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

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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