Solute transport by suspended buoyant particles

Abstract

The transport of a colouring solute, driven by the buoyant displacement of microscopic suspended particles, and in the absence of net flow, is studied experimentally in a Hele Shaw cell. Initially, a sharp interface between a transparent fluid without particles and an underlying coloured suspension is obtained. From this situation, the suspended particles rise, carrying the solute in the form of a fingering instability across the interface, where a light transmission technique is used to measure the local solute concentration. This one attains an asymptotic value that increases with the solid fraction ϕ of suspended particles, and decreases with the distance to the interface. The solute mass discharge also increases with ϕ, always being relatively small (< 3%). The onset and development of the instability as the mechanism driving the transport of the solute is discussed.