Particle Dynamics in an Electrohydrodynamic Flow Field investigated with a two‐component laser‐doppler velocimeter

Abstract

A laser-Doppler instrument has been used to measure the migration velocity of NaCl particles in an electrohydrodynamic flow field of an electrical precipitator. The measured average migration velocity of 1.40-pm particles (number distribution median with a geometric standard devitation of 1.46) is approximately five to six times higher than the calculated steady-state velocity for a 1.40-pm particle, provided there is a saturation charge of at least 90%. Further, the particle velocities in the main flow direction are also influenced by the electrical operation conditions. Both observations demonstrate the important role of the state of the electrohydrodynamic flow field (superposition of moving gas ions and neutral gas molecules) on the particle transport, characterizied by the dimensionless electrohydrodynamic number N,,,. A comparison between six different electrohydrodynamic states revealed that N,,, = 1 is a critical value for the mutual interactions between the gas ions and the neutral gas phase. Whereas for NEHD values >1 the stochastic particle motion is chiefly determined by the nonsteady-state character of the negative corona, for N,,, values < 1 the particle velocity fluctuations are governed by the turbulence level of the neutral fluid. These findings might be helpful in adjusting the operating conditions in electrical precipitators for an optimized particle separation.

Methodology for Performance Evaluation of Dust Control Systems with an Application to Electrostatic Precipitators

“…The model is based on the assumption that the concentration of particles is smaller at the centre of the precipitator duct and increases towards the collection plates. According to the authors, this assumption seems quite reasonable, is in agreement with the experimental data obtained by Schmid and Umhauer (1998), and is visually observed in photographs taken from inside a wireplate precipitator by Riehle and Loffler (1993). The Nobrega et al model also estimates an approximate combined field and diffusion particle charging, according to Cochet (1961), who modified the field charging equation using the Knudsen number K n to account for increased particle charging in the submicron particle range (Schmid and Vogel 2003).…”

Size Resolved Droplet Velocity Measurements in an Electrostatic Precipitator

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