Spectral Study of the Luminosity Produced during Coalescence of Oppositely Charged Falling Water Drops

Abstract

An experimental study was made of the luminosity that accompanies the coalescence of oppositely charged falling water drops in order to establish which of several possible mechanisms was responsible for the luminosity. Spectrograms which show excitation of the N2 2P and N2+ 1N systems when the drops fall through air, and which fail to show these systems when the drops fall through CO2, establish that for the range of parameters studied, dielectric breakdown of the gas through which the drops fall is the process responsible for the luminosity. Oscillographic studies showed that the production of luminosity and the transfer of charge occurred simultaneously and lasted less than 14 nsec. These observations, showing the importance of dielectric breakdown in effecting charge transfer, contrast with much that appears in the literature that stresses the importance of the bulk dielectric relaxation time and of surface tension as parameters that govern the rate at which charge is lost by water surfaces under slightly different circumstances. Typical conditions resulting in luminosity of the type studied are: drops radius ∼500 μ, drop charge ∼50 × 10−12 C, relative approach velocity of main body of drops ∼10 cm/sec, and bulk dielectric relaxation time for water of the quality used 10−5 sec.

An experimental investigation on the collision behaviour of hydrocarbon droplets

“…Such images are deceptive and mostly result from the difficulty in resolving the contrasts in photographic development ; the droplets are actually separated a t this instant when viewed from the negatives. These imaging difficulties are not to be confused with the experimental observations in the literature (Miller, Sheldon & Atkinson 1965;Santor & Abbott 1968;Ochs & Czys 1987) showing the existence of connecting ligaments for colliding water drops which are either oppositely charged or under the influence of strong electric fields. Such electric forces do not exist for the present experiments.…”

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.…”

Atmospheric electrical discharges in the presence of water and ice particles

“…When a falling, i.e., unattached, drop is used, its electrical isolation permits the drop to be charged, and this opportunity partially offsets the information loss caused by the failure of exact superposition of the images of the many streamers required. To minimize blur from the falling motion, techniques described by Atkinson and Miller [1965] and Miller et al [1965] were used to generate a train of charged water drops and a synchronizing signal that triggered a pulsed power supply that produced a 10-6-second 'motion, stopping' pulse of streamers to which the drops were exposed. In the various parts of Figure 2 the streamers were produced between pointpoint, point-plane, or plane-plane electrode gaps having horizontal symmetry axes situated so that the drops fell a few centimeters from the hypodermic needle that produced them into the pulsed field region between the electrodes.…”