Production of water drops and corona due to rupture of air bubbles at water surface under a positive dc electric field

The behavior of the surface of water after rupture of an air bubble under a positive dc electric field has been investigated, and the electric current of the corona discharge which occurs from the ruptured surface has been measured. A high-speed camera has revealed that fine droplets are subsequently ejected from the tip of the waterjet formed by the bursting of the air bubble. When no electric field is present at the water surface, both the size and the number of the drops depend on the size of the air bubble. Under a positive electric field at the water surface greater than 0.6 MV/m, a negative glow corona discharge occurs from the surface of the water jet. The time variation of the corona discharge current coincides with that of the time variation of the height of the water jet involved in the ejection of drops. The number of drops produced was found to increase with the electric field, regardless of the size of the air bubble. Based on the experimental results, a plausible mechanism is proposed to explain how charged drops can be produced above a body of water when a charged cloud passes overhead. (C) 2001 Published by Elsevier Science B.V.