A numerical methodology based on the Lagrangian approach is outlined to study the performance of a select class of electrostatic aerosol separators. This modeling method is used to perform a parametric study on the efficiency of a wire-cylinder separator in separation of water aerosols from air. The geometry consists of an 80 mu m diameter wire placed in the centerline of a 20mm diameter cylinder. The work focuses on the effect of applied voltage (in the range of 4 to 8kV), flow velocity (in the range of 0.3 to 1.5m/s), flow temperature (in the range of 280K to 320K), and separator length (in the range of 0.05 to 0.15m) on charging of water aerosols and on separator collection efficiency in laminar flow. The aerosols size ranges between 0.01-10 mu m. The results of the study show that applied voltage, flow rate, and separator length affect the separation efficiency significantly, while the effect of flow temperature seems negligible.