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University of h4innesotaMinneapolis, MN 55455Abstruct -A finite elementhethod of characteristics model of 3-dimensional electrode geometries with corona discharge is used to predict space charge density, current density, electric potential and electric field in point-to-plane, single barb plate-to-plane, and hexagonal barbed plate-to-plate geometries.Although a modification of Peak's formula for the hyperboid-to-plane was initially used to establish a boundary condition a t the edge of the corona, predicted total current did not agree with measured values.A s a result, it was necessary to use measured current-voltage characteristics to establish the space charge density a t the corona. An additional problem in modeling point discharges is specification of shape and size of the corona sheath.Both our results and much earlier work by Trichel suggest that the thickness of the corona sheath cannot be automatically neglected. I. INTRODUC~ONPrior measurements of current distributions in a barbed plate-to-plate electrode geometry indicate that a barbed plate electrostatic precipitator may provide more uniform current density and electric field distributions than the wimplate precipitator. However, measured values are restricted to current densities along the ground plate. This paper presents a combined fmite elementhethod of characteristics model capable of predicting distributions of space charge, current density, electric potential and electric field throughout the interelectrode space of threedimensional electrode geometries with point discharges. The computational approach is based on prior work on the 24iensional wire-plate precipitator [l].Results are presented for a point-to-plane, a single-barb plateto-plane, and a barbed plate-@plane electrostatic precipitator (ESP). Predicted results are compared to the analytical solution for the sphere-to-sphere geometry, to the Warburg distribution for the point-to-plane, and to experimental measurements of current density at the ground plane for the barbed plate-mplane. NUMERICAL METHODThe governing electrostatic equations for the region outside the corona sheath are Poisson's equation, 1 The support of th U.S. ~nvironmntal 815740 is gratefully acknowledged. Protection Agency through grant no. Rand the steady state conservation of current equation,where 0 is electric potential, p is ionic space charge density, E is a constant gas p d t t i v i t y , E is electric field, and p is negative ion mobility. Current density is related to electric field byad E=-V$. (4)Equations (1) and (2) are solved with an iterative technique.The finite element method (FEM) is used to compute + from (1) for a calculated space charge.The method of characteristics is used to transform (2) into an ordinary differential equation in time along a "characteristic" space-time trajectory (r) defmed by where U is the velocity of the ions. Substitution of (l), (4) and (5) into (2) yields U . v p = -p2 e, E which along the characteristic line becomes Integration of (5) and (7) yields p. [ ; +! $ 0-7803-1993...