Particle deposition in the wake of charged spheres

Abstract

Earlier work in this laboratory, wherein aerosols were collected from gas streams moving around charged water droplets, indicated the likelihood of high rates of deposition on the aft side of the droplet where flow conditions are not adequately represented by potential flow theory. Further tests were made with metal spheres and the aerosol deposition pattern observed with scanning electron microscopy. Results from these test confirm that the developed wake has a definite influence on the collection pattern as well as the overall collection efficiency. Generally, minima were observed aft of the separation point at an angle at which the vortices flow tangentially to the sphere. Maxima appeared forward of the separation and advanced toward the forward stagnation point as the Reynolds number increased and overall collection efficiency declined. At higher levels of field intensity the deposition profile appeared flat as one scanned around the sphere, with a peak at the rear stagnation point. Very little information is available concerning deposition in the wake of moving droplets. This seems particularly important for scrubbers and spray towers where particles are collected by droplets moving at high Reynolds numbers where wakes and eddies are quite common.