稠密性对微尺度与稀薄气体流动相似性的影响

Effect of denseness on the similarity between micro and rarefied gas flows

基于Enskog稠密气体理论,通过考察密度对气体物性及流动特性的影响,分析了微气体流动与稀薄气体流动相似性成立的条件。结果显示,若微气体流动中需要考虑稠密性对气体物性和宏观流动参数的影响时,表征微气体流动和稀薄气体流动的3个量纲一的特征数(Kn、Re和Ma)不可能同时对应相等,两种流动不可能相似。研究了稠密性对微气体流动特性和输运系数的影响,同时,分别以基于稠密气体理论的声速相对偏差小于5%和基于热力学分析的压力相对偏差小于0.5%为限,计算得出各种气体在两种流动相似性失效时的密度值。

The similarity conditions for micro and rarefied gas flows were analyzed based on Enskog＇s dense gas theory, by investigating the influence of the gas densities on the physical properties and flow parameters. The results show that if the influence of the gas density on the physical properties and flow parameters has to be considered, the three dimensionless parameters （Kn, Re, and Ma）, which define the similarity between the micro and rarefied gas flows, can not all simultaneously be equal and, thus the micro and rarefied gas flows cannot be similar. The effects of dense gases on the flow parameters and transport coefficients were studied, with recommended density limitations for different gases calculated using dense gas theory with relative sound velocity deviations of 5% and relative pressure deviations of 0. 5% based on thermodynamics analyses. If the gas density is larger than the limit, the similarity between the micro and rarefied gas flows breaks down.