The Influence of Gas–Wall and Gas–Gas Interactions on the Accommodation Coefficients for Rarefied Gases: A Molecular Dynamics Study

Abstract

Molecular dynamics (MD) simulations are conducted to determine energy and momentum accommodation coefficients at the interface between rarefied gas and solid walls. The MD simulation setup consists of two parallel walls, and of inert gas confined between them. Different mixing rules, as well as existing ab-initio computations combined with interatomic Lennard-Jones potentials were employed in MD simulations to investigate the corresponding effects of gas-surface interaction strength on accommodation coefficients for Argon and Helium gases on a gold surface. Comparing the obtained MD results for accommodation coefficients with empirical and numerical values in the literature revealed that the interaction potential based on ab-initio calculations is the most reliable one for computing accommodation coefficients. Finally, it is shown that gas-gas interactions in the two parallel walls approach led to an enhancement in computed accommodation coefficients compared to the molecular beam approach. The values for the two parallel walls approach are also closer to the experimental values.

Modeling rarefied gas-solid surface interactions for Couette flow with different wall temperatures using an unsupervised machine learning technique

“…The gas-gas and gas-solid interactions are modeled by the Lennard-Jones (LJ) potential and the potential parameters are listed in Table I. It is noteworthy to mention that in the atomistic study of the GSI, the pair potential parameters employed to describe the interaction strength at the gas-solid interface are of prominent importance [36,37]. It has been shown that the interaction potentials based on mixing rules cannot accurately describe GSI, and the quantum calculations based on pair potentials are the most reliable ones to study the GSI at the molecular scale [36,38,39].…”

“…It is noteworthy to mention that in the atomistic study of the GSI, the pair potential parameters employed to describe the interaction strength at the gas-solid interface are of prominent importance [36,37]. It has been shown that the interaction potentials based on mixing rules cannot accurately describe GSI, and the quantum calculations based on pair potentials are the most reliable ones to study the GSI at the molecular scale [36,38,39]. Therefore, in this work the gas-wall interaction potential parameters are calculated based on existing quantum ab initio computations [40].…”

“…To guarantee reliable statistics it is proceeded for the next 25 ns and 100 ns for Ar-Au and He-Au systems, respectively. More details regarding the gathering collisional data based on the discussed MD simulation setup can be found in our previous work [36]. All the MD simulations were performed using the LAMMPS [41] molecular dynamics package.…”

Nonclassical trajectories in head-on collisions

“…These effects will be more prominent at higher energies and must be accounted for by an inclusion of exchange terms in the Hamiltonian [35,36,37]. An even fuller approach would be to replace the Coulomb potential with more realistic interactions [38,39,40].…”

Editorial for the Special Issue “Selected Papers from the ISTEGIM’19—Thermal Effects in Gas Flow in Microscale”

“…Understanding gas–solid surface interactions under rarefied conditions is of primary importance for efficient modeling of gas flows and heat transfer in microsystems. Mohammad Nejad et al [ 1 ] used a molecular dynamics approach to simulate the behavior of two monoatomic gases, argon and helium, confined between two gold surfaces, kept at different temperatures in order to determine the corresponding energy and momentum accommodation coefficients. They showed that the pressure level has a minor influence on the accommodation coefficients value.…”