In this investigation, the motion of charged particles for incompressible flow in electrical field has been investigated. Two applications of this subject have been simulated and compared with experimental results. The first one is a simulation model for electrets filter made of split type fiber. This simulation has been developed to study the filtration efficiency. The filter was assumed to be composed of rectangular fibers arranged in staggered array field. Single fiber efficiencies under various filtration conditions were calculated and compared with results obtained from semi-empirical expressions derived from experimental results. Firstly charged and neutral particle collections in an electric filter composed of rectangular split-type fibers are simulated. Both the flow field and the electric field around the fiber are numerically determined. All the major collection mechanisms, mechanical and electrostatic, have been coupled in the differential equation of particle motion. The single fiber collection efficiency is obtained from tracing and recording the particle trajectories. Simulations have been conducted under wide range of filtration conditions and results are compared with those obtained from Kanaoka, et al. The second one is the numerical simulation of electrostatic powder painting. The purpose of this study was to understand the gas and particle flow fields inside a coating booth under given operating conditions and the effect of particle sizes on its trajectories. The continuous gas flow was calculated by solving Navier–Stokes equations including the standard k?? turbulence model and the discrete phase was modeled based on the Langrangian approach. In both cases the flow field and the collection mechanisms were determined by Fluent software. The numerical model for the simulations of the gas and solid particle flows in a powder coating system was presented and its results were compared with the experimental data. It was found that the numerical model predicts quite accurately the particle velocities and average particle diameter at different locations inside the coating booth when there was no electrostatic field. The numerical results showed similar effect of the electrostatic field on the flow field as that from experimental results. The differences between numerical results and experimental data, for the case of with the coating part and with electrostatic field, are most probably due to the assumption of constant charge to mass ratio and spherical shape of particles for this study. Thus, it should be important to numerically resolve particle charging using unsteady particle tracking or consider variable particle charge based on its diameter. Key words: Particle/gas flow , numerical simulation, electret filter, powder coating.