3D numerical study of wire-cylinder precipitator for collecting ultrafine particles from diesel exhaust

摘要

A precipitator section is modeled numerically in 3D to determine the collection efficiency for conductive diesel exhaust particulates. It consists of a circular tube and a wire electrode mounted at the center of the tube, supplied with a negative high dc voltage, while the tube is electrically grounded. The analytical solutions of Poisson and current continuity equations are implemented to obtain the ionic space charge density and electric potential distributions in the channel. Commercial CFD FLUENT software is used to solve the k-ε turbulent flow model, while also considering the electrical body forces. Particle charging and motion equations are solved using Discrete Phase Model (DPM) feature of the FLUENT and programming User Defined Functions (UDFs). Particles are assumed to be charged by combined field and diffusion charging mechanisms. Effects of some electrical characteristics of diesel exhaust particulates, such as charge-to-mass ratio and particle migration velocity, on collection efficiency are assessed. Patterns of particle deposition along the channel are evaluated and compared for different particle sizes. Numerical modeling of the 3D EHD flow pattern induced by corona discharge is demonstrated in the cross section of the tube when the corona wire is slightly off-center (eccentric) in an arbitrary direction.