Molecular Dynamics Study on the Thermodynamic Process of Self Oscillation of Micro Air Mass in the Pulse Tube at Different Temperatures

Abstract

采用分子动力学方法模拟了脉管中微气团在300~10 K温度范围内压比为12/6 bar时的自振荡过程，获得了不同温度下自振荡频率、冷、热端最大温差与冷端最低制冷温度。研究结果表明，随着初始温度的降低，自振荡周期时间呈幂指数增长，微气团冷、热端温差及最大温降也逐渐降低，因而，脉管的最佳运行频率是由自振荡周期而决定的。此外，温度和压力波自振荡强度随自振荡进行而衰减，且温度越高衰减速度越快，因而时均最低制冷温度与运行频率相关，考虑到沿脉管的温度梯度分布，单级脉管的冷、热端温差不宜过大，否则不能兼顾冷、热端的最佳运行频率。显然，级数越多，制冷效率越高，同时，高温级宜采用高频，低温级宜采用低频，以提高制冷效率。给出了脉管降温温差、最佳工作频率随制冷温度的变化曲线。The molecular dynamics method is used to simulate the self oscillation process of the micro air mass in the pulse tube when the pressure ratio is 12/6 bar in the temperature range of 300 - 10 k. The self oscillation frequency, the maximum temperature difference between the cold end and the hot end and the minimum cooling temperature at the cold end are obtained at different tempera-tures. The results show that with the decrease of the initial temperature, the time of the self oscil-lation period increases exponentially, and the temperature difference between the cold and hot ends of the micro air mass and the maximum temperature drop decrease gradually. Therefore, the optimal operation frequency of the pulse tube is determined by the self oscillation period. In addi-tion, the self oscillation intensity of temperature and pressure wave decays with the self oscillation, and the higher the temperature is, the faster the decay speed is. Therefore, the average minimum cooling temperature is related to the operating frequency. Considering the temperature gradient distribution along the pulse tube, the temperature difference between the cold end and the hot end of the single-stage pulse tube should not be too large. Otherwise, the optimal operating frequency of the cold end and the hot end cannot be considered. Obviously, the higher the number of stages, the higher the refrigeration efficiency. At the same time, high frequency should be used for high temperature stage and low frequency should be used for low temperature stage to improve the refrigeration efficiency. The curves of the temperature difference and the optimal working frequency of the pulse tube with the cooling temperature are given.