EXPERIMENTAL INVESTIGATION OF AERODYNAMIC FRAGMENTATION OF LIQUID DROPS MODIFIED BY ELECTROSTATIC SURFACE CHARGE

Pressure gradients from dispersed gas flow over the surface of a liquid drop lead to fragmentation above a critical Weber number. This is sometimes referred to as secondary atomization. Alternatively, electrostatic charge creates an outward surface stress that leads to fragmentation at the Rayleigh charge limit. This study reports the behavior of drops subject to both effects; i.e., the fragmentation of charged liquid drops exposed to an aerodynamic flow field. Individual charged drops are produced using a high-voltage capillary needle, passed through an inductive charge pickup tube, and inserted into the disruptive air flow field via the influence of gravity. The resulting fragmentation is recorded with high-speed digital shadowgraphy. The behavior for drop charges up to 84% of the Rayleigh limit and initial Weber numbers from 0 to 140 is reported. Contrary to predictions from existing theoretical analyses, no significant changes in fragmentation morphology or breakup times are observed. This indicates that the combination of electrostatic and aerodynamic forces does not enhance fragmentation. A physical explanation is proposed based on the differences in instability geometries for the limiting cases of isolated aerodynamic and isolated electrostatic forces.