Experimental study of the effect of air oscillations on vapor diffusion in a channel of variable cross-section and in a granular medium

Abstract

The diffusion of 2-propanol vapor in the air in a channel of variable radius and in a porous medium composed of spheres of equal diameter under longitudinal oscillations is experimentally studied. In the experiments, vapor concentration at the top and bottom of the channel (or porous medium) is constant. In the absence of oscillations, mass transfer along the channel (or porous medium) is carried out due to molecular diffusion. When air oscillations are imposed, additional mass transfer effects are activated, namely, Taylor dispersion and convective mass transfer due to steady vortex flows. In the studied range of frequencies and amplitudes, the total mass transfer exceeds molecular diffusion by one order of magnitude. In a channel of variable radius, mass is transferred mainly due to the steady vortex flows (convective mass transfer) arising in the viscous boundary layer due to the inhomogeneity of the amplitude of air oscillations in narrow and wide sections of the channel. In a porous medium, Taylor dispersion plays a major role while the convective mass transfer makes minor contribution.