Acceleration of coagulation of particles in oil utilizing an a.c. electric field

Abstract

This paper describes an experimental investigation of the coagulation of particles in oil accelerated by the action of an a.c. electric field. The ultimate goal of the investigation is to develop a high-performance electrostatic filter for insulating liquids. In order to reveal the coagulation mechanism and find out the mechanical conditions suitable for the coagulation, the effects of various factors on the coagulation are investigated using spherical silica particles of 2, 4 and 6 μm in diameter. The coagulating state of the silica particles in oil is observed using a video-microscope with a CCD (charge coupled device) camera under various conditions. It is shown that the coagulation is better promoted with larger particles and that the particles having a small diameter are not easily coagulated. It is also shown that the oscillation amplitude relative to the double-layer thickness dominates the coagulation phenomenon. The experimental results suggest that when the surface charge on a particle and the charge in the surrounding double layer are appropriately polarized by the influence of the a.c. electric field, the coagulation is accelerated by virtue of a (relatively) strong attractive force acting between two-particle-double-layer pairs.

Keywords

electrostatic filtration a.c. electric field coagulation DLVO theory zeta potential electrical double layer polarization contamination control

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