Lattice Boltzmann simulation of separation phenomenon in a binary gaseous flow through a microchannel

Abstract

Gas separation of a binary gaseous mixture is one of the characteristic phenomena in the micro-scale flows that differ from the conventional size flows. In this work, the separation in binary gas mixture flows through a microchannel is investigated by the lattice Boltzmann method with a diffuse-bounce-back boundary condition, where the wall function approach with effective relaxation time is combined in consideration of the high Knudsen numbers. The separation degree and rate are measured in the He–Ar and Ne–Ar systems for different mole fractions, pressure ratios, and Knudsen numbers. The results show that the separation phenomenon in the He–Ar mixture is more obvious than that in the Ne–Ar mixture at the same mole fraction owing to the larger molecular mass ratio. In addition, the increase in the pressure ratio reduces the difference in the molecular velocities between the two species, and the separation phenomenon becomes weaker. However, the gas separation is reduced with an increase in the Knudsen number. This is because the resulting rarefaction effect reduces the interactions between the gas molecules of the two species and thus increases the difference in the molecular velocity.