Free-molecular gas flow in microchannels with surface acoustic waves: Effect of mixture separation

Abstract

Present paper studies the possibility to separate gas mixtures in microchannels using surface acoustic waves (SAW). Considered flow regime is free-molecular and the problem is studied numerically using probe particle method. Two types of surfaces waves are considered, namely standing SAW (SSAW) and travelling SAW (TSAW). It was shown that TSAW and SSAW have qualitatively different influence on gas flow but demonstrate compatible separation efficiency. For both types of waves separation factor is shown to decrease with increasing ratio of wave length to wave amplitude and is shown to be negligible for values of this ratio around 10000 and higher. Separation factor also decreases with decreasing ratio of wave amplitude to channel height from 0.1 to 0.01 but almost does not change with further decrease. Using only one surface with SAW instead of two is demonstrated to approximately halve the magnitude of effect. Phase shift between upper and lower surfaces motion is shown to have negligible effect in general.