A three dimensional simulation of the ion-drift problem in electrostatic precipitators using an analytical finite element approach appropriate to a wide variety of geometries.

A computer simulation of the ion drift problem in air has been developed to predict the potential, electric field and space charge density in various geometries applicable to wire-duct electrostatic precipitators. The development of the design of the model is explained and its implementation in a fourth generation language is described. The generality of the overall design allows new features to be included. The model uses existing analytical expressions derived using the variational functionals for Poisson's equation and the Galerkin residual for current continuity which are solved iteratively. The resulting system of simultaneous equations are represented in a matrix formulation. Routines in the program: construct the matrices; set the boundary conditions; identify 'Known' and 'unknown' node parameters; iteratively solve the system of equations; test for convergence and output the solution. The Galerkin residual using a field dependent mobility has been derived and a one dimensional simulation for cylindrical geometry has been developed. Predictions are compared for linear relationships between field magnitude and ion mobility. The feasibility of extending this to other relationships is considered. The design and implementation of a three dimensional model with constant mobility is described. The grid can be fitted to a variety of geometries, with plane and curved electrodes, using a functional for equipotential surfaces. No further adaptations to the model are required to make predictions for these different geometries. Charge injection is modelled using a fixed field injection law. Predictions for plane-plane and cylindrical geometries are compared to analytical solutions. The need to improve the efficiency of the program is identified. Possible options to achieve this are discussed so that the model may be developed as a design tool for novel discharge electrodes in electrostatic precipitators.