Control of fluid flow properties by the solid surface formation in a molecular scale

我们研究了壁面特性如何影响气壁相互作用，从而影响气体与固体表面的容纳性、作用于表面的应力、表面热流密度等。我们把铂表面当作固体壁，把氙气和氩气分子当作气体分子。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。考虑了三种壁面结构，即光滑表面、分子尺度的粗糙表面和分子尺度的凹槽表面。我们还考虑了带有吸附气体分子的壁面，得到了如下结果：切向动量调节系数为0。…在干净光滑的铂表面上，Ar分子多19个，Xe分子多0.81个。在光滑和清洁的表面上，动能调节系数分别为0.49和0.85。相应的实验值分别为0.55和0.858，与目前的数值相当。物理吸附Xe分子的壁面上Ar分子的能量调节系数为0.73，与实验值0.85非常接近。当铂表面具有分子尺度的粗糙度时，其切向动量调节系数和能量动量调节系数分别为0.74和0.37。研究发现，当墙体温差不大时，粗糙度较大的墙体表面表现出隔热的作用。当槽平行于壁面运动时，切向动量调节系数为0.37，垂直于壁面运动时，切向动量调节系数为0.55。较少

We investigated how the characteristics of walls affect the gas-wall interaction and accordingly the accommodation of the gas with the solid surface, the stresses acting on the surface, the thermal flux to the surface, etc.. We took a platinum surface as a solid wall, and xenon 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. Three cases of wall surface structure are considered, that is, a smooth surface, a rough surface in molecular scale and a grooved surface of molecular scale. The wall surfaces with adsorbed gas molecules are also considered.We obtained the following results : The tangential momentum accommodation coefficients are 0. … More 19 for argon molecule and 0.81 for xenon molecule, respectively, at the clean and smooth platinum surface. The accommodation coefficients of kinetic energy are 0.49 for argon gas and 0.85 for xenon gas at the clean and smooth surface, respectively. The corresponding experimental values are 0.55 and 0.858, respectively, and are comparable with the present numerical values. The energy accommodation coefficient of argon molecule at the wall surface on which Xe molecules are physically adsorbed is 0.73 and this value is quite close the experimental value 0.85. When the platinum surface has a roughness in a molecular scale, the tangential and energy momentum accommodation coefficients are 0.74 and 0.37 for argon gas, respectively. It is found that the wall surface with the roughness show the insulation effect on heat transfer when the temperature difference between two walls is not so large. The tangential momentum accommodation coefficient in case of the grooved wall is found to be 0.37 when the groove is parallel to the wall motion and 0.55 when it is set normal to the wall motion. Less