Analysis of flow characteristics through micro and nano channels with adsorbates.

从理论上研究了微通道和纳米通道壁面物理吸附其他气体分子时反射气体分子的特性。针对不同的表面特征，计算了气体分子对壁面的容纳量，以及壁面上的应力和能流。我们把铂表面看作是一面固体墙，把氮和氩分子看作是气体分子。考虑了Couette流动和两个温度不同的平行壁面之间的热问题。本文所考虑的壁温为300K。对于气体分子在两个壁面之间的运动，我们采用了DSMC方法，而对于气体分子与壁面之间的相互作用，则采用了分子动力学方法。考虑了壁面结构的两种情况，即分子尺度的光滑表面和凹槽表面。同时考虑了吸附气体分子的壁面，得到了不同沟槽方向的调节系数。吸附壁面上的这些值远高于清洁壁面上的值。计算值与实验值吻合较好。提出了一种新的壁面反射分子速度分布函数边界条件。也就是说，在每个速度方向上的分布是分开的，并且具有麦克斯韦尔型分布，并计算了调节系数。利用所提出的边界条件，对气体混合物的微通道流动进行了分析，阐明了吸附物对通道流量的影响

The characteristics of the reflected gas molecules were theoretically investigated when other gas molecules are physically adsorbed on the wall surface of micro and nano channels. The accommodation of gas molecules to the wall, and the stress and energy flux on the wall are calculated for various surface characters. We took the platinum surface as a solid wall, and nitrogen and argon molecules as gas molecules. The Couette flow and the thermal problem between two parallel walls whose temperatures are different each other are considered. The wall temperature considered in the present analysis is 300K. We apply the DSMC method for the motion of gas molecules between two walls and the molecular dynamics methods for the interaction between gas molecule and the wall surface. Two cases of wall surface structure are considered, that is, a smooth surface and a grooved surface of molecular scale. The wall surfaces with adsorbed gas molecules are also considered.We obtained the following results : the accommodation coefficients are different for different groove direction. These values on the adsorbed wall surface are much higher than those on the clean surface. The values calculated are in good agreement with the experimental values. We proposed a new boundary condition of the velocity distribution function for the reflected molecules at the wall surface. Namely, the distributions are separated in each velocity direction, and it has the Maxwell-type distribution with accommodation coefficient calculated in the present study. It was found that the proposed boundary condition well describes the flow behavior.Using the boundary conditions proposed, we analyzed the micro-channel flow of gas mixtures, and clarified the effect of the adsorbates on the flux through the channel