Impact of surface physisorption on gas scattering dynamics

Engineering flow systems operating under low pressures and/or at the micro/nano scale generally include a physically adsorbed gas layer next to the surface. In this paper, we develop a scattering kernel that accounts for the effect of adsorption, arising from van der Waals interactions, on the dynam...

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Bibliographic Details
Published inJournal of fluid mechanics Vol. 968
Main Authors Chen, Yichong, Gibelli, Livio, Li, Jun, Borg, Matthew K.
Format Journal Article
LanguageEnglish
Published Cambridge, UK Cambridge University Press 27.07.2023
Subjects
Adsorption
Boundary conditions
Bulk density
Coefficients
Collisions
Equilibrium
Fluid mechanics
Gases
JFM Papers
Kernels
Molecular collisions
Molecular dynamics
Momentum
Physics
Scattering
Simulation
Surface chemistry
Velocity
molecular dynamics
kinetic theory
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Summary:Engineering flow systems operating under low pressures and/or at the micro/nano scale generally include a physically adsorbed gas layer next to the surface. In this paper, we develop a scattering kernel that accounts for the effect of adsorption, arising from van der Waals interactions, on the dynamics of molecules impinging on solid smooth surfaces. In the limit of low bulk density, surface adsorption becomes negligible and the scattering kernel recovers consistently the Cercignani–Lampis model, which best describes molecular collisions with a clean, smooth surface. In the limit of high bulk density, a dense adsorbed molecular layer forms next to the surface and its presence is picked up by the Maxwell model with complete diffuse reflection, which better captures the multiple collisions suffered by molecules. A weight coefficient based on the Langmuir adsorption isotherm is incorporated into the modelling to handle the transition between these two limiting conditions of low and high densities. The proposed model is validated against high-fidelity molecular dynamics simulations that are performed for a variety of gas–surface combinations and adsorbed molecular layers with different densities. It is shown that the proposed model very well captures the scattering patterns of beams of gas molecules at different velocities impinging on surfaces, as well as momentum and energy accommodation coefficients in the entire range of explored conditions.
ISSN:0022-1120
1469-7645
DOI:10.1017/jfm.2023.496