Charge transfer between uncharged water drops in free fall in an electric field

Abstract

The charging of uncharged, equal or very nearly equal radius drops falling freely in an electric field has been observed to occur in two different modes. When the electric field exceeds a threshold value that is a function of drop size, the charge is transferred via a spark in the air between the near surfaces of approaching drops. Below this threshold, the rate of charge transfer is slower and varies with the conductivity of the water. The onset of the spark transfer mode occurs when the voltage and the separation distance between the surfaces of the drops reaches the minimum sparking potential required for breakdown between parallel plate electrodes. The ambient field strength at the onset of sparking varies with drop size according to the theoretical enhancement of the local field between the surfaces for a fixed separation. The information obtained in this way assists studies of the electrification of clouds and cloud particles and the growth of precipitation in thunderstorms. The previous work on radio emission from colliding charged drops can presumably be extended to include uncharged and weakly charged drops in electric fields.

Some combined electrification processes in convective clouds

“…Studies of the charge transfer between water drops by Sartor and Abbott [19] show that the period charge flows from one coalescing water drop to another conforms rather closely to the computed relaxation time for the water used. The time required for coalescence or partial coalescence is considerably longer.…”

DC positive discharge performance of rod-plane short air gap under rain conditions

“…And then, the form of the drop will be an ellipsoid of revolution extended along the external field, which is more of advantage to initiate the corona emission from surface of water drop owing to the smaller radius of curvature at its two ends of long axis. Some research on the effect of electric field on the distortion and deformation of droplet and corona emission performance can be found in [14][15][16][17][18][19]. In [15], it is pointed out that positive corona can occur in the field of 2.5 kV/cm when a pair of water drops with a relative speed of 5.8 m/s and with an equivalent radius of 2.7 mm and 0.65 mm are colliding into a long filament.…”

A survey of Waterdrop Interaction Experiments

“…The fragments which result are approximately equal in mass to the masses of the original drops. The literature also contains descriptions of a different kind of drop separation which more nearly resembles a small drop splashing on the surface of a larger drop [see Sartor, 1969;Spengler, 1971]. At present, there are insufficient data to allow separation of the two types, but as the fragments are approximately the same in size and number as those in disruption, they may be treated as being the same without seriously affecting the accuracy of a model.…”

“…There is no evidence that this form of breakup ever occurs in equal drops falling at their natural terminal velocities. Sartor [ 1969] and Spengler and Gokhale [ 1970] report observations of splashing during nearly head-on collisions of un-equal drops. In Sartor's case, collision between a 200-#-radius drop and an 800-#-radius drop produced one fragment.…”

“…The present author has observed and has unpublished photographs of collisions, more grazing than head on, in which a splash appears to slide across the surface of large drops and eventually separates near the upper end of the drop, much as is seen in disruptive breakup. The sizes involved were the same as those in the work by Sartor [1969], in which the relative velocity was correct, although the larger drop was falling at less than its terminal velocity and the smaller drop at greater than its terminal velocity. In these cases the resulting fragments were never recaptured in the large-drop wake, although Blanchard [1949Blanchard [ , 1950 had reported having observed such recapture in drops freely suspended in a wind tunnel.…”