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Crossing of a liquid-liquid interface by a droplet under centrifugal effect for a micro-encapsulationprocess

El Itawi, Hassan. Crossing of a liquid-liquid interface by a droplet under centrifugal effect for a micro-encapsulationprocess. PhD, Dynamique des fluides, Institut National Polytechnique de Toulouse, 2020

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Abstract

The applications concerned by microencapsulation are constantly growing and cover sectors ofindustrial activities as varied as agriculture, pharmacy, food industry and even cosmetics. Thiswork is a part of the development of a microencapsulation process based on sub-millimeter-sizeddrops crossing a liquid-liquid (L-L) interface under the influence of an external force, in this casecentrifugal force. The objective of this work is to understand the hydrodynamics and interfacemechanisms before, during and after the passage of a drop through a L-L interface, and leading toits coating. For this purpose, numerical and experimental approaches have been combined andcomplemented by theoretical models. A numerical method solves the Navier-Stokes equations forthis three-phase flow by a finite volume discretization combined with the Level-Set and ghost-fluidmethods to capture the interface dynamics and to deal with the discontinuities at the interfaces; itallows to compute the velocity field around the deformable droplets during the interface crossing.An experimental device for forming aqueous drops of sizes (100-1400 m) and forcing theirpassage through a L-L interface using a centrifugal force of magnitude up to 2500g was designedto observe all stages of the process by a high-speed camera synchronized with the rotation of theencapsulation cell, and to analyze the crossing conditions and the different fluid entrainmentregimes. The crossing or the rebound of a droplet at the interface is a result of the competitionbetween interfacial forces, the weight of the drop and its inertial force, and is due to complexphenomena involving non-dimensional numbers. The two approaches made it possible to definethe crossing conditions as a function of the relevant non-dimensional numbers: _12/_13 andBo13, and to develop a scaling law of the maximum length of the column formed during crossing,and the resulting drop coating volume. This work has thus made it possible to determine theoptimal conditions, on the scale of a single drop, to encapsulate a liquid droplet by using thisprocess, a necessary step prior to the design of an industrial pilot operating at a continuousproduction rate.

Item Type:PhD Thesis
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Institution:Université de Toulouse > Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE)
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Research Director:
Le Sauze, Nathalie and Massiera, Gladys
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Deposited On:24 Nov 2020 10:23

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