Study on Gas Mixture in Micro Channel

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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.