The Stability of a Charged Viscous Dielectric Jet*

Atomization of a dielectric micro-jet is achieved using an electrohydrodynamic charge injection process. The atomizer is comprised of a grounded nozzle housing and a high voltage internal probe that is concentric with the emitting orifice. The internal probe is held at electric potentials up to 20 kV. A pressurized reservoir drives dielectric fluid through the orifice with a diameter ranging from 100 µm to 500 µm. Fluid fills the cavity between the probe and housing, impeding the transport of electrons as it passes through the atomizer. This process imparts charge into the flowing fluid. Before it is charged, the jet breaks up via the Rayleigh-Plateau (axisymmetric) instability. Once it is charged, the jet assumes a bending (non-axisymmetric) instability. Both instabilities grow with increasing jet electric charge; i.e. the intact jet length shortens and bending amplitude increases as the charge is increased. We utilized high speed microscopy and Fast Fourier Transform analysis of the bending mode to measure the dominate unstable wavelengths. Our results show good agreement with the predicted fastest growing unstable wavelength (Saville, J. Fluid Mech., 48:815, 1971).