Current-driven, corona-terminated water jets as sources of charged droplets and audible noise

Single flow-rate-dependent sites of water emission and corona discharge are experimentally investigated with the dual objectives of furthering the understanding of audible noise generation from high-voltage transmission lines in foul weather, and engineering electrically-driven sources of charged droplets for use in particulate pollution control devices. Three distinct modes of behavior are mapped as functions of flow rate and potential gradient for ac and dc excitations of both polarities. Each is characterized in terms of physical appearance, current, visual corona, and nature of audible noise. Detailed treatment is given to the high-flow-rate, high-gradient mode which consists of an electrohydrodynamic jet terminated in a corona discharge followed by a spray of charged droplets. In terms of noise generated, this mode is efficient in removing water from a high-voltage transmission line. It appears also to be practical as a source of charged droplets. The salient features of this mode are given a basic explanation by using an experiment to control the potential distribution around the site in such a way that the electrohydrodynamics of the jet formation, as well as the electrical discharge, can be quantitatively described. For the first time, the corona discharge is identified as a trigger mechanism for breakup of a current-driven jet. Estimates are given of the drop size and charge, and the electrical power requirement for atomization from an array of sites.