基本型脉管内气体振荡制冷机理的分子动力学模拟

Molecular Dynamic Simulation of Gas-oscillation Refrigeration Mechanism in a Basic-type Pulse Tube

脉管制冷机在当今社会应用广泛,但目前对脉管内部气体流动的热力动态过程缺乏微观机理研究。本文采用分子动力学模拟方法,建立微通道模型,并对微通道内进行充气和放气,模拟脉管的压缩和膨胀过程,研究脉管轴向压力、密度、速度和温度随时间的变化。结果表明:随着过程进行,气体轴向的压力与密度梯度逐渐减小,直至达到平衡,但会出现微小的逆向梯度。膨胀和压缩过程在64 ps时,在微通道出口附近出现最大速度,分别为775 m/s和864 m/s,且随着反应的进行,最大速度处逐渐向压力低的方向移动。微通道内各点压力波与速度波的相位随位置而变。在压缩过程中,微通道内靠近封闭端温度较高,可高达500 K;远离封闭端温度较低,可降至223 K,膨胀过程则相反。一次循环温度场叠加时,在热端处,时间积分的平均值为375 K;在冷端处,时间积分的平均值为244 K,有利于热端向环境散热和冷端制冷。

Pulse-tube refrigerators are widely used in our society today,but research on the microscopic mechanism of the dynamic process of gas flow inside the pulse tube is lacking.In this study,the molecular dynamic simulation method was used to establish a channel model,and the channel was inflated and deflated to simulate the compression and expansion process of a pulse tube.Subsequently,with variations in time,the axial pressure,density,velocity,and temperature of the pulse tube were studied.The results show that the pressure and density gradient in the axial direction of the gas gradually decreased until a balance was reached when the process continued,but a slight reversed gradient occurred.Expansion and compression process occurred at 64 ps,and the maximum velocities near the channel exit were 775 and 864 m/s,respectively.As the reaction progressed,the maximum velocity gradually moved toward lower pressure.The phases of the pressure and velocity waves in the channel varied with the position.In the compression process,the high temperature of the channel near the closed end reached up to 500 K.Simultaneously,the temperature away from the closed end could be reduced to 223 K,and the expansion process was opposite that in the previous condition.The average time integral at the hot end was 375 K at the time of one temperature cycle superposition,and the average time integral at the cold end was 244 K.Thus,cooling of the environment at the hot and cold ends of refrigeration was facilitated.