Research On Refined Simulation Key Technology For Space-borne Pulse Tube Cryocooler

Space infrared detection is an important method for ground and space information acquisition.The cryocooler is a key element of the infrared detection instrument.The Shanghai Institute of Technical Physics of the Chinese Academy of Sciences has conducted long-term research on dual-drive Stirling cryocoolers,pneumatic Stirling cryocoolers and pulse tube cryocoolers for space use,and currently there are 28 sets of cryocoolers in orbit.With the rapid development of space infrared detection technology in recent years,long-linear or large-format array large-scale infrared detectors with ten thousand pixels or even megapixels have been developed.The detectors can work in the short-wave,medium-wave,long-wave,and very long-wave band.Earth observation accuracy of the satellites reaches tens of meters in the geosynchronous orbit or sub-meter level in the sun-synchronous orbit.Series of networking satellites have developed to several stars in the high orbit,or dozens of stars in the low and medium orbit working at the same time for global detection,where a single satellite demands nearly 10 sets of cryocoolers.Thus,the space cryocoolers put forward the requirements of more cooling capacity,lower temperature,higher efficiency,lower vibration output and higher consistency.In this thesis,based on the in-depth understanding of the urgent needs of the applications,for the key technologies of core components of linear motor,regenerator and inertance tube,the simulation method for the inhomogeneous porosity and edged-gap when filling the regenerator and was proposed,and their effect on the performance was quantitatively analyzed.The simulation method and vibration suppression method for different structural linear motors,and the inertance tube adaptation optimization method for different heat rejection temperatures were also proposed.The key technologies in the refined simulation of the pulse tube cyocooler are studied in order to further improve the overall efficiency,reduce the vibration output,and thus achieve wider ambient temperature adaptation and higher consistency of performance in production.A comprehensive experimental facility for pulse tube cryocooler was established to verify the aforementioned three key technologies.Specific work is carried out as follows:1)Refined 2D/3D simulation models of the linear motor were established to improve the motor efficiency and to study the vibration output characteristics.The linear motor core loss and compressor vibration output are the key to the cryocooler efficiency and engineering applications.Theoretical analysis and experimental research were conducted respectively.Comparing the two states of soft magnetic material without slit and with uniform slit,the variation of iron loss with different input powers and excitation frequencies was analyzed.The difference between the experimental and simulated values of two-dimensional and three-dimensional simulation methods was compared.The axial vibration of a two-piston opposed compressor was investigated.The effects of inconsistent plate spring stiffness,kinetic mass,and magnetic induction strength on the first-order vibration of the motor on both sides,and the effects of the axial relative position of the kinetic on both sides on the second-order axial vibration force output were simulated and verified experimentally.Based on the study,the process improvement methods were proposed to reduce the first and second order vibration,and were verified experimentally.2)The influence of segmental porosity and edged-gap characteristics of regenerator was studied.The filling of the stainless steel wire meshes of the regenerator is the key to guarantee the performance of the cold finger.Theoretical and experimental studies were carried out on the segmental porosity and edged-gap characteristics in the filling process.The effect of uniform porosity filling and segmental different porosity filling on the refrigeration performance of the cold finger for 10W@80K was studied.When the inertance tube and the main structure of the cold finger remain unchanged,the low porosity filling in the low temperature section and high porosity filling in the high temperature section will cause deviation from the optimal impedance distribution of the cryocooler,which is not conducive to improve the refrigeration performance at lower temperatures.However,when the cooling temperature is higher,the impedance under segmented porosity filling is still in the optimal range,and will be beneficial to improve the cooling performance.At the same time,the study on the effect of the regenerator and cold finger performance under different edged-gaps was carried out.As the gap width in the middle of the regenerator increases,the regenerator losses increase and then results in lower cooling efficiency.3)The temperature characteristics of the inertance tube was studied and a wide range efficient phase adjustment at ambient temperature was achievedThe inertance tube is the main component to regulate the phase distribution of the pulse tube cryocooler.The inertance tube temperature in engineering applications varies by the environment temperature,which affects the phase shifting capability and the cooling performance.The impedances provided by the inertance tube at different rejection temperatures were simulated and analyzed to design the optimal length by minimizing the deviation from the optimal impedance distance.Three inertance tubes were optimized at 243 K,293 K and 313 K,respectively,and the experimental and simulation studies were conducted on the refrigeration performance of the cooler under different rejection temperatures for these three inertance tubes.The cooling performance of the cold finger deteriorates as the three inertance tubes deviate from their designed optimal rejection temperatures.The cooling performances are close when each inertance tube works at the corresponding optimal rejection temperature.When the rejection temperature changes,the optimal phase shifting at different rejection temperatures can be achieved by adjusting the length of the inertance tube,which is also verified by experiments.4)Optimized design of two pulse tube coolers based on the developed refined simulation method was carried out.Based on the improvement of the research method for the key technologies of the three components,the optimized designs were carried out for the development of two pulse tube cryocoolers,namely the PTC40-170 and PTC2-40.The parameters of the linear motor,regenerator filling and inertance tube length are optimized.After applying the refined simulation method on the engineering cryocoolers,the motor efficiency was significantly improved and the compressor vibration force output was reduced.Also,the production consistency of the cryocoolers was improved.