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Crown breakup by Marangoni instability

Published online by Cambridge University Press:  12 June 2006

S. T. THORODDSEN ,
T. G. ETOH  and
K. TAKEHARA
S. T. THORODDSEN
Affiliation:
Mechanical Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117576
T. G. ETOH
Affiliation:
Civil and Environmental Engineering, Kinki University, Higashi-Osaka 577-8502, Japan
K. TAKEHARA
Affiliation:
Civil and Environmental Engineering, Kinki University, Higashi-Osaka 577-8502, Japan
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Abstract

We present experimental observations of hole formation in ejecta crowns, when a viscous drop impacts onto a thin film of low-viscosity liquid with significantly lower surface tension than the drop liquid. The holes are promoted by Marangoni-driven flows in the sheet, resulting from a spray of fine droplets ejected from the thin film hitting the inner side of the crown. The puncturing of the sheet takes place in three distinct steps. First a circular patch of the sheet thins by Marangoni-driven flows. Then this thinner film ruptures and a hole quickly opens up spanning the patch. Finally, the hole opens up further at an accelerated rate, driven by the unbalanced surface tension at its edge. The holes grow until they meet adjacent holes, thus leaving a foam-like network of liquid filaments, which then breaks up into a cloud of droplets.

JFM classification

Drops and Bubbles: Drops Convection: Marangoni convection
Type
Papers
Information
Journal of Fluid Mechanics , Volume 557 , 25 June 2006 , pp. 63 - 72
Copyright
© 2006 Cambridge University Press

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Thoroddsen et al. supplementary movie

Movie 1. A high-speed video clip taken at 20,000 fps, showing the impact of a drop onto a thin film of ethanol coating a glass plate. A fine spray of ethanol droplets is thrown up by the impact and is subsequently brought down by the airflow around the edge of the crown. As these droplets touch the crown they produce gradients in surface tension, with the ensuing Marangoni instability puncturing numerous holes in the crown. The drop is 89% glycerin/water mixture and its horizontal diameter is 5.0 mm. The ethanol film is about 35 micrometres thick.  The impact Re = 460 and We = 5720, based on the liquid properties of the drop. The times are in microseconds.

Download Thoroddsen et al. supplementary movie(Video)
Video 3 MB

Thoroddsen et al. supplementary movie

Movie 2. A high-speed video clip taken at 50,000 fps, showing a close-up view of the formation of holes in the crown. Notice the sudden puncture of the thin films covering the Marangoni patches. The impact conditions are the same as in movie 1.

Download Thoroddsen et al. supplementary movie(Video)
Video 2 MB