Surface viscometry in a uniform magnetic field

This paper addresses an original numerical coupling between surface mechanics of a gradually oxidizing liquid metal surface, and a supporting annular MHD flow, in the general layout of the classical annular viscometer, originally developed by Mannheimer et al. [J. Colloid Interface Sci., 32:195-211, 1970]. A purely hydrodynamic interplay between a main azimuthal flow (induced by a rotating floor) and a secondary overturning flow generated by centrifugation is found to be strongly affected by both surface viscous shear and surface viscous dilatation. When centrifugation competes with electromagnetic effects, advection of the main flow by the secondary flow is proved to affect significantly the core MHD flow, leading to original MHD flow patterns. The latter phenomenology reveals to be relevant to characterise the surface viscosities of a gradually oxidising liquid metal surface

Rôle de la rhéologie de surface dans un écoulement diphasique MHD

In this thesis work, a first approach towards the description of magnetohydrodynamic(MHD) multiphase flows is proposed, based on the investigation of the role of surface rheologyin permanent regime. The study of the coupling between bulk MHD and surface rheology is particularlymotivated by the development of an annular surface viscometer devoted to liquid metalstopped with an oxidation layer. First, theoretical foundations of MHD and of surface rheologyare separately introduced. The modelling brings out a strong coupling between bulk and surfacevelocities, the latter being dependent on two interfacial parameters: the surface shear and dilatationalviscosities. Their respective influence is analytically and numerically investigated in the caseof a permanent annular (stratified) MHD end-driven flow. In the considered geometry, a vertical(uniform) magnetic field is imposed, perpendicular to the gradually oxidising liquid surface. Thecontribution of planar surface viscous stresses to the possible electrical activation of Hartmannlayers is demonstrated, leading to a variety of atypical MHD flow patterns. The annular MHDviscometer is then developed as a first device able to perform selective measurement of the surfaceviscosities of electroconductive fluids. First experiments lead to an estimated value of the surfaceshear viscosity for a liquid alloy (GaInSn) at room temperature. Some hints are finally given to investigatethe study case of aMHDflow past a rigid fluid sphere, with varying interfacial conditionsgoverned by surface rheology, as an additionalwork constituting a first step towards the descriptionof dispersed MHD flows.Dans les travaux de recherche développés durant cette thèse, une première approche desécoulements magnétohydrodynamiques (MHD) multiphasiques est proposée. Cette approche seconcentre sur les phénomènes liés à l’interaction entre une dynamique interfaciale et un écoulementde coeur MHD. Le couplage induit entre rhéologie de surface etMHDde sous-phase est particulièrementillustré par le développement d’un viscosimètre annulaire surfacique, dédié à l’étude desmétaux liquides progressivement oxydés. En premier lieu sont introduits les éléments théoriquespropres à laMHDet à la rhéologie de surface. La modélisation de leur couplage fait intervenir deuxparamètres interfaciaux : les viscosités surfaciques dilatationnelle et de cisaillement. L’influence respectivede ces deux paramètres sur l’écoulement MHD de sous-phase est étudiée analytiquementet numériquement dans le cas d’un écoulement (stratifié) annulaire MHD permanent. Dans la configurationretenue, un champ magnétique uniforme vertical est imposé, perpendiculairement à lasurface liquide graduellement oxydée. Le rôle décisif des contraintes visqueuses interfaciales concernantl’(in)activation des couches de Hartmann est démontré, conduisant à des topologies atypiquesd’écoulement MHD. Le viscosimètre annulaire MHD est ensuite proposé en tant que méthodeexpérimentale originale, permettant la mesure sélective des viscosités surfaciques de fluides électroconducteurs.Les premières campagnes expérimentales aboutissent à une estimation de la viscositéde cisaillement interfacial d’un alliage métallique (GaInSn) liquide à température ambiante. Finalement,une ouverture sur l’écoulement MHD à proximité d’une inclusion gazeuse sphérique rigideest discutée en annexe de ce projet, en lien avec des conditions mécaniques variables à l’interfaceliquide/gaz pilotées par la rhéologie de surface, constituant une première approche vers la descriptiondes écoulements MHD dispersés

On the role of surface rheology in a two-phase MHD flow

Dans les travaux de recherche développés durant cette thèse, une première approche desécoulements magnétohydrodynamiques (MHD) multiphasiques est proposée. Cette approche seconcentre sur les phénomènes liés à l’interaction entre une dynamique interfaciale et un écoulementde coeur MHD. Le couplage induit entre rhéologie de surface etMHDde sous-phase est particulièrementillustré par le développement d’un viscosimètre annulaire surfacique, dédié à l’étude desmétaux liquides progressivement oxydés. En premier lieu sont introduits les éléments théoriquespropres à laMHDet à la rhéologie de surface. La modélisation de leur couplage fait intervenir deuxparamètres interfaciaux : les viscosités surfaciques dilatationnelle et de cisaillement. L’influence respectivede ces deux paramètres sur l’écoulement MHD de sous-phase est étudiée analytiquementet numériquement dans le cas d’un écoulement (stratifié) annulaire MHD permanent. Dans la configurationretenue, un champ magnétique uniforme vertical est imposé, perpendiculairement à lasurface liquide graduellement oxydée. Le rôle décisif des contraintes visqueuses interfaciales concernantl’(in)activation des couches de Hartmann est démontré, conduisant à des topologies atypiquesd’écoulement MHD. Le viscosimètre annulaire MHD est ensuite proposé en tant que méthodeexpérimentale originale, permettant la mesure sélective des viscosités surfaciques de fluides électroconducteurs.Les premières campagnes expérimentales aboutissent à une estimation de la viscositéde cisaillement interfacial d’un alliage métallique (GaInSn) liquide à température ambiante. Finalement,une ouverture sur l’écoulement MHD à proximité d’une inclusion gazeuse sphérique rigideest discutée en annexe de ce projet, en lien avec des conditions mécaniques variables à l’interfaceliquide/gaz pilotées par la rhéologie de surface, constituant une première approche vers la descriptiondes écoulements MHD dispersés.In this thesis work, a first approach towards the description of magnetohydrodynamic(MHD) multiphase flows is proposed, based on the investigation of the role of surface rheologyin permanent regime. The study of the coupling between bulk MHD and surface rheology is particularlymotivated by the development of an annular surface viscometer devoted to liquid metalstopped with an oxidation layer. First, theoretical foundations of MHD and of surface rheologyare separately introduced. The modelling brings out a strong coupling between bulk and surfacevelocities, the latter being dependent on two interfacial parameters: the surface shear and dilatationalviscosities. Their respective influence is analytically and numerically investigated in the caseof a permanent annular (stratified) MHD end-driven flow. In the considered geometry, a vertical(uniform) magnetic field is imposed, perpendicular to the gradually oxidising liquid surface. Thecontribution of planar surface viscous stresses to the possible electrical activation of Hartmannlayers is demonstrated, leading to a variety of atypical MHD flow patterns. The annular MHDviscometer is then developed as a first device able to perform selective measurement of the surfaceviscosities of electroconductive fluids. First experiments lead to an estimated value of the surfaceshear viscosity for a liquid alloy (GaInSn) at room temperature. Some hints are finally given to investigatethe study case of aMHDflow past a rigid fluid sphere, with varying interfacial conditionsgoverned by surface rheology, as an additionalwork constituting a first step towards the descriptionof dispersed MHD flows

Impact of surface viscosity upon an annular magnetohydrodynamic flow

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Drag upon a sphere suspended in a low magnetic-Reynolds number MHD channel flow

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On the role of surface rheology in a magnetohydrodynamic swirling flow

International audienceThe original coupling between the surface rheology of a liquid metal surface and a supporting annular Couette magnetohydrodynamic (MHD) flow is theoretically and numerically investigated in this paper, in the general layout of the classical annular viscometer, as developed by Mannheimer and Schechter ["An improved apparatus and analysis for surface rheological measurements," J. Colloid Interface Sci. 32, 195-211 (1970)]. The purely hydrodynamic interplay between the main azimuthal flow (induced by a rotating floor) and the secondary overturning flow (generated by centrifugation) is found to be strongly affected by both surface viscous shear and surface viscous dilatation. When the flow is subjected to an outer vertical magnetic field, the impact of varying interface boundary conditions (through the surface shear and dilatational viscosities) at the gas/liquid interface profoundly alters the MHD flow topology. Particularly, when centrifugation competes with electromagnetic effects, advection of the main flow by the secondary flow is proved to affect significantly the core MHD flow, leading to a variety of atypical MHD flow patterns

Mannheimer and Schechter model revisited: Viscosimetry of a (non-)Newtonian and curved interface

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Synthesis of Fukushima Daiichi Cs-bearing microparticles through molten core-concrete interaction in nitrogen atmosphere

International audienceCs-bearing microparticles, released during the accident of Fukushima Daiichi, are a significant concern for health and environment due to their abundance over wide areas, associated with a low solubility. Since their discovery, efforts have been made to characterise these particles and use them as direct witnesses of the various events inside the reactors. This study reports the experimental synthesis of micrometric particles through molten core-concrete interaction. Primary chemical analyses on Al/Si, K/Si and Na/Si atomic ratios seem to confirm concrete as source of Si. Cs has also been identified in low concentrations

Experiments on interactions of molten steel with suboxidized corium crust for in-vessel melt retention

International audienceIn the framework of the European IVMR project, dedicated to the assessment of In-Vessel Retention (IVR) strategy for high power reactors, VITI-CORMET tests, performed in VITI facility (CEA-Cadarache/PLINIUS Severe Accident Platform), intend to study the interaction between a molten 304L stainless steel droplet and suboxidized solid corium crust, referred to as C-70 ((U$_{0.54 ,}$ Zr$_{0.46}$)O$_{1.74}$). In the present paper, original experimental results on molten steel penetration through a corium crust are presented. Identification of penetration mechanisms is performed by SEM/EDX analyses, and has shown that molten steel can penetrate through pre-existing cracks or by a dissolution process. The latter is found to be the dominant penetration mechanism and involves material transport from the crust to molten steel. Penetration kinetics is studied by measuring the average penetration length at different exposure times. It is found that the penetration by dissolution decelerates with time, while U and Zr contents tend to reach an equilibrium value within the metallic droplet

Low Rm magnetohydrodynamics as a means of measuring the surface shear viscosity of a liquid metal: A first attempt on Galinstan

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