Effect of shielded electrodes dimensions on corona charging systems

Dual-type corona electrodes, consisting of a thin ionizing wire attached to a larger radius metallic cylinder, both connected to the same high-voltage supply, are widely used to generate corona discharges in several electrostatic processes such as charging granular materials in electrostatic separation and charging of fibrous media in the manufacturing processes of industrial air filters. The principal aim of this work is to experimentally investigate the effect of geometric dimensions (width and height) of a ground-shielded wire-type dual electrode on the current to a nearby metallic plate. The experimental results of this work clearly show that the current intensity generated by the corona electrode is higher using a narrower shield width. Otherwise, as long as the lower limits of the shield exceed the horizontal axis of the ionizing wire, the shield height does not affect significantly the current intensity produced by the discharge. These experimental results are validated by a series of corona-charging tests of insulating granules in the belt-type electrostatic separator. The quantities of particles recovered in the electro-separator are higher in presence of the shield, with well-chosen dimensions producing the highest possible corona current. These results may help to formulate some recommendations concerning the design of this type of electrode configuration. As the shield increases the output current of the electrode and broadens the ionized field, the proposed arrangement may be very useful for various industrial electrostatic processes.