Particle transport phenomena have become significant in numerous industrial processes. Recently, the research on the particle transport in a complex geometry with an electric field has been carried out in the fields of electronic packages in computers, electrostatic precipitators (ESPs) and electrostatic sprays. It is of interest how inertial particles interact with the electric field in a complex geometry.
In the present work, the effect of electrostatic and inertial forces on the particle deposition was studied by introducing the wall-mounted blocks with various heights subjected to an electric field. The electric field was obtained by solving the Laplace equation and the turbulent gas velocity profile was given from the standard and nonlinear k-ε turbulence model. The trajectory model was adopted to obtain the information on the particle phase trajectories and number concentrations, and the equation of particle motion included inertial, viscous drag and electrostatic force. The Stokes number (the ratio of inertia to viscous drag force) and electrostatic number (the ratio of electrostatic force to viscous drag force) were introduced for interpreting the particle transport in an obstructed electrostatic precipitator. It was observed that the smaller particles were entrained into the recirculation zones whereas the inertial impaction for them was negligible. The deposition rate for larger particles were augmented by impaction as the obstruction height increased, even for smaller electric field strength. According to the trend of our results, we were able to define three particle size ranges in view of the dominant deposition mechanism. The electrostatic range was defined as the range that the deposition efficiency decreased with block height and the inertial range was defined as the range that the deposition efficiency increased. In addition there was an intermediate size range, the overlap range, where both inertial and electrostatic forces were important. As the Stokes number increased, the total efficiency did not increase monotonically and had a minimum efficiency point. The deposition efficiency had a minimum value at a certain Stokes number according to the electrostatic number and block height, and finally converged towards the ratio of the block height to the duct width on increasing the Stokes number.
Correlation between the electric field and particle space charge was investigated to verify the assumption that the particle space charge did not affect the electric field. A simple one-dimensional model was invented and the particle concentration was assumed to be homogeneous between the two infinite parallel plates in the steady state. The electric field was obtained by solving the Poisson equation. As a result, the increase of the electric field strength in the vicinity of the collecting electrode augmented the electrical migration velocity of particles, but excessive increase of space charges caused the degradation of deposition efficiency due to decrease of the electric field intensity nearby the non-collecting electrode. Total surface loading (ie. both Sauter mean diameter and volume concentration for micron particles) should be considered in estimating the effect of particle space charge even though the gas-particle flow is one-way coupled.
