Breakup of diminutive Rayleigh jets

Abstract

Discharging a liquid from a nozzle at sufficient large velocity leads to a continuous jet that due to capillary forces breaks up into droplets. Here we investigate the formation of microdroplets from the breakup of micron-sized jets with ultra high-speed imaging. The diminutive size of the jet implies a fast breakup time scale $\tau_\mathrm{c} = \sqrt{\rho r^3 / \gamma}$ of the order of 100\,ns{}, and requires imaging at 14 million frames per second. We directly compare these experiments with a numerical lubrication approximation model that incorporates inertia, surface tension, and viscosity [Eggers and Dupont, J. Fluid Mech. 262, 205 (1994); Shi, Brenner, and Nagel, Science 265, 219 (1994)]. The lubrication model allows to efficiently explore the parameter space to investigate the effect of jet velocity and liquid viscosity on the formation of satellite droplets. In the phase diagram we identify regions where the formation of satellite droplets is suppressed. We compare the shape of the droplet at pinch-off between the lubrication approximation model and a boundary integral (BI) calculation, showing deviations at the final moment of the pinch-off. Inspite of this discrepancy, the results on pinch-off times and droplet and satellite droplet velocity obtained from the lubrication approximation agree with the high-speed imaging results

High-efficiency ballistic electrostatic generator using microdroplets

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Monodisperse water microdroplets generated by electrohydrodynamic atomization in the simple-jet mode

“…4, the droplet formation mechanism happens in the jetting regime. [26][27][28][29][30][31][32][33] Just below this value it happens in the so called transition regime, 28 i.e., in between the dripping and the jetting regime. As mentioned by Cloupeau and Prunet-Foch 23 for electrified jets this transition is expected to happen at lower Weber number values, corresponding to the transition regime, because the tangential component of the electric field increases liquid acceleration.…”

Ultra-high-speed fluorescence imaging

“…In this thesis we pioneer the use of continuous laser excitation for ultra-highspeed fluorescence imaging at frame rates ranging from 1 kfps up to 25 Mfps. This imaging technique is applied to study the mechanisms of ultrasoundtriggered local drug delivery using microbubbles.…”

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