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Shape oscillations of an oil drop rising in water: effect of surface contamination

Published online by Cambridge University Press:  30 May 2012

Nicolas Abi Chebel ,
Jiří Vejražka ,
Olivier Masbernat  and
Frédéric Risso
Nicolas Abi Chebel
Affiliation:
Institut de Mécanique des Fluides de Toulouse, CNRS & Université de Toulouse, 31400 Toulouse, France Laboratoire de Génie Chimique, CNRS & Université de Toulouse, France IFP – Energies Nouvelles, 92852 Rueil-Malmaison CEDEX, France Fédération de Recherche FERMAT, CNRS, Toulouse, 31400 Toulouse, France
Jiří Vejražka
Affiliation:
Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, 165 02 Prague 6-Suchdol, Czech Republic
Olivier Masbernat
Affiliation:
Laboratoire de Génie Chimique, CNRS & Université de Toulouse, France Fédération de Recherche FERMAT, CNRS, Toulouse, 31400 Toulouse, France
Frédéric Risso*
Affiliation:
Institut de Mécanique des Fluides de Toulouse, CNRS & Université de Toulouse, 31400 Toulouse, France Fédération de Recherche FERMAT, CNRS, Toulouse, 31400 Toulouse, France
*
†Email address for correspondence: frederic.risso@imft.fr
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Abstract

Inertial shape oscillations of heptane drops rising in water are investigated experimentally. Diameters from 0.59 to 3.52 mm are considered, corresponding to a regime where the rising motion should not affect shape oscillations for pure immiscible fluids. The interface, however, turns out to be contaminated. The drag coefficient is considerably increased compared to that of a clean drop due to the well-known Marangoni effect resulting from a gradient of surfactant concentration generated by the fluid motion along the interface. Thanks to the decomposition of the shape into spherical harmonics, the eigenfrequencies and the damping rates of oscillation modes , 3, 4 and 5 have been measured. Frequencies are not affected by contamination, while damping rates are increased by a considerable amount that depends neither on drop instantaneous velocity nor on diameter. This augmentation, however, depends on the mode number: it is maximum for mode two (multiplied by 2.4) and then relaxes towards the value of a clean drop as increases. A previous similar investigation of a drop attached to a capillary has not revealed such an increase of the damping rates, indicating that the coupling between rising motion and surface contamination is responsible for this effect.

JFM classification

Drops and Bubbles: Bubble dynamics Drops and Bubbles: Drops Drops and Bubbles: Drops and Bubbles
Type
Papers
Information
Journal of Fluid Mechanics , Volume 702 , 10 July 2012 , pp. 533 - 542
Copyright
Copyright © Cambridge University Press 2012

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