Contrôle électromagnétique des transferts de masse aux interfaces liquide/liquide

Most metallurgical processes, such as steel refining or nuclear waste processing, the interfaces between two liquid phases are the regions of mass transfer. These transfers require the implementation of a means of stirring to accelerate the kinetics of the pollutants transfer between both phases. This thesis deals with the use of the electromagnetic forces to stir, without any material contact, the bath core and the interface in order to control or even increase the kinetic transfers. To achieve this, two complementary experimental installations were used. The first experiment allows the measurement of the Indium transfer, initially dissolved in mercury towards a covering electrolyte layer and the velocity field in mercury. The performed experiments, determine the topology of the fields flows speeds in the mercury bath, moreover the behaviour of the transfer kinetics versus the intensity of the magnetic field are established. This evolution is correlated with the dynamic behaviour of the mercury surface. The second installation allows the characterization of an element transfer (Pb, Zr or Ce) initially contained in a fluorinated salt towards an antimony matrix containing lithium. It appears that all transfers kinetics are very fast. The proposed experimental set-up is particularly efficient for Cerium transfer (limited by the interface) but does not present any action for Zirconium transfer.Dans divers procédés, comme lors de l'affinage de l'acier, ou bien, dans le retraitement des déchets nucléaires, les interfaces entre deux phases liquides sont le siège de transferts de masse. Ces derniers nécessitent la mise en oeuvre de moyen de brassage pour accélérer la cinétique du transfert des polluants d'une phase vers l'autre. Cette thèse s'intéresse à l'utilisation des forces électromagnétiques pour agiter, sans contact matériel, le coeur du bain et l'interface afin de contrôler voire d'augmenter la cinétique de ces transferts. Pour cela, deux installations expérimentales complémentaires ont été utilisées : La première a permis de mesurer le transfert d'Indium initialement dissous dans du mercure vers un électrolyte de couverture et le champ des vitesses dans le mercure. Les expériences réalisées ont permis, d'une part de déterminer la topologie des champs de vitesses des écoulements dans le bain de mercure, et d'autre part de compléter les lois d'évolution de la cinétique de transfert en fonction de l'intensité du champ magnétique. Cette évolution est corrélée aux comportements dynamiques de la surface du mercure. La seconde installation a permis de caractériser le transfert d'un élément (Pb, Zr ou Ce) initialement contenu dans un sel fluoré vers une matrice d'antimoine contenant du lithium. Il apparaît que les cinétiques des transferts sont toutes très rapides. Le dispositif proposé est particulièrement efficace lors du transfert du Cérium (limité par l'interface) mais sans action lors de transfert de Zirconium

Experimental investigation of the natural and forced convection on solidification of Sn-3wt. %Pb alloy using a benchmark experiment

International audienceWe deal with the development of a solidification benchmark experiment in order to investigate the structure formation as well as solute macro-mesosegregation, by means of a well-controlled solidification experiment. The experiment consists in solidifying a rectangular ingot of Sn-3wt.%Pb alloy, by using two lateral heat exchangers which allow extraction of the heat flux from one or two vertical sides of the sample. The domain is a quasi two dimensional parallepipedic ingot (100x60x10) mm. The temperature difference ΔT between the two lateral sides is 40 K and the cooling rate CR= 0.03 K/s. The instrumentation consists in recording the instantaneous temperature maps by means of an array of 50 thermocouples in order to provide the time evolution of the isotherms. After each experiment the patterns of the segregations have been obtained by X-ray radiograph and confirmed by eutectic fraction measurements. The local solute distribution determined by means of induction coupled plasma analysis is provided. The originality of the present study is to examine the effect of the forced convection driven by a travelling magnetic field (TMF) induced by a linear inductor located on the bottom part of the sample. A periodically reversed stirring with a modulation frequency equal to 0.5 Hz stirring have been investigated. This study allows us to evaluate the evolution due to the forced convection induced by a TMF field, as well as its influence on the initial conditions, the solidification macrostructure and the segregation behavior. Measurements of the velocity field by ultrasonic Doppler velocimetry (UDV) method in a Ga-In-Sn pool were performed and transposed to the tin-lead alloy case before solidification. Post-mortem patterns of the macro-mesosegregations have been obtained by X-ray radiography. The results show the transport effects of the flow on both the macrosegregations and the channel formation. The reversal of the TMF produces a decrease of the level of mesosegregations, namely channel formation

Contrôle électromagnétique des transferts de masse aux interfaces liquide/liquide

Most metallurgical processes, such as steel refining or nuclear waste processing; the interfaces between two liquid phases are the regions of mass transfer. These transfers require the implementation of a means of stirring to accelerate the kinetics of the pollutants transfer between both phases. This thesis deals with the use of the electromagnetic forces to stir, without any material contact, the bath core and the interface in order to control or even increase the kinetic transfers. To achieve this, two complementary experimental installations were used. The first experiment allows the measurement of the Indium transfer, initially dissolved in mercury towards a covering electrolyte layer and the velocity field in mercury. The performed experiments, determine the topology of the fields flows speeds in the mercury bath, moreover the behaviour of the transfer kinetics versus the intensity of the magnetic field are established. This evolution is correlated with the dynamic behaviour of the mercury surface. The second installation allows the characterization of an element transfer (Pb, Zr or Ce) initially contained in a fluorinated salt towards an antimony matrix containing lithium. It appears that all transfers kinetics are very fast. The proposed experimental set-up is particularly efficient for Cerium transfer (limited by the interface) but does not present any action for Zirconium transfer.Dans divers procédés, comme lors de l'affinage de l'acier, ou bien, dans le retraitement des déchets nucléaires, les interfaces entre deux phases liquides sont le siège de transferts de masse. Ces derniers nécessitent la mise en oeuvre de moyen de brassage pour accélérer la cinétique du transfert des polluants d'une phase vers l'autre. Cette thèse s'intéresse à l'utilisation des forces électromagnétiques pour agiter, sans contact matériel, le cœur du bain et l'interface afin de contrôler voire d'augmenter la cinétique de ces transferts. Pour cela, deux installations expérimentales complémentaires ont été utilisées :La première a permis de mesurer le transfert d'Indium initialement dissous dans du mercure vers un électrolyte de couverture et le champ des vitesses dans le mercure. Les expériences réalisées ont permis, d'une part de déterminer la topologie des champs de vitesses des écoulements dans le bain de mercure, et d'autre part de compléter les lois d'évolution de la cinétique de transfert en fonction de l'intensité du champ magnétique. Cette évolution est corrélée aux comportements dynamiques de la surface du mercure.La seconde installation a permis de caractériser le transfert d'un élément (Pb, Zr ou Ce) initialement contenu dans un sel fluoré vers une matrice d'antimoine contenant du lithium. Il apparaît que les cinétiques des transferts sont toutes très rapides. Le dispositif proposé est particulièrement efficace lors de transfert du Cérium (limité par l'interface) mais sans action lors de transfert de Zirconium

Configuration des dislocations dans l'acier Z3 CND 17-12 apres fatigue : correlation au comportement mecanique

CNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc

Modélisation de la propagation des fissures courtes en fatigue dans le cas du 316L

L’expérience a démontré que la fissure fatale n’est pas nécessairement la plus grande relevée à un moment donné de la fatigue d’un matériau et qu’elle peut être la résultante d’autres microfissures. Ainsi, le dommage (par fatigue) est souvent associé au développement et à la croissance de microfissures en surface. L’avantage de considérer une population de fissures comme facteur physique d’endommagement est que les longueurs de fissures et leur nombre sont des données quantifiables qui peuvent être mesurées en surface du matériau. La présente étude est conduite dans ce sens et vise à caractériser l’endommagement et son évolution par la mesure de la densité de fissures en surface. Un modèle numérique, basé sur des principes aléatoires de génération de fissures, de leur propagation et de leur interaction mutuelle, est proposé. Il est ensuite appliqué dans le cas du 316L à température ambiante et pour des déformations plastiques égales à 8 × 10-3, 4 × 10-3 et 8 × 10-4

Electrochemical studies of steel rebar corrosion in clay: Application to a raw earth concrete

International audienceReinforcement feasibility of a new ecological earth concrete was examined. Steel rebar corrosion, when in contact with three different types of clayey soil, was investigated using electrochemical methods, potentiodynamic voltammetry and impedance spectroscopy (EIS). Results have shown that the voltammetry method overestimates the corrosion rate while EIS supplies the most reliable results. Corrosion rate decreased and a steady state was reached after four months of contact. The type of clay does not have a significant influence on the corrosion rate of the steel rebar, and the average value of 3 µm/year was considered acceptable for the lifetime of the structure

Real-Time Synchronisation of Multiple Fractional-Order Chaotic Systems: An Application Study in Secure Communication

In this paper, we use two Fractional-Order Chaotic Systems (FOCS)—one for the sender and one for the receiver—to determine the optimal synchronisation for a secure communication technique. With the help of the Step-By-Step Sliding-Mode Observer (SBS-SMO), this synchronisation is accomplished. An innovative optimisation method, known as the artificial Harris hawks optimisation (HHO), was employed to enhance the observer’s performance. This method eliminates the random parameter selection process and instead selects the optimal values for the observer. In a short amount of time, the secret message that could have been in the receiver portion (signal, voice, etc.) was successfully recovered using the proposed scheme. The experimental validation of the numerical results was carried out with the assistance of an Arduino microcontroller and several electronic components. In addition, the findings of the experiments were compared with the theoretical calculations, revealing a satisfactory level of agreement

Numerical analysis of the influence of melting and application of electromagnetic stirring prior to solidification on macrosegregation formation during casting of a binary alloy

International audienceNumerical simulations of macrosegregation formation during horizontal solidification of a hypoeutectic Sn-Pb alloy in a rectangular cavity is presented and compared to experimental results. The experiment involves a melting phase, a holding stage at constant temperature with or without application of electromagnetic stirring, and finally solidification. We simulate all stages of the experiment and study the segregation of Pb throughout the experiment. A two-phase volume-averaged model is used for the numerical simulations, accounting for thermo-solutal convection and assuming perfect microscopic mixing (lever rule). The influence of the melting phase and of the electromagnetic stirring is studied with different cases to illustrate the consequences on the flow pattern and on Pb segregation during melting and during solidification. The numerical simulations are compared to the experimental data and the impact of chemical inhomogeneities prior to solidification on macrosegregation formation is discussed