Three-Dimensional Molecular Dynamic Study on Accommodation Coefficients in Rough Nanochannels

Abstract

The tangential momentum and energy accommodation coefficients (TMAC and EAC) are parameters to characterize the velocity slip and temperature jump in the gas-solid interface. To understand the wall effects on fluid flow and heat transfer in nanochannels, the accommodation coefficients for argon gas molecules and platinum wall atoms were calculated according to a proper statistical algorithm using a three-dimensional molecular dynamic method. Isothermal flows and thermal conductions were simulated in smooth and rough nanochannels, in which the roughness ranged from 0.2 nm to 1.4 nm. From the atomic viewpoint, different lattice arrangements of smooth walls would induce atomic roughness to different extents on the surface, which affected the momentum and energy exchange in gas-wall interactions and resulted in different accommodation coefficients. In channels with nanoscale roughness, the possibility of multiple gas-wall interactions were further increased so that the TMAC and EAC became much larger with more roughness.

Simulation of the gas density distribution in the large vacuum system of a fusion-relevant particle accelerator at different scales

“…A value of 0.9 is suggested for light gases in some non-isothermal conditions [16]; results in literature show that the TMAC decreases furthermore with increasing kinetic energy of the particles [17,18]. Also, gases exhibit partially specular reflections in the case of hydrogen adsorption at surfaces [19].…”

“…The thermal model overestimates by 10% the TMAC calculated by Sun [17] with a different approach based on multiple gas particles simulation, and on a wall modeled as atoms vibrating around the lattice sites with Einstein frequency. The cut plane of the crystal structure also has an effect and the TMAC is higher on Pt(100) than Pt(111).…”

“…The EAC was also estimated in one case as reported in Table 5; for comparison, the EAC calculated by Sun [17] is 0.22 at 200 K. It is difficult to compare the simulation of ideal surfaces with experimental measurements, given the uncertainties associated with the surface conditions during the experiment. In literature, reliable data on EAC for clean surfaces exists for tungsten surfaces, while most experimental measurements available in literature for Pt surfaces suffer from lack of cleaning or poor documentation of cleaning procedures.…”

Determination of Thermal Accommodation Coefficients on CaSiO3 and SiO2 using Molecular Dynamics and Experiments

“…Due to the neighboring nanoparticle interfaces the attractive forces tend to overlap and increase, which leads to a higher adsorption potential and thus to a higher value of α. Apart from predicting the values of α, the influence of surface roughness [10], gas-wall interaction strength [11,12,9], gas molecular mass [12,13] and gas temperature [13] on α have also been studied using MD. Higher solid wall surface roughness increases the number of gas-wall collisions through interaction of gas molecules with the lateral edges of the solid atoms [9], thus increasing α values.…”

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

“…These coefficients can be fed into semi-empirical GSI models such as Maxwell's model [10] or Cercignani-Lampis-Lord (CLL) model [11] that can be employed as boundary conditions for higher-scale simulation techniques such as Direct Simulation Monte Carlo (DSMC) [12], Lattice Boltzmann method (LBM) [13], and method of moments (MoM) [14] to describe heat and mass flow at macroscopic level under rarefied condition. In literature there are various numerical studies in which MD simulations are employed to determine accommodation coefficients for different gas-solid surface combinations [15][16][17][18][19][20][21][22]. The general objective of all such investigations is to find the correlation between the energy and momentum accommodation coefficients and input parameters such as the gas temperature or purity, gas molecular weight (MW), surface condition (i.e., surface roughness, cleanness, temperature and chemistry), as well as the gas-surface interaction strength.…”