Effect of gravity on Brownian flocculation

Abstract

In previous analyses of simultaneous Brownian and gravity-induced flocculation, it has been assumed that each mechanism contributes independently to the total flocculation rate. In this paper the rigorous problem of coupled Brownian and gravity-induced flocculation is considered for the case of strong Brownian/weak gravity effects. Using a singular perturbation expansion solution of the governing steady-state convective-diffusion equation, coupled flocculation rates are obtained. Comparison of the coupled rates with the rates found from the additivity approach show that additivity is justified only under very restrictive conditions.