Research On Key Technology Of 20K Cryogenic Temperature Two-stage Pulse Tube Cryocooler

The high frequency pulse tube cryocooler has the advantages of little volume,simple structure and high reliability,so it has gradually became a hotspot in the field of cryogenic refrigerator.The continuous development of space detection technology has put forward new requirements for cryocoolers,for example,to achieve cooling temperature below 30 K and to provide cooling power at multi-temperatures.To this end,domestic and foreign research institutions have actively carried out much research work on multi-stage high frequency pulse tube cryocoolers.In cryogenic temperature range,the two-stage high frequency pulse tube cooler has a variety of optional structures due to different coupling methods,boundary arrangements and cold head arrangements,however,studies on the influence of the structural characteristics is not comprehensive.In order to achieve high compactness,high applicability in space and high cooling efficiency,theoretical and numerical researches on the temperature field coupling characteristics between the regenerator and the pulse tube are carried out,and this paper tries to recommend a better cold head arrangement of the two-stage pulse tube cryocooler from the prospective of cooling efficiency.Specific research includes:1)Research on design method of the two-stage high frequency pulse tube cryocooler.By analyzing the heat transfer characteristics and flow resistance characteristics between the helium and the filler in the regenerator,the design parameters of the two-stage pulse tube cooler and the selection of the regenerative packing in different temperature zones are determined.According to the advantages of each software,the structural parameters of the components are respectively designed.In REGEN3.3,the influences on COP,phase shifting,PV loss and pre-cooling power are analyzed to determine the length and diameter of the regenerator.In Sage,the influences on expansion efficiency and phase shifting are analyzed to determine the volume and aspect ratio of the pulse tube.In DeltaE,the influences on the PV power required at the inlet of the inertance tube are analyzed to determine the length of inertance tubes.2)Theoretical research on the temperature field coupling characteristics between the regenerator and the pulse tube in coaxial head.The temperature filed coupling characteristic is divided into two aspects,the effect of heat conduction on the pulse tube and that on the regenerator,and thermodynamic analysis is carried out respectively.The result shows that heat flow from pulse tube to regenerator has a positive effect on the cooling performance.A simple calculation formula of the radial heat transfers between the regenerator and the pulse tube is deduced.The influences of temperature filed coupling on the two-stage structure are discussed.It's found that the coaxial arrangement will result in the need of more pre-cooling power,and there be a possibility that the efficiency of the entire two-stage cooler will be reduced.3)Numerical research on the temperature field coupling characteristics with Sage model.The influence of parameters such as cooling temperature,input PV power,pre-cooling temperature and operating frequency are analyzed.The results show that the coupling of the temperature field can always improve the enthalpy flow at the cold end and the cooling capacity.If the cooling temperature is lower or the cooling power is smaller,the lifting effect will be more obvious,and the cooling capacity of the second stage at 30 K can be doubled.But the increase in the amount of pre-cooling power at intermediate heat exchanger will certainly offset the increase in the cooling efficiency of the whole cooler.Only when the cooling temperature is too high or the efficiency of the first stage is too low will bring to a decrease in the whole efficiency of the thermally-coupled two-stage pulse tube cooler.Finally,the coaxial arrangement is recommended for cryogenic temperature,multi-stage structure and low cooling capacity pulse tube coolers,which will effectively improve the overall cooling performance.4)Experimental research on thermally-coupled two-stage coaxial pulse tube coolers.The experimental results verify the feasibility of multi-software design method.Two linear compressors are used to drive the two stage cold fingers,and the second stage reached the minimum no load temperature of 22.03 K with operating frequency of 52 Hz.When the input power of the two compressors were 280 W and 123 W,the two-stage pulse tube cooler achieves cooling capacity of 8W@80K and 1.0W@30K,which can meet with the dual temperature cooling needs of Shanghai Observatory Space VLBI cooling receiver.It's found that the increase of pre-cooling temperature leads to the decrease of the second stage efficiency while the required input power of the first stage is reduced,and the highest efficiency of the whole cooler is achieved when the pre-cooling temperture is 90 K.