,experiments and theoretical studies have been carried out on the basis of a high capacity pulse tube cryocooler working at liquid nitrogen temperatures.A Sage model is build.The factors that affect the regenerator temperature non-uniformity are studied experimentally and theoretically.Besides,several methods are used to optimize the regenerator temperature non-uniformity,thus improving the refrigeration performance.The theoretical and experimental studies are carried out as follows:The influence factors of temperature non-uniformity in the regenerator are investigated based on the clue of heat transfer and structure asymmetry.Several working parameters and the structural factors of the related components that may affect the temperature nonuniformity are studied experimentally.The experimental results show that the change of working parameters only affects the degree of regenerator temperature nonuniformity but does not change the circumferential temperature distribution of the regenerator.The irregular structure of the regenerator packing and the position of the inlet and outlet of the aftercooler have great influence on the regenerator temperature non-uniformity.The regenerator temperature non-uniformity caused by the heat exchange nonuniformity in the aftercooler is analyzed theoretically based on a pulse tube cryocooler Sage model which has two parallel aftercoolers and regenerators.The uneven heat transfer of the working fluid in the aftercooler can induce the micro direct current in the regenerator.Under the positive feedback effect of flow resistance and temperature,the temperature difference of the same cross-section gas in the regenerator expands continuously,resulting in severe temperature non-uniformity in the regenerator.The influence mechanism of the uneven heat transfer of the aftercooler on the regenerator temperature non-uniformity is revealed,which provides a theoretical basis for the further optimization of temperature non-uniformity.On the basis of experimental investigation and theoretical analysis,the method of selective arrangement of heat exchanger tubes is proposed to optimize the regenerator temperature non-uniformity.The maximum circumferential temperature difference of the regenerator is reduced by more than 20 K and the non-uniformity is reduced by 10 K,and the refrigeration capacity increased by 20 W.It enriches the optimization methods of regenerator temperature non-uniformity,and provides a reference for future nonuniformity optimization and design of aftercoolers.At the same time,it is proved that it is feasible to optimize the temperature non-uniformity by filling high thermal conductivity copper wire mesh in the hot end of regenerator.