Coagulation of particles in oil by an a.c. electric field (observation of the coagulation process under various mechanical conditions)

This paper describes an experimental investigation of the coagulation of particles in oil under the action of an a.c. electric field. The investigation is carried out to acquire fundamental data to develop an electrostatic liquid filter with higher performance. The coagulation process of spherical silica particles in oil is observed by tracking a certain particle arbitrarily chosen and using a video-microscope with a charge coupled device (CCD) camera under various mechanical conditions. The observations show that particles are coagulated by approaching one another, in particular, owing to the velocity gradient of flow and entering the region where attractive forces are exerted among them, and that the velocity gradient in the direction of the electric field is more effective for particles to be coagulated than that in the direction perpendicular to the electric field. The experiment shows that a certain frequency of the a.c. electric field at which the coagulation is most promoted exists, and that the frequency increases with increase in the strength of the a.c. electric field and the zeta potential of particles. The experimental results suggest that the mean amplitude of oscillation of particles in the direction of the a.c. electric field may dominate the degree of coagulation.