Дисертації з теми "Elasticity and Thermal Conductivity"
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1
Abidi, Sonia. "Matériaux composites à haute tenue thermique : influence de la micro-nanostructure sur les transferts moléculaires, électroniques et thermiques." Thesis, Toulon, 2014. http://www.theses.fr/2014TOUL0019/document.
Анотація:
Les matériaux de protection incendie sont largement utilisés pour assurer la sécurité des usagers des infrastructures. Les normes de protection incendie évoluant régulièrement, les matériaux doivent être de plus en plus performants. Ceux-ci sont généralement des mortiers constitués d’oxydes réfractaires et isolants. L’objectif de ce travail est de mettre au point un composite coupe-feu 4 h applicable par projection mais également de déterminer ses propriétés thermiques et mécaniques.Dans une première partie, cette étude reprend les différentes étapes de l’élaboration d’un matériau de protection incendie, après la présentation de la démarche qui a guidé l’élaboration de nos matériaux, nous nous sommes intéressés plus particulièrement à la composition chimique de la matrice ainsi que celle du ciment. Leurs propriétés thermiques et mécaniques ont été passées en revue.Les matières premières nécessaires à l’élaboration d’un mortier ont ensuite été sélectionnées. L’évolution, respectivement de la conductivité thermique, de la diffusivité, de la porosité, de la chaleur spécifique et des propriétés mécaniques des mortiers choisis en fonction de la nature et de la quantité de charges incorporées à la matrice a été étudiée. Une description des divers modèles analytiques et numériques permettant la représentation de la conductivité thermique et du module d’Young des matériaux a permis de développer un modèle capable de prédire le comportement thermique et mécanique des composites en fonction de la nature et de quantité de charges ajoutées.Dans une seconde partie, la cinétique de la réaction d’hydratation du plâtre afin de maîtriser les temps de prise et pour faciliter la production des projetés dans la chaîne industrielle a été étudiée. L’influence sur la cinétique d’hydratation, de la composition chimique du plâtre, de sa granulométrie et de l’ajout d’adjuvants couramment utilisés dans l’industrie plâtrière, a également été traitée.10A l’issue de cette étude, deux formulations de composites projetables ont été mises au pointFire protection materials are widely used to ensure the safety of users of the infrastructure. Standards of fire protection regularly operating, the materials must be more efficient. These are generally composed of refractory mortar and insulating oxides. The objective of this work is to develop a firewall composite 4 h applied by projecting but also to determine the thermal and mechanical properties.In the first part, this study describes the various stages of the development of a fire protection material, after the presentation of the approach that has guided the development of our materials, we are interested especially in the chemical composition of the matrix and that of the cement. Their thermal and mechanical properties have been reviewed.The raw materials for the preparation of mortar were selected. The evolution respectively of thermal conductivity, diffusivity, porosity, specific heat and the mechanical properties of mortars chosen according to the nature and amount of the fillers incorporated in the matrix has been studied. A description of the various analytical and numerical models for the representation of the thermal conductivity and Young's modulus of the materials led to the development of a model able to predict the thermal and mechanical behavior of composites based on the nature and amount of charges added.In a second part, the kinetics of the hydration reaction of gypsum to control setting time and to facilitate the production of the composite in the industrial chain was studied. The influence on the kinetics of hydration, of the chemical composition of the gypsum, particle size distribution and the addition of adjuvant commonly used in the plaster industry, has also been treated.At the end of this study, two formulations of composites applied by projection were developed
2
Chen, Fengjuan. "Modélisation micromécanique de milieux poreux hétérogènes et applications aux roches oolithiques." Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0134/document.
Анотація:
La problématique suivie dans ce travail est la détermination des propriétés effectives, élastiques et conductivité, de matériaux poreux hétérogènes tels que des roches, les roches oolithiques en particulier, en relation avec leur microstructure. Le cadre théorique adopté est celui de l’homogénéisation des milieux hétérogènes aléatoires et on suit les approches par tenseurs d’Eshelby. Ces approches sont basées sur la résolution des problèmes d’Eshelby : le problème de l’inclusion (premier problème) et le problème de l’inhomogénéité (second problème) isolées dans un milieu infini. La solution de ces problèmes de référence est analytique, en élasticité linéaire isotrope et en diffusion linéaire stationnaire, dans le cas d’inhomogénéités 2D ou 3D de type ellipsoïde. Elle conduit à la définition de tenseurs caractérisant les interactions entre l’inclusion/inhomogénéité et le milieu environnant. On utilise dans ce travail les tenseurs de contribution relatifs à une inhomogénéité isolée, définis par Kachanov et Sevostianov 2013, contributions à la souplesse (élasticité) et à la résistivité (conductivité). Ces tenseurs au cœur des méthodes d’homogénéisation de type EMA (Effective Medium Approximation), et en particulier les schémas NIA (Non Interaction Approximation), Mori Tanaka et Maxwell. Ce travail est centré sur la caractérisation des paramètres géométriques microstructuraux dont l’influence sur les propriétés effectives est majeure. On étudie en particulier les effets de forme des inhomogénéités, la nouveauté est l’aspect 3D. Les observations microstructurales de roches oolithiques, dont le calcaire de référence de Lavoux, mettent en évidence des hétérogénéités de forme 3D et concave. En particulier les matériaux de remplissage inter-oolithes, pores ou calcite syntaxiale. Ces formes peuvent être observées sur d’autres matériaux hétérogènes et ont été peu étudiées dans le cadre micromécanique. Cela nécessite de considérer des formes non ellipsoïdales et de résoudre numériquement les problèmes d’Eshelby. Le cœur de ce travail est consacré à la détermination des tenseurs de contribution d’inhomogénéités 3D convexes ou concaves de type supersphère (à symétrie cubique) ou supersphéroïde (à symétrie de révolution). Le premier problème d’Eshelby a été résolu, dans le cas de la supersphère, par intégration numérique de la fonction de Green exacte (solution de Kelvin dans le cas isotrope) sur la surface de l’inclusion. Des modélisations 3D aux éléments finis ont permis de résoudre le second problème d’Eshelby et d’obtenir les tenseurs de contribution à la souplesse et à la résistivité pour les superphère et supersphéroïde. Sur la base des résultats numériques, des relations analytiques simplifiées ont été proposées pour les tenseurs de contribution sous forme de fonctions des paramètres élastiques des constituants et du paramètre adimensionnel p caractérisant la concavité. Un résultat important, dans le cas de la superphère et dans le domaine concave, est l’identification d’un même paramètre géométrique pour les tenseurs de contribution à la souplesse et à la résistivité. Les résultats numériques et théoriques obtenus sont appliqués à deux problèmes : l’estimation de la conductivité thermique effective de roches calcaires oolithiques d’une part et l’étude de l’extension des relations dites de substitution définies par Kachanov et Sevostianov 2007 au cas non ellipsoïdal d’autre part. Pour le premier problème, un modèle micromécanique de type Maxwell, à deux échelles a permis de retrouver les résultats expérimentaux disponibles dans la littérature, en en particulier l’influence de la porosité sur la conductivité thermique effective dans les cas sec et humide. Dans le cas du second problème, les résultats obtenus ont permis de montrer que la validité de relations de substitution est restreinte, dans le cas non ellipsoïdal et en considérant une forme d’inhomogénéité de type supersphère, au domaine convexe seulementFocusing on the effect of shape factor on the overall effective properties of heterogeneous materials, the 1st and the 2nd Eshelby problem related to 3-D non-ellipsoidal inhomogeneities with a specific application to oolitic rocks have been discussed in the current work. Particular attention is focused on concaves shapes such as supersphere and superspheroid. For rocks, they may represent pores or solid mineral materials embbeded in the surrounding rock matrix. In the 1st Eshelby problem, Eshelby tensor interrelates the resulting strain about inclusion and eigenstrain that would have been experienced inside the inclusion without any external contraire. Calculations of this tensor for superspherical pores– both concave and convex shapes – are performed numerically. Results are given by an integration of derivation of Green’s tensor over volume of the inclusion. Comparisons with the results of Onaka (2001) for convex superspheres show that the performed calculations have an accuracy better than 1%. The current calculations have been done to complete his results. In the 2nd Eshelby problem, property contribution tensors that characterizes the contribution of an individual inhomogeneity on the overall physical properties have been numerically calculated by using Finite Element Method (FEM). Property contribution tensors of 3D non ellipsoidal inhomogeneities, such as supersphere and superspheroid, have been obtained. Simplified analytical relations have been derived for both compliance contribution tensor and resistivity contribution tensor. Property contribution tensors have been used to estimate effective elastic properties and effective conductivity of random heterogeneous materials, in the framework of Non-Interaction Approximation, Mori-Tanaka scheme and Maxwell scheme. Two applications in the field of geomechanics and geophysics have been done. The first application concerns the evaluation of the effective thermal conductivity of oolitic rocks is performed to complete the work of Sevostianov and Giraud (2013) for effective elastic properties. A two step homogenization model has been developed by considering two distinct classes of pores: microporosity (intra oolitic porosity) and meso porosity (inter oolitic porosity). Maxwell homogenization scheme formulated in terms of resistivity contribution tensor has been used for the transition from meso to macroscale. Concave inter oolitic pores of superspherical shape have been taken into account by using resistivity contribution tensor obtained thanks to FEM modelling. Two limiting cases have been considered: ‘dry case’ (air saturated pores) and ‘wet case’ (water liquid saturated pores). Comparisons with experimental data show that variations of effective thermal conductivity with porosity in the most sensitive case of air saturated porosity are correctly reproduced. Applicability of the replacement relations, initially derived by Sevostianov and Kachanov (2007) for ellipsoidal inhomogeneities, to non-ellipsoidal ones has been investigated. It it the second application of newly obtained results on property contribution tensors. We have considered 3D inhomogeneities of superspherical shape. From the results, it has been seen that these relations are valid only in the convex domain, with an accuracy better than 10%. Replacement relations can not be used in the concave domain for such particular 3D shape
3
Du, Kou. "Modélisation micromécanique de géomatériaux en prenant en compte des anisotropies microstructurale et matricielle." Electronic Thesis or Diss., Université de Lorraine, 2021. http://docnum.univ-lorraine.fr/public/DDOC_T_2021_0254_DU.pdf.
Анотація:
Les propriétés mécaniques des géomatériaux hétérogènes sont évaluées en prenant simultanément en compte l'anisotropie microstructurale ainsi que celle du matériau matriciel. A cet effet, l'anisotropie de la microstructure est représentée par la complexité de forme poreuse et/ou d'inclusion qui est considérée dans le présent travail comme concave ou convexe en portant nos attentions particulières aux pores supersphériques et supersphéroïdaux axisymétriques. Les tenseurs de concentration et de contribution sont calculés numériquement à l'aide de la méthode des élément finis (FEM), qui est ensuite utilisés au niveau de la modélisation semi-analytique pour l'objectif d'évaluer des propriétés effectives associées, telles que des réponses effectives élastiques et celles de conductivité. Plus précisément, afin de résoudre le 2ème problème d'Eshelby (Eshelby (1961)) dans le cas d'inhomogénéités 3D et non ellipsoïdales, nous utilisons conditions aux limites adaptées récemment développées par Adessina et al. (2017) basé sur une solution en champ lointain (Sevostianov and Kachanov (2011)) pour intégrer l'anisotropie matricielle et la correction du biais induit par le caractère borné du domaine du maillage, ce qui permet d'accélérer la convergence du calcul sans sacrifier sa précision. En adoptant la technique d'homogénéisation numérique, les tenseurs de contribution compliance/résistivité sont calculés pour différentes formes de pores (attention particulière des pores supersphéroïdaux et supersphériques) noyés dans une matrice isotrope transverse. La méthode numérique proposée s'avère efficace et précise après un grand nombre d'estimations et leurs validations. Dans certains cas particuliers, ces validations s'effectuent avec des comparaisons entre les résultats analytiques et numériques disponibles dans littérature. En prenant en compte les résultats numériques obtenus pour des microstructures tridimensionnelles (3D) considérées, les tenseurs de contribution dans les deux cas d'inclusions/pores concaves indiqués ci-dessus, supersphère et supersphéroïde axisymétrique, sont développées dans les contextes des problèmes élastiques et thermiques. Notons ici que la forme d'inclusion/pore sphérique (i.e. paramètre de concavité p=1) ainsi que celle de fissure circulaire (i.e. rapport d'aspect γ → 0), qui peuvent être considérés comme deux cas particuliers, sont également étudiés. Cela permet d'évaluer et de valider la méthode proposée dans le présent travail. De plus, dans le cadre de l'homogénéisation, une application aux géomatériaux poreux à matrice isotrope transverse, tels que les roches argileuses, est présentée pour illustrer l'impact du paramètre de concavité et celui de l'anisotropie de la matrice sur les propriétés globales à travers plusieurs schémas d'homogénéisation micromécanique, tels que l'approche basée sur l'approximation de non-interaction (i.e. NIA: Non-Interaction Approximation), schéma de Mori-Tanaka-Benveniste et celui de Maxwell. Les propriétés effectives des composites à pores réguliers sont également estimées à l'aide de l'approche dite champ complet par simulations numériques, puis comparées à la modélisation micromécanique. L'effet de microstructure complexes est étudié en considérant des Volumes Elémentaires Représentatifs (VERs) périodiques contenant des arrangements aléatoires des pores noyés dans des matrices isotropes transversesThe mechanical properties of heterogeneous geomaterials are evaluated by simultaneously taking into account the microstructural anisotropy as well as the one of matrix. To this end, the microstructural anisotropy is represented by the complexity of porous shape which is considered in the present work as concave or convex by particular attention to the superspherical and the axisymmetrical superspheroidal pores. The concentration and contribution tensors are numerically computed using Finite Element Method (FEM), which are next approximated by analytical expressions for the case of the concavity parameter being p<1, to evaluate the associated effective properties, such as effective elastic and thermal responses. Specifically, to solve the 2nd Eshelby problem (Eshelby (1961)) in the case of 3D non-ellipsoidal inhomogeneities, we make use of a recently developed adapted boundary condition (Adessina et al. (2017)) based on far-field solution (Sevostianov and Kachanov (2011)) to incorporate the matrix anisotropy and to correct the bias induced by the bounded character of the mesh domain, which allows to accelerate the computation convergence without sacrificing its accuracy. Simultaneously by complying with the numerical homogenization technique, the compliance/resistivity contribution tensors are computed for different forms of pores (particular attention of superspheroidal and superspherical ones) embedded in a transversely isotropic matrix. The proposed numerical method is shown to be efficient and accurate after several appropriate assessments and validation by comparing its predictions, in some particular cases, with analytical results and some available numerical ones. On the basis of these "3D" Finite Element Modeling, approximate relations of the property contribution tensors in the two aforementioned reference concave cases, supersphere and axisymmetric superspheroid, are developed for both elastic and thermal problems. Note here that the spherical pore (i.e. concavity parameter p=1) and circular crack (i.e. aspect ratio γ → 0), which can be considered as two particular cases, are also numerically studied. This allows to assess and validate the proposed method in the present work. Moreover, in the frame of homogenization, application to the typical porous geomaterials with transversely isotropic matrix such as clay rocks is presented to illustrate the impact of the concavity parameter and the matrix anisotropy on overall properties through several micromechanical homogenization schemes such as non-interaction approximation, Mori-Tanaka-Benveniste scheme and Maxwell scheme. The methodology of evaluation of the elastic and thermal properties of heterogeneous material aforementioned is proposed based on micromechanical homogenization via multiscale modeling. The overall properties of composites with regular pores are also predicted using direct finite element approaches and then compared against micromechanical modeling. The effect of microstructure is analyzed by considering periodic RVEs containing random arrangements of pores formed by transversely isotropic phases
4
He, Tianlong. "A new approach based on finite element method for numerical computation of effective properties for composite materials : Phantom Domain Finite Element Method." Thesis, Normandie, 2020. http://www.theses.fr/2020NORMC204.
Анотація:
Pour contourner la difficulté de maillage des méthodes numériques existantes de l’homogénéisation des composites, une méthode originale, nommée la méthode des éléments finis du domaine fantôme (PFEM), est proposée dans cette thèse. Le PFEM s'appuie sur les calculs d'intégrales avec des maillages distincts basés sur un principe de domaine fictif. En d'autres termes, un maillage structuré est utilisé pour l'ensemble du domaine et les autres maillages indépendants sont utilisés pour les inclusions. Les maillages des inclusions seront liés au maillage du domaine via une matrice de substitution. Le PFEM est non seulement capable de calculer les propriétés effectives avec KUBC, SUBC et les conditions périodiques, mais aussi peut être utilisé dans tous les problèmes qui peuvent être résolus par le FEM classique, comme les problèmes aux limites de Dirichlet ou de Neumann. Des expériences numériques dans les cas 2D et 3D, avec des inclusions de géométrie élémentaire telles que disque, carré, sphère, cube et ellipsoïde, ont été réalisées pour valider le PFEM. Les convergences linéaires d'erreurs relatives par rapport aux solutions de référence telles que le modèle de Mori-Tanaka et la méthode de transformation de Fourier rapide sont présentées pour les propriétés effectives en thermique et en élastique. Nous avons illustrés quelques caractéristiques intéressantes du PFEM, par exemple la flexibilité au niveau du maillage d'inclusion, en montrant un exemple avec une pellicule sphérique très minceTo circumvent the meshing difficulty of the existing numerical methods for composites homogenization, an original finite element method,named Phantom domain Finite Element Method (PFEM), is proposed in this thesis. The PFEM relies on computations of integrals with independent meshes based on a fictitious domain principle. In other words, one structured mesh is used for the entire domain, and independent meshes are used for the inclusions. The inclusion meshes will be related to the structured mesh through a substitution matrix. The PFEM is not only capable of calculating effective properties in homogenization technique with KUBC, SUBC and periodic condition, but also can be used in all the problems which can be solved by the FEM, such as the Dirichlet or Neumann boundary value problems. Numerical experiments in two or three dimensional cases, with inclusions of elementary geometry such as disk, square, sphere,cube and ellipsoid, have been performed to validate the PFEM method. Linear convergences of relative errors with respect to reference solutions such as the Mori-Tanaka model and the Fast Fourier Transform method are shown for thermal and elastic effective properties. We have illustrated some interesting features of the PFEM, such as the total flexibility concerning the inclusions meshes, by showing an example with a very thin pellicle sphere
5
Tardieu, Giliane. "Thermal conductivity prediction." Thesis, Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/10014.
6
Martin, Ana Isabel. "Hydrate Bearing Sediments-Thermal Conductivity." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6844.
Анотація:
The thermal properties of hydrate bearing sediments remain poorly studied, in part due to measurement difficulties inside the hydrate stability envelope. In particular, there is a dearth of experimental data on hydrate-bearing sediments, and most available measurements and models correspond to bulk gas hydrates. However, hydrates in nature largely occur in porous media, e.g. sand, silt and clay.
The purpose of this research is to determine the thermal properties of hydrate-bearing sediments under laboratory conditions, for a wide range of soils from coarse-grained sand to fine-grained silica flour and kaolinite. The thermal conductivity is measured before and after hydrate formation, at effective confining stress in the range from 0.03 MPa to 1 MPa. Results show the complex interplay between soil grain size, effective confinement and the amount of the pore space filled with hydrate on the thermal conductivity of hydrate-bearing sediments.
7
Mensah-Brown, Henry. "Thermal conductivity of liquid mixtures." Thesis, Imperial College London, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362870.
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Peralta, Martinez Maria Vita. "Thermal conductivity of molten metals." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391505.
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Jawad, Shadwan Hamid. "Thermal conductivity of polyatomic gases." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367922.
10
Valter, Mikael. "Thermal Conductivity of Uranium Mononitride." Thesis, Linköpings universitet, Tunnfilmsfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-122337.
Анотація:
Thermal conductivity is a crucial parameter for nuclear fuel, as it sets an upper limit on reactor operating temperature to have safety margins. Uranium mononitride (UN) is a prospective fuel for fast reactors, for which limited experimental studies have been conducted, compared to the currently dominating light-water reactor fuel, uranium dioxide. The aim of this thesis is to determine the thermal conductivity in UN and to determine its porosity dependence. This was done by manufacturing dense and porous high-purity samples of UN and examining them with laser flash analysis, which with data on specific heat and thermal expansion gives the thermal conductivity. To analyse the result, a theoretical study of the phenomenology of thermal conductivity as well as a review and comparison with previous investigations were carried out. The porosity range was 0.1–31% of theoretical density. Thermal diffusivity data from laser flash analysis, thermal expansion data and specific heat data was collected for 25–1400 C. The laser flash data had high discrepancy at higher temperatures due to thermal instability in the device and deviations due to graphite deposition on the samples, but the low temperature data should be reliable. As the specific heat data was also of poor quality, literature data was used instead. As for the thermal diffusivity data, the calculated thermal conductivity for lower temperatures are more accurate. A modified version of the porosity model by Ondracek and Schulz was used to analyse the porosity dependence of the thermal conductivity, taking into account the different impacts of open and closed porosity.Värmeledningsförmåga är en avgörande egenskap för kärnbränslen, eftersom det begränsar den maximala drifttemperaturen i reaktorn för att ha säkerhetsmarginaler. Uranmononitrid (UN) är ett framtida bränsle för snabba reaktorer. Jämfört med det dominerande bränslet i lättvattenreaktorer, urandioxid, har endast begränsade experimentella studier gjorts av UN. Målet med detta arbete är att bestämma värmeledningsförmågan i UN och bestämma dess porositetsberoende. Detta gjordes genom att tillverka kompakta och porösa prover av UN och undersöka dem med laserblixtmetoden, vilket tillsammans med värmekapacitet och värmeutvidgning ger värmeledningsförmågan. För att analysera resultatet gjordes en teoretisk studie av värmeledning såväl som en genomgång av och jämförelse med tidigare undersökningar. Provernas porositet sträckte sig från 0.1% till 31% av teoretisk densitet. Värmediffusivitetsdata från laserblixtmetoden, värmeutvidgningsdata och värmekapacitetsdata samlades in för 25–1400 C. Värdena från laserblixtmätningen hade hög diskrepans vid höga temperaturer p.g.a. termisk instabilitet i anordningen och avvikelser p.g.a. grafitavlagring på proverna, men data för låga temperaturer borde vara tillförlitliga. Eftersom resultaten från värmekapacitetsmätningen var av dålig kvalité, användes litteraturdata istället. Som en konsekvens av bristerna i mätningen av värmediffusivitet är presenterade data för värmeledningsförmåga mest exakta för låga temperaturer. En modifierad version av Ondracek-Schulz porositetsmodell användes för att analysera värmeledningsförmågans porositetsberoende genom att ta hänsyn till olika inverkan av öppen och sluten porositet.
11
Anderson, Stephen Ashcraft. "The thermal conductivity of intermetallics." Master's thesis, University of Cape Town, 1996. http://hdl.handle.net/11427/18185.
Анотація:
Includes bibliographical references.The thermal conductivity of titanium aluminide and several ruthenium-aluminium alloys has been studied from room temperature up to 500°C. Ruthenium aluminide is a B2-type intermetallic which is unusual and of special interest because of its toughness, specific strength and stiffness, oxidation resistance and low cost. The possible use of ruthenium aluminide in high temperature industrial applications required an investigation of the thermal properties of this compound. Apparatus, capable of measuring thermal conductivity at elevated temperatures has been designed and constructed. This study represents the first experimental results for the thermal conductivity of ruthenium aluminide alloys. The electrical resistivity of the intermetallic compounds has been measured using apparatus based on the Van der Pauw method. The Weidman-Franz ratio of the ruthenium aluminide alloys has been calculated and this indicates that the primary source of heat conduction in these alloys is by electronic movement and that the lattice contribution is minor. The electrical and thermal properties of ruthenium aluminide are shown to be similar to that of platinum and nickel aluminide. This has important implications for the use of these alloys in high temperature applications.
12
Karayacoubian, Paul. "Effective Thermal Conductivity of Composite Fluidic Thermal Interface Materials." Thesis, University of Waterloo, 2006. http://hdl.handle.net/10012/2881.
Анотація:
Thermally enhanced greases made of dispersions of small conductive particles suspended in fluidic polymers can offer significant advantages when used as a thermal interface material (TIM) in microelectronics cooling applications. A fundamental problem which remains to be addressed is how to predict the effective thermal conductivity of these materials, an important parameter in establishing the bulk resistance to heat flow through the TIM. The following study presents the application of two simple theorems for establishing bounds on the effective thermal conductivity of such inhomogeneous media. These theorems are applied to the development of models which are the geometric means of the upper and lower bounds for effective thermal conductivity of base fluids into which are suspended particles of various geometries.
Numerical work indicates that the models show generally good agreement for the various geometric dispersions, in particular for particles with low to moderate aspect ratios. The numerical results approach the lower bound as the conductivity ratio is increased. An important observation is that orienting the particles in the direction of heat flow leads to substantial enhancment in the thermal conductivity of the base fluid. Clustering leads to a small enhancement in effective thermal conductivity beyond that which is predicted for systems composed of regular arrays of particles. Although significant enhancement is possible if the clusters are large, in reality, clustering to the extent that solid agglomerates span large distances is unlikely since such clusters would settle out of the fluid.
In addition, experimental work available in the literature indicates that the agreement between the selected experimental data and the geometric mean of the upper and lower bounds for a sphere in a unit cell are in excellent agreement, even for particles which are irregular in shape.
13
Mutnuri, Bhyrav. "Thermal conductivity characterization of composite materials." Morgantown, W. Va. : [West Virginia University Libraries], 2006. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4468.
Анотація:
Thesis (M.S.)--West Virginia University, 2006.Title from document title page. Document formatted into pages; contains vii, 62 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 61-62).
14
Wei, Xiaohao, and 魏晓浩. "Nanofluids: synthesis, characterization and thermal conductivity." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B44765861.
15
Jiang, Wei, and 姜为. "Synthesis and thermal conductivity of nanofluids." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B45518063.
16
Freeman, J. J. "The thermal conductivity of amorphous polymers." Thesis, University of Leeds, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355947.
17
Dudnik, S. F., A. I. Kalinichenko, and V. E. Strel’nitskij. "On Thermal Conductivity of Anisotropic Nanodiamond." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35196.
Анотація:
Dependence of thermal conductivity of nanocrystalline diamond coating on grain size and form is
theoretically investigated. Nanodiamond is considered as two-phase material composed of dielectric
diamond grains characterizing by three main dimensions and segregated by thin graphite layers with
electron or phonon thermal conductivity. Influence of thermal conductance type and thickness of boundary
layer on nanodiamond thermal conductivity is analysed. Derived dependences of thermal conductivity on
grain dimensions are compared with experimental data.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35196
18
Webber, Christina Marie. "Prosthetic Sockets: Assessment of Thermal Conductivity." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1404224355.
19
Beck, Michael Peter. "Thermal conductivity of metal oxide nanofluids." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26488.
Анотація:
Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2009.Committee Chair: Teja, Amyn S.; Committee Member: Abdel-Khalik, Said I.; Committee Member: Meredith, Carson; Committee Member: Nair, Sankar; Committee Member: Skandan, Ganesh. Part of the SMARTech Electronic Thesis and Dissertation Collection.
20
Madrid, Lozano Francesc. "Thermal Conductivity and Specific Heat Measurements for Power Electronics Packaging Materials. Effective Thermal Conductivity Steady State and Transient Thermal Parameter Identification Methods." Doctoral thesis, Universitat Autònoma de Barcelona, 2005. http://hdl.handle.net/10803/5348.
21
Bihari, Kathleen L. "Analysis of Thermal Conductivity in Composite Adhesives." NCSU, 2001. http://www.lib.ncsu.edu/theses/available/etd-20010808-130536.
Анотація:
BIHARI, KATHLEEN LOUISE. Analysis of Thermal Conductivity in Composite Adhesives (Under the direction of H. Thomas Banks). Thermally conductive composite adhesives are desirable in many industrial applications, including computers, microelectronics, machinery and appliances. These composite adhesives are formed when a filler particle of high conductivity is added to a base adhesive. Typically, adhesives are poor thermal conductors. Experimentally only small improvements in the thermal properties of the composite adhesives over the base adhesives have been observed. A thorough understanding of heat transfer through a composite adhesive would aid in the design of a thermally conductive composite adhesive that has the desired thermal properties.In this work, we study design methodologies for thermally conductive composite adhesives. We present a three dimensional model for heat transfer through a composite adhesive based on its composition and on the experimental method for measuring its thermal properties. For proof of concept, we reduce our model to a two dimensional model. We present numerical solutions to our two dimensional model based on a composite silicone and investigate the effect of the particle geometry on the heat flow through this composite. We also present homogenization theory as a tool for computing the ``effective thermal conductivity" of a composite material.We prove existence, uniqueness and continuous dependence theorems for our two dimensional model. We formulate a parameter estimation problem for the two dimensional model and present numerical results. We first estimate the thermal conductivity parameters as constants, and then use a probability based approach to estimate the parameters as realizations of random variables. A theoretical framework for the probability based approach is outlined.Based on the results of the parameter estimation problem, we are led to formally derive sensitivity equations for our system. We investigate the sensitivity of our composite silicone with respect to the thermal conductivity of both the base silicone polymer and the filler particles. Numerical results of this investigation are also presented.
22
Ford, Theodore Robert. "Thermal conductivity of bonded hollow-sphere monoliths." Thesis, Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/20045.
23
Russell, Carissa Don. "INTERFACIAL THERMAL CONDUCTIVITY USING MULTIWALL CARBON NANOTUBES." UKnowledge, 2010. http://uknowledge.uky.edu/gradschool_theses/30.
Анотація:
Shrinking volume, coupled with higher performance, microprocessors and integrated circuits have led to serious heat dissipation issues. In an effort to mitigate the excessive amounts of waste heat and ensure electronic survivability, heat sinks and spreaders are incorporated into heat generating device structures. This inevitability creates a thermal pathway through an interface. Thermal interfaces can possess serious thermal resistances for heat conduction. The introduction of a thermal interface material (TIM) can drastically increase the thermal performance of the component. Exceptional thermal properties of multiwall carbon nanotubes (MWCNTs) have spurred interest in their use as TIMs. MWCNTs inherently grow in vertically-oriented, high aspect ratio arrays, which is ideal in thermal interface applications because CNTs posses their superior thermal performance along their axis. In this paper, laser flash thermal characterization of sandwich‐bonded and cap‐screw‐bonded aluminum discs for both adhesive-infiltrated and “dry”, 100% MWCNT arrays, respectively. Thermal contact resistances as low as 18.1 mm2K/W were observed for adhesive‐infiltrated arrays and, even lower values, down to 10.583 mm2K/W were measured for “dry” MWCNT arrays. The improved thermal performance of the arrays compared to thermal adhesives and greases currently used in the electronics and aerospace industries, characterize MWCNT arrays as a novel, lighter‐weight, non‐corrosive replacement.
24
Regan, Simon Edmund. "The low temperature thermal conductivity of polymers." Thesis, University of Leeds, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277153.
25
Zalaf, M. "The thermal conductivity of electrically-conducting liquids." Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47321.
26
Bilek, Jaromir. "Sensors for thermal conductivity at high temperatures." Thesis, University of Southampton, 2006. https://eprints.soton.ac.uk/47126/.
Анотація:
This thesis describes research undertaken to improve a technique for the measurement of the thermal conductivity of molten materials. The research follows on from the work of previous researchers who designed and tested an instrument for the measurements of the thermal conductivity of molten metals up to 750 K. The previously used transient hot-wire technique, which consisted of the experimental measurement of the voltage response of a sensor and a subsequent inverse Unite element analysis, has been significantly upgraded. The experimental part of the technique has been improved by the introduction of a new design of the sensor for the measurement of the thermal conductivity. Both the new and the original designs have been used to investigate the same material samples in order to demonstrate the robustness and repeatability of the experimental technique. Additionally, the finite element analysis employed has also undergone various major improvements and resulted in a new finite element model which not only represents the true geometry of the experimental device but also employs a more accurate solution of the transient, conductive heat transfer. The significant upgrade of the technique and the availability of two different sensor designs have helped to uncover systematic errors which could not have been previously identified and may have resulted in deviations of the measured thermal conductivity. Five original sensors and five sensors with the new design have been used to investigate the thermal conductivity of molten indium, tin and lead at various temperatures up to 750 K. The results have been compared to previously published data and the discrepancies have been discussed and explained. Each metal has been measured using at least two sensors and the consistency of the measured data has also been verified by using two different samples of pure tin. Besides the pure metals, the thermal conductivity of several metal alloys currently used in industry has been investigated within the same temperature range. The overall uncertainty of the measurements of the thermal conductivity is estimated to be ±3 %.
27
Kashfipour, Marjan Alsadat. "Thermal Conductivity Enhancement Of Polymer Based Materials." University of Akron / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron156415885613422.
28
Dougherty, Brian P. "An automated probe for thermal conductivity measurements." Thesis, Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/101183.
Анотація:
A transient technique was validated for making thermal conductivity measurements. The technique incorporated a small, effectively spherical, heat source and temperature sensing probe. The actual thermal conductivity measurements lasted 30 seconds. After approximately 15 minutes of data reduction, a value for thermal conductivity was obtained. The probe yielded local thermal conductivity measurements. Spherical sample volumes less than 8 cm² were required for the materials tested. Thermal conductivity (and moisture) distributions can be measured for relatively dry or wetted samples.
The technique employs an encapsulated bead thermistor. A thermistor, more commonly used as a temperature transducer, has the inherent feature of being readily self-heated. A computer-based data acquisition and control system regulates the power supplied to the thermistor such that its self-heated temperature response approximates a step change. Thermal conductivity is deduced from the transient measurement of the power dissipated by the probe as a function of time.
The technique was used to measure the thermal conductivity of fifteen liquids and five insulation materials. Two different thermistor types, glass-encapsulated and Teflon-encapsulated, were evaluated. Capabilities and limitations of each probe type and the measurement technique, in general, were observed.M.S.
29
Natchimuthu, Chinnaraj Anand. "THERMAL CONDUCTIVITY ENHANCEMENT IN NANOFLUIDS -MATHEMATICAL MODEL." OpenSIUC, 2011. https://opensiuc.lib.siu.edu/theses/758.
Анотація:
The study on developing a mathematical model for thermal conductivity enhancement in nanofluids was based on formation of nanoparticles into nanoclusters, nanolayer thickness, Brownian motion and volume fraction of nanoclusters. An equation for the thermal conductivity of nanofluids was developed. The expression developed successfully explained the enhanced thermal conductivity of nanofluids and led to some important conclusions. It was found that in this study the nanoparticles tend to form nanoclusters and the volume fraction of the nanoclusters and the trapped fluid in the nanocluster was contributing to the overall thermal conductivity enhancement. Various types of cluster formation was analyzed and it was understood that the nanoparticles forming a spherical nanoclusters are more effective in thermal conductivity enhancement. The contribution of Brownian motion of nanoparticles to the overall thermal conductivity of nanofluids was found to be very small. The study investigated the size distribution of nanoparticles which has been suggested to be an important factor and it gave satisfactory results. The values of the thermal conductivity for different nanofluid combinations were calculated using the expression developed from this study and they agreed with published experimental data. The present model was tested against several nanofluid combinations. To understand the properties that influence the thermal conductivity of nanofluids, parametric studies of a number of nanofluids were carried out. The parameters that were scrutinized to understand themal conductivity enhancement were nanoparticle diameter, nanolayer thickness and brownian motion. From the study, it was observed that Brownian motion is significant only when the particle diameter is less than 10 nm. From the parametric studies the mathematical model derived in this study was validated. The major factor for the thermal conductivity enhancement in nanofluids is the formations of nanoclusters. The combination of the base fluid and nanoparticles to from nanoclusters will provide better cooling solution than the convention cooling fluids.
30
Jensen, Colby. "TRISO Fuel Thermal Conductivity Measurement Instrument Development." DigitalCommons@USU, 2010. https://digitalcommons.usu.edu/etd/838.
Анотація:
Thermal conductivity is an important thermophysical property needed for effectively predicting fuel performance. As part of the Next Generation Nuclear Plant (NGNP) program, the thermal conductivity of tri-isotropic (TRISO) fuel needs to be measured over a temperature range characteristic of its usage. The composite nature of TRISO fuel requires that measurement be performed over the entire length of the compact in a non-destructive manner. No existing measurement system is capable of performing such a measurement. A measurement system has been designed based on the steady-state, guarded-comparative-longitudinal heat flow technique. The system as currently designed is capable of measuring cylindrical samples with diameters ~12.3-mm (~0.5″) with lengths ~25-mm (~1″). The system is currently operable in a temperature range of 400 K to 1100 K for materials with thermal conductivities on the order of 10 W/m/K to 70 W/m/K. The system has been designed, built, and tested. An uncertainty analysis for the determinate errors of the system has been performed finding a result of 5.5%. Finite element modeling of the system measurement method has also been accomplished demonstrating optimal design, operating conditions, and associated bias error. Measurements have been performed on three calibration/validation materials: SS304, 99.95% pure iron, and inconel 625. In addition, NGNP graphite with ZrO2 particles and NGNP AGR-2 graphite matrix only, both in compact form, have been measured. Results from the SS304 sample show agreement of better than 3% for a 300–600°C temperature range. For iron between 100–600°C, the difference with published values is < 8% for all temperatures. The maximum difference from published data for inconel 625 is 5.8%, near 600°C. Both NGNP samples were measured from 100–800°C. All results are presented and discussed. Finally, a discussion of ongoing work is included as well as a brief discussion of implementation under other operating conditions, including higher temperatures and adaptation for use in a glovebox or hot cell.
31
Liang, L. H., and Y. G. Wei. "Ultralow Thermal Conductivity and Thermal Stress of Ceramics with Surface Nanowire-structures." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/34880.
Анотація:
An analytical model on the size and fraction dependent thermal conductivity, elastic modulus and
thermal stress of nanowire-composites are developed, and the theoretical prediction agrees with the experimental
results of Si nanowires. And the model proposes that the high thermal shock strength of ceramics
can be achieved by surface nanostructurization, which is related to the low thermal conductivity and thermal
stress of the nanostructures and voids. The theory will be helpful to guide design of thermal barrier
coatings.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/34880
32
Ganvir, Ashish. "Microstructure and Thermal Conductivity of Liquid Feedstock Plasma Sprayed Thermal Barrier Coatings." Licentiate thesis, Högskolan Väst, Avd för tillverkningsprocesser, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-9061.
Анотація:
Thermal barrier coating (TBC) systems are widely used on gas turbine components to provide thermal insulation and oxidation protection. TBCs, incombination with advanced cooling, can enable the gas turbine to operate at significantly higher temperatures even above the melting temperature of the metallic materials. There is a permanent need mainly of environmental reasons to increase the combustion turbine temperature, hence new TBC solutions are needed.By using a liquid feedstock in thermal spraying, new types of TBCs can be produced. Suspension plasma/flame or solution precursor plasma spraying are examples of techniques that can be utilized for liquid feedstock thermal spraying.This approach of using suspension and solution feedstock, which is an alternative to the conventional solid powder feed stock spraying, is gaining increasing research interest, since it has been shown to be capable of producing coatings with superior coating performance.The objective of this research work was to explore relationships between process parameters, coating microstructure, thermal diffusivity and thermal conductivity in liquid feedstock thermal sprayed TBCs. A further aim was to utilize this knowledge to produce a TBC with lower thermal diffusivity and lower thermal conductivity compared to state-of-the-art in industry today, i.e. solid feed stock plasma spraying. Different spraying techniques, suspension high velocity oxy fuel,solution precursor plasma and suspension plasma spraying (with axial and radialfeeding) were explored and compared with solid feedstock plasma spraying.A variety of microstructures, such as highly porous, vertically cracked and columnar, were obtained. It was shown that there are strong relationships between the microstructures and the thermal properties of the coatings.Specifically axial suspension plasma spraying was shown as a very promising technique to produce various microstructures as well as low thermal diffusivity and low thermal conductivity coatings.
33
Kolen, Alexander Franciscus. "Elasticity imaging for monitoring thermal ablation therapy in liver." Thesis, Institute of Cancer Research (University Of London), 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404968.
34
Mathis, Nancy Elaine. "Measurements of thermal conductivity anisotropy in polymer materials." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1996. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/NQ62173.pdf.
35
Delap, Martin Richard. "Thermal conductivity studies of YBa₂Cu₃O₇₋δ". Thesis, Durham University, 1990. http://etheses.dur.ac.uk/9301/.
Анотація:
Apparatus to measure the thermal conductivity of YBa(_2)Cu(_3)O(_7-δ) at temperatures between 20K and 120K has been designed and constructed. The thermal conductivity is measured using a longitudinal steady state heat flow technique. Thermal conductivity measurements have been performed upon a sample of YBa(_2)Cu(_3)O(_7-δ) which has been subjected to a series of heat treatments in order to remove oxygen from the material. The measurements show conclusively that the thermal conductivity of YBa(_2)Cu(_3)O(_7-δ) is very strongly influenced by the oxygen content of the material. A reduction of the oxygen content of the material results in a substantial lowering of the thermal conductivity. To explain this result, a quantitative model has been constructed; the model demonstrates that consideration of the changes in phonon interactions alone cannot account for the differences in the behaviour of the thermal conductivity of YBa(_2)Cu(_3)O(_6) and YBa(_2)Cu(_3)O(_7). In addition; the model, shows that there must be a significant carrier contribution to the thermal conductivity in both the normal and superconducting states. A physical process has been proposed which provides the required large carrier contribution below T(_c). Further studies have been performed on a series of samples of YBa(_2)Cu(_3)O(_7-δ) which were sintered at slightly different temperatures. Qualitative analysis of the physical properties, of these samples has been performed.
36
Rees, Mary Frances. "Thermal conductivity measurements on high Tâ†c superconductors." Thesis, University of Liverpool, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317234.
37
Low, Jasmine. "Thermal conductivity of soils for energy foundation applications." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/389737/.
Анотація:
Ground source heat pumps are a low-carbon method of providing space heating. Thermal energy is extracted by means of a heat transfer fluid pumped through a series of pipes buried in the ground. For new builds, construction costs can be minimised by installing the pipes within the building foundations, eliminating the need for further excavations. These are known as energy foundations. Designing such a system requires knowledge of the ground thermal properties, in particular the thermal conductivity. This can be determined by conducting a field thermal response test, or by laboratory tests on soil samples. In this thesis, the thermal response test was compared to the needle probe and thermal cell laboratory methods. For each method, the main sources of error were investigated. Previously, the needle probe transient temperature data was analysed by visual inspection or rules of thumb. A new analysis method was developed and trialled on agar-kaolin samples, which reduces errors associated with the previous methods. The greatest source of error in the thermal cell method was identified as heat losses. A finite element model of the thermal cell showed that it overestimates the thermal conductivity by at least 35% due to heat losses. The needle probe was found to be the more reliable method. Both laboratory methods gave significantly lower values of thermal conductivity than the thermal response test. Possible reasons for this include differences in scale and sampling disturbances. The final stage of this research considered the required accuracy in soil thermal conductivity measurement for a well-designed energy foundation system. A numerical model of an energy foundation system was used to simulate different thermal loading scenarios. Variations in thermal conductivity had little effect on balanced systems, but had a significant impact on heating only or cooling only systems.
38
Andersson, Robin. "Modeling Radiation Induced Degradation of Lattice Thermal Conductivity." Thesis, KTH, Materialvetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-277885.
Анотація:
Nuclear power technology is currently experiencing a revolutionary development process and its utilization is researched and debated throughout the world whereas sustainability is one of the most important topics in the material science arena. Some components in a nuclear power plant are subject to an irradiating environment which will cause significant damage to the material over time. Thus, it is of utmost importance that the affected materials are well designed for enduring such conditions because of the extensive lifetime of a nuclear power plant. The highly energetic particles that are inherent with nuclear reactions will generate point defects in the microstructure of the material which will alter its macroscopic behavior. Managing heat is crucial in a nuclear power plant and therefore this thesis is devoted to modeling the degradation effect on the lattice thermal conductivity as a result of the point defects, and to establish the intervening relation. This is achieved by ab initio simulations on supercells where the quantum-mechanical forces are calculated with density functional theory and with the generalized gradient approximation for the exchange-correlation term. The phonon Boltz- mann equation is solved by linearization and by using the relaxation-time ap- proximation which allows the lattice thermal conductivity to be calculated for the model. The phonon band modes and the phonon density of states is examined as well. To date there are no reports currently found in the literature where this topicis approached with similar methods.Kärnkraftsteknologin genomgår just nu en revolutionerande utvecklingspro- cess och dess användning debatteras över hela världen där hållbarhet är en av de viktigaste ståndpunkterna i materialvetenskapsområdet. Vissa komponenter i ett kärnkraftverk blir utsatta för en bestrålande miljö vilket orsakat stor skada på materialet över tid. Det är därför av högsta vikt att dessa material är desig- nade för att motstå sådana miljöer på grund av kärnkraftverkens långa livstid. De högenergetiska partiklarna som är förekommande vid kärnreaktioner gene- rerar punktdefekter i materialets mikrostruktur vilka ändrar de makroskopiska egenskaperna hos materialet. Värmehantering är kritiskt i ett kärnkraftverk och därför är detta arbete de- dikerat till att modellera effekten av försämring av värmeledningsförmågan i kristallgittret, som resultat av punktdefekterna, och att definiera sambandet. Detta uträttas genom ab initio simuleringar av superceller där de kvantmekaniska krafterna beräknas med täthetsfunktionalsteori med en generaliserad approximation av täthetsgradienten för den tillhörande utbytes- och korrela- tionstermen. Boltzmann ekvationen löses med hjälp av linjärisering och med en approximation av relaxationstiden vilket används för att beräkna värmeledningen i gittret för modellen. Fononernas band-moder och tillståndstäthet undersöks därtill. För närvarande finns det inga rapporter bland litteraturen där detta ämne behandlas med samma metoder.
39
Stolk, Jonathan Douglas. "Development of low thermal expansion, high conductivity nanocomposites /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
40
Hua, Zilong. "Hybrid Photothermal Technique for Microscale Thermal Conductivity Measurement." DigitalCommons@USU, 2013. https://digitalcommons.usu.edu/etd/1491.
Анотація:
Most existing thermal conductivity measurement techniques of nuclear fuel only measure the overall effective thermal conductivity of the fuel, cladding, and gap, with low spatial-resolution. However, damage to nuclear fuel microstructure caused by neutron-irradiation can result in sharp, local changes of thermal conductivity. Additionally, extremely large temperature-gradients (~1600 K/cm) from the fuel centerline to the coolant result in similar gradients of thermal conductivity. Therefore, in pursuit of greater understanding of nuclear fuel performance, the objective of this study was to develop a non-contact thermal conductivity measurement technique to provide micron-sized spatial-resolution capability. Based on photothermal techniques and using both frequency and spatial-domain photothermal reflectance methods, an experimental measurement system was designed, built, and tested for measuring the thermal conductivity of a thin-film coated material with micron resolution. This hybrid method involves separate measurement of thermal diffusivity, D, and thermal effusivity, e, from which, thermal conductivity, k = (e2/D)1/2 is calculated. A detailed parametric analysis using analytical solutions and a numerical model has been performed to guide the experiment and optimize measurement conditions. The measurement system was validated using two calibration samples having thermal conductivities at both the upper and lower limit of the common range of nuclear fuels (~1 - 10 W/m/K). Sources of experimental errors are discussed qualitatively and the uncertainty of the measurement system for the thermal conductivity range of interest is quantified. The measured error is found to be about 10%, and up to close to 20% for the worst case (upper limit of k range). An extended application of the modulated laser excitation technique is explored to measure mechanical properties of solid materials. This technique involves obtaining the natural frequencies of different vibrational modes of a cantilever beam sample allowing for the extraction of the elasticity constants of the material. From Neumann's principle, the number of independent elasticity constants is dependent on the symmetry of the material structure. Specifically, symmetries of crystalline materials and composite materials are analyzed. Experimental results of two validation samples with cubic crystal system agreed well with the published values with experimental errors of ~10%.
41
Ghai, Ramandeep Singh. "Modelling Thermal Conductivity of Porous Thermal Barrier Coatings for High-Temperature Aero Engines." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/37035.
Анотація:
Thermal Barrier Coatings (TBC) are used to shield hot sections of gas turbine engines, helping to prevent the melting of metallic surfaces. TBC is a sophisticated layered system that can be divided into top coat, bond coat, and the super-alloy substrate. The highly heterogeneous microstructure of the TBC consists of defects such as pores, voids, and cracks of different sizes, which determine the coating’s final thermal and mechanical properties. The service lives of the coatings are dependent on these parameters.
These coatings act as a defensive shield to protect the substrate from oxidation and corrosion caused by elevated temperatures. Yttria Stabilized Zirconia (YSZ) is the preferred thermal barrier coating for gas turbine engine applications. There are a certain number of deposition techniques that are used to deposit the thermal coating layer on the substrate; commonly used techniques are Air Plasma Sprayed (APS) or Electron Beam Physical Vapour Deposition (EB-PVD).
The objective of this thesis is to model an optimized TBC that can be used on next-generation turbine engines. Modelling is performed to calculate the effective thermal conductivity of the YSZ coating deposited by EB-PVD by considering the effect of defects, porosities, and cracks. Bruggeman’s asymmetrical model was chosen as it can be extended for various types of porosities present in the material. The model is used as an iterative approach of a two-phase model and is extended up to a five-phase model. The results offer important information about the influence of randomly oriented defects on the overall thermal conductivity. The modelled microstructure can be fabricated with similar composition to have an enhanced thermal insulation.
The modelling results are subsequently compared with existing theories published in previous works and experiments. The modelling approach developed in this work could be used as a tool to design the porous microstructure of a coating.
42
Kalkundri, Kaustubh. "Development and verification of an apparatus for thermal resistance and thermal conductivity measurements." Diss., Online access via UMI:, 2006.
43
Lin, Wen-chin, and 林文進. "Thermal Conductivity Measurement of Thermal Interface Materials." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/40127527963600451177.
Анотація:
碩士國立臺灣科技大學
機械工程系
96
Applying a Thermal Interface Material (TIM), which has an excellent heat conductivity value, into the interface between the heat source surface and the heat-spreading module could greatly reduce the temperature drop across the interface between the heat source and the heat-spreading module. In order to obtain the optimal choice of TIM, the thermal conductivity of TIM should be determined precisely. The materials used in this study were thermal pad and thermal grease, and two thermal conductivity measuring methods were compared, including measuring the thermal conductivity value using a steady-state heat transfer equation and a transient state heat transfer equation, respectively. The steady state heat transfer equation is based on a one-dimensional heat conduction principle, wherein the temperature difference across a material becomes constant and the thermal conductivity of this material can be determined using a formula. The measurement of thermal conductivity value using transient-state heat conduction employs a line heat source, whose heat dissipates laterally to the material to be tested. The variation of temperature with time in the heat source was used to derive the thermal conductivity value of the tested material. The results showed that measuring the thermal conductivity value by the steady-state heat conduction method obviously needed a longer measuring time, but it could obtain more precise results. On the other hand, the precision of the transient-state heat conduction method was less precise because of the possible existence of air bubble next to the thermocouple and the utilization of a simplified equation for fitting the measured data.
44
Wang, Shize. "Thermal Conductivity of Nanocrystalline Nickel." Thesis, 2011. http://hdl.handle.net/1807/31628.
Анотація:
The grain-size dependences of thermal conductivity and electrical resistivity of polycrystalline and nanocrystalline nickel were measured by the flash method and four-point probe method, respectively. Nanocrystalline nickel was made by the pulsed-current electrodeposition process, while polycrystalline nickel was commercially available Ni 200 in annealed condition. The grain sizes of the materials examined ranged from 28 nanometers to 57 micrometers. Noticeable changes in thermal conductivity and electrical resistivity with grain size were observed in particular for samples with grain sizes less than 100 nm. These results can be explained on the basis of the rapid increase in the intercrystalline grain boundary and triple junction volume fractions at very small grain sizes. The relationship between thermal conductivity and electrical resistivity of nanocrystalline nickel follows the classic Wiedemann-Franz law.
45
Abbasy, Farzaan. "Thermal conductivity of mine backfill." Thesis, 2009. http://spectrum.library.concordia.ca/976499/1/MR63157.pdf.
Анотація:
Energy conservation is a national strategy for every country. To avoid shortage of energy and high prices, the green sustainable energy resources have become the center of attention. Mining as a prominent industry in Canada consumes a huge amount of energy, so any reduction in energy consumption would result in higher production and profit. In 2005, Hassani of McGill University proposed the use of mine stopes as the heat exchange area for the production of low temperature geothermal energy, since the extraction of ore/ rocks and the backfilling is a part of normal mining operation, then the very low cost associated with the implementation of such system, will make it very viable for mining industry. This work is in collaboration with energy research team of professor Hassani of McGill University (EMERG). This is a part of an overall research program on low temperature geothermal energy from mines. The research was focused primarily on investigating and obtaining a range values for thermal conductivity of different mine backfills, as well as the effect of some of the associated physical parameters. More than 800 samples and 2000 measurements were done on different backfills with different physical properties. This preliminary investigation indicates that pulp density, binder consumption, curing time, and sodium silicate content have negligible to slight influence on the thermal conductivity of backfill. However parameters such as saturation, and to a lesser extent porosity and the thermal conductivity of the inert material, have more significant influence.
46
童資芸. "Thermal Conductivity of Magnetic Nanowires." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/37380308712321489520.
47
周正三. "= Thermal-conductivity micro pressure sensor." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/00892565758379687449.
48
周暄苹. "Thermal conductivity, thermal expansion and electrical conductivity in AlxCoCrFeNi ((0 ≤ x ≤ 2) high-entropy alloys." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/16057731030636336468.
Анотація:
碩士國立清華大學
材料科學工程學系
96
In order to investigate fundamental properties of high-entropy alloys, this study has selected 5 elements, such as Al, Co, Cr, Fe and Ni, to prepare various AlxCoCrFeNi alloys for 0 �T x �T 2, and to explore the effects of microstructure on the heat conductivity, thermal expansion and electrical conductivity of the alloys in the temperature ranges of 298 – 573 K, 298 – 1073 K, and 298 – 400 K, respectively. Besides, the relation between properties and atomic bonding among elements in the alloys is also explored in this study. Experimental results from XRD and SEM show that the microstructure of these alloys is single FCC, duplex FCC + BCC, and single BCC for as-cast alloys (C-alloys) in the composition ranges of 0 �T xFCC �T 0.375, 0.5 �T xduplex �T 0.75, and xBCC �d 0.875, respectively, while the duplex phase area xduplex extends from 0.375 to 1.25 and xBCC �d 1.25 for the homogenized and quenched alloys (H-alloys). DSC analyses show no evidences of phase transformation in the temperature range of 298 to 773 K, indicating that the high-entropy effect makes the alloys more soluble among components in the alloys. The XRD peak intensities for H-alloys are lower than those of the pure component elements indicates that FCC and BCC structures in H-alloys have larger scattering effect for x-ray diffraction and more electron-phonon scattering and hence H-alloys have lower thermal and electrical conductivity. The ratio of thermal conductivity to electrical conductivity shows the contribution of phonon is comparable to that of electron in thermal conductivity. The anharmonic oscillation for atoms due to lattice distortion is large. As temperature increases the thermal expansion coefficient increases accordingly. This study shows various aspects of microstructural influence on the properties of the alloys. Since the atomic radius of Al is approximately 14.4 % greater than the radii of Co, Cr, Fe and Ni, the increasing amount of Al addition to the alloys decreases the XRD intensities of the alloys. This in turn increases the x-ray scattering in the alloys and influences properties of both single phases and duplex phase of the alloys. The relation of both thermal conductivity and electrical conductivity as a function of the amount of Al addition is seen to divide in three regimes just as that in the case of microstructure, i.e., FCC, FCC + BCC, BCC regimes. In both single-phase regimes, both thermal conductivity and electrical conductivity decrease as the amount of Al, x, increases. In duplex FCC/BCC regime both thermal conductivity and electrical conductivity are smaller than those in single-phase regimes. This is because of the additional scattering effect of FCC-BCC phase boundaries. Hardness increases monotonically with x for both C- and H-alloys, indicating that the atomic bonding strength also increases with x. In both single-phase regimes although the hardness increases slightly with x, the hardness keeps roughly constant in single-phase regimes, while the hardness of alloys in the duplex regime increases linearly with x. In BCC regime the hardness for H-alloys is slightly higher than that for C-alloys. This is attributed to the spinodal decomposition during homogenization of H-alloys at 1100 oC. The thermal expansion coefficient of H-alloys decreases with x is also attributed to the increase in bond strength as x increases. There are two phase-transformation temperatures for H-alloys in both thermal expansion measurements and DTA analyses. One is for ferromagnetic-to-paramagnetic transition (i.e., Curie temperature,) the other is for �耤VNiCoCr precipitation that is characterized by HTXRD and DTA. Curie temperature for single-phase H-alloys increases slightly with x, while there is a lower point for Curie temperature for duplex H-alloys. Since Curie temperature is proportional to molecular field in the Weiss theory of magnetism, the molecular field is also closely related to bond strength and microstructure of the alloys.
49
Schneider, Donald A. "Thermal contact resistances in a thermal conductivity test system." Thesis, 1998. http://hdl.handle.net/1957/33742.
Анотація:
The thermal contact conductance (TCC) between two machined pieces of
stainless steel was studied. A guarded hot plate thermal conductivity test fixture was
designed and built for the experiment. Factors investigated included the contact pressure,
surface roughness, interface material and average test temperature. The contact pressure
at the interface ranged from 80 to 800 psi. The mean surface roughness of the opposing
surfaces was 2.8 ��in (.0708 ��m) parallel to the sanding direction and 1.9 ��in (.0482 ��m)
perpendicular to the sanding direction. Interface materials included air, indium foil,
copper foil, Teflon tape, silver filled paint and thermal grease. Average test temperatures
ranged from 0��C to 100��C, in 20��C increments.
With air alone in the interface gap the TCC was nearly insensitive to contact
pressure. The thermal grease and silver filled paint most increased the TCC over air
alone while being nearly insensitive to pressure. With indium foil the TCC was similar to
air, but improved somewhat with increasing pressure. With copper foil the TCC was
lower than air alone, but increased with increasing pressure. The Teflon tape had a lower
TCC than air at low contact pressure, but a higher TCC than air at higher pressures. In
general the TCC improved somewhat at higher temperatures. The ability of an interface
material to improve the TCC is more a function of its flow stress and wetting ability than
its thermal conductivity.
An existing mathematical model was used to predict the TCC with air as the
interface material, and was found to over-estimate the TCC by an order of magnitude. It
was found that the model did not accurately predict the effective surface spacing for very
smooth surfaces as used in this work. When a modification for smooth contact surfaces
was incorporated into the model it yielded results that were consistent with experimental
results.Graduation date: 1999
50
Chi, Fu Yao, and 紀富耀. "The Thermal Conductivity of Asphalt ConcreteMeasurement Using Thermal Probe." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/a3k5yd.
Анотація:
碩士國立高雄應用科技大學
土木工程與防災科技研究所
102
Global warming primarily caused by modern industrial pollution has been a long-existing issue attracting great concerns. Taiwan is located around the fault where Eurasian Plate and Philippine Sea Plate are merged, resulting in a high reoccurrence of earthquakes. In addition to this, high degrees of temperature and natural hazards such as typhoons frequently occurred during summer season have resulted in a fast deterioration of civil infrastructures. Pavement among many of those is gaining problems such as lowered performance and durability than ever, which will indirectly affect the economy of the entire society. This study mainly focuses on the investigation of thermal conduction characteristics of asphalt concrete (AC) at high temperature. One of the research novelties is to employ by design an economic measuring apparatus. A low-cost thermal probe and self-assembled data acquisition system (both software and hardware) were used in this study. AC specimens were prepared for heating test by drilling two sizes of apertures (Φ5mm and Φ12mm) at the center, filling with thermal cement, and inserting properly the thermal probes. The coefficients of thermal conductivity (CTC) of AC specimens were obtained by observing and analyzing the temperature histories of the heating test. The study results show that CTC of AC materials varies with temperatures. Specifically, CTC is higher at low temperature and lower at higher temperature – there exists an inversely proportional relationship. Furthermore, CTC of AC materials was affected by the heating rates as well. Testing results indicate that CTC varies from 1.207 to 2.047 W/mK for low heating rate test (supplied with 2.5 to 15V), and from 1.326 to 1.718 W/mK for high heating rate test (supplied with 5 to 30V). The obtained CTCs in this study using thermal probe apparatus are shown to be comparable with other literature works. This suggests that thermal probe apparatus to be an economic, feasible and practical approach for extracting CTC of AC materials in fields.