Multiple-needle corona electrodes for electrostatic processes application

Corona from high-voltage electrodes is employed in various electrostatic in stallations, such as ozonizers, air filters, powder sprayers, and separator s. Multiple-needle electrode designs are preferred whenever low corona onse t voltage and good resistance to mechanical shocks are required. This paper aims at identifying a simple solution to overcome the main drawback of thi s type of electrodes, the nonuniformity of the generated space charge. The experiments were carried out with various models of electrodes, having one or several rows of stainless steel needles. A current probe, consisting of an enameled copper wire (0.4 mm diameter), was embedded in the center of a plane collecting electrode. For a given interelectrode distance (5-50 mm) a nd a fixed position of the multiple-needle electrode, the collecting plate was translated along two orthogonal directions, so that the current probe c ould scan a 75 mm x 75 mm square. The results depended on the interelectrod e distance and on the high-voltage level. An explanation is given to some o bservations made on a roll-type electrostatic separator provided with two m odels of multiple-needle corona electrodes. An improved electrode design wa s proposed for the industrial installations.