Break-up instabilities and resulting droplet distributions in a gas-liquid coaxial atomizer combined with electro-spray

We present an experimental study that explores the combined physics of gas-assisted atomization and electrosprays, based on a canonical coaxial gas-liquid atomizer. The laminar liquid stream is injected through a long metallic needle at the center of the turbulent gas jet, with gas-to-liquid momentum ratio from 1 to 80. The needle is at high-voltage and the gas nozzle exit is grounded, creating a strong electric field in which the dielectric liquid is charged up to 1-10 C/m³. The relative influence of the high-speed gas to the liquid electric charge on the primary instability and jet break-up is studied, using high speed visualizations in the near field and Phase Doppler Particle Analysis in the mid field. The quantitative visualization captures the fast dynamics of the interface destabilization and shows the changes in the liquid instabilities caused by the electric charge, which control the droplet sizes and their spatial distribution in the spray. We apply an additional electric field along the spray development region, characterizing the ability of an external radial forcing to modify the structure of the electrically-charged spray as it develops, enabling control of the droplet position, velocity and acceleration distributions through modulated charge and external field.