| With the development of high temperature superconductivity (HTS), high power pulse tube cryocoolers (HPPTC), benefiting for the characteristics of low vibration, high reliability and long maintenance time, are becoming the most potential cryocoolers in HTS applications for supplying hundreds of Watts at liquid nitrogen temperatures. Generally mental mesh screens are considered as the most important regenerative fillings in pulse tube cryocoolers, but another characteristics of flow distribution in alternative flow field are not noticed enough for mesh screens. However, there are notable multi-dimensional flow and heat transfer in HPPTCs, so that mesh screens in different positions have totally different behaviors. Especially mesh screens have non-ignored contribution for inhomogeneity suppression in HPPTCs. A HPPTC even could not cool down if the flow distribution is not considered.In this study, the mesh screens at both ends of the pulse tube and in the regenerator are focused, and the regenerative characteristics and effect on flow distribution are investigated. Aimed for a method of fast performance prediction of meshes and flow distribution mechanism, the theoretical and experimental studies are carried out as follows:1. The regenerative factor (Rf) is derivate as an index of the regenerative performance for meshes, based on the analysis of the loss and refrigeration mechanism of regenerators.The energy flows were detailed analyzed in ideal and real regenerators, the different losses and their weight functions in different operation conditions were summarized and discussed. The effective heat capacity (Cp) was derivate as an index by considering the heat penetration depth and thermal characteristics of meshes, and then Rf was derivate based on Cβ. Compared with others’ research, Rf is more accurate and can distinguish the meshes with more than 3% performance difference. Both simulation and experiments results proved the reliability of Rf in the range of 77-300 K.2. The effect of non-uniform porosity of mesh screens on inhomogeneous flow in regenerators were studied by CFD method, and the flow distribution in the pulse tube with mesh screens in direct current (DC) and alternative current (AC) field were simulated.Based on CFD method, the non-uniform porosity meshes were proved to be an inducement for the inhomogeneous flow in regenerators. And a model consist of a pulse tube, a hot end heat exchanger, and a part of the inertance tube was set up. The velocity and temperature fields in AC and DC flow fields are compared. The characteristics of meshes were studied for the affection on the flow distribution. Also, the thickness optimization for the jet flow inhibition was discussed.3. A high power stirling type pulse tube cryocooler was set up based on the global optimization design. The impedance match experiment, flow distribution experiment and the verification experiment for Rf were carried out.A design method with global optimization based on SAGE was propose, and a high power stirling type pulse tube cryocooler was set up working on 60Hz and 2.5MPa, aimed for 650W@77K. The impedance match between the cryocooler and the compressor was investigated, and the resonance frequency was decreased from higher than 100 Hz to 67.3 Hz. The no load cold end temperature was dropped from 280 K to 86.01 K by flow straighteners optimization. And with different combinations of 400#,500# woven mesh and the random fiber, the no load cold end temperature was dropped to 78.9 K with the optimized combination screens, the result agreed well with the Rf’s prediction and the reliability of Rfwas certificated in 77 to 300 K. |
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