Study on Gas Mixture in Micro Channel

为研究微通道内混合气体的流动，通过分析微通道内稀薄气体的Couette流动问题，确定了微通道内各组分混合气体的切向动量调节系数.将研究气体分子与壁面相互作用的分子动力学方法与研究气体分子运动的DSMC方法相结合。这些获得的调节系数被施加到通过微通道的气体混合物的流动作为麦克斯韦型边界条件，和表面的吸附物和气体浓度上的微通道的流量的影响进行了检查。模拟结果表明，混合气体的速度滑移和调节系数不同于单一气体。混合气体的摩尔浓度和壁面特性的差异导致了通道内流量的变化。此外，用气体-表面相互作用的分子动力学方法研究了氮分子在铂表面的散射行为。假设铂表面物理吸附氙分子。得到了在小范围内以指定速度撞击的分子在反射后的速度分布。散射分布表现出双峰行为，包括漫反射和分布转移到撞击分子的速度分布。本散射分布和Cercignani-Lampis-Lord散射核之间的比较显示出很大的差异。提出了一个简单的散射核使用双峰分布假设在每个速度分量的分布相互独立，并有利地比较到目前的散射分布。此外，还讨论了分子转动能的散射核。

To investigate flow of gas mixtures through micro channel in detail, the tangential momentum accommodation coefficients of each species for gaseous mixtures were determined by analyzing the Couette flow problem of a slightly rarefied gas between two walls. The molecular dynamics (MD) method for the interaction of gas molecule with the wall surface was combined with the DSMC method for the motion of gas molecules. These obtained accommodation coefficients were applied for the flow of gas mixture through the micro channel as the Maxwell-type boundary conditions, and influence of the surface with adsorbates and the gas concentration on the flow rate of the micro channel was examined. The simulation results showed that the velocity slip and the accommodation coefficients for gas mixtures differ from that for a single gas. The differences of the molar concentration of gas mixtures and wall characteristics leaded to variations of the flow rate in the channel. Furthermore, the scattering behaviors of nitrogen molecules reflected at a platinum surface were studied by the molecular dynamics method for the gas-surface interaction. The platinum surface was assumed to physically adsorb xenon molecules. Distributions of molecular velocities after reflection were obtained for the impinging molecules with specified velocities within a small range. The scattering distribution showed a bimodal behavior consisting of diffuse reflection and a distribution shifting to the velocity distribution of the impinging molecules. Comparison between the present scattering distribution and the Cercignani-Lampis-Lord scattering kernel showed large differences. A simple scattering kernel using a bimodal distribution was proposed assuming mutual independence of distributions in each velocity component and was compared favorably to the present scattering distribution. In addition, the scattering kernel of the rotational energy of the molecule was discussed.