Mechanism of stable jet formation in electrohydrodynamic atomization

Abstract

The disruption of a liquid into a spray of charged droplets, when subjected to an intense electric field, has attracted considerable interest from both a fundamental and applied point of view. On the applied side, the process has been used in paint spraying, electrostatic printing, electrostatic emulsification, fuel atomization in combustion systems and in space vehicle propulsion systems. More recently, the phenomenon has found potential application in crop spraying because of the low energies required, the ability to produce fine sprays within a narrow size distribution and the preferential deposition on the target surfaces. Despite its wide range of applications, the mechanism of liquid disruption is only poorly understood. At a critical potential, the so-called Taylor¹ cone develops, with a fine stable jet issuing from its tip. The formation of such cones and jets is essential for the production of an electrohydrodynamic spray. Most previous work aimed at understanding jet formation has been based on high-speed photographic techniques. We have made direct observations of jet formation and our results, presented here, demonstrate the role of electrical shear effects in this process, and invalidate those theories that assume a uniform velocity profile² for the liquid in the conical base of the jet.