Droplet characterization of high-flowrate water electrospray using shadowgraph image analysis

Differently from conventional electrospray studies on the ‘cone-jet mode’ to produce homogenous droplets, a wet electrostatic precipitator requires high flowrate which shows significantly different spray patterns and droplet sizes. Since the droplet are distributed much sparser than cone-jet electrospray, this study focused on the high flowrate water electrospray characteristics. The size measurement methods were compared between shadowgraph and phase Doppler anemometry (PDA). In shadowgraph method, the droplet sizes were measured from the electrospray photos through multi-stage image processing algorithm. PDA failed to determine most of the large droplets, whereas shadowgraph measured all droplets larger than 20µm. In terms of the corresponding volume measured using the diameter distribution, small sized droplets had a very small effect on the total atomization. This study proffers the appropriate method to measure the distribution of large size droplets in a disperse high flowrate electrospray, which may provide essential parameters for wet electrospray precipitator design.