Dissertations / Theses on the topic 'Energy conversion technologie'

This thesis focuses on the synthesis of different types of NCs, their application to energy conversion and storage technologies, particularly LIBs, KIBs and DEFCs, and their structural transformation during electrochemical processes within these energy storage and conversion applications. The morphology and composition of target transition metal oxides, bimetallic NCs and phosphorous incorporated intermetallic NRs are characterized in detail to follow the alterations during application. An understanding of the correlation between structural, chemical and electrochemical properties will allow a more rational design of functional nanomaterials. The 1st chapter gives a general introduction to the rapid development and importance of renewable energy technologies in modern human society. Among which electrochemical energy storage and conversion technologies are particularly appealing in terms of cost, safety and environmental friendliness. The basic principles of Li-, Na- and K- ion battery technologies are discussed, including the battery structures, electrode materials and working mechanisms. Additionally, I describe the working principle of DEFCs and the electrocatalytic EOR. Strategies for synthesizing high performance NCs for electrochemical energy storage and conversion applications are also explained. Finally, in this chapter I discuss the phenomenon of NCs structural and chemical evolution during electrochemical operations and how their characterization in each system is needed for a thorough understanding of nanomaterials properties and applications. Chapter 1 also includes the objectives of the thesis. Chapter 2 describes a simple seed-mediated growth method at low temperature to grow heterstructered Mn3O4 on hollow Fe3O4 seeds. A moderate temperature (500 °C) annealing process is conducted to promote the solid-state reaction for hollow MnxFe3-xO4 NPs while conserving the original morphology. When serving as anode electrode materials, the polycrystalline shell, the internal void space and the high surface area of MnxFe3-xO4 NPs can effectively buffer the volume change of the NCs during lithiation and delithiation process to improve the stability and cycle life. The electrochemical activity of MnxFe3-xO4 NPs toward lithium reaction is evaluated and the relationship between the structure and electrochemical properties is explored. The excellent performance of hollow MnxFe3-xO4 NPs is associated with their crystal structure and composition, and with the presence of carbonized ligands, which further promote electrical conductivity and rapidly accommodate and release lithium ions while retaining a stable structure even after continuous charge/discharge cycles. This work was published in Nano Energy in 2019. Chapter 3 talks about the performance of bimetallic NPs as anodes in LIBs and KIBs. Monodisperse CoSn and NiSn NPs are synthesized through co-reduction and supported on commercial carbon materials. The obtained nanocomposites are tested as anode materials in half-cell LIBs, KIBs and full-cell LIBs. CoSn@C electrodes display excellent charge-discharge capacities with LIB half-cell and LIB full-cells. The capacities for KIB are stabilized at around 200 mAh g-1 with high coulombic efficiency over 400 cycles for CoSn@C and 100 mAh g-1 for NiSn@C over 300 cycles. The oxidation of NPs, the formation of SEI layer, the vast volume change during lithiation and delithiation processed caused the capacities decrease. This work was published in ACS Applied Materials & Interfaces in 2020. In chapter 4, a simple approach to produce intermetallic Pd3Pb nanocubes with well-defined cubic geometry and average size ranged from 6 nm to 10 nm is detailed. Pd3Pb/C catalysts present improved EOR electrocatalytic activities and stabilities. The EOR activity of Pd3Pb nanocubes is investigated through CV and CA techniques, which is size-dependent. All the catalysts exhibit a pronounced current decay during the first 500 s of continuous EOR operation, which is associated to the accumulation of strongly adsorbed reaction intermediates and the related blockage of reaction sites. The catalysts can be reactivated by simply cycling to effectively remove the poisoning species adsorbed on the surface and recover the electrocatalytic activity. A reorganization of Pd and Pb elements happens on Pd3Pb nanocubes during EOR, involving an outward/inward diffusion of Pd/Pb to equilibrate the stoichiometry of the NCs surface, which is driven by the different affinity of Pb and Pd towards oxygen and possibly ethanol, and the electrochemical oxidation/reduction of Pd. This work was published in Chemistry of Materials in 2020. Chapter 5 demonstrates the synthesis of colloidal Pd2Sn:P NRs through phosphorization of Pd2Sn NPs with a highly active reagent- hexamethylphosphorous triamide (HMPT) in a one-pot two-steps reaction. The Pd2Sn:P/C catalyst exhibits significantly enhanced activity toward EOR in alkaline media compared with Pd2Sn/C, PdP2/C and commercial Pd/C catalysts. The performance improvement is rationalized with the aid of DFT calculations considering the different phosphorous chemical environments. Depending on its oxidation state, surface phosphorus introduces sites with low energy OH- adsorption and/or strongly influences the electronic structure of palladium and tin to facilitate the oxidation of the acetyl to acetic acid, which is considered the EOR rate limiting step. The Pd2Sn:P NRs is characterized with Sn- and P-rich surface, which correlates well with the higher percentages of oxidized tin and phosphorous, and the higher tendency to oxidation of Sn compared with Pd. DFT calculations prove that the presence of P can induce a higher chemical adsorption of OH- to facilitate the formation of CH3COOH, resulting in EOR activity increase. This work was accepted in Nano Energy in 2020.
Esta tesis se centra en la síntesis de diferentes tipos de nanocristales, su aplicación a las tecnologías de conversión y almacenamiento de energía, particularmente LIBs, KIBs y DEFCs, y su transformación estructural durante los procesos electroquímicos dentro de estas aplicaciones de almacenamiento y conversión de energía. La morfología y composición de nanocristales de óxidos de metales de transición, bimetálicos e intermetálicos que incroporan fósforo se caracterizan en detalle para seguir las alteraciones durante la aplicación. La comprensión de la correlación entre las propiedades estructurales, químicas y electroquímicas permitirá un diseño más racional de nanomateriales funcionales. El primer capítulo ofrece una introducción general al rápido desarrollo y la importancia de las tecnologías de energía renovable en la sociedad moderna. Entre ellas, las tecnologías de conversión y almacenamiento de energía electroquímica son particularmente atractivas en términos de costo, seguridad y respeto al medio ambiente. Se discuten los principios básicos de las tecnologías de baterías de iones de litio, sodio y potasio, incluidas las estructuras de las baterías, los materiales de los electrodos y los mecanismos de trabajo. Además, describo el principio de funcionamiento de las DEFCs y el EOR electrocatalítico. También se explican las estrategias para sintetizar nanocristales de alto rendimiento para aplicaciones de almacenamiento y conversión de energía electroquímica. Finalmente, en este capítulo discuto el fenómeno de la evolución estructural y química de los nanocristales durante las operaciones electroquímicas y cómo se necesita su caracterización en cada sistema para una comprensión profunda de las propiedades y aplicaciones de los nanomateriales. El capítulo 1 también incluye los objetivos de la tesis. El Capítulo 2 describe un método de crecimiento simple mediado por semillas a baja temperatura para crecer Mn3O4 en nanoparticulas huecas de Fe3O4. Se lleva a cabo un proceso de sinterizado a temperatura moderada (500 °C) para promover la reacción en estado sólido de las NPs y obtener partículas huecas de MnxFe3-xO4. Al ser usados como materiales de electrodo anódico, la cubierta policristalina, el espacio vacío interno y la gran área de superficie de las NPs de MnxFe3-xO4 pueden amortiguar de manera efectiva el cambio de volumen de los nanocristales durante el proceso de litiación y delitizacion para mejorar la estabilidad y la vida útil del ciclo. Se evalúa la actividad electroquímica de las NPs de MnxFe3- xO4 hacia la reacción de litio y se explora la relación entre la estructura y las propiedades electroquímicas. El excelente rendimiento de las NPs huecas de MnxFe3-xO4 está asociado con su estructura y composición cristalinas, y con la presencia de ligandos carbonizados, que promueven aún más la conductividad eléctrica y acomodan y liberan rápidamente iones de litio mientras retienen una estructura estable incluso después de ciclos continuos de carga/descarga . Este trabajo fue publicado en Nano Energy en 2019. El Capítulo 3 vesra sobre el rendimiento de los NPs bimetálicos como ánodos en LIBs y KIBs. NPs monodispersas de CoSn y NiSn se sintetizan mediante co-reducción y se soportan en materiales comerciales de carbono. Los nanocompuestos obtenidos se prueban como materiales anódicos en LIBs de media celda y KIBs y LIBs de celda completa. Los electrodos CoSn@C muestran excelentes capacidades de carga y descarga en media celda y celdas completas LIB. Las capacidades para KIB se estabilizan alrededor de 200 mAh g-1 con alta eficiencia culombiana durante 400 ciclos para CoSn@C y 100 mAh g-1 para NiSn@C durante 300 ciclos. La oxidación de las NPs, la formación de la capa SEI, el vasto cambio de volumen durante la litiación y la delitiación causaron la disminución de las capacidades. Este trabajo fue publicado en ACS Applied Materials & Interfaces en 2020. En el capítulo 4, se detalla un enfoque simple para producir nanocubos intermetálicas de Pd3Pb con geometría cúbica bien definida y un tamaño promedio de 6 nm a 10 nm. Los catalizadores de Pd3Pb/C presentan actividades y estabilidades electrocatalíticas EOR mejoradas. La actividad EOR de las NPs de Pd3Pb se investiga en función de su tamaño a través de técnicas CV y CA. Todos los catalizadores exhiben una disminución de corriente pronunciada durante los primeros 500 s de operación EOR continua, que está asociada con la acumulación de intermedios de reacción fuertemente adsorbidos y el bloqueo relacionado de los sitios de reacción. Los catalizadores pueden reactivarse simplemente ciclando para eliminar eficazmente las especies adsorbidas en la superficie y recuperar la actividad electrocatalítica. Una reorganización de los elementos Pd y Pb ocurre en las NPs de Pd3Pb durante EOR, lo que implica una difusión hacia afuera/hacia adentro de Pd/Pb para equilibrar la estequiometría de la superficie de los NCs, que es impulsada por la diferente afinidad de Pb y Pd hacia el oxígeno y posiblemente el etanol, y la oxidación/reducción electroquímica de Pd. Este trabajo fue publicado en Chemistry of Materials en 2020. El Capítulo 5 demuestra la síntesis de NRs coloidales de Pd2Sn que incorporan P a través de la fosforización de las NPs de Pd2Sn con un reactivo altamente activo. El catalizador Pd2Sn:P/C exhibe una actividad significativamente mejorada hacia EOR en medios alcalinos en comparación con Pd2Sn/C, PdP2/C y catalizadores comerciales de Pd/C. La mejora del rendimiento se racionaliza con la ayuda de los cálculos de DFT teniendo en cuenta los diferentes entornos químicos de fósforo. Dependiendo de su estado de oxidación, el fósforo superficial introduce sitios con adsorción de OH de baja energía y/o influye fuertemente en la estructura electrónica del paladio y el estaño para facilitar la oxidación del acetilo al ácido acético, que se considera el paso limitante de la tasa de EOR. El Pd2Sn:P se caracteriza por una superficie rica en Sn y P, que se correlaciona bien con los porcentajes más altos de estaño oxidado y fósforo, y la mayor tendencia a la oxidación de Sn en comparación con Pd. Los cálculos de DFT demuestran que la presencia de P puede inducir una mayor adsorción química de OH- para facilitar la formación de CH3COOH, lo que resulta en un aumento de la actividad EOR. Este trabajo fue aceptado en Nano Energy en 2020.

La présence d'une fonction de stockage avec des sources d'énergie intermittentes permet d'obtenir une meilleure adéquation entre la consommation et la production d'énergie. Aujourd'hui, le stockage d'énergie est le plus souvent réalisé avec des batteries conventionnelles, principalement au plomb-acide, pour des raisons de coût, de fiabilité et de disponibilité industrielle. Cependant, la durée de vie des éléments de stockage actuels, l'impact sur l'environnement et le rendement trop faible entrainent la recherche d'autres moyens de stockage ayant des durées de vie compatibles avec les applications et présentant des fonctions plus flexibles. La technologie lithium parait être aujourd'hui un bon compromis si elle est associée à une électronique de précision assurant diverses fonctions. Cette thèse porte sur l'optimisation de moyens de stockages lithium-ion utilisés dans les énergies renouvelables et le développement de l'électronique associée. La validation de ces travaux a été faite à travers des systèmes de conversion photovoltaïques. Le rendement de conversion de l'ensemble a particulièrement été étudié en tenant compte de différents profils de charge et de décharge, du vieillissement et des sécurités des batteries ainsi que des derniers développements technologiques de batterie. Pour valider les algorithmes de gestion et qualifier les chaînes de conversion, un banc de mesure spécifique a été développé.

Soiling, the process of particle deposition onto surfaces, has been studied since the 40’s. Initially, it was studied as a physical process, including types of adhesion forces, and later its effect on performance of solar energy conversion technologies was analyzed, such as in photovoltaics and concentrated solar power. This thesis approaches the problem from a cause-effect point of view and how it can be mitigated. Soiling is characterized, mineral and chemically, using a Scanning Electron Microscope. Polycristalline photovoltaic modules deposition rates are retrieved and related to environmental parameters, as well as, to long-range Saharan desert dust transport, a non-local phenomenon. Attention is also given to Spring, where atmospheric pollen concentration enhances soiling. The effect of soiling on the photovoltaic optimum tilt angle, for fixed and multiple angles, is studied along with a simple economic analysis. Cleaning schedules, for a desired system efficiency, are calculated based on annual soiling. Mirror soiling, related to concentrated solar power technologies, is also analyzed. Soiling rates are calculated and interlinked with environmental parameters such as air temperature, relative humidity, particulate mater concentration and vertical wind speed. From a collaboration with the Institut de Recherche en Energie Solaire et Energies Nouvelles, Morocco, an insightful study is made comparing soiling effect between Portugal and Morocco. A passive cleaning method, impregnated anti-soiling coating, is tested. Comparison between coated and uncoated mirrors is done to evaluate its performance and conclude if it stands as a possible tool to reduce water consumption in cleaning solar harvesting technologies; Resumo: Sujidade em Tecnologias de Conversão de Energia Solar: Avaliação e Mitigação A sujidade, o processo de deposição de partículas em superfícies, tem sido estudada desde os anos 40. Inicialmente, começou a ser estudada como um processo fisico, incluindo tipos de forças de adesão, e mais tarde o seu efeito no desempenho de tecnologias de conversão de energia solar, como na tecnologia fotovoltaica e e de concentração. Esta tese aborda este problema de um ponto de vista causa-efeito e como pode ser mitigado. A sujidade é caracterizada, mineral e químicamente, usando um Microscópio Eletrónico de Varrimento. As taxas de deposição em módulos fotovoltaicos policristalinos são calculadas e relacionadas com parametros ambientais, tal como com o transporte de longo alcance de areia do deserto do Sahara, um fenómeno não local. Também é dada atenção à Primavera, onde a concentração de pólen na atmosfera aumenta a sujidade. O efeito da sujidade no ângulo de inclinação fotovoltaico óptimo, para ângulos fixos e múltiplos, é estudado juntamente com analises económicas. Calendários de limpeza, para uma eficiência de sistema desejada, são calculados com base em dados anuais de deposição de particulas. A sujidade em espelhos, relacionada com as tecnologias de energia solar concentrada, é também analisada. As taxas de deposição são calculadas e relacionadas com parâmetros ambientais, tais como temperatura do ar, humidade relativa, concentração de particulas e velocidade vertical do vento. A partir de uma colaboração com o Institut de Recherche en Energie Solaire et Energies Nouvelles, Marrocos, fez-se um estudo esclarecedor, comparando o efeito da sujidade entre Portugal e Marrocos. Um método passivo de limpeza, revestimentos impregnados anti-sujidade, é testado. A comparação entre espelhos revestidos e não revestidos é realizada para avaliar o seu desempenho e concluir se é um método importante para alcançar uma redução no consumo de água na limpeza de tecnologias de energia solar.

Metal phosphides are an important class of functional materials that exhibit a wide range of applications for energy storage and conversion. However, the synthesis of metal phosphide nanoparticles and its scalability is often limited by the toxicity, air sensitivity and high cost of reagents used. In this thesis, a simple, scalable and cost-effective procedure was developed to produce metal phosphides using inexpensive, low-toxicity and air-stable triphenyl phosphite as phosphorus source. The use of chlorides or metal carbonyl as metal precursors and hexadecylamine as ligand allowed the synthesis of a variety of phosphide nanocrystals (NCs) including phosphides of Ni, Co, Cu, Fe, Mo. The use of NiCl2 and CoCl2 mixture as metal precursors, ternary metal phosphide Ni2-xCoxP (0≤x≤2) NCs could be obtained. The synthesis of Ni2-xCoxP involved the nucleation of amorphous Ni-P and its posterior crystallization and simultaneous incorporation of Co. Tuning the experimental parameters allows producing NCs with different composition, morphology and particle size. Ni2-xCoxP-based electrocatalysts exhibited enhanced electrocatalytic activity toward the hydrogen evolution reaction compared to binary phosphides. In particular, NiCoP electrocatalysts displayed very low overpotential of 97 mV at J = 10 mA cm-2 and an excellent long-term stability. Density functional theory (DFT) calculations of the Gibbs free energy for hydrogen adsorption at the surface of Ni2-xCoxP NCs showed NiCoP to have the most appropriate composition to optimize this parameter within the whole Ni2-xCoxP series. The use of chromium hexacarbonyl as metal precursor and high boiling point oleylamine as ligand, less-studied CrP NCs could also be produced. This method allows producing CrP with nanometric particle size and with a very high throughput and material yield. CrP NCs were mixed with carbon to prepare electrocatalysts, which exhibited remarkable activity and stability toward oxygen reduction reaction in an alkaline electrolyte and an absolute tolerance to methanol. DFT calculations demonstrated CrP to provide a very strong chemisorption of O2 which facilitates its reduction and explains the excellent performance. Besides, another phosphorus source hexamethylphosphorous triamide (HMPT) and new synthetic strategies were applied for the synthesis of SnP and PdP2 NCs. SnP NCs were produced from the reaction of HMPT and a tin phosphonate prepared from tin oxalate and a long chain phosphonic acid. SnP NCs obtained from this reaction displayed a spherical geometry and a trigonal crystallographic phase with a superstructure attributed to ordered diphosphorus pairs. Such NCs were mixed with carbon black and used as anode materials in sodium-ion batteries, which displayed a high reversible capacity of 600 mA h g-1 at a current density of 100 mA g-1 and cycling stability for over 200 cycles. The excellent cycling performance was associated with both the small size of the crystal domains and the particular composition and phase of SnP which prevent mechanical disintegration and major phase separation during sodiation and desodiation cycles. The synthesis of PdP2 involves the reaction of palladium acetylacetonate and HMPT to nucleate defective Pd5P2 nanoparticles that subsequently, with further phosphorus incorporation, crystallize into PdP2. The produced PdP2 NCs showed high mass activity and long-term stability toward the ethanol oxidation reaction in alkaline media. The activity and stability of the PdP2-based catalyst were further improved by supporting PdP2 NCs onto reduced graphene oxide (rGO). PdP2/rGO catalysts showed high current densities up to 51.4 mA cm-2 and mass activities of 1.60 A mg-1Pd, that is 4.8 and 15 times higher than Pd NCs. Overall, in this thesis serval metal phosphide nanomaterials were produced by colloidal synthetic strategy, and showed highly performance for electrochemical energy conversion and storage applications.
Los fosfuros metálicos son materiales funcionales de gran interés e impacto en la sociedad debido a su gran rendimiento en almacenamiento y conversión de energía. Sin embargo, la síntesis de nanopartículas de fosfuros metálicos y su escalabilidad es limitada. En la presente tesis, se ha desarrollado un proceso de producción para nanopartículas de fosfuros metálicos simple, escalable y rentable. El éxito de los resultados radica en el uso de fosfito de trifenilo, considerado como una fuente de fósforo barata, estable al contacto con el aire y no tóxica, que además permite la síntesis de una gran variedad de nanocristales (NCs) (fosfuros de Ni, Co, Cu, Fe, Mo, así como fosfuros ternarios de Ni2-xCoxP). Optimizando los parámetros experimentales, es posible producir NCs de diferente composición, morfología y tamaño. Además, el uso de solventes de alto punto de ebullición, facilita la síntesis de materiales menos estudiados como el CrP. Los NCs de Ni2-xCoxP y CrP NCs pueden ser combinados con carbono dando lugar a electrocatalizadores útiles para reacciones tales como evolución de hidrógeno y reducción de oxígeno, respectivamente. El uso de otras fuentes de fósforo, como por ejemplo la triamida de hexametilfósforo, permite a su vez producir NCs de SnP y PdP2. En el caso particular de SnP, los NCs demostraton poseer una geometría esférica y una fase cristalográfica trigonal con una superestructura atribuida a los pares difósforos ordenados. Mezclados con carbón negro y utilizados como ánodos en baterías de ion sodio, estos NCs demostraron una alta capacidad reversible de 600 mA h g-1 a una densidad de corriente de 100 mA g-1 y estables durante más de 200 ciclos. Por otro lado, los NCs de PdP2 soportados sobre óxido de grafeno se utilizaron como electrocatalizadores para la oxidación de etanol, mostrando una alta densidad de corriente de hasta 51.4 mA cm-2 y una actividad de masa de 1.60 A mg-1Pd. En resumen, se han desarrollado métodos de síntesis basados en estrategias coloidales para poder producir una gran variedad de fosfuros metálicos a escala nanométrica, mostrando estos un gran rendimiento para su uso en conversión y almacenamiento de energía electroquímica.

Ces travaux de thèse portent sur le développement de nouveaux systèmes piézoélectriques récupérateurs d’énergie à partir de vibrations mécaniques environnementales. L’objectif recherché est d’apporter des solutions à certaines contraintes fortes liées à la miniaturisation de ces systèmes, en vue de leur intégration en technologie MEMS. Les 2 axes majeurs suivis lors de ces travaux sont :(i) la nanostructuration par porosification du substrat silicium. Ce procédé permet de créer des zones fonctionnalisées possédant des propriétés locales de masse volumique et de rigidité plus faibles que celles du substrat silicium. Ceci permet d’une part d’améliorer le coefficient de couplage électromécanique global de la structure et, d’autre part, de maintenir la fréquence de résonance du mode fonctionnel dans une gamme fréquentielle basse (< que 1KHz) compatible avec le spectre de nombreuses sources vibratoires usuelles. Une série de modélisation par éléments finis d’un convertisseur type (poutre avec masse sismique) a établi les paramètres dimensionnels optimaux de la zone nanostructurée. L’efficacité de ce procédé de nanostructuration localisée a ensuite été évaluée expérimentalement sur des membranes en silicium. Il a été observé une réduction de la fréquence de résonance du mode fondamental, tout en minimisant les pertes par un choix judicieux de l’emplacement et de la largeur de la zone poreuse. (ii) Le développement de dispositifs récupérateurs à sensibilité multidirectionnelle. Ces dispositifs permettent de récupérer l’énergie quel que soit la direction de la sollicitation externe. Ils exploitent 3 modes propres distincts de flexion sollicités chacun par une composante particulière (ax, ay ou az) du vecteur accélération caractéristique de la sollicitation. Ces dispositifs basés sur une structure planaire de type double poutres orthogonales avec masse sismique centrale sont facilement intégrables et peuvent être déclinés de l’échelle centimétrique à l’échelle millimétrique en utilisant dans ce cas les technologies de type MEMS. Un modèle analytique simple a d’abord mis à jour les mécanismes énergétiques qui permettent d’obtenir une quantité d’énergie constante lorsque le dispositif est soumis à un vecteur sollicitation de direction quelconque. L’optimisation du coefficient de couplage électromécanique de chaque mode fonctionnel, ainsi que l’ajustement de leur fréquence de résonance ont été obtenu à l’aide d’un modèle à éléments finis. L’ensemble de ces résultats théoriques a été expérimentalement validé à l’aide de prototypes centimétriques
This thesis work focuses on the development of new piezoelectric energy recovery systems from environmental mechanical vibration. The goal is to provide solutions to some strong constraints on the miniaturization of these systems, their integration in MEMS technology. The 2 major lines followed in this work are: (i) the nanostructuring by porosification silicon substrate. This method allows to create functionalized areas having local properties of density and lower rigidity than those of the silicon substrate. This allows on the one hand to improve the overall electromechanical coupling coefficient of the structure and, secondly, to maintain the resonant frequency of the operational mode in a low frequency range (< 1KHz) compatible with the spectrum of Many conventional vibratory sources. A series of finite element modeling of a type converter (beam with seismic mass) established the optimum dimensional parameters of nanostructured area. The effectiveness of this localized nanostructuring method was then evaluated experimentally on silicon membranes. It was observed a reduction of the resonance frequency of the fundamental mode, while minimizing losses by a judicious choice of the location and the width of the porous zone. (Ii) The development of recovery devices multidirectional sensitivity. These devices allow to recover energy regardless of the direction of the external load. They use 3 different eigenmodes bending each solicited by a particular component (ax, ay and az) vector solicitation characteristic acceleration. These devices based on a planar structure type double orthogonal beams with central seismic mass can be easily integrated and can be broken down to centimeter scale at the millimeter scale using in this case the MEMS technologies. A simple analytical model was first updated energy mechanisms that enable a constant amount of energy when the device is subjected to a bias vector in any direction. The optimization of the electromechanical coupling coefficient of each functional mode, and the adjustment of their resonance frequency were obtained using a finite element model. All these theoretical results has been experimentally validated using centimeter prototypes

Le développement de lubrifiants à haute valeur ajoutée subissant des conditions opératoires de plus en plus draconiennes, économes en carburant et performants pendant une longue durée reste un défi considérable pour les fabricants d’huiles. Cette thèse concerne l’étude du rôle et des actions des améliorants d’indice de viscosité (ou Viscosity Index Improvers (VII)) dans les lubrifiants moteurs. Le premier objectif visé dans ce travail est la caractérisation des comportements rhéologiques et la modélisation de la viscosité en fonction de conditions réelles de température, pression et contrainte de cisaillement pour des solutions d’huile de base et de polymère sans additifs fonctionnels. Plusieurs polymères (PAMA, OCP et PISH) de masses moléculaires et conformations (peigne, linéaire et étoile) différentes sont utilisés à 1,2% en masse dans une huile de base minérale hydrocraquée. L’originalité de la thèse réside dans l’utilisation de rhéomètres non-commerciaux à haute pression (jusqu’à 800 MPa). Un deuxième défi réside dans la compréhension de la relation entre la réponse rhéologique des lubrifiants automobiles simplifiés et les mécanismes présents à l’échelle moléculaire en explorant les notions de conformation, de solubilité et de rayon hydrodynamique grâce à l’extension de la loi d’Einstein à haute pression. Enfin, l’étude se concentre sur le lien entre rhéologie et tribologie et par extension, entre la composition chimique du lubrifiant et la tribologie. Les épaisseurs de film sont mesurées et comparées avec les prédictions analytiques de Hamrock-Dowson et avec les simulations numériques basées sur l’équation de Reynolds généralisée en incluant les modèles rhéologiques. Les données expérimentales et numériques sont en adéquation
The development of high value-added lubricants overcoming more and more drastic operating conditions, fuel-efficient and providing excellent performance during a long time remains a huge challenge for oil makers. This thesis is dedicated to the study of the role and the actions of Viscosity Index Improvers (VII) in engine lubricants. The first objective targeted in this work is the characterization of the rheological behaviors and the modeling of viscosity in function of realistic conditions of temperature, pressure and shear stress for polymer-thickened base oil solutions without functional additives. Several polymers (PAMA, OCP and PISH) with different molecular weights and conformations (comb, linear and star) are used with a concentration of 1.2% (w/w) in a hydrocracked mineral base oil. The originality of the thesis lies in the use of non-commercial rheometers under high pressure (up to 800 MPa). A second challenge is the understanding of the relationship between the rheological response of simplified engine lubricants and the mechanisms occurring at the molecular scale by exploring the notions of conformation, solubility and hydrodynamic radius by the extension of the Einstein’s law at high pressure. Finally, the study focuses on the link between rheology and tribology and by extrapolation, between the chemical composition of the lubricant and tribology. The film thickness is measured and compared with the Hamrock-Dowson analytical predictions and with the numerical simulations based on the generalized Reynolds’ equation including the rheological models. Both experimental and numerical data are in good agreement

L'amélioration de l'autonomie énergétique des systèmes communicants constitue aujourd'hui une des préoccupations majeures pour leur déploiement massif dans notre environnement. On souhaite rendre complètement autonome ces dispositifs électroniques (on pense entre autres aux capteurs et réseaux de capteurs) en s'affranchissant des sources d'énergie embarquées qui nécessitent des opérations de remplacement ou de recharge périodiques. Parmi les sources d'énergie disponibles qui peuvent être exploitées, on trouve les ondes électromagnétiques. Le dispositif qui permet de capter cette énergie et la convertir en puissance continue utile est dénommé Rectenna (Rectifying antenna) qui associe une antenne de captation à un circuit de rectification à base de diodes. Les rectennae ont fait l'objet d'un nombre important de communications dans la littérature ces dernières années avec pour fil conducteur, la recherche de performances optimales compte tenu de l'atténuation des ondes électromagnétiques et des faibles niveaux de champ récupérés. C'est dans ce contexte que s'est déroulé ce travail de thèse dont le financement a été assuré par un contrat ANR (REC-EM).Dans ce travail, on s'est attaché à développer, à concevoir et à caractériser expérimentalement des structures planaires qui présentent des propriétés intéressantes :- En terme de polarisations orthogonales, ceci de façon à s'affranchir de l'orientation arbitraire de l'onde incidente à la rectenna. Une rectenna à double polarisation circulaire à 2.45 GHz et à double accès sera réalisée pour, de plus, s'affranchir de la perte de 3 dB lorsque l'onde récupérée est à polarisation linéaire à orientation arbitraire.- En termes de résonances multiples, ceci pour augmenter le niveau de puissance récupérée par l'antenne et optimiser la puissance continue convertie. Une rectenna à double fréquence (1.8 et 2.45 GHz) et à accès unique sera conçue ainsi qu'une rectenna constituée d'un réseau de deux antennes double fréquence.- En terme de réduction de taille en s'affranchissant de l'utilisation du filtre HF entre l'antenne et le circuit de conversion ceci pour l'ensemble des structures rectennae développées dans ce travail. Dans tous les cas, il sera nécessaire de développer le circuit de rectification le plus adapté à la topologie de l'antenne de captation et évaluer la technique de recombinaison optimale coté DC pour s'affranchir au mieux des déséquilibres qui peuvent apparaître entre les voies d'accès de l'antenne. Pour contenir les dimensions de la structure globale, des circuits mono diode seront dimensionnés et réalisés pour chacune des structures. Enfin, on exploitera l'antenne à double polarisation circulaire double accès, dont on cherchera à diminuer les dimensions, pour alimenter un capteur de température à affichage LCD. Pour augmenter le niveau de tension nécessaire au fonctionnement du capteur, nous associerons entre la rectenna et le capteur un convertisseur DC-DC. Il s'agit, dans ce cas, d'un dispositif de gestion d'énergie adapté pour les faibles puissances. Deux convertisseurs seront employés dont celui développé par les laboratoires Ampère de l'Ecole Centrale de Lyon et SATIE à l'ENS Cachan. Ce convertisseur a fait l'objet d'une thèse également financée par l'ANR dans le cadre de ce contrat REC-EM
Improving energy autonomy of communication systems constitutes one of the major concerns for their massive deployment in our environment. We want to make these electronic devices (sensors and sensor networks) completely autonomous, avoiding the embedded energy sources that require replacement operations or periodic charging. Among the available energy sources that can be harvested, there are electromagnetic waves. The device that can capture this energy and convert it into useful DC power is called Rectenna (Rectifying antenna), combining antenna with diode-based rectifier. In recent few years, rectennas have reached a significant number of papers in the literature. The main challenge consists in improving performances in term of efficiency, in an attempt to overcome the electromagnetic wave attenuation and the low available field level. According to this context, this PhD work supported by the ANR project REC-EM has taken place. In this study, we have developed, designed and characterized planar structures that have interesting properties:- In term of orthogonal polarizations, so energy harvesting becomes feasable regardless the arbitrary orientation of the incident wave on the rectenna. A dual-circularly polarized rectenna at 2.45 GHz with dual-access will be set up to overcome the 3 dB power loss in the case of linearly-polarized incident wave with unknown orientation.- In term of multiple resonances, so the amount of total RF power collected by the antenna can be increased and consequently the converted DC power level can also be improved. A dual-frequency rectenna (1.8 and 2.45 GHz) with single access will be designed, as well as a rectenna based upon a dual-frequency antenna array.- In term of size compactness by avoiding the use of the HF filter between the antenna and the rectifier for all developed rectenna structures during this work. In all cases, it will be necessary to define the most suitable rectifier topology to each antenna and select, if it is appropriated, the optimum DC recombination technique to overcome the effects of RF power imbalance that may occur between the different antenna accesses. Besides, single-diode circuits will be designed and fulfilled for each structure. Finally, we will miniaturize the dual-circularly polarized dual-access antenna, and exploit it to power a LCD display temperature sensor. To enhance the DC voltage level required to activate the sensor, a DC-DC converter is inserted between the rectenna and the sensor. Such energy management device should be able to operate under low delivered DC power. Two converters will be used. The first one is developed by Ampere Lab at Ecole Centrale de Lyon and SATIE Lab at ENS Cachan. This converter was the subject of another dissertation also supported by the ANR under the REC-EM project

The kinetic energy present in tidal currents and other water courses has long been appreciated as a vast resource of renewable energy. The work presented in this doctoral thesis is devoted to both the characteristics of the hydro-kinetic resource and the technology for energy conversion. An assessment of the tidal energy resource in Norwegian waters has been carried out based on available data in pilot books. More than 100 sites have been identified as interesting with a total estimated theoretical resource—i.e. the kinetic energy in the undisturbed flow—in the range of 17 TWh. A second study was performed to analyse the velocity distributions presented by tidal currents, regulated rivers and unregulated rivers. The focus is on the possible degree of utilization (or capacity factor), the fraction of converted energy and the ratio of maximum to rated velocity, all of which are believed to be important characteristics of the resource affecting the economic viability of a hydro-kinetic energy converter. The concept for hydro-kinetic energy conversion studied in this thesis comprises a vertical axis turbine coupled to a directly driven permanent magnet generator. One such cable wound laboratory generator has been constructed and an experimental setup for deployment in the river Dalälven has been finalized as part of this thesis work. It has been shown, through simulations and experiments, that the generator design at hand can meet the system requirements in the expected range of operation. Experience from winding the prototype generators suggests that improvements of the stator slot geometry can be implemented and, according to simulations, decrease the stator weight by 11% and decrease the load angle by 17%. The decrease in load angle opens the possibility to reduce the amount of permanent magnetic material in the design.

The present research seeks to advance the understanding and application of Principal Component Analysis (PCA)-based combustion modelling for practical systems application. This work is a consistent extension to the standard PC-transport model, and integrates the use of Gaussian Process Regression (GPR) in order to increase the accuracy and the potential of size reduction offered by PCA. This new model, labelled PC-GPR, is successively applied and validated in a priori and a posteriori studies.In the first part of this dissertation, the PC-GPR model is validated in an a priori study based on steady and unsteady perfectly stirred reactor (PSR) calculations. The model showed its great accuracy in the predictions for methane and propane, using large kinetic mechanisms. In particular, for methane, the use of GPR allowed to model accurately the system with only 2 principal components (PCs) instead of the 34 variables in the original GRI-3.0 kinetic mechanism. For propane, the model was applied to two different mechanisms consisting of 50 species and 162 species respectively. The PC-GPR model was able to achieve a very significant reduction, and the thermo-chemical state-space was accurately predicted using only 2 PCs for both mechanisms.The second part of this work is dedicated to the application of the PC-GPR model in the framework of non-premixed turbulent combustion in a fully three-dimensional Large Eddy Simulation (LES). To this end, an a posteriori validation is performed on the Sandia flames D, E and F. The PC-GPR model showed very good accuracy in the predictions of the three flames when compared with experimental data using only 2 PCs, instead of the 35 species originally present in the GRI 3.0 mechanism. Moreover, the PC-GPR model was also able to handle the extinction and re-ignition phenomena in flames E and F, thanks to the unsteady data in the training manifold. A comparison with the FPV model showed that the combination of the unsteady data set and the best controlling variables for the system defined by PCA provide an alternative to the use of steady flamelets parameterized by user-defined variables and combined with a PDF approach.The last part of this research focuses on the application of the PC-GPR model in a more challenging case, a lifted methane/air flame. Several key features of the model are investigated: the sensitivty to the training data set, the influence of the scaling methods, the issue of data sampling and the potential of a subgrid scale (SGS) closure. In particular, it is shown that the training data set must contain the effects of diffusion in order to accurately predict the different properties of the lifted flame. Moreover, the kernel density weighting method, used to address the issue of non-homogenous data density usually found in numerical data sets, allowed to improve the predictions of the PC-GPR model. Finally, the integration of subgrid scale closure to the PC-GPR model allowed to significantly improve the simulations results using a presumed PDF closure. A qualitative comparison with the FPV model showed that the results provided by the PC-GPR model are overall very comparable to the FPV results, with a reduced numerical cost as PC-GPR requires a 4D lookup table, instead of a 5D in the case of FPV.
Le double défi de l'énergie et du changement climatique mettent en avant lanécessité de développer des nouvelles technologies de combustion, étantdonné que les projections les plus réalistes montrent que la plus grandeaugmentation de l'offre d'énergie pour les décennies à venir se fera à partirde combustibles fossiles. Ceci représente donc une forte motivation pour larecherche sur l'efficacité énergétique et les technologies propres. Parmicelles-ci, la combustion sans flamme est un concept nouvellementdéveloppé qui permet d'obtenir des rendements thermiques élevés avecdes économies de carburant tout en maintenant les émissions polluantes àun niveau très bas. L'intérêt croissant pour cette technologie est égalementmotivé par sa grande flexibilité de carburant, ce qui représente uneprécieuse opportunité pour les carburants à faible valeur calorifique, lesdéchets industriels à haute valeur calorifique et les combustibles à based'hydrogène. Etant donné que cette technologie est plutôt récente, elle estde ce fait encore mal comprise. Les solutions d'une application industriellesont très difficiles à transposer à d'autres. Pour améliorer les connaissancesdans le domaine de la combustion sans flamme, il est nécessaire de menerdes études fondamentales sur ce nouveau procédé de combustion afin defavoriser son développement. En particulier, il y a deux différencesmajeures par rapport aux flammes classiques :d’une part, les niveaux deturbulence rencontrés dans la combustion sans flamme sont rehaussés, enraison des gaz de recirculation, réduisant ainsi les échelles de mélange.D'autre part, les échelles chimiques sont augmentées, en raison de ladilution des réactifs. Par conséquent, les échelles turbulentes et chimiquessont du même ordre de grandeur, ce qui conduit à un couplage très fort.Après un examen approfondi de l'état de l'art sur la modélisation de lacombustion sans flamme, le coeur du projet représentera le développementd'une nouvelle approche pour le traitement de l'interaction turbulence /chimie pour les systèmes sans flamme dans le contexte des simulationsaux grandes échelles (Large Eddy Simulations, LES). Cette approche serafondée sur la méthode PCA (Principal Component Analysis) afin d'identifierles échelles chimiques de premier plan du processus d'oxydation. Cetteprocédure permettra de ne suivre sur la grille LES qu'un nombre réduit descalaires non conservés, ceux contrôlant l'évolution du système. Destechniques de régression non-linéaires seront couplées avec PCA afind’augmenter la précision et la réductibilité du modèle. Après avoir été validégrâce à des données expérimentales de problèmes simplifiés, le modèlesera mis à l'échelle afin de gérer des applications plus grandes, pertinentespour la combustion sans flamme. Les données expérimentales etnumériques seront validées en utilisant des indicateurs de validationappropriés pour évaluer les incertitudes expérimentales et numériques.
Doctorat en Sciences de l'ingénieur et technologie
info:eu-repo/semantics/nonPublished

In this project, nanoparticles were produced by solution-based one-pot synthesis, particularly colloidal methods. A series of powerful tools were used to characterize the structure and surface compositions before they were tested as anode materials in the field of energy conversion and storage. Firstly, we produced colloidal Ni polyhedral (16 ± 2 nm) and spherical (13 nm) NCs. The electrocatalytic properties of electrodes based on these NCs were first investigated in variable concentrations of KOH. Electrodes based on Ni polyhedral NCs displayed impressive current densities (59.4 mA cm 2) and mass activities (2016 mA mg 1) at 0.6 V vs. Hg/HgO in the presence of 1.0 M methanol and 1.0 M KOH, which corresponds to a twofold increase over electrodes based on spherical Ni NCs and over most previous Ni-based electrocatalyts previously reported. Electrodes based on faceted polyhedral NCs displayed a 30% loss of activity during the first few operation hours, but activity stabilized to around a 65% of the initial value after ca. 20000 s operations. And also, we developed a new synthetic route to produce NiSn intermetallic NPs with composition control. Detailed electrochemical measurements showed that these NPs exhibited excellent performance for MOR in alkaline solution. Ni-rich NiSn-based electrocatalysts displayed slightly improved performances over Ni-based electrocatalysts. Most notorious was the significantly improved stability of NiSn catalysts compared with that of Ni. This work represented a significant advance in developing cost-effective electrocatalysts with high activity and stability for MOR in DMFCs. In another sub-section of the energy conversion, a series of Ni3 xCoxSn2 (0 ≤ x ≤ 3) NPs were produced based one the protocol. A preliminary optimized catalyst composition, Ni2.5Co0.5Sn2, showed a current density of 65.5 mA cm 2 and a mass current density of 1050 mA mg 1 at 0.6 V vs. Hg/HgO for the MOR in 1.0 M KOH containing 1.0 M methanol. While the introduction of Co slightly decreased the durability with respect to Ni3Sn2, Ni2.5Co0.5Sn2 NP-based electrodes demonstrated significant stability during continuous cycling and increased activity at high methanol concentrations. The presence of Sn was found to be essential to improve stability with respect to elemental Ni, although Sn was observed to slowly dissolve in the presence of KOH. In the energy storage field, we focused on the performance as anode material in LIBs and SIBs. Among the different NixSn compositions tested, best performances toward Li+ ion and Na+ ion insertion were obtained for Ni0.9Sn NP-based electrodes. This optimized cycling charge-discharge performance for LIBs provided 980 mAh g 1 at 0.2 A g 1 after 340 cycles. Additionally, Ni0.9Sn NP-based electrodes were tested in Na+-ion half cells, exhibiting 160 mAh g 1 over 120 cycles at 0.1 A g 1. The pseudocapacitive charge-storage accounted for a high portion of the whole energy storage capacity, which was associated to the small size and the composition of the NixSn NPs used. In the last chapter of the project, the CoxSn NP composition was adjusted over the range 1.3 ≤ x ≤ 0.3. These Co-Sn solid solutions were tested as anode materials in LIBs on a half-cell battery system. Among the different compositions tested, Co0.9Sn and Co0.7Sn NPs provided the best performance, with a charge-discharge capacity above 1500 mAh g 1 at a current density of 0.2 A g 1 after 220 cycles and up to 800 mAh g 1 at 1.0 A g 1 after 400 cycles. Through the kinetic analysis of Co0.9Sn NPs by the CV measurement, we found these charge-discharge capacities to include a very large pseudocapacitive contribution, up to 81% at a sweep rate of 1 mV s 1, which we related to the small size of the particles.

La différence de température entre l’eau de mer chaude de surface (d’origine solaire tropicale) et celle qui est froide en profondeur (qui vient des pôles) constitue une source d’énergie stable, propre et renouvelable disponible dans l’océan. Cette énergie thermique des mers (ETM) peut être convertie en électricité par le cycle organique de Rankine (ORC). Le faible écart de température entre les sources chaudes et froides représente ce-pendant un défi technique à la fois pour les transferts thermiques et pour les performances du cycle. L’objectif de cette thèse est d’explorer les possibilités d’amélioration du fonctionnement d’un ORC appliqué à l’ETM, de compléter les connaissances des composants du système et de mettre en évidence les avantages de cette technologie nouvelle sur un réseau non-interconnecté comme celui de La Réunion. Les travaux présentés se basent à la fois sur des simulations et sur des résultats expérimentaux obtenus sur un banc d’essai de 450 kW thermique nommé le PAT ETM. Dans le premier chapitre, une nouvelle méthode de choix du fluide de travail est proposée. L’étude fait ressortir certains fluides peu considérés jusqu’à présent pour l’ETM. Dans le second chapitre, l’outil expérimental (PAT ETM) est présenté en détail. Le troisième chapitre dresse le bilan des technologies d’échangeurs qui ont été testées et caractérisées. Le quatrième chapitre traite de la modélisation dynamique d’un système ETM. Cette étude aboutit sur l’évaluation de la pilotabilité d’une centrale complète et met en évidence une opportunité encore peu explorée : celle d’utiliser l’ETM comme un outil de gestion pour assurer le contrôle d’un réseau électrique
The temperature difference between the hot surface seawater (of tropical solar origin) and the cold one at depth (which comes from the poles) constitutes a stable, environmentally-friendly and renewable source of energy available in the ocean. This ocean thermal energy conversion (OTEC) can be used to produce electricity by the way of an organic Rankine cycle (ORC). However, the small temperature difference between hot and cold sources represents a technical challenge both for heat transfers and for cycle performances. The objective of this thesis is then to explore the operation improvement possibilities of an ORC applied to OTEC, to complete the knowledge of the system components and to highlight the advantages of this new technology on a non-connected grid such as that of Reunion Island. This work is based both on simulations and on experimental results obtained on a 450 kW thermal energy onshore prototype named PAT ETM. In the first chapter, a new method for the choice of the working fluid is proposed. The study brings out some fluids so far little considered for OTEC. In the second chapter, the experimental tool (the PAT ETM) is presented extensively. The third chapter reports the heat exchanger technologies that have been tested and characterized. The fourth chapter deals with the dynamic modeling of an OTEC system. This study leads to the assessment of the control-lability of a complete power plant and shows a still little explored opportunity: that of using OTEC as a management tool to control an electrical network

Ambient energy harvesting has attracted significant attention over the last years for applications such as wireless sensors, implantable devices, health monitoring systems, and wearable devices. The methods of vibration-to-electric energy conversion can be included in the following categories: electromagnetic, electrostatic, and piezoelectric. Among various techniques of vibration-based energy harvesting, piezoelectric transduction method has received the most attention due to the large power density of the piezoelectric material and its simple architectures. In contrast to electromagnetic energy harvesting, the output voltage of a piezoelectric energy harvester is high, which can charge a storage component such as a battery. Compared to electrostatic energy harvester, the piezoelectric energy harvester does not require an external voltage supply. Also, piezoelectric harvesters can be manufactured in micro-scale, where they show better performance compared to other energy harvesters, owing to the well-established thick-film and thin-film fabrication techniques. The main drawback of the linear piezoelectric harvesters is that they only retrieve energy efficiently when they are excited at their resonance frequencies, which are usually high, while they are less efficient when the excitation frequency is distributed over a broad spectrum or is dominant at low frequencies. High-frequency vibrations can be found in machinery and vehicles could be used as the energy source but, most of the vibration energy harvesters are targeting at low-frequency vibration sources which are more achievable in the natural environment. One way to overcome this limitation is by using the frequency-up-conversion technology via impacts, where the source of the impacts can be one or two stoppers or more massive beams. The impact makes the piezoelectric beam oscillate in its resonance frequency and brings nonlinear behavior into the system.

Free-flowing water currents such as tides and unregulated water courses could contribute to world electricity production given the emergence of robust technical solutions for extracting the energy. At Uppsala University, a concept for converting water currents to electricity using a vertical axis turbine with fixed blade pitch and a direct drive permanentmagnet generator is studied. A system approach is desired, and in this thesis, a first analysis of two system components, the generator and the turbine, is presented. This thesis also deals with some issues concerning the design and construction of a low speed generator for this application. An experimental generator for verification of simulations has been designed and constructed. For the electromagnetic design, a FEM simulation tool has been used. The construction work has given valuable practical experience concerning for example handling permanent magnets and winding the generator with cable. Simulations and measurements of the experimental generator have been carried out for different speeds and loads. The generator can operate at the speeds and loads corresponding to maximum power capture for different turbines for water current velocities between approximately 0.5 and 2.5 m/s. At higher water current velocities the turbines may need to be run at a tip speed ratio that gives a lower power capture in order to limit the electrical currents in the generator, cavitation of the blades, or mechanical loads. Comparisons of measurements and simulations show an agreement. The FEM simulation tool can be used to simulate and design electrical machines with a low electrical frequency, i.e. 2–16 Hz.

Wave energy is a renewable energy source with a large potential to contribute to the world's electricity production. There exist several technologies on how to convert the energy in the ocean waves into electric energy. The wave energy converter (WEC) presented in this thesis is based on a linear synchronous generator. The generator is placed on the seabed and driven by a point absorbing buoy on the ocean surface. Instead of having one large unit, several smaller units are interconnected to increase the total installed power. To convert and interconnect the power from the generators, marine substations are used. The marine substations are placed on the seabed and convert the fluctuating AC from the generators into an AC suitable for grid connection. The work presented in the thesis focuses on the first steps in the electric energy conversion, converting the voltage out from the generators into DC, which have an impact on the WEC's ability to absorb and produce power. The purpose has been to investigate how the generator will operate when it is subjected to different load cases and to obtain guidelines on how future systems could be improved. Offshore experiments and simulations have been done on full scale generators connected to four different loads, i.e. one linear resistive load and three different non-linear loads representing different cases for grid connected WECs. The results show that the power can be controlled and optimized by choosing a suitable system for the WEC. It is not obvious which kind of system is the most preferable, since there are many different parameters that have an impact on the system performance, such as the size of the buoy, how the generator is designed, the number of WECs, the highest allowed complexity of the system, costs and so on. Therefore, the design of the electrical system should preferably be carried out in parallel with the design of the WEC in order to achieve an efficient system.

Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 727

Thesis (DTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2016.
The water desalination process needs large quantities of energy, either directly from fossil fuel or electricity from the national grid. However, these sources of energy significantly contribute to problems such as global warming in addition to creating a drain on the economy, due to their high cost. This dissertation is a description of the research undertaken with the aim of producing a water desalination prototype; a novel approach that was designed using state-of-the-art solar water heating equipment, incorporating the technologies of evacuated tubes and heat pipes. During the execution of the project, various modifications to the original commercially-available solar water heating system were attempted, each aimed at increasing the production of pure water. Finally, the system proved capable of producing a reasonable amount of pure water after twelve lengthy indoor experiments conducted in a laboratory in the department of Mechanical Engineering at the Cape Peninsula University of Technology, Bellville Campus, Cape Town, South Africa. Each experiment lasted five days on the basis of seven hours of exposure to an average amount of simulated solar radiation, followed by seventeen hours daily of inactivity and partial cooling down of the system.

The solid oxide fuel cell (SOFC) is a potential high efficient electrochemical device for vehicles, auxiliary power units and large-scale stationary power plants combined heat and power application. The main challenges of this technology for market acceptance are associated with cost and lifetime due to the high temperature (700-1000 oC) operation and complex cell structure, i.e. the conventional membrane electrode assemblies. Therefore, it has become a top R&D goal to develop SOFCs for lower temperatures, preferably below 600 oC. To address those above problems, within the framework of this thesis, two kinds of innovative approaches are adopted. One is developing functional composite materials with desirable electrical properties at the reduced temperature, which results of the research on ceria-based composite based low temperature ceramic fuel cell (LTCFC). The other one is discovering novel energy conversion technology - Single-component/ electrolyte-free fuel cell (EFFC), in which the electrolyte layer of conventional SOFC is physically removed while this device still exhibits the fuel cell function. Thus, the focus of this thesis is then put on the characterization of materials physical and electrochemical properties for those advanced energy conversion applications. The major scientific content and contribution to this challenging field are divided into four aspects except the Introduction, Experiments and Conclusions parts. They are: Continuous developments and optimizations of advanced electrolyte materials, ceria-carbonate composite, for LTCFC. An electrolysis study has been carried out on ceria-carbonate composite based LTCFC with cheap Ni-based electrodes. Both oxygen ion and proton conductance in electrolysis mode are observed. High current outputs have been achieved at the given electrolysis voltage below 600 oC. This study also provides alternative manner for high efficient hydrogen production.  Compatible and high active electrode development for ceria-carbonate composite electrolyte based LTCFC. A symmetrical fuel cell configuration is intentionally employed. The electro-catalytic activities of novel symmetrical transition metal oxide composite electrode toward hydrogen oxidation reaction and oxygen reduction reaction have been experimentally investigated. In addition, the origin of high activity of transition metal oxide composite electrode is studied, which is believed to relate to the hydration effect of the composite oxide. A novel all-nanocomposite fuel cell (ANFC) concept proposal and feasibility demonstration. The ANFC is successfully constructed by Ni/Fe-SDC anode, SDC-carbonate electrolyte and lithiated NiO/ZnO cathode at an extremely low in-situ sintering temperature, 600 oC. The ANFC manifests excellent fuel cell performance (over 550 mWcm-2 at 600 oC) and a good short-term operation as well as thermo-cycling stability. All results demonstrated its feasibility and potential for energy conversion. Fundamental study results on breakthrough research Single-Component/Electrolyte-Free Fuel Cell (EFFC) based on above nanocomposite materials (ion and semi-conductive composite) research activities. This is also the key innovation point of this thesis. Compared with classic three-layer fuel cells, EFFC with an electrolyte layer shows a much simpler but more efficient way for energy conversion. The physical-electrical properties of composite, the effects of cell configuration and parameters on cell performance, materials composition and cell fabrication process optimization, micro electrochemical reaction process and possible working principle were systematically investigated and discussed. Besides, the EFFC, joining solar cell and fuel cell working principle, is suggested to provide a research platform for integrating multi-energy-related device and technology application, such as fuel cell, electrolysis, solar cell and micro-reactor etc. This thesis provides a new methodology for materials and system innovation for the fuel cell community, which is expected to accelerate the wide implementation of this high efficient and green fuel cell technology and open new horizons for other related research fields.

QC 20131122

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2009.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references.
The purpose of this research was to study the various factors affecting the economic and technical feasibility of Engineered Geothermal Systems, with a special emphasis on advanced drilling technologies. The first part of the thesis was devoted to modeling and analysis of the technologies used to develop EGS projects. Since the cost of completing wells is a major factor in determining the economic feasibility of EGS projects, it is vital to be able to accurately predict in determining the economic feasibility of EGS projects, it is vital to be able to accurately predict their costs. Historic well cost data was analyzed to identify trends, and a drilling cost index for updating historic geothermal well costs to present day costs was developed. The effects of different advanced drilling technologies on drilling costs were estimated and incorporated into a techno-economic model to estimate their impact, as well as the impact of advanced reservoir stimulation technologies, on EGS levelized electricity costs. A technical analysis of geothermal binary Rankine cycle surface power plants was also performed to determine the effect of novel working fluids on plant efficiency for both sub- and supercritical binary cycles. The objective of the second part of the thesis was the application of thermal spallation drilling to deep boreholes. Thermal spallation is the fragmentation of a brittle solid into small, disc-like flakes by rapidly heating a confined fraction of the rock. It was proposed that the necessary temperatures and heat fluxes needed to induce thermal spallation in the high pressure, high density deep borehole environment could be achieved using hydrothermal flame technologies. An autoclave reaction system was designed and constructed to create flame jets in water at a pressure of 250 bar. The temperatures of these flames were measured, and attempts were made to use the flames to spall small rock samples. The experimental system was modified to study the centerline temperature decay of supercritical water jets injected at temperatures up to 525 °C into ambient temperature water. A device for measuring the heat flux from these jets was designed, constructed, and used to determine the heat transfer coefficients of the jets impinging against a flat surface. Together, these studies indicate that the necessary temperatures and heat fluxes required to induce thermal spallation in rocks can be achieved in a deep borehole.
by Chad R. Augustine.
Ph.D.

Research goal. We seek to validate optimal composition of straw biomass fuel and energy efficiency of straw utilization for energy needs, to assess straw biomass fuel preparation technology in respect to energy efficiency, and to determine emissions that are generated during straw combustion. Research objectives. The following objectives were planned to reach the goal of the research: 1) Process analysis of preparation of biomass fuel (pellets and briquettes) for burning, 2) Validation of mixture of lime additive (CaO) into straw biomass fuel, 3) Property analysis of prepared biomass fuel, 4) Measurement and assessment of emissions generated while burning straw biomass fuel, 5) Assessment of energy consumption by straw pellet production equipment.
Tyrimų tikslas. Pagrįsti šiaudų biokuro optimalios sudėties paruošimo ir panaudojimo energinėms reikmėms efektyvumą, atlikti šiaudų biokuro paruošimo technologijos energinį vertinimą ir nustatyti deginimo metu išskiriamas emisijas. Tyrimų uždaviniai. Tyrimų tikslui pasiekti numatyta: 1) Atlikti šiaudų biokuro (briketų ir granulių) paruošimo deginimui technologinę analizę; 2) Pagristi kalkių priedo (CaO) įmaišymo į šiaudų biokuro sudetį tikslingumą; 3) Ištirti pagaminto šiaudų biokuro savybes; 4) Nustatyti ir įvertinti šiaudų biokuro deginimo metu išskiriamas emisijas; 5) Įvertinti šiaudų granulių gamybos technologinės įrangos energijos sanaudas.

This thesis gives an approach how to develop newperovskite and nanocomposite cathode material for low temperature solid oxidefuel cells on the basis of nanocomposite approach to lower the operatingtemperature of SOFC. BaxCa1-xCoyFe1-yO3-δ(BCCF) and BSCF perovskite or nanocomposite oxides have been synthesized andinvestigated as catalytically potential cathode materials for low temperaturesolid oxide fuel cells (LTSOFC). Some single component materials have been alsosynthesized for new energy conversion device or EFFC. These nanocomposite andperovskite electrical conductors were synthesized by wet chemical, sol gel,co-precipitation and solid state reaction methods. Comparison with that ofcommercial Ba0.5Sr0.5Co0.8Fe0.2O3-δ(BSCF) cathode material, BCCF and locally prepared BSCF exhibit higher electricalconductivities as compared to that of commercial BSCF at same setup andconditions. In particular, novel Ba0.3Ca0.7Co0.8Fe0.2O3-δhas shown the maximum conductivity of 143 S/cm in air and local BSCF withconductivity of 313 S/cm in air at 550°C were measured by DC 4 probe method. Anadditional positive aspect of BCCF is that it is cost effective and works atroom temperature but with small output which will lead SOFC to operate atextremely low temperatures. XRD patterns of the samples reveal perovskite andnanocomposite structures of the said materials. Microstructure studies give thehomogeneous structure and morphology of the nanoparticles by using HighResolution Scanning Electron Microscopy (SEM). Cell resistance has beendetermined by Electrochemical Impedance Spectroscopy (EIS). Devised materialshave shown very good mechanical strength and stability proving their importancein advanced fuel cell technology. Power density of devices from 126 to 192 mWcm-2hasbeen achieved.

Thermochemical technologies have been proven effective in treating municipal solid waste (MSW) for many years. China, with a rapid increase of MSW, plans to implement more environmental friendly ways to treat MSW than landfill, which treats about 79 % of total MSW currently. The aim of this master thesis was to find out a suitable thermochemical technology to treat MSW in Shanghai, China. Several different thermochemical technologies are compared in this thesis and plasma gasification was selected for a case study in Shanghai. A model of the plasma gasification plant was created and analysed. Other processes in the plant including MSW pre-treating and gas cleaning are also proposed. By calculating the energy balance, it is demonstrated that plasma treatment of 1000 ton/day MSW with 70 % moisture reaches an efficiency of 33.5 % when producing electricity, which is higher than an incineration WtE plant (27 % maximum) and a gasification WtE plant (30 % maximum). Besides of the efficiency comparison, costs and environmental impacts of different technologies are also compared in this paper. The result indicated that given the characteristics and management situation of MSW in Shanghai, plasma gasification is a better choice to treat MSW in Shanghai.

Due to size effects, the microtechnologies that are used to manufacture micro-sensors, allowed a drastic reduction of electrical power consumption. This feature contributed to the emergence of the concept of autonomous sensors, which have the ability to take the energy needed for their operation from the environment where they are located. Among the different energy sources, our choice was made on ambient mechanical vibrations. The electromechanical conversion is done within a transducer integrated with a micromechanical structure. In this work, we have designed and fabricated an electrostatic transducer based on silicon-glass technology, which required the development of a dedicated deep etching process. The device was tested experimentally and we have obtained a conversion of mechanical energy into electrical energy, corresponding to a power of 61 nW, with a device whose surface area is only 66 mm². This device is the first miniaturized silicon converter based on electrostatic transduction which does not use an electret

During the past decade, there has been a considerable increase in the number of published works on multiphase machines and drives. This increased interest has been largely driven by a need for the so-called green energy, i.e. energy generated from renewable sources such as wind, and also an increased emphasis on greener means for transportation. Some of the advantages multiphase machines offer over three-phase counterparts are better fault tolerance, smaller current and power per phase, and higher frequency torque ripple. This thesis examines use of a multiphase induction generator in wind energy conversion systems (WECS). In particular, multiphase generators that comprise multiple 3-phase winding sets, where each winding set is supplied using an independent 3-phase voltage source inverter (VSI), are studied. It is claimed that these topologies offer advantages in cases where a WECS is connected to a multitude of independent ac or dc microgrids, systems where a single high-voltage dc link is needed or where a simple fault tolerance is achieved when a complete winding set is switched off. All of these examples require an arbitrary power or current sharing between winding sets. In order to achieve arbitrary current and power sharing, the control can be implemented using multi stator (MS) variables, so that the flux and torque producing currents of each winding set can be arbitrarily set. As an alternative, this thesis uses vector space decomposition (VSD) to implement the control, while individual winding set flux/torque producing currents are governed by finding the relationships between MS and VSD variables. This approach has all the advantages of both MS and VSD, i.e. access to individual winding set variables of MS and the ability to implement control in the multiple decoupled two dimensional subspaces of VSD, while heavy cross coupling between winding set variables, a weakness of MS, is avoided. Since the goal of the thesis is to present use of multiphase machines in WECS, modelling and simulation of a simple multiphase WECS in back-to-back configuration has been performed at first. All systems relevant to machine control where considered, such as grid and machine side VSIs, grid filter, indirect rotor field oriented control, current control in both flux/torque producing and non-producing subspaces, low order harmonic elimination, maximum power point tracking control, and voltage oriented control of the grid side VSI. Moreover, various WECS supply topologies were considered where developed current and power sharing would be a necessary requirement. Development of the proposed current sharing control commences with an analysis of multiple 3-phase machine modelling in terms of both MS and VSD variables. Since the actual control is implemented using decoupled VSD variables, VSD modelling has been studied in detail, resulting in an algorithm for creation of the VSD matrix applicable to any symmetrical or asymmetrical multiphase machine with single or multiple neutral points. Developed algorithm always decouples the machine into orthogonal two-dimensional subspaces and zero sequence components while making sure that all odd-order harmonics are uniquely mapped. Harmonic mapping analysis is offered as well. Next, relationship between MS and VSD variables has been developed by mapping MS variables into VSD subspaces. Since VSD matrix creation algorithm is valid for any multiphase machine, relationship between MS and VSD variables is applicable to any multiple 3-phase machine regardless of the configuration (symmetrical/asymmetrical), number of neutral points or machine type (synchronous or induction). Established relationship between MS and VSD has been used to implement current sharing control in decoupled VSD subspaces of the machine. It is shown that in order to achieve arbitrary current sharing it is only necessary to impose currents in flux/torque non-producing subspaces. Hence, total machine’s flux and torque are not affected at all. Besides verification by Matlab simulations, two topologies are experimentally investigated, a parallel machine side converter configuration and the case when a single high voltage dc link is created by cascading dc-links of the machine side VSIs. In the first case the ability of arbitrary current sharing between winding sets is validated, while the second tested topology demonstrates use of the developed control for the purpose of voltage balancing of the cascaded dc links.

Greenhouse gas emissions caused by iron and steel industry are an important part of the world’s total greenhouse gas emissions. This bachelor’s thesis aims to compare different biofuels, which could replace the fossil fuels use in the process. The comparison takes place mainly in production costs and production technologies angles. The data used in this work is collected together from articles about bioenergy and biofuels, that are published in year 2005 or after. When comparing the biofuels, their feedstock, production capacity, production technology, location, base year and production costs are taken into account. Each biofuel is also analysed in more detail in their own chapters. Finally, the data is tabulated for easier comparison. To ease the comparison, the production costs of different biofuels are collected and unified into a single table. It can be stated from the results, that as a general rule, the surveyed biofuels are uneconomical compared to the fossil fuels used in the iron and steel industry. However, as bio reductants are receiving constantly more attention, new production methods as well as new possibilities for their future exploitation in industry can be assumed, while replacing fossil fuels and reducing greenhouse gas emissions
Rauta- ja terästuotannon aiheuttamat kasvihuonepäästöt ovat merkittävä osa maailman kokonaiskasvihuonepäästöistä. Kandidaatintyön tavoitteena on vertailla eri biopolttoaineita, joilla olisi mahdollista korvata prosessissa käytettäviä fossiilisia polttoaineita. Vertailu tapahtuu pääosin tuotantokustannuksien ja -teknologioiden näkökulmista. Työssä käytetyt tiedot on koottu vuonna 2005 ja sen jälkeen julkaistuista bioenergiaa ja -polttoaineita koskevista artikkeleista. Biopolttoaineita vertaillessa on otettu huomioon niiden valmistuksessa käytettävät raaka-aineet, tuotantokapasiteetti, tuotantoteknologia, sijainti, perusvuosi ja tuotantokustannukset. Jokainen työssä käsitelty biopolttoaine on myös analysoitu tarkemmin omassa luvussaan. Tiedot ovat lopuksi taulukoitu helpompaa vertailua varten. Vaihtoehtojen valmistuskustannuksia on myös pyritty yhtenäistämään taulukossa. Tuloksista voidaan todeta tarkasteltavien biopolttoaineiden olevan pääsääntöisesti taloudellisesti kannattamattomia verrattuna rauta- ja terästeollisuudessa käytössä oleviin fossiilisiin polttoaineisiin. Biopelkistimien saaman kasvavan huomion voidaan kuitenkin olettaa tuovan uusia valmistusmenetelmiä sekä mahdollisuuksia niiden hyödyntämiselle tulevaisuuden teollisuudessa korvaten fossiilisten polttoaineiden käyttöä, samalla kasvihuonepäästöjä pienentäen

The objectives of this thesis are to investigate the theory of direct energy conversion, research the development of space nuclear power systems, evaluate the status of current systems, and draw conclusions about the feasibility and merit of using nuclear power for future space missions. Development of the earliest systems began in 1955 with the Systems for Nuclear Auxiliary Power (SNAP) Program and Project Rover. A detailed review of system design and performance is provided for the reactors and radioisotope thermoelectric generators (RTG's) of past and current programs. Thermoelectric and thermionic energy conversion techniques have been used predominantly in space nuclear power systems. The theory of these direct energy conversion methods is analyzed. Also, the safety review procedures and regulations governing the launch of nuclear sources into space are characterized. Conclusions compare accomplished levels of system performance to theoretically predicted limits and comment on the usefulness of space nuclear power for space applications

Access to sustainable energy in the developing world has become a fundamental challenge in development and environmental policy in the 21st Century, and rural electrification in developing countries constitutes a central element of access to energy goals. However, traditional ways of providing electricity to dispersed rural populations (i.e. through centralised electricity infrastructure or fuel-based on-site generation) is proving to be ineffective, inefficient and less sustainable than the use of renewable energy technologies (RETs) in off-grid settings. Such ‘system innovations' for sustainable electricity services in rural areas are the focus of this study, which seeks to understand the reasons underlying success or failure in the diffusion of radical innovations. Embracing evolutionary and constructivist theories of socio-technical change and sustainability transitions, the thesis attempts to explain the use and diffusion of PV (photovoltaic) and wind technology in off-grid rural electrification over the last 20 years in Chile, a country where access to rural electricity has increased from 53% to 95%. RETs have contributed to nearly 10% of that increment. By using a framework that combines Strategic Niche Management (SNM), systemic intermediation and power, agency and conflicts in decision making, the thesis analyses the dynamics between the development and adaptation of new technologies and their influence in regime shift through replication, scaling up and translation of new socio-technical practices. The thesis attempts to shed light on processes affecting niche construction and it concludes that internal niche processes are relevant to understanding how radical innovations are structured and stabilised from the aggregation of projects. However, those processes are not only a managerial activity that can be steered but a politically underpinned (and iterative) process between specific (socio-political) settings. The study also highlights the role of systemic intermediaries, government and incumbent actors in the dynamic interaction between emergent niche dynamics and traditional ways of improving electricity access.

Thesis (M.S.)--University of Missouri--Rolla, 2007.
Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed November 16, 2007) Includes bibliographical references (p. 71-74).

This thesis deals with the performance of a Wind Energy Conversion System operating as a power generator and Active Filter simultaneously. As a power generator, the Wind Energy Conversion System converts wind energy into electric energy; as an Active Filter, it sinks the harmonic currents injected by Non-Linear Loads connected at the same feeder. Three control systems are developed to ensure the described operation; a specific study regarding the compensation of the triplen harmonics is carried out; Doubly-Fed Induction Generator derating is defined; and an engineering economic analysis is performed to determine the profitability of the proposed operation. The Wind Energy Conversion System performance as generator and Active Filter has been studied for steady-state analysis, fast transients and low transients. It is concluded that the proposed control systems allow operating the Wind Energy Conversion System as power generator and harmonic compensator both during steady state and transient operation; the described operation causes power loss increase and voltage distortion that determine the choice of the component and require system derating.

A data centre can consist of a large group of networked servers and associated power distribution, networking, and cooling equipment, all that application consumes enormous amounts of energy as a small city, which are driving to a significant increase in energy inefficiency problems in data centre, and high operational costs. Also the massive amounts of computation power contained in these systems results in many interesting distributed systems and resource management problems. In recent years, research and technologies in electrical engineering and computer science have made fast progress in various fields. One of the most important fields is the energy consumption in data centre. In recent years the energy consumption of electronic devices in data centre, as reported by. Choa, Limb and Kimb, nearly 30000000 kWh of power in a year, may consume by a large data centre and cost its operator around £3,000,000 for electricity alone. Some of the UK sites consume more than this. In the UK data centre the total power required are amid 2-3TWh per year. Energy is the largest single component of operating costs for data centres, varying from 25-60%. Agreeing to many types of research, one of the largest losses and causes of data centre energy inefficiency power distribution is from the uninterruptible power supply (UPS). So a detailed study characterized the efficiencies of various types of UPSs under a variety of operating conditions, proposed an efficiency label for UPSs, also investigate challenges related to data centre efficiency, and how all new technologies can be used to simplify deployment, improve resource efficiency, and saving cost. Data centre energy consumption is an important and increasing concern for data centre managers and operators. Inefficient UPS systems can contribute to this concern with 15 percent or more of utility input going to electrical waste within the UPS itself. For that reason, maximizing energy efficiencies, and reduce the power consumption in a data centre has become an important issue in saving costs and reducing carbon footprint, and it is necessary to reduce the operational costs. This study attempts to answer the question of how can future UPS topology and technology improve the efficiency and reduce the cost of data centre. In order to study the impact of different UPS technologies and their operating efficiencies. A model for a medium size data centre is developed, and load schedules and worked diagrams were created to examine in detail and test the components of each of the UPS system topologies. The electrical infrastructure topology to be adopted is configured to ‘2N’ and ‘N+1’ redundancy configuration for each UPS systems technologies, where ‘N’ stands for the number of UPS modules that are required to supply power to data centre. This work done at RED engineering designs company. They are professionals for designing and construction of a new Tier III and Tier IV data centres. The aim of this work is to provide data centre managers with a clearer understanding of key factors and considerations involved in selecting the right UPS to meet present and future requirements.

This thesis is focused on development of models and modelling of a wave energy converter in operation. Through the thesis linear potential wave theory has been used to describe the wave-buoy interaction. The differences lie in the generator models, in the simplest model the generator is a mechanical damper characterized by a damping factor. In the most advanced generator model the magnetic fields is calculated the by a FE-method, which gives detailed description of the electric properties and the effect it has on the buoy dynamics. Moreover, an equivalent circuit description of the generator has been tested. It has the same accuracy as the field based model but with a strongly enhanced CPU time. All models are verified against full scale experiments. The models are intended to be used for design of the next generation wave energy converters. Further, the developed models have also been used to study what effect buoy geometry and generator damping have on the ability to energy absorption. In the spring 2006 a full scale wave energy converter was installed at the west coast of Sweden. It was in operation and collected data during three months. During that period the load resistance was varied in order to study the effect on the energy absorption. These collected data was then used in the verification of the developed models. In the year 2002 a wave energy project started at Uppsala University; this work is a part of that larger project which intendeds to develop a viable wave energy conversion concept.

On March 13th, 2006, the Division of Electricity at Uppsala University deployed its first wave energy converter, L1, in the ocean southwest of Lysekil. L1 consisted of a buoy at the surface, connected through a line to a linear generator on the seabed. Since the deployment, continuous investigations of how L1 works in the waves have been conducted, and several additional wave energy converters have been deployed. This thesis is based on ten publications, which focus on different aspects of the interaction between wave, buoy, and generator. In order to evaluate different measurement systems, the motion of the buoy was measured optically and using accelerometers, and compared to measurements of the motion of the movable part of the generator - the translator. These measurements were found to correlate well. Simulations of buoy and translator motion were found to match the measured values. The variation of performance of L1 with changing water levels, wave heights, and spectral shapes was also investigated. Performance is here defined as the ratio of absorbed power to incoming power. It was found that the performance decreases for large wave heights. This is in accordance with the theoretical predictions, since the area for which the stator and the translator overlap decreases for large translator motions. Shifting water levels were predicted to have the same effect, but this could not be seen as clearly. The width of the wave energy spectrum has been proposed by some as a factor that also affects the performance of a wave energy converter, for a set wave height and period. Therefore the relation between performance and several different parameters for spectral width was investigated. It was found that some of the parameters were in fact correlated to performance, but that the correlation was not very strong. As a background on ocean measurements in wave energy, a thorough literature review was conducted. It turns out that the Lysekil project is one of quite few projects that have published descriptions of on-site wave energy measurements.

Dans le cadre de cette thèse de doctorat, nous présentons la conception et la réalisation d’un banc dédié à l’étude de la fiabilité de structures piézoélectriques et plus précisément des micro-dispositifs de récupération d'énergie destinés aux implants médicaux autonomes actifs (stimulateurs cardiaques de nouvelle génération). Les structure étudiées se présentent sous la forme d’un bimorphe piézoélectrique encastré-libre comportant une masse sismique à leur extrémité. Une bonne compréhension du vieillissement des matériaux et des modes de défaillance mécanique et électrique est essentielle pour ce type de système où la vie du patient au sein duquel est implanté le dispositif est directement mise en jeu. Pour étudier la fiabilité et la durabilité de la partie active du récupérateur, nous proposons d'établir une nouvelle méthodologie de vieillissement accélérée via un banc d'essai dédié où l'environnement et les stimuli peuvent être contrôlés avec précision sur une large période de temps. Une caractérisation électromécanique des structures est périodiquement réalisée via l’extraction d’une série d’indicateurs (force de blocage, raideur, tension en régime harmonique) au sein même du banc tout au long du vieillissement. Il est donc ainsi possible d'identifier les différents modes de défaillance potentiels et d’étudier leurs impacts sur le bon fonctionnement du système
Within the framework of this PhD we present the design and realization of a bench dedicated to the study of the reliability of piezoelectric structures and more precisely micro-devices of energy harvesting for the new generation of active and autonomous medical implants. The structures studied are in the form of a free-clamped piezoelectric bimorph having a seismic mass at their tip. A good understanding of the aging of the materials and of the mechanical and electrical failure modes is essential for this type of system where the life of the patient implanted by this device is directly involved. To study the reliability and durability of the active part of the harvester, we propose to establish a new accelerated aging methodology via a dedicated test bench where the environment and stimuli can be controlled accurately over a large period of time. An electromechanical characterization of the structures is periodically carried out by the extraction of a series of indicators (blocking force, stiffness, tension in harmonic regime) within the bench throughout the aging process. Therefore it is possible to identify the different potential failure modes and to study their impact on the proper functioning of the system

The development of renewable energy has become increasingly important as countries strive to become less dependent on fossil-derived energy. Biomass accounts for a large part of energy derived from renewable energy sources in Africa. However, the biomass is used in primitive ways like cooking and heating, which is not at all effective at taking advantage of the biomass's true energy potential and contributes to premature death due to pollution. Scarce water supply and infrastructure built around an energy production from coal have hindered the development of bioenergy in South Africa. The Stated Policy scenario has developed energy targets for South Africa to reached by 2040 to streamline South Africa's use of available biomass. To find out if these goals can be achieved, data regarding biomass quantities for different biomass types have been collected to see how much biomass is available for energy production. Various types of technologies for converting biomass have been investigated to compare the efficiency of each technology and production costs to be able to analyze which technology is considered best for application in South Africa. Various scenarios have been developed where previous research and insights from interviews have been involved and influenced the type of technology used to convert the biomass and which end product is considered to have the highest potential. The different scenarios were modeled in Excel and then simulated in to optimize total production costs and energy production. The bioenergy produced has then been compared with the current energy production from fossil fuels to see how much can be replaced. The technologies that were considered to be applicable were combined heat and power together with hydroprocessing. These technologies contributed to efficient energy production and low production costs as well as lower transport costs. Due to drought and lack of water supply, the most optimal places for the implementation of this type of technology were in the northeastern parts of South Africa. These areas have better access to water and, therefore produces more biomass. Considering the current infrastructure in South Africa, transport by trucks was considered to be the most flexible choice of transport mode for transporting the biomass. With the available biomass and the selected technologies, bioenergy can replace up to 15% of the energy produced from coal in South Africa, and prices are competitive with today's electricity and fuel prices in South Africa. For this to happen, political support, public confidence, and investment are required. Increased bioenergy in South Africa would reduce dependence on energy from fossil fuels and also streamline the use of available renewable energy that would contribute to increased and safer energy supply. A more efficient use of bioenergy would also contribute with less premature deaths caused by primitive use of biomass, less emissions and a healthier environment.

Le Convertisseur Analogique Numérique (CAN) est une brique essentielle de la ré- ception et du traitement des données à très haut débit. L’architecture de type "flash" effectue la quantification en comparant simultanément le signal analogique d’entrée à l’ensemble des références du codeur, ce qui en fait, par construction, l’architecture la plus rapide de CAN. Par le passé, cette architecture a démontré des capacités de codage supérieures à 20GS/s dans les conditions de Nyquist. Cependant, cette capac- ité à travailler à très haute vitesse a donné le jour à des réalisations très consommantes (plusieurs Watts) donc peu efficaces énergétiquement. Cette thèse explore différentes approches d’optimisation de l’efficacité énergétique des CAN "flash". Afin de min- imiser la consommation du CAN, il n’y a pas d’Echantillonneur-Bloqueur (EB) en tête du circuit. Les étages d’entrée du codeur sont ainsi exposés à la pleine bande passante du signal, à savoir DC-10GHz. Ceci impose des contraintes très strictes sur la précision temporelle de la détection et de la quantification du signal. L’essentiel de cette thèse est donc concentré sur l’analyse des effets hautes frèquences impactant la conception des éléments frontaux du CAN. La validité et l’efficacité des méthodes présentées sont démontrées par des mesures autour d’un CAN 6 bit 20 GS/s. En em- pruntant les techniques de conception des circuits ultra-rapides et en exploitant le po- tentiel haute-fréquence de la technologie à l’état de l’art SiGe BiCMOS, un circuit complètement analogique a ainsi pu être réalisé. Ce CAN est mono-voie et n’a besoin d’aucune calibration ou correction, ni d’assistance digitale. Avec à peine 1W, ce cir- cuit atteint un record d’efficacité énergétique dans l’état de l’art des CAN rapides non entrelacés
High speed Analog-to-Digital Converters (ADC) are essential building blocks for the reception and processing in high data rate reception circuits. The flash ADC archi- tecture performs the digitization by comparing the analog input signal to all refer- ence levels of the quantization range simultaneously and is thus the fastest architecture available. In the past the flash architecture has been employed successfully to digitize signals at Nyquist rates beyond 20 GS/s. However the inherent high speed operation has led to power consumptions of several watts and hence to poor energy efficien- cies. This thesis explores approaches to optimize the energy efficiency of flash ADCs. In particular, no dedicated track-and-hold stage is used at the high speed data input. This imposes very stringent requirements on the timing accuracy and level accuracy in the high speed signal distribution to the comparators. The comparators need to ex- hibit a very high speed capability to correctly perform the quantization of the signal against the reference levels. The main focus of this thesis is hence the investigation of design relevant high frequency effects in the analog ADC frontend, such as the bandwidth requirement of overdriven comparators, the data signal distribution over a passive transmission line tree and the dynamic linearity of emitter followers. The correctness and efficacy of the presented methods is demonstrated by measurement results of a 6 bit 20 GS/s Nyquist rate flash ADC fabricated within the context of this work. The demonstrator ADC operates without time interleaving, no calibration or correction whatsoever is needed. By employing design techniques borrowed from high speed analog circuits engineering and by exhausting the high speed potential of a state-of-the-art SiGe BiCMOS production technology, a flash ADC with a record energy efficiency could be realized

L’objectif du présent travail a été de concevoir et de fabriquer des dispositifs sur silicium pour convertir de l’énergie thermique en une énergie électrique en utilisant le changement de phase liquide-gaz dans le but de générer une variation subite de pression suivie d’une conversion d’énergie mécanique vers une énergie électrique à l’aide d’un piézoélectrique. La construction des dispositifs a dû rester simple, avec des matériaux courants et en respectant des limites dimensionnelles. Empreinte inférieure à un diamètre de 20 mm et une épaisseur en dessous des 2 mm.Les prototypes fabriqués sont composés de 3 plaques en silicium, contenant une chambre d’évaporation, une chambre de condensation et un canal réunissant les deux. Un transducteur piézoélectrique a été reporté sur la chambre de condensation et assure l’étanchéité ainsi que la génération d’énergie électrique.Le processus de conception inclut plusieurs étapes, dont la définition de la géométrie et du type de fluide de travail utilisé en tant qu’agent thermique. Le travail effectué a permis de sélectionner le type de piézoélectrique, sa taille ainsi que sa méthode d’intégration. Une étude a également été conduite pour déterminer la méthode optimale d’assemblage des plaques en silicium.La réalisation pratique des dispositifs a été orientée vers la sélection des meilleurs procédés technologiques pour la fabrication des structures. Toutes les expériences ont été conduites en salle blanche avec utilisation de l’oxydation humide, la photolithographie, la gravure KOH, ainsi que d’une technique d’assemblage des plaques silicium avec utilisation de la résine SU-8 comme couche intermédiaire. En plus, quelques outils spécifiques ont été conçus lors du présent travail, pour faciliter la fabrication des dispositifs, dont un système sous vide dédié à l’assemblage des plaques en silicium.Les dispositifs ont été testés afin d’établir leur mécanisme d’oscillation thermique ainsi que leurs propriétés électriques. L’influence tu taux de remplissage et de la température de surface chaude sur le signal en sortie ont également été étudiées. Le calcul de l’énergie générée a aussi été effectué. Dans la dernière partie de l’étude, des étapes d’optimisation pour les dispositifs développés dans le présent travail sont proposées
The goal of the present work was to design and fabricate a fully silicon oscillating device that converts thermal energy into electricity, applying phenomena of liquid to gas phase-change and piezoelectricity. It should be characterized by simplicity of construction, small size, and ease of manufacture. The diameter should not exceed 2 cm, while the thickness should be within 2 mm.The device was composed of three Si wafers comprising evaporation and condensing chambers, and the channel connecting these two elements. A PZT-based transducer mounted on top of the structure was applied to ensure energy conversion.The design process included the establishment of the device geometry, the type of the working fluid enclosed inside the system, a type, size and assembly technique of a piezoelectric element, as well as a bonding method of several silicon elements of the device.The practical realization of the designed prototypes was aimed at selecting the most suitable technological processes for structure fabrication. All the experiments had been performed in a clean room environment and employed wet oxidation, photolithography, a well-known, easily available wet chemical etching in KOH solution, and a silicon bonding technique with the use of SU-8 photoresist as an intermediate layer. Additionally, during the practical work a few tools have been designed and developed to enhance the device fabrication, amongst which a vacuum pump dedicated to bond the three silicon wafers as structural elements of the prototypesThe fabricated prototypes were tested in terms of oscillation mechanism and electrical properties. The influence of the filling ratio and the hot temperature value on the generated signal was established. Additionally, the power range of the prototypes has been evaluated. In the last part of the study, optimization steps for the devices developed in the present work have been proposed

This thesis outlines the use of a new design of Tidal Energy Conversion device which has application in near shore shallow water. The design is applicable for use by coastal communities, either to generate revenue through power sales or just a stand alone system to generate off grid electricity. Previous work conducted on large scale tidal installations have shown that they suffer from excessive costs and time lines, due to their up front design philosophy. This thesis discusses the reasons behind such cost/time overruns and concludes that several technologies and techniques can be incorporated from the subsea oil and gas industry. The early ethos in the offshore oil industry in the 1970’s and 1980’s was to build large offshore structures such as steel and concrete platforms. This has now been replaced by a field development philosophy that looks at simple lower cost subsea well infrastructure as the most cost effective route to exploit a reservoir. The emerging tidal industry has not learned this lesson, yet. A set of new Tidal Energy exploitation designs are proposed and Patented. The chief advantages of this new design are their modular nature, fabrication simplicity, lower build and installation cost. Prototype work is described and further work also highlighted.

Розглянуто деякі особливості використання ТПВ на комплексному підприємстві, яке може забезпечувати всі свої енергетичні потреби самостійно. Дослідження спрямовані на вивчення таких питань, як розробка моделей утилізації-модифікації полімерної частини ТПВ або тари та пакування. При цьому враховувалися фактори вибору науково-обґрунтованих методів переробки та утилізації полімерів; розробку необхідних технологічних схем і устаткування для переробки полімерних відходів; вибір підприємств для реалізації утилізації полімерів і виду енергетичних ресурсів для реалізації цих проектних рішень.
Some features of the possibilities of solving evidence-based problems of improving the use of wastes of different industries on a complex enterprise that can provide all its energy needs alone. The problem of wastes utilization and recycling is present as complex research and analysis of energy- and resource saving processes for treatment of polymer wastes of various origin. The research focused on the study of issues such as the development of models of waste-modifying polymer. The investigation are focused in researching such problems as selection of scientific based methods of wastes to be utilized or recycled; the development of appropriated process flow sheets and choice of modifications additives and equipment for polymers waste recycling. The choice of appropriate plants with selected energy resources is very important for projects realization.

Dissertation (DTech(Electrical Engineering))--Cape Peninsula University of Technology, 2012
The confluence of the limited resources of fossil fuels (e.g. coal, oil and natural gas), environmental degradations leading to climate change, security of supplies and fossil fuels high costs have demanded a tremendous efforts on humanity to seek for a sustainable and unlimited natural energy sources. Amongst these renewable energy sources stands out solar energy because of its ubiquitousness. Solar energy is converted to DC electricity by the photovoltaic effect. Photovoltaic (PV) power systems installed in commercial and industrial buildings are a good example of distributed power generation. Here the energy consumption and production match and thus electricity taken from the grid during daytime peak hours can be reduced. This is beneficial as the transmission losses in the grid are avoided and also transmission need is reduced. The cost effectiveness of a solar energy system has hindered its wide adoption and deployment in terms of the initial capital cost even though it has a zero energy cost and very minimal operating and maintenance costs. Different governments have instituted many financial incentives for fast adoption of PV systems for both residential and commercial applications. However, all these incentives are not sustainable in the longer term forecast. For PV system to attain grid parity requires more than unsustainable approach of many governments providing time limited subsidies. The technical solution to the problem is to reduce the overall system cost through technical innovations. One such method is the adoption of transformerless inverter technology as the grid interface system. Transformerless inverter topology provides galvanic isolation through innovative inverter topology and switching strategies that eliminates problems created by not employing the service of transformer.

Au cours des dernières décennies, l’intérêt pour la gazéification de biomasses a considérablement augmenté, notamment en raison de la grande efficacité de recouvrement énergétique de ce procédé par rapport aux autres procédés de génération de bioénergies. Les composants majoritaires du gaz de synthèse, le monoxyde de carbone (CO) et l’hydrogène (H2) peuvent entre autres servir de substrats à divers microorganismes qui peuvent produire une variété de molécules chimiques d’intérêts, ou encore produire des biocarburants, particulièrement le méthane. Il est donc important d'étudier les consortiums méthanogènes naturels qui, en syntrophie, serait en mesure de convertir le gaz de synthèse en carburants utiles. Cette étude évalue principalement le potentiel de méthanisation du CO par un consortium microbien issu d’un réacteur de type UASB, ainsi que les voies métaboliques impliquées dans cette conversion en conditions mésophiles. Des tests d’activité ont donc été réalisés avec la boue anaérobie du réacteur sous différentes pressions partielles de CO variant de 0.1 à 1,65 atm (0.09 à 1.31 mmol CO/L), en présence ou absence de certains inhibiteurs métaboliques spécifiques. Dès le départ, la boue non acclimatée au CO présente une activité carboxidotrophique relativement intéressante et permet une croissance sur le CO. Les tests effectués avec de l’acide 2- bromoethanesulfonique (BES) ou avec de la vancomycine démontrent que le CO est majoritairement consommé par les bactéries acétogènes avant d’être converti en méthane par les méthanogènes acétotrophes. De plus, un plus grand potentiel de méthanisation a pu être atteint sous une atmosphère constituée uniquement de CO en acclimatant auparavant la boue. Cette adaptation est caractérisée par un changement dans la population microbienne désormais dominée par les méthanogènes hydrogénotrophes. Ceci suggère un potentiel de production à large échelle de biométhane à partir du gaz de synthèse avec l’aide de biofilms anaérobies.
Syngas produced through the thermal gasification of biomass for energy recovery has received increased attention in the past decades due to its higher efficiency compared to other bioenergy processes. The gas components of syngas, CO and H2, can serve as substrates for the conversion of desirable chemicals and fuels, namely methane, by a wide range of microorganisms. Meanwhile, anaerobic wastewater-treating sludges have been reported as good sources of carboxidotrophic microorganisms which can be exploited for methane production. Thus it is important to investigate existing methanogenic consortiums which, in syntrophy, are able to convert syngas into useful fuels. This study is mainly focused on the assessment of the carboxidotrophic methanogenic potential present in a natural consortium of microorganisms from a UASB reactor and the identification of CO conversion routes to methane under mesophilic temperatures. To achieve this, a series of kinetic-activity tests with the anaerobic sludge were performed under CO partial pressures varying from 0.1 to 1.65 atm (0.09-1.31 mmol/L) in both the presence and absence of specific metabolic inhibitors. The non-adapted sludge presented an interesting carboxidotrophic activity potential for growing conditions on CO alone. Inhibition experiments with 2- bromoethanesulfonic acid (BES) and vancomycin showed that CO was converted mainly to acetate by acetogenic bacteria, which was further transformed to methane by acetoclastic methanogens. Moreover, it was possible to achieve higher methanogenic potential under 100% CO by acclimation of the sludge. This adaptation led to a shift in the microbial population predominated by hydrogenophilic methanogens. This suggests a possible enrichment potential with anaerobic biofilms for large scale methane production from CO-rich syngas, and further advances the knowledge base for anaerobic reactor development.

Solid waste can be considered either as a burden or as a valuable resource for energy generation. Therefore, identifying an environmentally sound and technoeconomically feasible solid waste treatment is a global and local challenge. This study focuses on identifying an Alternative Waste Technology (AWT) for meeting this global and local demand. AWT recovers more resources from the waste flow and reduces the impact on the environment. There are three main pathways for converting solid waste into energy: thermo-chemical, biochemical and physicochemical. This study deals with thermochemical conversion processes. Mainly four thermo-chemical conversion processes of AWTs are commonly used in Australia: anaerobic digestion, pyrolysis, gasification and incineration. The main aim of this study is to identify and test the most suitable AWT for use in Australia. A decision-making tool, Multi-Criteria Analysis (MCA), was used to identify the most suitable AWT. MCA of the available AWTs was performed using five criteria, that is, capital cost, complexity, public acceptability, diversion from landfill and energy produced, from which Gasification technology has been identified as the most suitable AWT for energy recovery from solid waste. This study then mainly focused on assessing the performance of gasification technology for converting solid waste into energy both experimentally and numerically. Experimental investigation of solid waste gasification was performed using a pilotscale gasification plant of Corky’s Carbon and Combustion P/L plant in Mayfield, Australia. In this experiment, wood chips were used as feedstock (solid waste) under specified gasifier operating conditions. Syngas composition was measured at different stages of gasification, such as raw, scrubbed and dewatered syngas. Mass and energy balance was analysed using the experimental measured data. It was found that 65 per cent of the original energy of solid waste was converted to syngas, 23 per cent converted to char and 6 per cent converted to hot oil. The remaining 6 per cent was lost to the atmosphere. Firstly, a numerical investigation was performed by developing a computational process model using Advanced System for Process ENgineering (ASPEN) Plus software. Computational models were developed for both fixed bed gasification and fluidised bed gasification processes. A simplified, small scale fixed bed gasification model was initially developed in order to observe the performance of the solid waste gasification process. The model is validated with experimental data of Municipal Solid Waste (MSW) and food waste from the literature. Using this validated model, the effects of gasifier operating conditions, such as gasifier temperature, air-fuel ratio and steam-fuel ratio were examined and performance analyses were conducted for four different feedstocks, namely wood, coffee bean husks, green wastes and MSWs. Secondly, a computational model was developed for the fluidised bed gasification process. The model was validated with experimental data for wood chips (solid waste) measured at Corky’s Carbon and Combustion plant. A very good agreement was found between simulation and experimental results, with a maximum variation of 3 per cent. The validated model was used to analyse the effects of gasifier operating conditions. Using the fluidised bed gasification model, a detailed analysis was done for both energy and exergy in order to achieve a complete picture of the system outcome. Energy efficiency of 78 per cent and exergetic efficiency of 23 per cent were achieved for the system. The developed fixed bed and fluidised bed gasification models were useful to predict the various operating parameters of a solid waste gasification plant, such as temperature, pressure, air-fuel ratio and steam-fuel ratio. This research outcome contributes to a better understanding by stakeholders and policy makers at national and international levels who are responsible for developing different waste management technologies. In future, this research can be extended for other feedstocks, such as green waste, sugarcane bagasse and mixed MSW.