INTERACTION OF ELECTROSTATIC AND FLUID DYNAMIC FIELDS IN WIRE PLATE ELECTROSTATIC PRECIPITATORS

Gas flow through wire-plate electrostatic precipitators is influenced by a secondary flow of electrical origin known as electric wind. This phenomenon arises when significant momentum is transferred from corona-generated ions to the gas. Electric wind can produce turbulence and recirculation. This complex flow field was characterized in a simple, three-wire precipitator by flow visualization, electrostatic and fluid dynamic numerical modelling, and laser-Doppler anemometry (LDA). Velocity of seeded smoke was measured by two-component LDA. Coulomb effects were regionally eliminated by performing measurements along symmetry axes where the electric field and streamwise velocity component were mutually perpendicular. Coulomb drift velocities were also estimated from field charging theory to allow interpretation of measured transverse velocities. For a low inlet velocity (0.5 m/s), mean flow recirculation was evident and turbulence intensities as high as 50% were measured. Higher inlet velocities (1.0, 2.0 m/s) yielded no flow recirculation and lower turbulence levels that were polarity-dependent. Measured profiles of streamwise velocity showed that flow acceleration zones occurred upstream of each wire and also between wires near the collecting plate. The induced turbulence displayed significant inhomogeneity and anisotropy. A combined finite-element. finite-difference electrostatic model was developed to yield ion density and electric field distributions within the precipitator. These predictions were used to incorporate an electric body force into a two-dimensional, turbulent fluid dynamic model based upon the k-epsilon formulation. The model predicted recirculating mean flow and turbulent diffusivities that were consistent with the smoke flow visualizations and LDA measurements.