Experimental Investigation of EHD Flow Regimes Map in an Electrostatic Air-Oil Droplets Separator

The applications of ESPs in liquid droplets separation have not been implemented thoroughly as in dust separation. In this paper, flow visualization measurements of the electrohydrodynamic (EHD) flow field in a narrow wire-plate electrostatic precipitator (ESP) were conducted when the primary gas flow was seeded with oil droplets with average diameter of 2μm. The EHD flow field was visualized under wide range of operating conditions by a high speed camera. The tested gas velocities were from 0 to 0.5m/s, and a positive DC voltage varying from 0 to 16kV was applied to the ESP. Experimental results clearly confirmed formation of the secondary flow and the EHD flow patterns changed significantly during corona discharge, depending on the gas velocity and applied voltage. Six typical EHD flow patterns were summarized based on the visualization and an EHD flow regime map was plotted against Reynolds number (Re) and electrohydrodynamic number (Ehd), which represents the relationship between inertial forces and electrical forces. The EHD flow structures were pronounced for high applied voltage (high Ehd) and low gas velocity (low Re) and the primary flow acted to suppress the formation of EHD flow. The EHD flow patterns obtained with oil droplets showed different characteristics, compared to EHD flow with solid particles from previous studies, when both electrics and inertial forces are weak. The high adhesive forces of oil droplets might be the main cause of these differences.