Sedimentation Potential and Velocity of Solid Spherical Particles

Abstract

The electrical effects accompanying the steady fall of solid charged spherical particles under gravity in an electrolyte are examined theoretically. For a single particle falling in an infinite electrolyte, it is shown that, owing to fluid flow round the particle, the double layer field is modified. The effect in the double layer region is complicated, but outside this region a field is set up of the same form as that which would arise from a dipole fixed at the center of the particle with its axis vertical. A general expression is given for this dipole field in the case of nonconducting particles. The calculations extend previous work in that no restriction on the relative dimensions of the particle size and the double‐layer thickness is imposed. It is shown that the interaction between the charge on the particle and the modified field alters the sedimentation velocity of the particle. The calculations show that in practical cases the effect might, in favorable circumstances, reduce the velocity by a few percent. The analysis is extended to suspensions containing a large number of particles uniformly distributed.