The effects of water droplet oscillations on the scavenging of micron sized particles

The scavenging of particles by droplets involves several different mechanisms. It has been hypothesized that drop oscillations and vortex shedding within the droplet wake affect scavenging of particles. However, no conclusive experimental results have been presented to quantify the effect that these oscillations and vortices might have on particle scavenging. To address this need, experiments have been performed using droplets of pure water and of water/glycerol solutions to provide a reduction in droplet oscillation amplitude. The scavenging efficiencies of these droplets have been measured for 2.6, 3.0, and 3.9 mm diameter droplets collecting 2.2, 3.8, and 4.5 mum diameter particles. The results of this research show a decrease in efficiency for the larger 4.5 mum particles and an increase in efficiency for the smaller 2.2 mum particles, for the oscillatory damped conditions. The data suggest that these differences in the effect of oscillatory damping on the scavenging efficiencies for these two particle sizes is due to the influence of different scavenging mechanisms: inertial impaction on the front of the droplet and by wake capture on the back. Further research in this area may promote the understanding of particle removal due to rainfall and the efficacy of spray droplet scrubbers to control the introgression of particle emissions from industrial and commercial pollution sources into the environment.