Effects of Concentration on the Stability and Efficiency of Inclined Super-Settlers

A linear stability analysis of the base-state convective flows, which occur when a sedimenting suspension is placed beneath an inclined wall, is performed. The spatial growth of small two dimensional disturbances at the clear fluid-suspension interface is determined over the entire range of the governing parameters through numerical solutions of the relevant Orr-Sommerfeld and Rayleigh equations. Two mechanisms for the growth of instability waves at the interface are identified. The results demonstrate that the base -state flow becomes more unstable as inertial effects in the base-state become more pronounced and thus, contrary to what has been suggested by earlier investigators, there is no restabilization as the base-state approaches the inviscid limit. Increasing the concentration of the suspension is predicted to have a stabilizing effect on the two-phase interface, particularly when inertial effects dominate the base-state. On the other hand, increasing the angle of inclination is found to enhance the stability of the interface when viscous forces are dominant in the base flow. The results are consistent with the experimental observations in our laboratory and those of other investigators.