Theoretical And Experimental Investigations On The High Efficient Regenerator In The Stirling-type Pulse Tube Cryocooler Below 30K

In recent years,urgent needs for refrigeration below 30 K have been proposed in both the defence and the civilian fields.The Stirling-type pulse tube cryocooler?SPTC?becomes the main choice of above applications because of their advantages,such as high efficiency,small size,light weight,low comsumption,high reliability and long life.The regenerator to isolate the cold end from the hot end and to achieve a stable temperature gradient is the core of the SPTC.What's more,the irreversible loss caused in the regenerator usually accounts for an overwhelming proportion of the overall ones.According to the above background,in order to improve the efficiency of the SPTC,theoretical and experimental investigations on the high efficient regenerator in the single-stage,two-stage and three-stage SPTCs below 30 K have been conducted.The main contents and conclusions are as follows:?1?The properties and constructions of the common regenerator matrices are analyzed.The abnormal heat capacity of magnetic matrices in the low temperature is explained.The models of the wire mesh and grain are compared and the essential parameters are listed for the subsequest calculations.What's more,the effects of the frequency and charge pressure on the viscosity penetration depth of working fluid are presented.?2?A numerical method which can predict regenerator performance is established and its experimental validation is conducted.A two-dimensional regenerator model based on Brinkman-Forchheimer equations is established to obtain a model with fast speed and acceptable accuracy.Several important factors are considered,such as the real gas effect of helium,the pressure drop and the heat transfer of the regenerator.The theoretical results have been validated by the experiments.?3?Theoretical and experimental investigations on the high efficient regenerator in the single-stage SPTC below 30 K are conducted.To improve the performance of the SPTC,the different filling proportions of mixed matrices made of stainless steel?SS?screens are simulated and compared,and then the optimal proportion is suggested.The analyses are mainly focused on the cooling performance and the losses caused by the different entropy generations.The experiments are then conducted to verify the theoretical investigations based on a single-stage coaxial SPTC,in which the cooling characteristics with various frequencies and temperatures are tested and then compared with the analyses.The cooling performance can be enhanced based on the optimized mixed matrix,in which for a reject temperature of 300 K and an input electric power of 220 W,the SPTC has experimentally achieved the cooling capacity of 0.45 W at 30 K and a no-load temperature of 26.7 K.The performance is impressive considering that only the conventional SS matrices are employed and neither double-inlet nor multi-bypass phase-shifting approach is used.?4?Theoretical and experimental investigations on the high efficient regenerator in the two-stage SPTC below 20 K are conducted.In order to reach the temperature below 20 K,the regenerator can't work well with the pure SS screens.The SS screens filled in the segment near the cold end are replaced by the magnetic matrices which have larger heat capacity below 20 K.A design method is raised to determine the optimized grain diameter by both qualitative analysis and quantitative calculation.Both the pre-cooling position and the filling rate are also optimized at one time.The experiments show the no-load temperature of cryocooler decreases from 21.02 K to 17.4 K.When the cold end temperature is 30 K,the cooling capacity raises from 1.2 W to 1.72 W.?5?Optimization and experimental investigations on third stage of three-stage SPTC are conducted.The optimized first and second stages can provide 5.2 W@80 K and 1.72 W@30K for the third stage,respectively.According to the limited pre-cooling capacity,the regenerator and pulse tube of the third stage are designed and optimized.The parts of the third stage and installation process are introduced in detail.A two-dimensional CFD model for the third stage is established and its internal mechanism is analyzed.The results show a good agreement between simulations and experiments.The no-load temperatures for both simulations and experiments are 7.7 K and 8.9 K,respectively.?6?Theoretical and experimental investigations on the high efficient regenerator in the three-stage SPTC below 10 K are conducted and the developed three-stage SPTC with efficient regenerator has been built.Cryogenic phase-shifting and mixed regenerator matrices are employed to improve the performance of the third stage.Simulations of the phase relationship,dynamic pressure and mass flow rate are presented with third-stage phase-shifters pre-cooled at 40 K,50 K and 293 K,respectively.Mixed regenerator matrices of conventional stainless steel?SS?screens and rare-earth materials such as Er₃Ni,HoCu₂ and Er_0.6Pr_0.4 are optimized theoretically.Different ratios and combinations are analyzed and compared,and the quantitative analyses by the entropy analysis are made.A three-stage SPTC without external precooling is developed based on the theoretical analyses,and experiments were conducted.The results show a good agreement between simulations and experiments.With an overall input electric power of 370 W,the three-stage SPTC has experimentally reached a no-load temperature of6.82 K and achieved a cooling capacity of 112 mW at 10 K.