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

The jet break-up mechanism has been investigated with a high-resolution cam era. A model is presented, which is able to predict the droplet size, the v elocity at jet break-up, and the wavelength at jet break-up. A new theoreti cal 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 str ess 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 i s much lower than the number of main droplets. With increasing flow rate, t he current increases, the stress ratio increases, and the number of seconda ry 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 redu ce the number of secondary droplets, the current through the liquid cone sh ould be reduced. It is shown, that viscosity, surface charge, and the accel eration of the jet, have to be taken into account in the jet break-up proce ss. 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 r egime, then the main droplet size scales as d(d) similar to Q(0.33). (C) 19 99 Elsevier Science Ltd. All rights reserved.