A parameter-free physical model for gas–surface interaction

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Phenomenological gas–surface interaction models and various slip models are nowadays used as the boundary condition in the study of rarefied gas flows and microflows at the microscopic and macroscopic levels, respectively. However, most existing models depend on certain accommodation coefficients which are difficult to be determined prior to application. A physical-based gas–surface interaction model developed recently shows great flexibility and promising performance in capturing the complex gas–surface interaction process at the boundary. Particularly, the new model only employs three input parameters with clear physical meanings. In this work, a “bottom-up” approach for determining the input parameters of the model from the microscopic properties of the gas–surface system is explored. Because of the limitation of the estimation model for the local collision accommodation coefficient, this approach is restricted to light gas-heavy solid surface systems. Consequently, the physical-based gas–surface interaction model no longer involves unknown parameters like the accommodation coefficients in the traditional boundary conditions for rarefied gas flows. Benchmarked by molecular dynamics simulations of the non-isothermal gas–surface interaction process, the parameter-free gas–surface interaction model can accurately predict the reflected velocity distribution as well as the accommodation coefficients on the surface with different corrugation, binding strength, and relative stiffness. Its capability of capturing the influences of surface temperature and gas molecular mass on the gas–surface energy exchange is also demonstrated.