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Développement et caractérisation de CMC oxyde/oxyde élaborés par imprégnation de mèches en continu
No full textThe use of oxide/oxide ceramic matrix composites (CMCs) is being considered for new generation engines. The main obstacle to the industrialisation of these materials are the diversity of production processes, their costs, and the heterogeneity of the microstructures and mechanical properties. This thesis is a collaboration between Onera, IRT Saint-Éxupéry and ICA. It investigates a new way of producing alumina/alumina CMC by using a continuous tow impregnation process. Firstly, a study was carried out into the formulation of aqueous alumina slurries compatible with the production of composites using a continuous tow impregnation line, followed by autoclave shaping and sintering. Two hygroscopic organic plasticisers, sorbitol and glycerol, as well as a gelling agent, boehmite, were evaluated. Autoclave thermal cycles were adapted to slurries compositions, with particular regard to the organic additives. Several compositions were selected and the microstructures of the resulting CMCs were characterised. The relationships between slurry composition, process adaptability and composite microstructure were investigated. Finally, the mechanical behaviour at ambient temperature of the different CMC grades were examined in relation to their microstructures, and tensile damage scenarios were proposed.L’introduction de composites à matrice céramique (CMC) oxyde/oxyde est envisagée dans les turbomachines de nouvelle génération. Les principaux freins à l’industrialisation de ces matériaux sont la diversité des procédés d’élaboration, leurs coûts, ainsi que l’hétérogénéité des microstructures et des propriétés mécaniques. Ces travaux de thèse en collaboration entre l’Onera, l’IRT Saint-Éxupéry et l’ICA étudient une nouvelle voie d’élaboration de CMC alumine/alumine, par une étape d’imprégnation de mèche en continu. Pour commencer, une étude de formulation de suspensions aqueuses d’alumine compatibles avec l’élaboration de composites par le procédé d’imprégnation en ligne suivi d’une mise en forme en autoclave et d’un frittage a été menée. Deux plastifiants organiques hygroscopiques, le sorbitol et le glycérol, ainsi qu’un gélifiant, la boehmite, ont été évalués. Les cycles thermiques en autoclave ont été adaptés à la composition des suspensions et en particulier aux additifs organiques. Plusieurs compositions de suspensions ont été retenues et les microstructures des CMC résultants ont été caractérisées. Les relations composition de la suspension – adaptabilité au procédé – microstructure du composite ont été investiguées. Enfin, les comportements mécaniques à température ambiante des différentes nuances de CMC ont été examinés en lien avec leurs microstructures, et des scénarios d’endommagement en traction ont été proposés
Integrate and mobile solution for low-cost cooking and power generation for African rural areas
No full textInternational audienceRural energy needs have been met by biomass for many centuries, albeit in a traditional way, which is associated with high per capita fuel use/low thermal efficiency, health risks (smoke inhalation and fire risks) [1]. In this context, the objective of the LEAP-RE Smart Home Africa (SHE) project is to propose and optimize an affordable smart energy device, flexible in terms of feedstock, that can provide electricity and cook/heat to support grid independence and self-sufficiency. The proposed device is based on an existing portable micro-gasifier cookstove used with compressed wood pellets, which is currently the best performing cookstove available regarding CO emissions [2]. However, the use of wood as fuel is problematic because of the natural deforestation due to the use of harvested wood as the primary fuel. The objective of the present study in the framework of the SHE project is assessing the suitability of agricultural residues and perennial energy crops as feedstock for the cookstove, as they are affordable and readily available fuels. The conformity of using alternative biofuels in the cookstove must be checked, particularly in terms of WHO (world health organization) cooking standards related to emissions and efficiency. For this purpose, three reference biomass (wood, miscanthus and rice husk pellets) will be characterized into detail as reference biomass species. Secondly, agricultural wastes from Western Nile Region will be characterized to determine if they meet ISO recommendations. They will be also compared to the reference biomass species to identify common patterns allowing the prediction of their emissions as a function of their characterization. Then, the reference biomass species will be tested in the cookstove and their emissions will be characterized into detail (permanent gases, tars, water, particle matter)
Rhéologie multi-échelle des poudres dans des mélangeurs convectifs (thèse sous embargo)
No full textUnderstanding powder flow behaviour during mechanical agitation is crucial for optimising mixing processes in industrial applications. This study introduces μ(I)-rheology, a novel rheological law developed to analyse powder rheology in dense flows within a laboratory mixing setup. The framework focuses on the interactions between paddles and the powder bed, addressing the challenges of measuring complex powder parameters such as the effective friction coefficient µeff. μ(I)-rheology, developed through dimensional analysis and shear band visualisation, demonstrates strong predictive capabilities across different powder configurations with similar particle shapes but varying sizes. The μ(I)-rheology framework proved applicable across various agitated system configurations and has laid the groundwork for initial scale-up studies that includes powder characteristics. Comparisons with Hatano's equation confirm the robustness of μ(I)-rheology, particularly for deep powder beds. Future improvements will focus on refining shear band width evaluation and reassessing normal stress assumptions to enhance model accuracy. This research contributes to a deeper understanding of powder dynamics in mixing systems and supports efficient scaling-up of industrial processes.Comprendre le comportement d'écoulement des poudres lors de l'agitation mécanique est crucial pour optimiser les processus de mélange dans les applications industrielles. Cette étude introduit la rhéologie μ(I), une loi rhéologique développée pour analyser la rhéologie des poudres dans les écoulements denses au sein d'un dispositif de mélange en laboratoire. Le cadre se concentre sur les interactions entre les pales et le lit de poudre, en abordant les défis de mesure de paramètres complexes des poudres tels que le coefficient de friction effectif µeff. La rhéologie μ(I), développée grâce à l'analyse dimensionnelle et à la visualisation des bandes de cisaillement, démontre de fortes capacités prédictives pour différentes configurations de poudres ayant des formes de particules similaires mais des tailles variées. Le cadre de la rhéologie μ(I) s'est révélé applicable à diverses configurations de systèmes agités et a posé les bases des premières études de mise à l'échelle incluant les caractéristiques des poudres. Les comparaisons avec l'équation de Hatano confirment la robustesse de la rhéologie μ(I), notamment pour les lits de poudre profonds. Les améliorations futures se concentreront sur le raffinement de l'évaluation de la largeur des bandes de cisaillement et la réévaluation des hypothèses de contrainte normale pour améliorer la précision du modèle. Cette recherche contribue à une compréhension approfondie de la dynamique des poudres dans les systèmes de mélange et soutient l'efficacité de la mise à l'échelle des processus industriels
Simulation-Based Framework for Assessing Synchromodal Transportation Solutions in Low-Density Ecosystems
No full textPart 6: Simulation FrameworksInternational audienceTransport and mobility play a crucial role in collaborative networks, facilitating access to resources. While this strengthens economic and social integration, the expansion of collaborative networks poses major challenges in terms of effectiveness, sustainability and equity. Improving transport services is consequently crucial, particularly in sparsely populated areas, to reduce economic and social disparities. If urban areas benefit from Smart City principles to optimize the flow of people and goods, rural areas are often marginalized. Some authors have demonstrated qualitatively the potentiality of using Physical Internet and synchromodality paradigms to change this situation. But no quantitative demonstration has been done yet. The purpose of this research work is to design and present our multi-agent vision of a simulation framework for evaluating synchromodal transport solutions in low-density ecosystems. Composed of four components (demand estimator, transportation planner, simulator engine and performance assessor), this framework is intended to be tested on ECOTRAIN case study
Thermal treatment of fiber-free multilayer packaging solid residue: synergism and effects on volatiles yield
No full textInternational audiencePotential of thermal treatment of multilayer packaging after cellulose recovery.Synergism observed between different components of the multilayer packaging
Low-Temperature Hot Corrosion Behavior of DS200 + Hf Nickel-Based Superalloy At 650 °C: Review
No full textInternational audienceThe morphologies of Type-II hot corrosion attacks were investigated at 650 °C for the DS200 + Hf nickel-based superalloy. The relationship between corrosion rate and microstructural features, i.e., grain boundaries, carbides, eutectics, dendrites, was considered at different scales and for three environments. Corrosion tests and related characterizations were carried out on a total of forty-five samples, including different sampling strategies, test conditions (air, air + 150 ppm SO2 and air+ 400 ppm SO2) and exposure times (24, 50 and 100 h). The amount of SO2 in the inlet gas was found to be the main factor in the degradation, affecting both the duration of the incubation period and directly the corrosion rate. The proportion of grain boundaries as well as their orientation did not have any influence on the degradation kinetics. On the contrary, MC carbides and γ + γ′ eutectic pools, i.e., the interdendritic area resulting from the solidification stage, underwent deeper attacks for all gaseous atmospheres. The global mechanism can be explained by the SO3-induced hot corrosion mechanism
Tri‐reforming of methane over a hydroxyapatite supported nickel catalyst
No full textInternational audienceFor the first time, a catalyst containing 5wt.% Ni supported on a hydroxyapatite support (HAP) has been synthesized and evaluated in tri‐reforming of methane (TRM) for synthetic gas (syngas) production. Nickel nanoparticles could be easily formed on HAP surface by using the conventional incipient wetness impregnation technique. In TRM, under unfavorable reaction conditions from the thermodynamic point of view (e.g. medium reforming temperature of 700‐800 °C, low steam‐to‐carbon ratio, etc.), this catalyst showed high methane conversion (up to 90%), however, some deactivation took place. The latter could be explained by both the thermal sintering of nickel nanoparticles and the solid carbon formation. The impact of the main operational parameters has been studied. Increasing the reaction temperature, the molar ratio of oxygen‐to‐carbon and steam‐to‐carbon ratio are favorable for the methane conversion and mostly for the stability of the catalyst. High methane conversion of ca. 90% with a perfect catalytic stability during 300 hours‐on‐stream could be achieved at 800 °C and 1.4 bar, using a mixture containing low ratio of oxidant‐to‐carbon (molar ratio of CH4/CO2/H2O/O2/N2 = 1.0/0.67/0.9/0.1/0). These results offer the opportunity to further design an optimal Ni/HAP catalyst by improving metal‐support interaction and downsizing nickel nanoparticles
Modélisation et optimisation des actifs pour l'aide à la prise de décision stratégique dans les entreprises
No full textThe tools and methods used to assist in strategic decision-making, particularly in SMEs, face several limitations. It is observed that they are primarily deterministic, based on past data, and are framed by an approach that is almost exclusively accounting and financial. However, strategic decisions in a company are activities aimed towards the future, highly subject to uncertainty, which aim to maximize the generated value of the company, whether it is financial or not. In this context, the research question addressed in this thesis is how to assist business leaders in making prospective strategic decisions in a context subject to uncertainty ? In terms of contributions, we first propose a conceptual framework based on a meta-model that allows representing a company according to a logic of assets and value. This modeling is then enriched with a causality diagram that establishes the existing dynamics between the assets that create value. To illustrate the applicability of this conceptual framework, an approach is proposed using experimental design based on a simulation model on one hand, and an optimization model in Mixed Integer Programming on the other hand. A set of experiments validates the relevance of the proposal, notably identifying the consequences of the decisions made on each asset in terms of generated value for the company.Les outils et méthodes d'aide à la décision stratégique, notamment utilisés dans les PME, font face à plusieurs limites. On note qu'ils sont essentiellement déterministes, basés sur des données passées, et sont cadrés par une approche quasi exclusivement comptable et financière. Pourtant, les décisions stratégiques en entreprise sont des activités tournées vers le futur, fortement soumis à incertitude qui visent à maximiser la valeur générée de l'entreprise qu'elle soit financière ou non. Dans ce contexte, la question de recherche adressée dans cette thèse est comment aider les dirigeants d'entreprise à prendre des décisions stratégiques prospectives dans un contexte soumis à une incertitude ? En termes de contributions, nous proposons d'abord un cadre conceptuel basé sur méta-modèle qui permet de représenter une entreprise selon une logique d'actifs et de valeur. Cette modélisation est ensuite enrichie d'un diagramme de causalité qui établit la dynamique existante entre les actifs permettant de créer de la valeur. Pour illustrer l'applicabilité de ce cadre conceptuel, on propose une approche par plan d'expériences basée sur un modèle de simulation d'une part, et un modèle d'optimisation en Programmation Mixte en Nombres Entiers d'autre part. Un ensemble d'expérimentations permet de valider la pertinence de la proposition et notamment d'identifier les conséquences des décisions prises sur chaque actif en matière de valeur générée pour l'entreprise
Refining intra-patch connectivity measures in landscape fragmentation and connectivity indices
No full textInternational audienceContext: Measuring intra-patch connectivity, i.e. the connectivity within a habitat patch, is important to evaluate landscape fragmentation and connectivity. However, intra-patch connectivity is mainly measured with patch size, which can conceal diverse intra-patch connectivity patterns for similar patch size distributions. Objectives We suggest a method to refine the intra-patch connectivity component of fragmentation and connectivity indices. This method allows for distinguishing different intra-patch connectivity patterns for similar patch size distributions. Methods We used normalized patch complexity indices to weight patch size in common fragmentation and connectivity indices. Patch complexity indices included two existing geometrical indices (SHAPE and FRAC), and a new index derived from spatial network analysis, the mean detour index (MDI). We analyzed the behaviours of adjusted fragmentation and connectivity indices theoretically and empirically on both artificial and real landscapes. Results While maintaining the mathematical properties of fragmentation and connectivity indices, our method could distinguish landscapes with identical patch size distributions but different spatial configurations. The mean detour index had a different response than geometrical indices. This result indicates that, at the patch level, topological complexity can exhibit different patterns from geometrical complexity. Conclusions Measuring intra-patch connectivity with patch size in fragmentation and connectivity indices cannot distinguish landscapes having similar patch sizes distribution but different spatial configurations. This paper introduces a method to distinguish such patterns relying on geometrical and topological indices and shows to which extent it can impact conservation planning
Functional estimation of the junction temperature with Monte Carlo method for electronic module cooling
No full textIn power electronics modules, accurately estimating the junction temperature is crucial for ensuring proper cooling and preventing device failure.Recent breakthroughs on the integral formulation of thermal couplings allows the estimation of physical quantities as transfer functions with Monte Carlo algorithms. The transfer function is estimated with a single Monte Carlo algorithm in which random walks are sampled to solve the coupled thermal problem involving conduction and convection in potential complex geometries. In the context of estimating junction temperature in power electronics modules, this involves simulating the thermal behavior of the module under various operating conditions, such as different levels of power dissipation and ambient temperatures. This paper addresses the junction temperature estimation as a function depending on a decisive parameter for the electronics power components cooling: the convective heat transfer coefficient.The different steps leading to the estimation of the transfer function are presented as well as its numerical validation against a results from a reference multiphysics electronics cooling simulation software (Celsius EC Solver). The results from the transfer functions are exposed for typical configurations of power modules and in both situations, the functions demonstrates the accuracy and reliability of the approach without degrading the geometrical or multiphysics complexities of the problem.Moreover, due to the computational time gain when estimating the junction temperature for different cooling configurations, the function obtained with Monte Carlo is prove being a relevant candidate for assessing thermal peformance of power electronics modules, accounting for uncertainties and variations inherent in operating conditions