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

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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