Electrostatic precipitation of airborne dust in the wake of a perforated plate

Abstract

An experimental investigation was conducted to determine the mechanisms by which electrically charged dust particles are collected electrostatically in the wake of a grounded perforated plate (or grid) placed at right angles to an airstream moving at about 180 cm s−1. The electric field was applied by means of a second perforated plate placed just downstream of the first and at high negative potential. Dust passing through the first of these two grids was collected on the downstream face of the first grid as a result of the electrical forces acting on the particles in the direction opposing the gas flow. A theoretical model for the collection mechanism describes how this is greatly assisted by the formation of eddy pockets in the wake of the first grid, and by the entrainment of dust particles into these eddies. Using industrial fly-ash samples, experimental measurements of collection efficiency as functions of applied grid voltage and dimensionless grid aspect ratio indicate that the theoretical model is basically correct.

Note On The Grid-Type Electrostatic Precipitator

“…In this case we call the mechanism vortex-enhanced electrostatic precipitation. A theoretical analysis of the simple 2-grid case based on this physical model 2 accounted satisfactorily for all the experimentally measured data, and clearly demonstrated that vortex-enhanced electrostatic precipitation was by far the most powerful contributing collection mechanism, outweighing straightforward back repulsion (i.e., electric field acting directly against the full mainstream force of the flowing gas) by an order of magnitude. Collection efficiency is dependent on electric field, gas velocity, grid solidity, particle size distribution and particle charge.…”

Experiments of fluid flow and heat convection in the wake of a disk facing a uniform stream

“…The pressure distribution was presented as a function of distance from the disk. Vincent [6] utilized the circulation of the wake for the development of the electrostatic dust precipitator.…”

“…Nu o = 0.81Pr 0.36 Re 0.5(6) at the upstream stagnation point andNu o,W = 0.34Pr 0.Re Stagnation point Nu number versus Re number in the wake region of the disk.…”

An experimental investigation of the detention of airborne smoke in the wake bubble behind a disk

“…Some experiments have been reported which investigated the electrostatic precipitation of charged dust particles on to the downstream surface of a metallic perforated plate placed perpendicular to a stream of dusty air (Vincent 1971). In order to explain the results a mechanism was invoked whereby charged dust particles passing through the holes in the plate were said to be entrained into the zones of recirculating air on the immediate downstream side of the solid portions of the perforated plate.…”