Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Neste trabalho, três técnicas para resolver numericamente problemas inversos de transporte de partículas neutras a uma velocidade para aplicações em engenharia nuclear são desenvolvidas. É fato conhecido que problemas diretos estacionários e monoenergéticos de transporte são caracterizados por estimar o fluxo de partículas como uma função-distribuição das variáveis independentes de espaço e de direção de movimento, quando os parâmetros materiais (seções de choque macroscópicas), a geometria, e o fluxo incidente nos contornos do domínio (condições de contorno), bem como a distribuição de fonte interior são conhecidos. Por outro lado, problemas inversos, neste trabalho, buscam estimativas para o fluxo incidente no contorno, ou a fonte interior, ou frações vazio em barras homogêneas. O modelo matemático usado tanto para os problemas diretos como para os problemas inversos é a equação de transporte independente do tempo, a uma velocidade, em geometria unidimensional e com o espalhamento linearmente anisotrópico na formulação de ordenadas discretas (SN). Nos problemas inversos de valor de contorno, dado o fluxo emergente em um extremo da barra, medido por um detector de nêutrons, por exemplo, buscamos uma estimativa precisa para o fluxo incidente no extremo oposto. Por outro lado, nos problemas inversos SN de fonte interior, buscamos uma estimativa precisa para a fonte armazenada no interior do domínio para fins de blindagem, sendo dado o fluxo emergente no contorno da barra. Além disso, nos problemas inversos SN de fração de vazio, dado o fluxo emergente em uma fronteira da barra devido ao fluxo incidente prescrito no extremo oposto, procuramos por uma estimativa precisa da fração de vazio no interior da barra, no contexto de ensaios não-destrutivos para aplicações na indústria. O código computacional desenvolvido neste trabalho apresenta o método espectronodal de malha grossa spectral Greens function (SGF) para os problemas diretos SN em geometria unidimensional para gerar soluções numéricas precisas para os três problemas inversos SN descritos acima. Para os problemas inversos SN de valor de contorno e de fonte interior, usamos a propriedade da proporcionalidade da fuga de partículas; ademais, para os problemas inversos SN de fração de vazio, oferecemos a técnica a qual nos referimos como o método físico da bissecção. Apresentamos resultados numéricos para ilustrar a precisão das três técnicas, conforme descrito nesta tese. / In this work, three techniques for numerically solving one-speed neutral particle inverse transport problems for nuclear engineering applications are developed. It is well known that direct steady-state monoenergetic transport problems are characterized by estimating the flux of particles as a distribution function of space and direction-of-motion independent variables, when the material parameters (cross sections), the geometry, and the incoming flux at the boundaries of the domain (boundary conditions), as well as the interior source distribution are known. Conversely, inverse problems, in this work, seek for estimates to the incident boundary flux, or interior source, or void fractions in homogeneous slabs. The mathematical model used for direct and inverse problems is the time-independent one-speed slab-geometry transport equation with linearly anisotropic scattering in the discrete ordinates (SN) formulation. In the boundary-value inverse problems, given the existing flux at one boundary of the slab, as measured by a neutron detector, for example, we seek for accurate estimate for the incident flux at the opposite boundary. On the other hand, in the interior source inverse SN problems, we seek for accurate estimate for the interior source stored within the slab for shielding purpose, given the exiting flux at the boundary of the slab. Furthermore, as with the void fraction inverse SN problems, given the exiting flux at one boundary of the slab due to prescribed incident flux at the opposite boundary, we seek for accurate estimate of the void fraction within the slab in the context of non-destructive testing applications in industry. The computer code developed in this work presents the coarse-mesh spectral Greens function (SGF) nodal method for direct SN problems in slab geometry to generate accurate numerical solutions to the three inverse SN problems described above. For the boundary-value and interior source inverse SN problems, we use the proportionality property of the leakage of particles; moreover, for the void fraction inverse SN problems, we offer the technique that we refer to as the physical bisection method. We present numerical results to illustrate the accuracy of the three techniques, as described in this dissertation.

Cette thèse se situe dans le cadre du projet ASTRID du CEA. La surveillance de la présence de gaz dans un RNR est importante pour son fonctionnement en toute sécurité. Cette thèse porte sur la détection et la caractérisation de présence de gaz par un débitmètre à distorsion de flux (DDF). Du point de vue technologique, l’objectif est d’évaluer la faisabilité de l’utilisation d’un DDF, et s’il est possible de mesurer le débit et le taux de vide simultanément avec un DDF. Du point de vue de la physique, le DDF mesure la perturbation du flux magnétique due aux courants de Foucault induits par l’hydrodynamique d’un écoulement de liquide conducteur. En présence de vide dans le conducteur, une nouvelle source de perturbation apparaît du fait de la modification, par le taux de vide, de la distribution du champ magnétique. En effet, la présence de vide agit sur les distributions locales de courants électriques dues au couplage des phénomènes d’induction et de forces de Lorentz. Notre objectif est de comprendre la nature de ces couplages et de proposer une méthode qui permette de caractériser la présence de vide à partir du signal de sortie du DDF, de mesurer le taux de vide et d’étudier la sensibilité de cette mesure aux variations des paramètres de l’écoulement et du champ électromagnétique (vitesse et pulsation, en particulier). Dans ce travail, des expériences spécifiques ont été développées pour étudier les effets de la vitesse, du taux de vide et de la pulsation du flux magnétique sur la réponse d’un DDF. Ces expériences modélisent un écoulement diphasique idéal (écoulement piston) consistant en une barre mobile d’aluminium contenant des trous et des cannelures pour simuler le taux de vide. Dans ces expériences la vitesse, le taux de vide et la pulsation sont parfaitement contrôlé et leur domaine de variations sont les suivants : 0<U<1 m/s pour la vitesse, 0< <6.9% pour le taux de vide et 1500<<12000 rad/s pour la pulsation (dans cette gamme de pulsations, on notera que la profondeur de pénétration du champ électromagnétique est de l’ordre de, mais plus petit que, le rayon du barreau d’aluminium). Une méthode d’ellipse-fitting appliqué au signal de sortie du DDF a été utilisée pour caractériser l’effet du taux de vide. Les résultats montrent que le DDF est sensible pour des fractions volumique de vide entre 0.3 % and 6.9% . En outre, la réponse aux variations de taux de vide est insensible à la vitesse du barreau. Cette technique est peu adaptée aux mesures des faibles taux de vide (< 0.1%). Une deuxième approche a été développée, sur la base de l’analyse du signal démodulé du DDF. Cette analyse s’appuie sur un modèle théorique du flux magnétique obtenu par un développement au 1er ordre par rapport à U et a. Ce modèle permet d’interpréter les résultats expérimentaux en termes de contributions de U et a au flux magnétique. Malgré le couplage fort entre l’induction Faraday et les forces de Lorentz, les résultats montrent que les contributions de U et alpha peuvent être séparées correctement pour des petites valeurs du nombre de Reynolds magnétique (Rem < 0.12), et de faible taux de vide ( < 6.9%). Un résultat très important est que la contribution de a sur le flux magnétique est insensible aux variations de vitesse dans cette gamme de Rem . De plus, l’effet de la géométrie du vide a été étudié pour deux configurations : cannelures et trous. Il a été observé que la géométrie du vide n’a pas d’effet sur les variations du flux magnétique avec a. Cette seconde approche est plus sensible aux variations de fraction volumique du vide que la méthode de l’ellipse-fitting. Enfin, des expériences préliminaires avec un liquide métallique (galinstan) contenant des perles de verre, ont été faites et ont montré une bonne sensibilité du signal du DDF avec la vitesse et le taux de vide. En conclusion, ce travail a montré qu’il est possible de mesurer simultanément un taux de vide et un débit pour la gamme de variations des paramètres étudiés. / A Generation IV Sodium cooled Fast Reactor (SFR) is being researched and developed at CEA, Cadarache France under the project named ASTRID. Monitoring gas presence in SFR is important with respect to its safe operation. In accordance with the principles of diversity, techniques based on different measurement principles have been proposed. This thesis concerns the detection and characterization of void using magnetic flux perturbation principle. An Eddy Current Flow Meter (ECFM) device is used for this purpose. From the technological point of view, the objective is to evaluate the feasibility of ECFM as a flow and/or void monitoring/characterizing device; and to determine which parameters are of interest and what are the precision of these measurements; and whether it is possible to measure the flow rate and void fraction simultaneously with the same ECFM device. From the physics point of view, the ECFM system involves the magnetic flux perturbation due to voids in the presence of Faraday induction and Lorentz force effects. Therefore ECFM integrated signal contains informations about the void, Faraday induction and Lorentz force effects based perturbation in magnetic flux and their couplings. Our objective is to understand the nature and extent of these couplings. Specific experiments have been developed to study the effects of flow velocity, void fraction and magnetic flux pulsations on the response of an ECFM. It consists in modeling the two-phase flow by a moving aluminium rod (plug flow) with holes and grooves to simulate voids. Flow velocity range of variation was 0<U<1 m/s, void fraction 0<<6.9% and pulsation 1500<<12000 rad/s (for this range of pulsations the electromagnetic skin depth is of order but smaller than the aluminium rod radius). An ellipse fitting method was proposed to analyze the output signal of the secondary coils. The results show that ECFM is sensitive to void fractions between 0.3 % and 6.9%. Furthermore, the response to void fraction is insensitive to the mean velocity of the twophase medium. A second approach based on demodulation analyses of the secondary coils output signal has been developed. We have proposed a theoretical model based on a first order expansion of magnetic flux in U and a. With this model it was possible to interpret the experimental results in terms of contributions of U and a. Despite the strong coupling between Faraday induction and Lorentz force effects, the results show that the contributions of U and a. can be well separated at low magnetic Reynolds number (Rem < 0.12) and low a values ( < 6.9%). A very important result is that the contribution of _ on magnetic flux is insensitive to variations of velocity in this range of Rem. Moreover, different geometries of void have been studied: grooves and holes. It was observed that the geometry of void do not change the variation of magnetic flux with a. This second approach revealed to be more sensitive to void fraction variations than ellipse fitting method. Finally, preliminary experiments with liquid metal galinstan with glass beads were done, which showed sensitivity of ECFM signal with velocity and void. In conclusion, this work has shown that ECFM can measure simultaneously void and velocity in the range of parameters studied, in particular 0.06%< < 6.9%.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Neste trabalho, três técnicas para resolver numericamente problemas inversos de transporte de partículas neutras a uma velocidade para aplicações em engenharia nuclear são desenvolvidas. É fato conhecido que problemas diretos estacionários e monoenergéticos de transporte são caracterizados por estimar o fluxo de partículas como uma função-distribuição das variáveis independentes de espaço e de direção de movimento, quando os parâmetros materiais (seções de choque macroscópicas), a geometria, e o fluxo incidente nos contornos do domínio (condições de contorno), bem como a distribuição de fonte interior são conhecidos. Por outro lado, problemas inversos, neste trabalho, buscam estimativas para o fluxo incidente no contorno, ou a fonte interior, ou frações vazio em barras homogêneas. O modelo matemático usado tanto para os problemas diretos como para os problemas inversos é a equação de transporte independente do tempo, a uma velocidade, em geometria unidimensional e com o espalhamento linearmente anisotrópico na formulação de ordenadas discretas (SN). Nos problemas inversos de valor de contorno, dado o fluxo emergente em um extremo da barra, medido por um detector de nêutrons, por exemplo, buscamos uma estimativa precisa para o fluxo incidente no extremo oposto. Por outro lado, nos problemas inversos SN de fonte interior, buscamos uma estimativa precisa para a fonte armazenada no interior do domínio para fins de blindagem, sendo dado o fluxo emergente no contorno da barra. Além disso, nos problemas inversos SN de fração de vazio, dado o fluxo emergente em uma fronteira da barra devido ao fluxo incidente prescrito no extremo oposto, procuramos por uma estimativa precisa da fração de vazio no interior da barra, no contexto de ensaios não-destrutivos para aplicações na indústria. O código computacional desenvolvido neste trabalho apresenta o método espectronodal de malha grossa spectral Greens function (SGF) para os problemas diretos SN em geometria unidimensional para gerar soluções numéricas precisas para os três problemas inversos SN descritos acima. Para os problemas inversos SN de valor de contorno e de fonte interior, usamos a propriedade da proporcionalidade da fuga de partículas; ademais, para os problemas inversos SN de fração de vazio, oferecemos a técnica a qual nos referimos como o método físico da bissecção. Apresentamos resultados numéricos para ilustrar a precisão das três técnicas, conforme descrito nesta tese. / In this work, three techniques for numerically solving one-speed neutral particle inverse transport problems for nuclear engineering applications are developed. It is well known that direct steady-state monoenergetic transport problems are characterized by estimating the flux of particles as a distribution function of space and direction-of-motion independent variables, when the material parameters (cross sections), the geometry, and the incoming flux at the boundaries of the domain (boundary conditions), as well as the interior source distribution are known. Conversely, inverse problems, in this work, seek for estimates to the incident boundary flux, or interior source, or void fractions in homogeneous slabs. The mathematical model used for direct and inverse problems is the time-independent one-speed slab-geometry transport equation with linearly anisotropic scattering in the discrete ordinates (SN) formulation. In the boundary-value inverse problems, given the existing flux at one boundary of the slab, as measured by a neutron detector, for example, we seek for accurate estimate for the incident flux at the opposite boundary. On the other hand, in the interior source inverse SN problems, we seek for accurate estimate for the interior source stored within the slab for shielding purpose, given the exiting flux at the boundary of the slab. Furthermore, as with the void fraction inverse SN problems, given the exiting flux at one boundary of the slab due to prescribed incident flux at the opposite boundary, we seek for accurate estimate of the void fraction within the slab in the context of non-destructive testing applications in industry. The computer code developed in this work presents the coarse-mesh spectral Greens function (SGF) nodal method for direct SN problems in slab geometry to generate accurate numerical solutions to the three inverse SN problems described above. For the boundary-value and interior source inverse SN problems, we use the proportionality property of the leakage of particles; moreover, for the void fraction inverse SN problems, we offer the technique that we refer to as the physical bisection method. We present numerical results to illustrate the accuracy of the three techniques, as described in this dissertation.

This dissertation focused on development and utilization of numerical and experimental approaches to improve the CFD modeling of fluidization flow of cohesive micron size particles. The specific objectives of this research were: (1) Developing a cluster prediction mechanism applicable to Two-Fluid Modeling (TFM) of gas-solid systems (2) Developing more accurate drag models for Two-Fluid Modeling (TFM) of gas-solid fluidization flow with the presence of cohesive interparticle forces (3) using the developed model to explore the improvement of accuracy of TFM in simulation of fluidization flow of cohesive powders (4) Understanding the causes and influential factor which led to improvements and quantification of improvements (5) Gathering data from a fast fluidization flow and use these data for benchmark validations. Simulation results with two developed cluster-aware drag models showed that cluster prediction could effectively influence the results in both the first and second cluster-aware models. It was proven that improvement of accuracy of TFM modeling using three versions of the first hybrid model was significant and the best improvements were obtained by using the smallest values of the switch parameter which led to capturing the smallest chances of cluster prediction. In the case of the second hybrid model, dependence of critical model parameter on only Reynolds number led to the fact that improvement of accuracy was significant only in dense section of the fluidized bed. This finding may suggest that a more sophisticated particle resolved DNS model, which can span wide range of solid volume fraction, can be used in the formulation of the cluster-aware drag model. The results of experiment suing high speed imaging indicated the presence of particle clusters in the fluidization flow of FCC inside the riser of FIU-CFB facility. In addition, pressure data was successfully captured along the fluidization column of the facility and used as benchmark validation data for the second hybrid model developed in the present dissertation. It was shown the second hybrid model could predict the pressure data in the dense section of the fluidization column with better accuracy.

The modern, contemporarily used cement composite types make use of various additives. This diploma thesis is focused on designs of mortars that have been enriched with micro and nano additives, which lead to higher mechanical strength through optimized grading of mortar mixes. This thesis also evaluates the influence of material properties on resulting properties of mortars in fresh and hardened state.

Ce travail porte sur l’étude expérimentale et numérique de l’écoulement des mousses humides dans un canal horizontal droit de section carrée avec ou sans singularités. Il est consacré tout particulièrement à déterminer les paramètres pertinents de l’écoulement dont la chute de pression longitudinale, les champs de vitesse de l’écoulement de mousse en proche parois, les épaisseurs de films liquides minces et épais en paroi et l’évolution de la contrainte pariétale pour une mousse humide dont la fraction gazeuse varie de 55 à 85% et la vitesse débitante de la mousse est 2, 4 puis 6 cm/s. Une fois ces paramètres déterminés en conduite horizontale droite, nous avons ensuite effectué des mesures sur différentes géométries représentant un élargissement brusque, une chicane verticale et écoulement de mousse autour d’un cylindre, dont le but est d’étudier la réorganisation de l’écoulement en vue de déterminer le comportement rhéologique des mousses en écoulement à l’aval et à l’amont des singularités. Finalement, une étude de simulation numérique (CFD) en utilisant les lois de comportement de type Bingham, pour fluides non newtoniens, a été effectuée afin de tester sa capacité de représenter des écoulements type mousse humide dans une conduite horizontale avec ou sans singularités. Nous avons vérifié tout d’abord l’évolution longitudinale de la pression statique qui est linéaire à l’amont comme à l’aval loin des zones influencées par les singularités. La chute de pression singulière reste à peu près constante pour une vitesse débitante donnée de la mousse. À partir de la technique de Vélocimétrie par Image de Particule (PIV), nous avons déterminé les composantes de vitesse au voisinage immédiat des singularités. Ces mesures nous ont permis de mettre en évidence l’existence de différents régimes d’écoulement, et de déterminer la réorganisation et le comportement rhéologique de l’écoulement de mousse autour des géométries étudiées. L’analyse des mesures d’épaisseur de films liquides, obtenues par la méthode conductimétrique, indique que la paroi reste mouillée par un film liquide suffisamment épais pour qu’on puisse appliquer la méthode électrochimique. Les signaux polarographiques obtenus avec la mousse présentent alors de fortes fluctuations. La comparaison de celles-ci avec les contraintes pariétales déduites à partir des mesures de la chute de pression montre bien une bonne concordance. L’étude numérique (CFD), effectuée pour une fraction volumique de gaz égale à 70% et qui s’écoule avec une vitesse débitante de 2 cm/s, montre que le modèle rhéologique de Bingham pourrait être bien adapté à ce genre de mousse humide évoluant en écoulement en bloc. / This work is an experimental and numerical study of aqueous foam flow inside a horizontal square duct, with and without flow disruption devices (fdd). It is especially devoted to determine the pertinent parameters of the flow: longitudinal pressure losses, velocity fields of foam flow near the walls, liquid film thickness (thick and thin), and the wall shear stress evolution, for an aqueous foam with a void fraction range between 55 and 85%, for a mean foam flow velocity of 2, 4 and 6 cm/s. Once they were determined, inside the horizontal channel, we carried out measurements over different geometries: half-sudden expansion, vertical fence and foam flow around a cylinder. The goal was to study the foam flow reorganization to well understand the rheological behavior of aqueous foam flow in the vicinities of different fdd. Finally, a numerical simulation (CFD), using the Bingham behavior model of non-Newtonian fluid, was undertaken to test its capacity to represent the aqueous foam flow inside the horizontal duct with flow disruption devices. First of all, we verified the static longitudinal pressure evolution, which varies linearly upstream and downstream far from the fdd. The singular pressure loss remains constant for a given mean foam velocity and a foam quality (void fraction). From the Particle Imaging Velocimetry (PIV) technique (2D), we determined the two velocity components in the immediate vicinities of the disruption devices. They allowed us to put into evidence the different foam flow regimes and to observe the foam flow reorganization and rheological behavior through the studied fdd. The slip-layer thickness analysis, obtained using the conductimetry method, shows that the wall presents a liquid film thick enough to apply an electrochemical technique (polarography). Thus, the polarographic signals, obtained for the foam flow, present important fluctuations. They were compared to the wall shear stress deducted from the measurement of pressure losses, showing a good similarity between them. The numerical study (CFD), carried out for aqueous foam flow with a void fraction of 70% and a mean foam flow velocity of 2 cm/s, shows that the Bingham rheological model can be adapted to this kind of aqueous foam flow which is flowing like a block.

<p>  </p> <p>The study of two-phase flow in different orientations can allow for greater understanding of the fundamentals of two-phase flow dynamics. While a large amount of work has been performed for vertical flows and recent work has been done for horizontal flows, limited research has been done studying inclined upward two-phase flows between those two orientations. Studying two-phase flows at various inclinations is important for developing physical models and simulations of two-phase flow systems and understanding the changes between what is observed for symmetric vertical flows and asymmetric horizontal flows. The present work seeks to systematically characterize the effects of inclination on adiabatic concurrent air-water two-phase flows in straight pipes. An experimental database is established for local and global two-phase flow parameters in a novel inclinable 25.4 mm inner diameter test facility using four-sensor conductivity probes, high speed video capabilities, a ring-type impedance meter, a pressure transducer, and a gamma densitometer. Rotatable measurement ports are employed to allow for local conductivity probe measurements across the flow profile to capture asymmetric parameter distributions during experiments without stopping the flow. Some of the major effects of inclination are investigated, including the effects on flow regime transition, bubble distribution, frictional pressure loss, and relative motion between the two phases. Flow visualization and machine-learning methods are employed to identify the transitions between flow regimes for inclined orientations, and these transitions are compared against existing theoretical flow regime transition criteria proposed in literature. The theoretical transitions in literature agree well with both methods for vertical flow, but additional work is necessary for angles between 0 degrees and 60 degrees. The effect of inclination on two-phase frictional pressure drop is explored, and a novel adaption of the Lockhart-Martinelli pressure drop correlation is proposed, which is able to predict the pressure drop for the conditions investigated with an absolute percent difference of 2.6%. To explore the relationships between orientation, void fraction, and relative motion, one-dimensional drift flux analyses are performed for the data at each angle investigated. It is observed that the relative velocity between phases decreases as the angle is reduced, with a relative velocity near zero at some intermediate angles and a negative relative velocity for near-horizontal orientations.  Existing modeling capabilities that have been developed for vertical and horizontal flows are evaluated based on the local two-phase parameters collected at multiple orientations. The performance of the one-dimensional interfacial area transport equation for vertical and horizontal flows is tested against experimental data and a novel model for horizontal and inclined-upward bubbly flows is proposed. Finally, an evaluation of existing momentum transfer relations is performed for the two-fluid model using three-dimensional computational fluid dynamics tools for horizontal and inclined. The prediction of the void fraction distribution and gas velocity profiles are compared against experimental data, and improvements to the lift force model are identified based on changes in the relative velocity between phases. </p>