Research On Key Technology And Optimization Of A Thermal Coupled Three-stage Stirling-type Pulse Tube Cryocooler Working At 5～7 K

The booming development of space exploration technology in China in recent years leads to the emergence of advanced space detectors,which require the cryocoolers to provide much lower temperature,as well as low vibration and high reliability.Due to their advantage of high reliability,low vibration and good integration,Stirling-type pulse tube cryocoolers play important roles in the cooling of space detectors.During infrared astronomical observations,the midwave and longwave infrared bands are used to detect weak signals in complex cosmic environment with a temperature requirement of 5～7 K.At present,the cooling capacity of three-stage pulse tube cryocoolers in this temperature range is small and the cooling efficiency is generally low.The JWST telescope adopted the scheme of a three-stage pulse tube coupling J-T cryocooler to realize relatively higher cooling capacity under 6 K,but with the problem of complex system at the same time.Improving the cooling capacity and efficiency of multi-stage pulse tube cryocoolers in the temperature range of 5～7 K is an important foundation of cryogenic technology for China’s space infrared astronomy detection programs in the future.In this thesis,based on researches on the three-stage pulse tube cryocooler,much effort has been made to achieve a greater cooling capacity in 5～7 K.The specific work is as follows:1)The key variables of the pulse tube cryocooler in liquid helium temperature were identified,and the parameter designs of all three stages were carried out.To solve the complex problem of muti-parameters design and optimization of three-stage pulse tube cryocooler systems,the random forest algorithm was introduced based on the thermodynamic analysis.The importance evaluation and performance prediction of the characteristic parameters of the thermodynamic model of the pulse tube cryocooler were carried out,and the optimization scheme of three-stage pulse tube cryocooler in this study was put forward.Using the REGEN3.3 and other numerical calculation programs,the design and optimization on structural parameters of all stages in the pulse tube cryocooler were conducted in the order of “operating parameters-low temperature part of regenerator-high temperature part of regenerator-pulse tube-phase shifter”.2)The parameters of the regenerator and phase shifter in the 2nd stage pulse tube which cooling at liquid hydrogen temperature were optimized to meet the precooling demand of the 3rd stage pulse tube.Based on numerical simulation,the irreversible loss characteristics of regenerators with high mesh stainless steel wire mesh and magnetic particles as regenerative fillers were compared,and the cooling characteristics of pulse tube cryocoolers with these fillers at liquid hydrogen temperature were experimentally studied.The cooling performance and impedance distribution of the 2nd stage pulse tube with the active warm displacer and inertance tube as the phase shifter were compared,and the phase shifting strategy varying with cooling temperature was proposed.Finally,with a mixed filling mode of the regenerator and an active warm displacer as the phase shifter,a minimum temperature of 8.91 K was achieved in the 2nd stage pulse tube.Moreover,the cooling capacity at 15 K was more than 0.6 W,and the cooling capacity was more than 1.4 W at 20 K,which can meet the precooling requirements of the third stage pulse tube.3)Performance test and research on parameter coupling characteristics of the pulse tube cryocooler in liquid helium temperature were conducted.Numerical analysis and experimental research were carried out to clarify the specific effects of various factors on the coupling mechanism of regenerator filling modes,phase shifters,precooling temperatures and operating parameters in the pulse tube cryocooler cooling at 5～7 K.With the REGEN and Delta EC software,the influence mechanism of regenerator filling modes and parameters of the cold inertance tube on performance was systematically discussed.Based on the developed prototype of thermal coupled three-stage pulse tube cryocooler,the cooling performance test and the experimental research on the coupling characteristics between operating parameters and precooling temperatures were carried out.Experimental data samples were established,and the relevance and correlation between cooling performances and characteristic parameters were obtained through random forest algorithm and multivariate nonlinear fitting analysis.Within a total input power of 500 W,the three-stage pulse tube cryocooler prototype realized a minimal temperature of 3.96 K with He-4,and the maximum cooling capacity at 5 K,6 K and 7K were 24 m W,79 m W and 145 m W,respectively.The developed thermal coupled three-stage pulse tube cryocooler in this study can provide relatively large cooling capacity in 5～7 K,and the cooling efficiency is higher than the same type of pulse tube cryocoolers reported at home and abroad,providing a selection scheme and technical support for infrared astronomical exploration in China.