Cloud droplet collision efficiency in electric fields

Abstract

A mathematical model describing the effects of forces acting on two spherical droplets immersed in a viscous medium is described. The model includes the interaction of the droplets with an externally applied electric field. The collision efficiencies between pairs of droplets ranging in size from 5 to 70 microns in radius are given as results of computations of the grazing trajectories of the smaller droplets relative to the larger drops in electric fields up to 10,000 volts per centimeter. The collision efficiency for a given pair of droplets increases as the applied electric field increases. For example the collision efficiency of a 30 micron drop in relation to a 5 micron droplet increases 34.5 times when the horizontal field is changed from 0 to 3600 volts per centimeter. Results of calculations are given to show how collision efficiencies vary as the orientation of the electric field is varied in relation to the axis of droplet motion. The results show that the maximum and minimum collision efficiencies occur with field orientations of 90 and 42 degrees respectively.