Study of Gas Velocity Distribution in Electrostatic Precipitators

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Abstract
Turbulence and secondary flows influence particle transport and lower the efficiency of electrostatic precipitators. A theoretical expression of gas velocity is developed on the basis of the Navier-Stokes and Shaughnessy equations; this expression includes the effects of the corona discharge on the fluid field in the precipitators. The calculation results show that as the linear current density is increased, for positive corona discharge, the centerline velocity increases, but as the bulk velocity is increased, the effect of the corona discharge on the fluid field decreases. The centerline velocity at a linear current density of 1.8 mA/m is 72% for a bulk velocity of 1 m/s and 15% for a bulk velocity of 2.0 m/s, higher than the velocity at zero current density. The increasing centerline velocity has a detrimental effect on the collection efficiency of the precipitators. There is a good agreement when the theoretical expression compares with the laser-anemometry experiments of Leonard et al. Because the current density always perturbs the flow and its distribution may be determined by the electrode geometry alone, the electrodes should be designed to deliver a desired total current but to cause as minimal flow disturbance as possible.