THE COLLISION EFFICIENCY OF CLOUD DROPS OF EQUAL SIZE

Abstract

An investigation by modeling techniques has been made of the collision between cloud drops of equal size in the diameter range from 11 to 22 microns. It was found that such drops will collide with an initial vertical separation as large as 20 drop radii and an initial horizontal separation of approximately 0.3 drop radii. The approach velocity of the two drops, averaged over a vertical separation of 20 radii, is nearly constant at 0.1 of the terminal velocity of the drops. An analysis was made of the collision rate between drops of equal size under the assumption that the drops are located randomly in space. It is shown that the collision rate is proportional to the square of the ratio of cloud liquid-water content to drop size.