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Caractérisation et modélisation du comportement de la phase dispersée dans les colonnes pulsées

Abstract : In a context that requires the reduction of human impact on the environment, optimizing the recycling of nuclear spent fuel is of increasing importance. The liquid-liquid extraction, one of the main processes of spent fuel recycling, brings together two immiscible phases one of which dispersed into droplets. The mass exchange between both liquids is closely linked to interfacial area produced by the equipment used. Already operated on an industrial scale, the pulsed column is the subject of this work which aims at providing a mathematical model for the prediction of the amount of interfacial area produced so as to allow a better design of devices. The work in this thesis focuses on two main themes : the characterization of emulsions produced by pulsed columns and modelling the dispersed phase behaviour. The characterization step is intented to mesure the data required for a better understanding of the emulsion and to calibrate the model. In order to comply with the eulerian nature of the model, measures were synchronized with the pulsation cycle. Innovative measurement techniques based on image processing and exploiting this synchronization have been developed to assess the average hold-up rate, the drop sizes distribution, the anisotropy and the average interfaciale area density. These experimental works have been the subject of an oral presentation at the International Conference on Multi-phase Flows (ICMF 2010). The modellig was based on D. LHUILLIER's work who provides an eulerian mixture model for the emulsion. The emulsion is perceived as a pseudo-continous single phase whose properties are weighted by the respective volume fraction of each present phase. The novelty of the model lies on the use of a transport equation for interfacial area density which is the keystone of the design and the assessment of the efficiency of liquid-liquid extraction devices. The evolution of Interfacial area density is the result of the competition between four main phenomena that are : the drops deformation, the return to isotropy, coalescence and drops break-up. The correct reproduction of this physics necessitated a splitting of the time step where the effects of each phenomenon are taken into account sequentially. Otherwise, as a consequence of the equations of the model, the return to isotropy instantly balance deformations effects making it impossible to trigger fragmentation from drops deformation. Initial fitting of the model was based on data taken from literature involving academic geometries like the convergent-divergent. The newly acquired experimental data were then used to make an first validation of the model on a less common geometry, the pulsed column.
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  • HAL Id : tel-00825558, version 1

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Tojonirina Randriamanantena. Caractérisation et modélisation du comportement de la phase dispersée dans les colonnes pulsées. Mécanique des fluides [physics.class-ph]. Université Pierre et Marie Curie - Paris VI, 2011. Français. ⟨NNT : 2011PA066047⟩. ⟨tel-00825558⟩

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