Molecular dynamics simulations of shear-driven gas flows in nano-channels

Abstract

Using the recently developed smart wall molecular dynamics algorithm, shear-driven gas flows in nano-scale channels are investigated to reveal the surfacegas interaction effects for flows in the transition and free molecular flow regimes. For the specified surface properties and gas-surface pair interactions, density and stress profiles exhibit a universal behavior inside the wall force penetration region at different flow conditions. Shear stress results are utilized to calculate the tangential momentum accommodation coefficient (TMAC) between argon gas and FCC walls. The TMAC value is shown to be independent of the flow properties and Knudsen number in all simulations. Velocity profiles show distinct deviations from the kinetic theory based solutions inside the wall force penetration depth, while they match the linearized Boltzmann equation solution outside these zones. Results indicate emergence of the wall force field penetration depth as an additional length scale for gas flows in nano-channels, breaking the dynamic similarity between rarefied and nano-scale gas flows solely based on the Knudsen and Mach numbers.

Molecular free paths in nanoscale gas flows

“…Figure 3a shows the velocity profiles for k = 1 flows in different height channels for ε wf /ε ff = 1. Same surface configuration was studied in our earlier work on sheardriven gas flows, where the tangential momentum accommodation coefficient (TMAC, α) for this surface/gas couple at ε wf /ε ff = 1 was calculated as α = 0.75 (Barisik and Beskok 2011b). In that study, we also validated TMAC values to be independent of the channel height, gas density, and Knudsen number.…”

Analytical solution of thermally developing microtube heat transfer including axial conduction, viscous dissipation, and rarefaction effects

“…For 0.1 b Kn b 10 flow is in transition regime (moderately rarefied). Finally, the flow is considered as free-molecular flow for large values of Kn (N10) (highly rarefied); the tool for dealing with this type flow is kinetic theory of gases, Direct Simulation of Monte Carlo (DSMC) [3] and Molecular Dynamics [4][5][6][7][8].…”

“Law of the nano-wall” in nano-channel gas flows

“…• Transport in the bulk and near-wall regions is determined by the gas-wall interaction parameter and the Knudsen number (Barisik and Beskok 2011b;2012, 2014, 2015.…”