The exit velocity of the launch object along with the values of electric and thermal conductivity at the interfaces between the rails and the armature of a rail gun are critical issues. This thesis, using finite element method, estimates the former by solving the proper multiphysics governing equations, along with exploiting the contact theory between flat surfaces. A parametric analysis in the vicinity of the standard deviation of the normalized distance between the references planes of the rough surfaces was made for a variety of materials and textures at the interfaces. Furthermore, the amount of ohmic heat that is generated due to the application of the electric potential and the resistance of materials is estimated along with the average temperature at the interfaces. Finally, thermal stresses were also studied.

A photovoltaic thermal solar collector (PVT) produces both heat and electricity from a single panel. PVT collectors produce more energy, for a given area, than conventional electricity and heat producing panels, which means they are a promising technology for applications with limited space, such as building integration. This work has been broken down into 3 subprojects focusing on the development of PVT technology. In the first subproject an experimental testing facility was constructed to characterise the performance of PVT collectors. The collectors under investigation were assembled by combining bespoke thermal absorbers and PV laminates. Of the two designs tested, the serpentine design had the highest combined efficiency of 61% with an 8% electrical fraction. The header riser design had a combined efficiency of 59% with an electrical fraction of 8%. This was in agreement with other results published in literature and highlights the potential for manufacturers of bespoke thermal absorbers and PV devices to combine their products into a single PVT device that could achieve improved efficiency over a given roof area. In the second project a numerical approach using computational fluid dynamics was developed to simulate the performance of a solar thermal collector. Thermal efficiency curves were simulated and the heat removal factor and heat loss coefficient differed from the experimental measurements by a maximum of 12.1% and 2.9% respectively. The discrepancies in the findings is attributed to uncertainty in the degree of thermal contact between the absorber and the piping. Despite not perfectly matching the experimental results, the CFD approach also served as a useful tool to carry out performance comparisons of different collector designs and flow conditions. The effect of 5 different flow configurations for a header collector was investigated. It was found that the most efficient design had uniform flow through the pipe work which was in agreement with other studies. The temperature induced voltage mismatch, that occurs in the PV cells of PVT collector was also investigated. It was concluded that the temperature variation was not limiting and the way in which PV cells are wired together on the surface of a PVT collector did not influence the combined electrical power output.

Buildings consume around half of the UK's total energy consumption and are responsible for almost 50% of UK's total carbon dioxide (CO2) emissions. Use of high thermal resistance insulation in buildings is critical to save the substantial amounts of space heating energy lost through building fabric. Conventional building insulation materials have higher thermal conductivity values ranging from 40 mWm-1K-1 (Glass fibre) - 26 mWm-1K-1 (Polyurethane foam) and require larger thicknesses to achieve stringent building regulation requirements which may not be feasible due to techno-economic constraints. Vacuum Insulation Panel (VIP) is a relatively new insulation for building applications that offers 5-8 times higher thermal resistance and can achieve significant space savings in buildings. VIPs are produced as a rigid panel comprising inner core board laminated in an outer high barrier envelope under evacuated conditions (< 5mbar). However, the main challenge for large scale acceptance of VIPs in building applications is their higher cost. VIPs have been shown to have an approximately 10 times longer payback compared to conventional EPS insulation due to their high initial cost. Expensive materials currently being used for VIP manufacturing such as fumed silica contribute to high cost of VIPs and it is critical to identify alternative low cost materials for VIP components to overcome the challenge of high cost. The aim of this thesis was to develop an alternative low cost material and investigate its suitability for use as VIP core. Expanded perlite, a low cost material was identified as a replacement of expensive fumed silica in a VIP core. Composite samples containing expanded perlite, fumed silica, silicon carbide (SiC) and polyester fibres were developed by dry mixing of the constituents in different mass ratios and their different properties were experimentally measured to identify optimum composition of composite. Gaseous thermal conductivity at different pressures was calculated from the pore size data obtained using Mercury Intrusion Porosimetry (MIP), gas adsorption and electron microscopy. Radiative conductivity of composite samples was measured using Fourier Transform Infrared (FTIR) to ascertain the opacifying effect of expanded perlite and opacifier (SiC). Centre of panel thermal conductivity of core boards of size 100mm x 100mm made of composite material at atmospheric pressure was measured by using a small guarded hot plate device. Average pore diameter values of expanded perlite decreased with the partial filling of fumed silica aggregates and was found to be in the range of 150-300 nm yielding lower gaseous conductivity values of 1.2-2.1 mWm-1K-1 at 100mbar and became negligible upon further decreasing pressures below 10 mbar. Core boards made of optimised composite containing 30% expanded perlite and 50% fumed silica along with SiC and polyester fibres was found to achieve centre of panel thermal conductivity of 28 mWm-1K-1 at atmospheric pressure and the average radiative conductivity of 0.67 mWm-1K-1 at 300K with its gaseous thermal conductivity at 1 mbar being 0.016 mWm-1K-1. According to the results of the thesis VIP prototypes consisting of core made with optimised composite consisting (50 mass% of fumed silica, 30 mass% of expanded perlite along with 8 mass% of fibre and 12 mass% of SiC) yielded centre of panel thermal conductivity of 7.4-7.6 mWm-1K-1 at pressure of 0.53-0.64 mbar. Opacifying properties of expanded perlite were observed and quantified. Expanded perlite reduced the radiative conductivity of the composite requiring smaller quantities of high density opacifiers such as SiC. For sample containing no expanded perlite, average radiative conductivity was calculated to be 1.37 mWm-1K-1 and radiative conductivity values decreased to 1.12 mWm-1K-1, 0.67 mWm-1K-1, 0.63 mWm-1K-1 and 0.50 mWm-1K-1 with mass ratio of expanded perlite 20%, 30%, 40% and 60% respectively. It was concluded that the solid conductivity of prototypes VIPs was 1.8-2 times higher compared to those of commercially available VIPs and is the main reason for higher centre of panel thermal conductivity.

Anisotropic thermoelectric effects can be measured in certain materials. Anisotropy can also be simulated using a repeated, layered structure of two materials cut at an angle. Various aspect ratios and angles of inclination are investigated in device geometry in order to maximize the thermopower. Eddy currents have been shown to occur in thermoelectric devices, and evidence of these currents are revealed in finite element analysis of the artificially synthesized anisotropic Peltier effect.

The thermal conductivity of various porous thermal barrier coating (TBC) systems used in elevated temperature for industrial applications has been evaluated using a proposed six-phase model. These porous TBC systems rely on microstructural properties and yield different types of porosity. These microstructural properties can influence the thermal conductivity of TBC systems. The purpose of this thesis is to assess the thermal conductivity of TBC systems based on microstructural attributes, particularly the effect of different types of porosity. Thus, the first component of this thesis investigates the microstructural characterization of various TBC systems using image analysis (IA) technique. In this technique, scanning electron microscopy (SEM) and light optical microscopy (LOM) micrographs were used to measure the porosity level of different TBC materials. The volumetric fraction of porosity along with orientation, shape, and morphology have a considerable impact on the total thermal conductivity of TBCs. The second component of this thesis evaluates the thermal conductivity of these porous TBC systems by taking into account the effect of the heat treatment process. The IA results reveal that as long as the porosity content increases, the thermal conductivity decreases for all of the TBC materials studied in this thesis. Further, while the content of microcracks and non-flat porosity play a crucial role in reducing the thermal conductivity of TBC materials, the other types of porosity (open randomly oriented, penny-shaped, and interlamellar) exert less impact on the thermal conductivity of TBCs. Comparing the results of the proposed six-phase model to experimental values and finite element analysis (FEA) values showed a relatively good agreement. The proposed six-phase model can predict the thermal conductivity of porous microstructure of TBC systems close to real measured values; therefore, the proposed six-phase model may be utilized to fabricate the porous microstructure of TBCs.

Le groupe Montupet est un spécialiste de la conception et de la production de pièces de fonderie en aluminium usinées pour l’automobile. Les moules métalliques utilisés pour la réalisation de culasses automobiles en aluminium sont protégés par un revêtement appelé le poteyage. La principale fonction du revêtement de poteyage est de protéger l’outillage en acier de la corrosion chimique de l’alliage. Du fait de ses propriétés thermiques, une autre fonction du poteyage est la modulation des échanges thermiques entre le moule et la pièce en cours de solidification dont dépend fortement la microstructure finale de l’alliage. Le procédé utilisé aujourd’hui pour l’application du poteyage sur les parois du moule en acier consiste à projeter manuellement une barbotine au moyen d’un pistolet. Ce procédé ne permet pas d’obtenir la répétabilité des caractéristiques des couches déposées nécessaire au contrôle des gradients de solidification locaux. De plus, les outillages actuels souffrent de l’insuffisance de la protection du poteyage, ce qui conduit à une usure prématurée ayant un coût important et conduisant à des diminutions du rendement de l’outil industriel. Dans le cadre du projet PROOF de robotisation de l’étape de poteyage, les objectifs suivants ont été fixés. Il s’agit de mieux définir ce que devraient être les propriétés physicochimiques du poteyage. L’objectif à long terme est de réaliser une rupture technologique par l’application d’un revêtement permanent ou de longue durée de vie. Dans un premier temps, ces travaux présentent une caractérisation complète de la nature physico-chimique des suspensions des poteyages utilisés actuellement ainsi que l’étude de leur comportement en pulvérisation. Dans un second temps, après que des revêtements aient été produits par projection plasma sous air (APS), il est apparu nécessaire de comparer leurs propriétés thermiques à celles des revêtements de poteyage. Des valeurs de diffusivité thermiques ont été mesurées, les valeurs de conductivités thermiques des revêtements étudiés ont ensuite été calculées puis confirmées expérimentalement. La dernière partie de ces travaux s’attache à présenter les outils mis en place en usine afin de tester les revêtements créés par projection plasma et de vérifier leur adéquation (thermique et chimique notamment) avec la coulée de pièces en alliage d’aluminium. Ces essais en conditions réelles ou semi-réelles permettent la comparaison de l’efficacité de tous les revêtements étudiés. / Montupet is specialized in the manufacture of aluminium foundry components for the automotive industry. The metallic molds used for aluminium cylinder heads are protected by a specific coating called die coating. The main objective of this die coating is to protect the steel tool from chemical corrosion of the liquid alloy. Because of its thermal properties, another of its aims is the adjustment of the thermal exchanges between the mold and the solidifying aluminium, which strongly affects the final microstructure of the alloy. The process used nowadays to coat the die coating on the steel mold walls consists in spraying manually a suspension. However, this process does not allow to obtain reproducible characteristics of the coated layers necessary to control the local solidification gradients. Furthermore, the current tools suffer from the inadequate protection of the die coating, which leads to premature wear resulting in important costs and a decrease of the efficiency of the industrial tool. In the frame of the PROOF project, aiming in the automatisation of the die coating projection, several objectives were set: better know what should be the physico-chemical properties of the die coating and realize a technological jump by creating a long-life or even permanent coating. Firstly, this work shows a complete characterization of the physico-chemical state of the suspensions used nowadays as well as the study of their behavior during spraying. Then, once the coatings were produced by Air Plasma Spraying (APS), it appeared necessary to compare their thermal properties to the ones measured on the die coatings. Hence, thermal diffusivity values have been measured. Afterwards thermal conductivity of the studied coatings have been calculated and finally experimentally checked. Eventually, this work shows the tools developed within the company in order to test the plasma coatings and to check their thermal and chemical compatibility to the process of aluminium casting. These trials in real or semi-real conditions allow the efficiency comparison of the whole studied coatings.

L’élévation de la température est l’un des principaux paramètres limitant la puissance nominale des machines électriques. La température atteinte au niveau des bobinages, peut avoir de graves conséquences sur le système d’isolation des enroulements et peut ainsi réduire la durée de vie des machines électriques. Le travail de recherche effectué dans cette thèse s’attache à l’extraction de modèles thermiques simplifiés permettant la prédiction des niveaux d’échauffement. Nous avons alors mis en place une démarche basée sur une méthode numérique (Finite Intgeration Technique) qui permet une identification naturelle des grandeurs du modèle thermique. Cette démarche nécessite d’homogénéiser le bobinage en le remplaçant par un seul matériau homogène équivalent permettant de reproduire le même comportement thermique du cas réel du bobinage. Pour ce faire, plusieurs techniques d’homogénéisation ont été employées. Nous nous sommes également intéressés aux différentes configurations des conducteurs dans l’encoche en vue d’obtenir une meilleure évacuation de la chaleur dans le bobinage des machines électriques. La démarche proposée dans ce travail a pout objectif d’obtenir des modèles thermiques simplifiés qui peuvent être réduit à un seul nœud pour calculer la température du point chaud. La validité des modèles est évaluée par comparaison aux éléments finis en considérant deux formes géométriques de l’encoche : une encoche simple puis une encoche de géométrie plus complexe que l’on retrouve dans une machine à commutation de flux. / The temperature rise is one of the main parameters limiting the power of electrical machine. In fact in the stator windings the temperature rise decreases the performances of its insulation system and it can reduce the life time of the motors and it may even lead to the motor failure. Appropriate models of the windings are necessary to find the hot spot of the machine. The work proposed in this thesis focuses on the extraction of simplified thermal models in order to evaluate the temperature distribution. An approach based on a numerical method (Finite Integration Technique) has been developed allowing the identification of the thermal model parameters. As a first step the homogenization of the winding is necessary to obtain the thermal model of the stator slot which has a complex heterogeneous structure requiring careful modeling. The objective is then to replace the conductors and the resin by one homogenous material that reproduces a similar thermal behavior. Several homogenization techniques are used to determine the effective thermal conductivity of the composite material. We are also interested to study different configurations or distributions of the conductors in the slot to limit heat dissipation in the windings of electrical machines. The second part of this thesis presents a method, based on the Finite Integration Technique (FIT) for the discretization that gives us an equivalent thermal model allowing the evaluation of transient temperature evolutions in the slot with low calculation cost.

No presente trabalho, as propriedades termofísicas do pão francês durante o assamento foram determinadas. Os pães foram feitos na Padaria Piloto do Laboratório de Engenharia de Alimentos do Departamento de Engenharia Química da Escola Politécnica da Universidade de São Paulo, com formulação semelhante aos pães comercializados. Durante o assamento, mudanças profundas ocorreram nos pães como diminuição do conteúdo de água de 44,1 para 30,8 % e aumento do volume de 382 para 420 cm3. Devido ao aumento do volume e diminuição da massa, a densidade aparente do pão francês variou de 0,231 g/cm3 para o pão sem assamento a 0,324 g/cm3 para o pão com 14 minutos de assamento. A difusividade térmica efetiva do pão francês foi determinada a partir das curvas de penetração de calor considerando o pão como um cilindro bidimensional. As curvas foram registradas a uma taxa de 30 aquisições/minuto durante o assamento dos pães em um forno turbo com dispositivo de vaporização. O valor médio da difusividade térmica encontrada para o pão francês durante o assamento foi de 4,1 ´ 10-7 m2/s. A condutividade térmica efetiva do pão francês foi determinada pelo método da sonda linear de aquecimento em diferentes tempos de assamento. A sonda linear utilizada nos ensaios foi dimensionada e construída no laboratório para o pão francês. A condutividade térmica efetiva do pão francês variou de 0,283 W/m K para o pão sem assamento a 0,136 W/m K para o pão com 14 minutos de assamento. Os resultados foram comparados com dados existentes na literatura. Um modelo empírico foi proposto para correlacionar a condutividade térmica do pão francês com o seu conteúdo de água e sua densidade aparente. / In this work, thermophysical properties of the french bread during baking were determined. Breads were produced at the Pilot Bakery of the Food Engineering Laboratory of the Chemical Engineering Department of Escola Politécnica of São Paulo University, with a formulation similar to breads purchased at the market. During baking, deep changes ocurred in the breads such as a water content decrease from 44,1 to 30,8 % and an increase of volume from 382 to 420 cm3. Due to the increase of volume and mass decrease, the bulk density of french bread changed from 0,324 g/cm3 for the dough to 0,231 g/cm3 for the bread with 14 minutes of baking. Effective thermal diffusivity of french bread was determined through heat penetration curves in a bidimensional cylinder. Temperature history was registred at a rate of 30 samples/minute during bread baking in a turbo oven with a vaporization device. The average value of thermal diffusivity to the french bread during baking was 4,1´10-7 m2/s. The effective thermal conductivity of the french bread was determined by the line heat source method in different times of baking. The thermal conductivity probe used was designed and built at the laboratory for french bread. The effective thermal conductitivy of the french bread changed from 0,283 W/m K for the dough without baking to 0,136 W/m K for the bread with 14 minutes of baking. Results were compared with literature data. An empiric model was proposed to correlate the french bread thermal conductivity with its water content and bulk density.

Este trabalho trata da caracterização de propriedades termodinâmicas e de transporte de nanofluidos baseados em nanopartículas de alumina em água para diferentes concentrações. Suspensões estáveis foram elaboradas por meio de um agitador ultrassônico. As seguintes propriedades foram analisadas: i) condutividade térmica com o método da sonda-linear; ii) viscosidade dinâmica através do reômetro do tipo cone e placa e iii) ângulo de contato com base em registros fotográficos de gotas em uma superfície plana e o tratamento de imagem através de um programa elaborado em LabVIEW. Procedimentos foram utilizados visando validar os métodos experimentais adotados, entre eles a comparação com resultados para fluidos puros. Além do estudo experimental, foi realizada uma análise crítica da literatura sobre condutividade térmica e viscosidade dinâmica de nanofluidos. Com base nesta análise, os resultados experimentais foram comparados a dados empíricos da literatura e métodos de previsão de propriedades desenvolvidos para nanofluidos e para suspensões de particulado sólido em líquido. De uma maneira geral, os resultados levantados neste estudo para condutividade térmica e viscosidade dinâmica de nanofluidos foram significativamente superiores a maioria dos dados experimentais da literatura e aos resultados proporcionados pelos métodos de previsão. Entretanto, para nanofluidos com composições distintas de nanopartículas de alumina em água, comportamentos similares ao do presente estudo também são observados na literatura. No caso do ângulo de contato, verificou-se seu decréscimo com o incremento da concentração de nanopartículas. Tal resultado coincide com a bibliografia consultada, segundo a qual a molhabilidade do nanofluido se eleva com o incremento da concentração de nanopartículas. / The present study concerns the characterization of thermodynamic and transport properties of nanofluids based on alumina nanoparticles in deionized water. Stable suspensions were obtained using an ultrasonic homogenizer (Sonicator). The following properties were measured: i) thermal conductivity using the linear probe method, ii) dynamic viscosity through a cone-plate rheometer iii) contact angle, based on photographic of nanofluid drops on a flat surface and image processing through a program based on LabVIEW. The methods and experimental procedures were validated by performing measurements properties of pure fluids with well known characteristics. Besides the experimental study, it was performed a comprehensive literature review on thermal conductivity and dynamic viscosity of nanofluids. Experimental results were compared against the data from the literature and the respective predictive methods developed for suspensions of nanofluids and micro solid particles in liquid. Generally speaking, the nanofluid thermal conductivity and dynamic viscosity measured in the present study were higher than the empirical values from the literature and the values given by predictive methods. However, it should be highlighted that although for different compositions of nanofluids behaviors similar to the one observed in this study are also reported in the literature. In case of contact angle, it was found that its value decreases with increasing the nanoparticle volumetric concentration. Such results is coincident with literature reports according to which the nanofluid wettability, given in terms of the contact angle, increases with increasing the nanoparticle concentration.

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