Multiscale study of gas slip flows in nanochannels
Résumé
A multiscale modeling of the anisotropic slip phenomenon for gas flows is presented in atree-step approach: determination of the gas–wall potential, simulation and modeling ofthe gas–wall collisions, simulation and modeling of the anisotropic slip effects. The densityfunctional theory (DFT) is used to examine the interaction between the Pt–Argas–wall couple. This potential is then passed into molecular dynamics (MD) simulationsof beam scattering experiments in order to calculate accommodation coefficients. Thesecoefficients enter in an effective gas–wall interaction model, which is the base of efficientMD simulations of gas flows between anisotropic surfaces. The slip effects are quantifiednumerically and compared with simplified theoretical models derived in this paper. Thepaper demonstrates that the DFT potential is in good agreement with empirical potentialsand that an extension of the Maxwell model can describe anisotropic slip effects due tosurface roughness, provided that two tangential accommodation parameters are introduced.MD data show excellent agreement with the tensorial slip theory, except at largeKundsen numbers (for example, Kn ’0.2) and with an analytical expression whichpredicts the ratio between transverse and longitudinal slip velocity components.