Simulation And Optimization Research On Linear Pulse Tube Refrigerator

With the development of cryogenic technology,pulse tube coolers stand out for their advantages of no moving parts at the cold end and high reliability,and have broad prospects in the fields of aerospace,low-temperature superconductivity,and military affairs.The flow condition in a refrigerator seriously affects the performance of the refrigerator.As the core component of the refrigerator,the optimization of the pulse tube structure is of great significance for improving the flow in the pulse tube and improving the performance of the refrigerator.Based on this,this paper has carried out simulation and optimization research on a single stage linear pulse tube refrigerator.The main research work includes:Firstly,a two-dimensional numerical model of a single stage linear pulse tube refrigerator was established,and the simulation results were compared with literature to verify the effectiveness of the model.On the basis of this model,the variation of operating frequencies from 30 to 80 Hz on the performance parameters,temperature field,and flow field of the refrigerator was studied.The simulation results showed that the optimal frequency of this refrigerator model was 60 Hz,and the inner diameter temperature difference of the pulse tube was small at the optimal frequency.Secondly,simulation models of cylindrical pulse tubes,gradually expanding and gradually shrinking conical pulse tubes were established,and the changes in performance parameters,multi-dimensional flow field,and temperature field of the refrigerator under three structures were analyzed.The results showed that the refrigeration performance of conical pulse tubes was higher than that of cylindrical pulse tubes,and conical pulse tubes could improve the temperature uniformity in the pulse tubes and reduce the impact of eddy currents.Based on the analysis results,a simulation and optimization study of the cone angle was conducted.The results show that with the increase of the cone angle,the refrigeration performance first increases and then decreases.With the increase of the taper angle of the tapered pulse tube,the eddy current on the right side of the pulse tube significantly decreases or even disappears,and the eddy current on the left side increases.The tapered type is the opposite.Therefore,there is an optimal angle to minimize the impact of acoustic flow within the refrigerator.Due to the loss caused by abrupt changes in the cross section of the conical pulse tube and heat exchanger,as well as the severe turbulence at the cross section,the refrigeration performance is relatively poor.Based on this,three different models of local conical pulse tube are proposed.The simulation results show that adding local conical pulse tubes on both sides of the pulse tube has the best structure,which can improve the radial temperature gradient in the pulse tube and reduce the impact of turbulence in the middle region of the pulse tube.Subsequently,the effect of the cone angle on heat and mass transfer in the pulse tube under the optimal structure was studied.The results showed that with the increase of the cone angle,the refrigeration performance first increased,then decreased,and then increased.The uniformity of the axial flow rate in the pulse tube also showed a trend of first increasing,then decreasing,and then increasing.As the angle increases,the eddy current intensity in the middle region of the pulse tube decreases first and then increases,and the eddy current intensity on both sides increases first and then decreases.Finally,the effects of operating frequency,piston displacement amplitude,and inflation pressure on the performance of gradually expanding conical pulse tube and local conical pulse tube refrigerators were studied.The results show that the refrigeration performance first increases and then decreases with the operating frequency,so there is an optimal frequency for the overall performance.The refrigeration performance corresponding to different piston displacement amplitudes and inflation pressures presents a monotonically increasing trend within the simulation range.However,the selection of piston displacement amplitudes requires consideration of the overall volume and compressor operating parameters,and the magnitude of inflation pressure requires consideration of factors such as safety and mechanical strength of the refrigerator.