Theoretical And Experimental Investigations On The Four-stage Stirling-type Pulse Tube Cryocooler

In recent years,the rapid development of space detecting technology and superconducting technology require reliable and efficient cryogenic environment.The pulse tube cryocooler which eliminates moving component at its cold end,owns advantages of high reliability,low vibration,long lifetime,high efficiency and low EMI noise,and thus being welcomed in plenty of applications.The multi-stage pulse tube cryocooler can not only reach lower cooling temperature but also achieve multiple cooling capacities simultaneously.This paper introduces the work on the four-stage Stirling-type pulse tube cryocooler firstly in China,in which the theoretical and experimental investigations are included.The operating mechanisms of the four-stage Stirling-type pulse tube cryocooler will be studied in detail.The work will fill up the domestic blank of this area and lay the foundation of theoretical and experimental experience for promoting the independent application of the cryocooler in the fields of spaceflight and military.The main contents of this paper are as follows:1.The operating mechanisms and loss characteristics in the four-stage Stirling type pulse tube cryocooler will be clarified.The two dimensional CFD model of the fourth cold finger of the four-stage pulse tube cryocooler will be established,in which the three irreversible losses in the regenerator will be simulated.The effects of the ratio of mixed matrices in the fourth segment of the regenerator on the three losses will be analyzed,and the optimal ratio will be found.The effects of charge pressure and operating frequency on the pressure drop loss and the ineffective heat transfer loss will also be studied.The phase characteristics in the fourth cold finger will be studied based on the CFD modeling.The effects of the operating frequency and phase-shifter temperature on the phase distribution in the regenerator will be simulated.The optimal operating frequency and phase-shifter temperature will be determined according to the cooling performance of the fourth stage cold finger.2.The interactions of cooling performances among four stages of the four-stage pulse tube cryocooler will be investigated.The analytical model for the four-stage pulse tube cryocooler will be established.The relations among the cooling temperatures of the four stages will be studied,and the effects of input power,charge pressure and operating frequency on the cooling performance of each stage analyzed as well.Based on the theoretical analyses,the geometrical dimensions of the regenerator and phase-shifter of the fourth stage will be optimized.3.The mix-coupled arrangement of the four-stage pulse tube cryocooler will be studied.Based on the above work,a new design of the four-stage pulse tube cryocooler will be introduced and relevant optimizations conducted as well.The first two stages and the last two stages have gas-coupled arrangements,and then the two are thermally-coupled.Two linear compressors will be applied to drive the four-stage cold fingers.The working fluids of the first two stages and the last two stages are He-4 and He-3,respectively.4.The analytical model based on exergy theory for the four-stage mix-coupled pulse tube cryocooler will be established.Exergy analysis method will be used to clarify the operating mechanism of the mix-coupled four-stage pulse tube cryocooler.The exergy analysis model of each stage will be established,in which the mass distribution and exergy distribution between stages will be calculated.The effects of geometries of regenerator and pulse tube on the exergy distribution will be studied in detail.The effects of operating frequency and input power on the exergy distribution will also be clarified.The exergetic efficiency will be applied to evaluate the cooling efficiency of the gas-coupled stages.Then the cooling performance of the mix-coupled four-stage pulse tube cryocooler will be analyzed.5.The prototype of the four-stage Stirling-type pulse tube cryocooler will be introduced and corresponding experimental verifications conducted initially in China.The design,fabrication and assembling will be finished,and the experimental table set up as well.The effects of operating parameters of the compressor on the cooling performance of each stage will be investigated.The interactions among the four stages will be clarified.The cooling performance of He-4 and He-3 will also be compared while being used in the last two stage of the four-stage pulse tube cryocooler.The experimental results can verify the accuracy of simulated ones.According to the experimental results,the four-stage pulse tube cryocooler reaches no-load temperatures of 62.40 K,35.70 K,13.50 K and 4.23 K.While using He-3 in the last two stages,the cooling temperatures of the last two stages further reduce to 9.5 K and 3.3 K,respectively.The simultaneous cooling capacities of the four stages are 4.4 W at 70 K,1.0 W at 40 K,0.29 W at 15 K and 0.025 W at 5 K,respectively.The cooling performance of the four-stage pulse tube cryocooler has reached the international advanced level(LMATC designed a four-stage SPTC which reached 3.0 K and provided 0.29 W at 15 K and 0.025 W at 5 K,simultaneously).