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.

Cloud physics

“…The penetration of the air film by the water filament may therefore promote coalescence of the droplets. This argument is consistent with the observations of Allan and Mason (1961), Hendricks andSemonin (1962, 1963), Lindblad (1964), Plumlee (1964), and Jayaratne and Mason that the delay time between apparent collision and coalescence of two droplets decreases with increasing external field strength. A more detailed exposition of the calculations of Latham and Roxburgh is presented in 6 3.6, in a discussion of the disintegration of raindrops.…”

“…T h e collision efficiencies of cloud droplets will be influenced appreciably when the electrostatic forces between a pair of interacting droplets become comparable with the aerodynamic and gravitational forces. Computations of the effect of electric forces on droplet collision efficiencies have been made by Sartor (1960), Lindblad and Semonin (1963), Krasnogorskaya (1965), Plumlee and Semonin (1965), Davis (1965), Sartor and Miller (1965), Plumlee (1966), and. The electrostatic forces between charged cloud droplets situated in an electric field have been derived in the majority of these studies from the equations of Davis (1964) for conducting spheres, which have been verified experimentally by Saunders (1968 a).…”

Binary Collisions of Water Drops in Presence of Horizontal Electric Fields: A Wind Tunnel Study

“…In the earlier studies, the interaction between electrically charged drops in the external electric field in Strokes flow has been determined by Davis (1965), Lindblad and Semonin (1963), and Plumlee and Semonin (1965) using the electrostatic force model. Their calculations of collision and coalescence efficiencies are strongly dependent on the size of the droplets, the charge residing on the drop, and the external electric fields.…”