Influence of gas-solid kinetic energy exchange processes on gas effusion from slitpores in non-equilibrium molecular dynamics simulations

The boundary-driven type non-equilibrium molecular dynamics (BD-NEMD) simulations have been carried out to clarify the influence of solid flexibility on gas effusion through a slitpore, by using a rigid solid model (R-model) and a flexible solid model (F-model). The LJ potential particles with parameters of argon are chosen for both the effusing gas molecules and the solid atoms. It is found that the R-model combined with a velocity scaling technique provides a reasonable effusion flux, probably a maximum in magnitude, compared with the fluxes calculated from the F-model without a fictitious thermostat (a velocity scaling) for effusing molecules. In the F-model, temperature lowering has been observed at the pore exit, being enhanced with an increase in the strength of springs that unite the solid atoms. This observation indicates that the molecules escaping from the pore exit take the excess kinetic energy for evaporation from solid atoms or surrounding molecules, which results in the low exit temperature, and that the rate of gas-solid kinetic energy exchange decreases with increasing spring strength (i.e. decreasing solid flexibility). It is suggested that the effusion flux is influenced by two factors: the solid flexibility and the molar potential energy in the pore.