ID 361

Primary break-up instabilities in a gas-liquid coaxial atomizer combined with electro-spray and spray control via modulated radial electric field in the development region

 

Abstract:

We present an experimental study that explores the combined physics of gas-assisted atomization and electro-sprays, based on a canonical coaxial gas-liquid atomizer. The laminar liquid stream is injected through a long straight metallic needle at the center of the turbulent gas jet. The needle is connected to a high-voltage source and the gas nozzle exit is grounded, creating a very strong electric field in which the dielectric liquid is charged up to approximately 0.1-1 Coulomb per kilogram. The liquid mass loading is varied from 0.05 to 0.5 (keeping the liquid jet laminar) and the gas momentum ratio varies from 5 to 125. The relative influence of the high-speed gas to the liquid electric charge on the primary instability and jet break-up is studied, using both high speed visualizations in the near field and droplet size and radial velocity measurements in the mid field, after break-up process has ended. The quantitative visualization captures the fast dynamics of the interface de-stabilization and clearly shows the changes in the liquid stream instabilities caused by the electric charge. These instabilities control the liquid droplet sizes and their spatio-temporal distribution in the spray, as measured from light interferometry. We apply an additional electric field in the spray development region, characterizing the ability of an external radial forcing to modify the structure of the spray in the mid field, by a study of the effect of control on the droplet number density, velocity and acceleration spatial distributions.