The charging of water drops falling and colliding in an electric field

Abstract

Studies have been made of the charge transfer resulting from the collision and separation of water drops falling in an electric field. The charge transferq was measured for values of field strengthE, impact velocityV, drop radiiR, r, radius ratioR/r, and angle Θ ranging from 0.5 to 80 kV/m, 0.5 to 3 m·sec−1, 200 to 600 μ, 1.0 to 3.0 and 0 to 90 degrees respectively, where Θ is the angle between the field and the line of centres of the drops at the moment of separation. Two uniformly sized drop-streams were ejected from hypodermic needles by modulating the flow of water through them and then collided between a pair of electrodes across which a potential difference existed. The drops coalesced temporarily, swung around each other and separated, each resulting stream being collected in a vessel connected to an electrometer in order to measure the charge. The measured values ofq were generally in good agreement with theoretical values derived from the equationq = 1.1 · 10-10 γ1 E r 2 Cos Θ, where γ1 is a function ofR/r. Calculations based on this equation, the Marshall-Palmer drop-size distribution and established values of separation probabilities of colliding drops showed that collisions between raindrops within electrified clouds will act powerfully to dissipate the existing fields.