The role of the space charge density in particulate processes in the example of the electrostatic precipitator

Numerical calculations and experimental investigations of gas-particle flows involving an electrical field, as they are found in the electrostatic precipitation process, are presented. A test facility was set up, which allows observation and optical measurement in the precipitation gap under realistic conditions as far as possible. The numerical part is based on the Euler-Lagrange approach. The gas flow is calculated by solving the Reynolds-averaged Navier-Stokes equations including the k-epsilon turbulence model. In order to solve the coupled equations for the electrostatic field, a finite-volume approach is applied. The particle phase is simulated by using a Lagrangian treatment where a large number of particles are tracked through the flow and the electrostatic field. In addition to the drag and gravity, the electric field force is considered in the equation of motion. Average properties of the particle phase are obtained by ensemble averaging. The experimental investigations were performed with a Laser Doppler Anemometer (LDA), in contrast to the majority of publications, where concentration profiles are detected, and used to validate the numerical results, which showed reasonable good agreement between calculations and measurements; however, this holds not for the particle's velocity fluctuations. It is a well-known fact that velocity fluctuations are strongly modified by electrostatic fields and often reported as part of the "ionic wind" phenomenon. Nevertheless, the increase of turbulent energy is not fully explained by that. A discussion of the probable origin of the turbulence modification are given, as well as some impulsive remarks on possible ways to proceed. (C) 2003 Elsevier B.V. All rights reserved.