Creeping motion of charged particles around a cylinder in an electrical field

Abstract

A series of experiments is described which demonstrate how electrical forces can influence the slow motion of small charged particles around a circular cylinder. The tangential and radial components of particle velocity, as evaluated from motion pictures, are compared with predictions for the behavior of point particles in a gas traveling around a body as given by Oseen's theory. Cases are included where an uncharged and a charged cylinder are placed in an external electrical field, the direction of which is parallel to the gas flow far from the cylinder. The experimental results agree satisfactorily with the theory, except for the particle velocities attained during approach to the forward stagnation point of the cylinder. When there are attractive forces acting on the spheres in this case, an acceleration of particles is predicted theoretically near the cylinder at the forward stagnation point, but a deceleration is observed. The marked disagreement between theory and experiment in these particular results cannot be explained by the increased drag on the sphere as it approaches the cylinder or by the influence of electrical image forces. The presence of closed particle orbits was observed under some conditions at a location 90° downstream from the forward stagnation point. These circulations are predicted by the theory for regimes in which the electrical forces just balance the viscous forces acting on the particles.