1,721,074 research outputs found
Étude multi-échelle du comportement hygrothermique, environnemental et mécanique des bâtiments en paille
No full textLes matériaux biosourcés, tels que la paille, ont généralement une faible énergie intrinsèque. Ils deviennent donc une alternative prometteuse pour améliorer la performance énergétique des bâtiments et réduire leur empreinte carbone. Comparés aux matériaux de construction courants, les matériaux biosourcés permettraient un meilleur contrôle de la température intérieure et des variations d'humidité relative, améliorant ainsi le confort thermique. Bien que largement étudié, il y a encore un manque de données concernant la performance thermique, hygrique et énergétique de telles structures. L'objectif de cette thèse est d'apporter une partie des réponses à travers des travaux expérimentaux et numériques.Bio-based materials such as straw have generally a low embodied energy. Therefore, they are becoming a promising alternative to improve buildings energy performance and reduce their carbon footprint. When compared to common building construction materials, bio-based materials allegedly provide better control of the indoor temperature and relative humidity variations, thus ameliorating thermal comfort. Although widely studied, there is still a lack of data concerning the thermal, hygric, and energetic performance of such structures. The purpose of this thesis is to provide some of the answers through experimental and numerical work
Study of the thermal behavior of an electrochemical battery thermoregulated by phase change materials for electric vehicles
No full textLa gestion thermique des batteries Li-ion pour le véhicule électrique est essentielle, pour assurer une autonomie et une durée de vie optimales de ces batteries. Habituellement, des circuits d'air ou de liquide de refroidissement sont utilisés comme systèmes de gestion thermique. Cependant, ces systèmes sont coûteux en termes d'investissement et d'exploitation et doivent être dimensionnés sur la puissance maximale à extraire. L'utilisation de matériaux à changement de phase (MCP) pour l’absorption sous forme de chaleur latente de la chaleur à dissiper peut représenter une alternative moins coûteuse et plus facile à utiliser. En effet, les MCP peuvent stocker passivement la chaleur excédentaire produite et être utilisés en tant que systèmes passifs. Cependant, les MCP présentent de nombreux inconvénients comme la difficulté de décharger l’énergie thermique stockée, ce qui limite l’aptitude du système au cyclage, ou encore leur conductivité thermique peu élevée qui limite les capacités d’échange. Pour résoudre le problème de la régénération des MCP, un système actif supplémentaire peut être ajouté, dimensionné sur une puissance modérée; l'ensemble devient alors un système semi-passif. Dans cette étude, un système de gestion thermique composé d'un MCP et d’air en convection forcée est évalué. Ce système permet de coupler les avantages de ces deux techniques. Une modélisation du système est développée pour une cellule de batterie. Une comparaison avec de l’air uniquement, en convection forcée, montre l'utilité du MCP. Pour augmenter la capacité d’échange du MCP, un matériau à haute conductivité thermique peut être ajouté au MCP, ce qui permet d’obtenir un composite ayant une conductivité thermique plus élevée. Des composites basés sur les MCP étudiés et des nanostructures de carbone sont élaborés, leur conductivité thermique est mesurée. Ensuite, un système expérimental simulant la dissipation d’une cellule de batterie est construit et utilisé pour évaluer le MCP seul, le MCP inclus dans une mousse métallique et le meilleur composite obtenu. Enfin, pour se rapprocher des conditions réelles, un modèle représentant un stack entier de batterie est développé, des simulations sont produites et les résultats obtenus sont commentés.Li-ion battery thermal management is essential for electric vehicles (EVs), to ensure an optimal autonomy and lifespan of those batteries. Usually, air or coolant circuits are employed as thermal management systems. However, those systems are expensive in terms of investment and operating costs and must be dimensioned on the maximal power to be extracted. The use of phase change materials (PCMs) as latent heat storage medium allowing the absorption of the heat to be dissipated as latent heat may represent an alternative cheaper and easier to operate. In fact, PCMs can passively store the excess heat produced by a device and be used as passive systems. However, PCMs have several drawbacks like the difficulty to discharge the stored thermal load which limits the system’s cyclability or their low thermal conductivity which limits their heat transfer capacity. To solve the problem of the PCM regeneration, an additional active system can be added, dimensioned on a moderate power; the whole becomes a semi-passive system. In this study, a thermal management system composed of a PCM and forced air convection is evaluated. This system permits to combine the respective advantages of the two techniques. A model of the system is developed for one battery cell. A comparison with forced air convection only points out the usefulness of the PCM. To overcome the PCM low thermal conductivity, a highly conductive material can be added to the PCM permitting to obtain a composite with a higher thermal conductivity. Composites based on the PCMs studied and carbon nanostructures are elaborated, and their thermal conductivity is measured. Then, an experimental system permitting to simulate the dissipation of a battery cell is build and used to evaluate the PCM alone, the PCM embedded in metal foam and the better obtained composite. Finally, to be closer to the real conditions, a model representing an entire battery stack is developed, simulations are produced and the obtained results are discussed
Thermo-hygric behavior of silica aerogel blankets and applications to building insulation
No full textEn Europe, le secteur du bâtiment est le plus énergivore et représente environ 40 % de l’énergie totale consommée. A court terme, la façon la plus efficace de baisser cette consommation est de réduire les déperditions thermiques à travers l’enveloppe du bâtiment en augmentant son isolation thermique, tout en minimisant la perte de surface habitable. Dans ce contexte, les travaux de thèse portent sur l’étude et la mise au point pour pré-industrialisation de matériaux super-isolants composites à base d'aérogel de silice. Le matériau composite étudié fait partie de la famille des blankets aérogels et est obtenu via un procédé de séchage ambiant innovant. Grâce à leur faible conductivité thermique et leurs propriétés mécaniques renforcées, les blankets aérogels sont d’un grand intérêt pour l’isolation thermique qui nécessite de fines épaisseurs d’isolants. Les travaux de thèse visent dans un premier temps à effectuer une analyse des propriétés thermophysiques des blankets aérogels étudiés à la sortie du moule de fabrication et vis-à-vis de leur mise en œuvre lorsqu’ils sont soumis à différentes sollicitations (mécaniques, hygriques ...). Des travaux de modélisation du transfert de chaleur dans le blanket aérogel sont développés afin d’étudier les relations entre le transfert thermique et les paramètres morphologiques du matériau. Dans un second temps, les travaux de thèse portent sur l’étude des performances à attendre d’un système d’isolation basé sur le blanket aérogel mis en œuvre sur un bâtiment, à la fois par l’analyse du comportement thermique d’une cellule test en climat réel, ainsi que par la conduite de simulations numériques de bâtiments prenant en compte plusieurs techniques constructives, configurations de murs, et ce, pour plusieurs climats européens. Les résultats obtenus montrent que les blankets aérogels étudiés ont une très faible conductivité thermique –0,016 W.m-1.K-1– et ont un fort potentiel d’application dans l’isolation thermique du bâtiment.Buildings are the largest energy end-use sector and account for about 40 % of the total final energy consumption in the EU-28. A short-term strategy to efficiently reduce this consumption is to decrease thermal losses through the building envelope by improving its thermal insulation, while minimizing the reduction of the available indoor living space. In this context, the thesis deals with the study and development for pre-industrialization of super-insulating composite materials based on silica aerogel. The studied material is part of the aerogel blanket family and is obtained by an innovative ambient drying process. With a very low thermal conductivity and reinforced mechanical properties, aerogel blankets are of great interest for applications where they can offer a cost advantage due to a space-saving effect. Firstly, the thesis work aims at performing analyses of the thermo-physical properties of the studied aerogel blankets at the exit of the molding and drying processes, and during application, when they are subjected to different environmental stresses (mechanical, hygric …). Heat transfer modeling is developed to study the relationship between the morphological parameters of the material and thermal transfer within it. Secondly, the thesis work focuses on the study of the expected performances of an insulating system based on the aerogel blanket, by the study of the thermal behavior of an experimental building monitored under actual climate, as well as the use of whole building energy numerical simulations taking into account several constructive techniques, different wall configurations, for various European climates. The results obtained show that the aerogel blankets studied have a thermal conductivity as low as 0.016 W.m-1.K-1 and have promising applications for building thermal insulation needs
Three-dimensional particle tracking velocimetry for the study of thermal convection airflow in buildings
No full textL'objectif de cette thèse est de réaliser une étude approfondie sur la vélocimétrie par suivi 3D de particules (3D Particle Tracking Velocimetry, 3D PTV) pour l'air intérieur convective thermique. Ce travail se concentre principalement sur l'étude de la littérature, l'évaluation des performances des algorithmes de mesure de la 3D PTV, et l'étude expérimentale pour l'air intérieur convective thermique en utilisant la technologie 3D PTV. Tout d'abord, la technologie 3D PTV typique et ses principales applications précédentes pour l'étude de d'air intérieur sont examinés. Ensuite, les performances de différents algorithmes de mesure de la 3D PTV sont évalués numériquement et expérimentalement. Deux sections se compose de cette partie, on est de comparer les performances de mesure de l'algorithme de PIV typique et l'algorithme de 3D PTV, une autre est de comparer les performances des sept algorithmes complets de 3D PTV. Enfin, sur la base de l'analyse présentée dans la thèse, l'étude expérimentale de l'écoulement d'air intérieur généré par la méthode de ventilation mélange est réaliséeThe objective of this thesis is to conduct a comprehensive study on 3D Particle Tracking velocimetry (PTV) for thermal convective indoor airflow. This work mainly concentrates on the literature survey, the performance evaluation of 3D PTV measurement algorithms, and the experimental investigation for thermal convective indoor airflow using 3D PTV measurement technology. First, typical 3D PTV technology and its main previous applications for indoor airflow study are carefully reviewed. Then, the performances of different 3D PTV measurement algorithms are evaluated numerically and experimentally. Two sections consist of this part, one is to compare the measurement performances of typical PIV algorithm and 3D PTV algorithm, another is to compare the performances of seven complete 3D PTV algorithms. Last, based on the analysis in the thesis, the experimental investigation for indoor airflow generated by mixing ventilation method is conducte
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Thermal behavior of a passive solar wall with silica aerogel and phase change materials
No full textInternational audienceThe present contribution discusses the thermal behavior of a passive solar wall composed of a glazing facing the outside, a channel filled with highly insulating and translucent silica aerogel, and glass bricks filled with an eutectic phase change material (PCM), facing the inside. First, the experimental building with the tested wall, south-oriented, is described. Second, the experimental results on four different weather conditions are detailed. Thanks to a numerical model, the wall behavior is simulated for the French climatic zones of Nice (Mediterranean climate), La Rochelle (oceanic climate), Embrun (inland mountain climate) and Nancy (cold continental climate). Results show that the wall is translucent and may save 27% to 83 % on the building energy bill for heating, depending on the building location. The wall performs best on cold sunny climates, where the phase change can occur all year. The air temperature inside the building is always 1 to 9°C above the external temperature. Overheating may occur in summer for Mediterranean and oceanic climates when the PCM stays in liquid state. This may be prevented by the use of shading
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Thermal behavior of a passive solar wall with silica aerogel and phase change materials
No full textInternational audienceThe present contribution discusses the thermal behavior of a passive solar wall composed of a glazing facing the outside, a channel filled with highly insulating and translucent silica aerogel, and glass bricks filled with an eutectic phase change material (PCM), facing the inside. First, the experimental building with the tested wall, south-oriented, is described. Second, the experimental results on four different weather conditions are detailed. Thanks to a numerical model, the wall behavior is simulated for the French climatic zones of Nice (Mediterranean climate), La Rochelle (oceanic climate), Embrun (inland mountain climate) and Nancy (cold continental climate). Results show that the wall is translucent and may save 27% to 83 % on the building energy bill for heating, depending on the building location. The wall performs best on cold sunny climates, where the phase change can occur all year. The air temperature inside the building is always 1 to 9°C above the external temperature. Overheating may occur in summer for Mediterranean and oceanic climates when the PCM stays in liquid state. This may be prevented by the use of shading
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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