| The detection bands of low-temperature infrared detectors have developed towards long wave infrared,very long wave,and higher microwave bands with the development of the Earth,space science and reconnaissance technologies.The operating temperature range of the corresponding detector element is continuously reduced,from the liquid nitrogen temperature zone in the infrared band to the liquid hydrogen,liquid helium temperature zone and even near absolute zero degree.At the same time,the optical components and thermal insulation components of the detection system also need to be cooled to a lower operating temperature to ensure the detection accuracy of the entire detection system.If two single-stage refrigerators with different cooling temperature are used,on the one hand,the volume and weight of the entire refrigeration subsystem will be increased.On the other hand,single-stage refrigerators cannot efficiently reach the cooling temperature below liquid hydrogen.In response to such application requirements,research institutes at home and abroad have actively carried out research work on two stage pulse tube refrigerators.Two-stage pulse tube refrigerators have a variety of structures because of the two stage coupling arrangement and the boundary arrangement.The two stage thermal-coupled pulse tube refrigerator with single compressor developed by NGAS,USA(the cooling performance is 14.1 W @ 85 K,and 3.1 W @ 35 K with 500 W electric power input,the relative Carnot Efficiency was 10.7%)is the world leader in terms of refrigeration performance and volume performance,with light weight and high refrigeration efficiency.This article takes it as a prototype and combines the background of engineering requirements to carry out related theoretical and experimental research work on the two stage thermal-coupled pulse tube refrigerators.The specific contents include:1.Combining the thermoacoustic theory,the impedance matching method is used to indicate that the inlet pressure ratio of the first and second stage pulse tube is the key parameter of the thermal-coupled cryocooler.The enthalpy analysis indicates that the coaxial structure helps to improve second stage pulse tube cooling efficiency.2.Two wire meshes of 350 mesh and 400 mesh are custom-designed in combination with the wire mesh preparation process.The experimental results show that when the first stage pulse tube cold finger packed with the customed 350 mesh displace the original wire mesh(normal 300 mesh + 350 mesh),the relative Carnot Efficiency(calculated as acoustic power)increased from the original 18.8% to 21.26%,the cooling performance of second stage pulse tube cold finger filled with a customed 400 mesh and normal 500 mesh stainless steel mesh improved by 6.8% contrast with normal 400 mesh and normal 500 mesh stainless steel mesh filled.3.For phase shifting capability at the second stage pulse tube cold finger,the phase distribution and refrigeration performance of the two-segment room temperature inertance tube,the active room temperature displacer,and the pneumatic room temperature displacer are compared and analyzed.The experimental results show that the cooling performance of second stage pulse tube cold finger shifted by active room temperature displacer phase shifter is improved by 23.8% contrast with two-segment room temperature inertance tube phase shifter,and the pneumatic room temperature displacer can improve by 15.8%.4.A high efficiency coaxial two stage pulse tube cooler driven by one compressor was developed.With the hot end temperature kept at 300 K,the two stage pulse tube refrigerator can provide 1.47 W @ 30 K and 8.03 W @ 80 K cooling performance with 336 W electric power input,the relative Carnot Efficiency is 10.51%. |
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