Design Study Of 4 K Stirling Type Pulse Tube Cryocooler With Precooling

The 4 K cryocoolers have many important applications for low temperature superconductors,helium liquefiers,space detector technologies and so on.Most of 4 K cryocoolers have the problems of low efficiency,big volume,heavy weight and periodical maintenance,such as Gifford-McMahon(GM) cryocoolers and G-M-type pulse tube cryocoolers(PTCs).Howerver,Stirling-type PTCs driven by linear compressors have the advantage of simple and compact structure,reduced volume and weight,high reliability and efficiency,and no maintenance,which makes it a very attractive candidate at liquid helium temperature.The mechanism of losses in 4 K PTCs is summarized at first.Those losses would be enhanced with the frequency increased.In order to improve the efficiency of 4 K Stirling-type PTC,comprehensive theoretical investigation of 4 K Stirling type PTCs has been carried out,which mainly includes the following sections:1.Research on staging configurations.Based on existing staging configurations of the 4 K GM-type PTCs,the possible schemes for 4 K Stirling-type PTCs are given. A novel cryogenic configuration coupling a single-stage Stirling type PTC with a two-stage G-M type PTC is proposed in this thesis.2.Design study of a 4 K Stirling type PTC with precooling.By combining the analysis and calculation of the thermal penetration depth of sphere packing and working fluid,and the performance of the linear compressor at different frequencies,the operating parameters for Stirling-type PTC in this design are determined. Based on the latest NIST numerical regenerator simulation software known as REGEN3.3,effect of regenerator length,mass flow rate,warm-end temperature, working fluid,pressure ratio,regenerator matrix and phase angle on the performance of regenerators of the 4 K Stirling-type PTC are calculated and analyzed.And the mechanism of 4 K regenerator losses is analyzed.The analysis shows that helium 3 in place of helium 4 can significantly improve the performance.GOS and Er_0.9Yb_0.1Ni mixture as regenerator matrix is the best choice in regenerators which hot end temperature is 10K and cold end temperature is 4K.Furthermore,a Stirling-type PTC is designed and fabricated based on the calculation.3.Cold inertance tube introduced.Because the acoustic power at cold end of 4 K regenerator is quite small,the inertance tube at ambient temperature can't supply well phase shifting.Considering the inertance effect of fluids will be enhanced at low temperature,ideal phase shift between pressure and mass flow at cold end of 4K regenerator would be possible given with cold inertance tube.Phase shifting mechanism of cold inertance tube is studied.And cold inertance tube is applied in our experiment system.