Phase-dependence of sorption-induced mass streaming in an acoustic field

A nonzero time-averaged mass flux is generated in oscillating flows due to phase-lags between the fluctuating velocity field and the diffusive transport. Herein, we demonstrate how, in addition, the acoustic phasing of a sound wave - the phase difference between pressure and velocity oscillations - interacts with material properties and geometry to affect the preferential transport of a "reactive" species undergoing reversible sorption. Experimental results illustrate how phasing affects the induced mass flux, its dependence on the diffusive and oscillation time-scales, and how they compare well with model calculations. The model is used to reveal the underlying mechanisms that generate the concentration gradient, vs those that dissipate it. This insight can assist the future development and design of acoustic gas separation processes.