Molecular dynamics simulations of energy accommodation coefficients for gas flows in nano-channels

Abstract

The energy accommodation coefficient (EAC) used in thermal boundary condition in micro-and nano-gas flows is reported to be always less than unity and greatly influenced by wall characteristics, for example, the wall temperature. A statistical EAC definition was described to calculate the EAC for thermal conduction in argon gas between two smooth platinum plates from two-dimensional non-equilibrium molecular dynamics simulations. The non-equilibrium EAC at the upper wall was calculated for different upper wall temperatures and a fixed bottom wall temperature. The equilibrium EAC at each temperature can then be extrapolated from a series of non-equilibrium EACs as the temperature difference between the two walls approaches zero. The analyses of the effects of wall temperature for various Knudsen number on non-equilibrium and equilibrium EACs show that, for a given lower bottom wall temperature, the non-equilibrium EAC at a high temperature wall increases with an increase in the wall temperature. For a given wall temperature difference, the non-equilibrium EAC increases with the increase in the wall temperatures. The equilibrium EAC also becomes larger at higher temperatures.

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

“…According to the Einstein model, wall atoms vibrate harmonically at the FCC lattice sites in x, y, and z directions, and the spring constant [20,21] is (8) in which m w is the atomic mass of the wall and is the reduced Planck constant. The Einstein temperature of platinum is T E = 180 K so that k = 179.5 N/m.…”

“…From the preceding definitions, the key point to calculate the accommodation coefficients is to distinguish between the incident and reflected molecules during the gas-wall interactions, which are detected and determined in the computational processes [20,21]. In MD simulations of gas flows, the short range force dominates in both the gas-gas and gas-wall interactions so that the intermolecular forces are cut off.…”

Flow Condensation Heat Transfer Characteristics of Nanochannels with Nanopillars: A Molecular Dynamics Study

“…Herein, the lattice constant a of 3.923 Å is set to be the unit size. To keep wall atoms vibrating at equilibrium positions, each Pt atom is regulated by the harmonic spring with the spring constant k of 179.5 N m –1 . , A channel that is formed between upper and bottom walls is filled with fluids. Ar atoms playing the role of the fluid are distributed randomly in the channel with the average density of 600 kg m –3 .…”

Effect of Surface Interatomic Potential on Thermal Accommodation Coefficients Derived from Molecular Dynamics

“…Kamat et al used a more refined ReaxFF reactive force field to account for the scattering of multiple gas species and to model chemical reactions between those species and carbon nanoparticles. Several other studies − used MD to model energy transferred when gases flow through nanochannels. Hu and McGaughey and Schiffres et al performed similar simulations but within multiwalled carbon nanotubes.…”