Jet break-up in electrohydrodynamic atomization in the cone-jet mode

The jet break-up mechanism has been investigated with a high-resolution camera. A model is presented, which is able to predict the droplet size, the velocity at jet break-up, and the wavelength at jet break-up. A new theoretical derivation of the droplet size scaling will be given. It was found that the jet break-up mechanism depends on the ratio of the electric normal stress over the surface tension stress. At a low value of this ratio, the jet breaks up due to varicose instabilities. The number of secondary droplets is much lower than the number of main droplets. With increasing flow rate, the current increases, the stress ratio increases, and the number of secondary droplets and satellites increases. A threshold value of the stress ratio on the jet was found, above which the jet starts to whip. In order to reduce the number of secondary droplets, the current through the liquid cone should be reduced. It is shown, that viscosity, surface charge, and the acceleration of the jet, have to be taken into account in the jet break-up process. The main droplet diameter for varicose jet break-up scales with the Row rate as d(d) similar to Q(0.48). When, the jet breaks up in the whipping regime, then the main droplet size scales as d(d) similar to Q(0.33). (C) 1999 Elsevier Science Ltd. All rights reserved.