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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
191

Impact of Solar Resource and Atmospheric Constituents on Energy Yield Models for Concentrated Photovoltaic Systems

Mohammed, Jafaru January 2013 (has links)
Global economic trends suggest that there is a need to generate sustainable renewable energy to meet growing global energy demands. Solar energy harnessed by concentrated photovoltaic (CPV) systems has a potential for strong contributions to future energy supplies. However, as a relatively new technology, there is still a need for considerable research into the relationship between the technology and the solar resource. Research into CPV systems was carried out at the University of Ottawa’s Solar Cells and Nanostructured Device Laboratory (SUNLAB), focusing on the acquisition and assessment of meteorological and local solar resource datasets as inputs to more complex system (cell) models for energy yield assessment. An algorithm aimed at estimating the spectral profile of direct normal irradiance (DNI) was created. The algorithm was designed to use easily sourced low resolution meteorological datasets, temporal band pass filter measurement and an atmospheric radiative transfer model to determine a location specific solar spectrum. Its core design involved the use of an optical depth parameterization algorithm based on a published objective regression algorithm. Initial results showed a spectral agreement that corresponds to 0.56% photo-current difference in a modeled CPV cell when compared to measured spectrum. The common procedures and datasets used for long term CPV energy yield assessment was investigated. The aim was to quantitatively de-convolute various factors, especially meteorological factors responsible for error bias in CPV energy yield evaluation. Over the time period from June 2011 to August 2012, the analysis found that neglecting spectral variations resulted in a ~2% overestimation of energy yields. It was shown that clouds have the dominant impact on CPV energy yields, at the 60% level.
192

Frozen concentrated orange juice processed by high pressure homogeneization technology = Processamento de suco de laranja concentrado e congelado por tecnologia de homogeneização a alta pressão / Processamento de suco de laranja concentrado e congelado por tecnologia de homogeneização a alta pressão

Leite, Thiago Soares 24 August 2018 (has links)
Orientadores: Marcelo Cristianini, Pedro Esteves Duarte Augusto / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-24T10:15:18Z (GMT). No. of bitstreams: 1 Leite_ThiagoSoares_M.pdf: 1645658 bytes, checksum: 5cef9e21cdc929b63d32c29376a6edbc (MD5) Previous issue date: 2014 / Resumo: O Brasil é o maior produtor mundial de laranja, sendo que a maior parte desta produção é destinada a fabricação do suco concentrado congelado (Frozen concentrated Orange Juice - FCOJ). Devido ao seu grande volume de exportação e sua alta consistência (viscosidade aparente), o conhecimento de suas propriedades reológicas se torna necessária para um melhor dimensionamento de equipamentos e processos. Na homogeneização a alta pressão (HAP), uma tecnologia de processamento não térmica, o produto é pressurizado e forçado a passar por um pequeno orifício aumentando drasticamente sua velocidade, fazendo a pressão diminuir para a atmosférica, causando forte cisalhamento e cavitação. Estes fenômenos causam alteração na estrutura de células e biopolímeros, impactando no tamanho das partículas e na maneira como se interagem, alterando assim, as características reológicas do produto. O presente trabalho se baseou na utilização desta tecnologia em FCOJ visando diminuição da sua consistência, e alteração de demais comportamentos reológicos, para gerar uma economia de energia em diversas operações unitárias como bombeamento, congelamento, transporte e estocagem. Reduções mesmo que pequenas na consistência possibilitam grande economia de energia devido aos grandes volumes de suco processado no Brasil. Este trabalho teve como objetivo avaliar a influência da alta pressão de homogeneização (HAP) no comportamento reológico em estado estacionário (independente e dependente do tempo). Foram avaliados também, a energia de ativação de Arrhenius, comportamento reológico dinâmico (viscoelasticidade), distribuição de tamanho de partículas, microestrutura e cor do suco concentrado, bem como a estabilidade à sedimentação, turbidez e cor do produto reconstituído. Também foi verificada a influência do numero de ciclos de homogeneização nos comportamentos reológicos (estado estacionário) e tamanho de partícula do suco de laranja concentrado. A consistência do FCOJ foi reduzida com o aumento de pressão no processamento de HAP. Para processos a 150 MPa a viscosidade aparente reduziu para cerca de metade do valor original, a tixotropia e viscoelasticidade também tiveram suas magnitudes reduzidas. A energia de ativação de Arrhenius teve seu valor aumentado com a utilização de HAP, indicando que pequenas variações de temperatura acarretam em variações significativas nos valores de consistência. O tamanho de partículas foi reduzido, bem como no perfil de distribuição das mesmas. Houve um aumento na proporção total de partículas pequenas em relação às partículas maiores. Estas mudanças foram possíveis de perceber pela microestrutura observada com microscópio óptico. As cores dos produtos concentrado ou diluído não apresentaram alterações devido à pressão. A HAP não praticamente não reduziu a viscosidade do suco diludo (RTD). Nenhum dos parâmetros estudados apresentou mudanças devido ao tempo de estocagem. O comportamento da sedimentação de polpa também não sofreu alterações com a HAP. Os múltiplos ciclos de HAP a baixas pressões apresentaram ser uma alternativa ao ciclo único com pressão elevada / Abstract: Brazil is the world's largest orange producer, most of the production being intended for the manufacture of frozen concentrated orange juice (FCOJ). Due to the large export volume and high consistency (apparent viscosity) of FCOJ, knowledge of its rheological properties becomes necessary for a better design of the equipments and processes. In high-pressure homogenization (HAP), a non-thermal processing technology, the product is pressurized and forced through a small gap that dramatically increases its speed, followed by a sudden drop to atmospheric pressure, causing high shear stress and cavitation. These phenomena are able to change the structure of cells and biopolymers, impacting on the particle size and the way they interact, thus changing the rheological characteristics. In the present study this technology was used aiming at decreasing the consistency and other rheological properties. Even small reductions in viscosity can result in great energy savings in various unit operations, such as pumping, given the large volume of juice processed in Brazil. The objective of this work was to evaluate the influence of high pressure homogenization on the rheological steady-state behaviour (time independent and time dependent properties), Arhenius activation energy, dynamic rheological behaviour (viscoelasticity), particle size distribution, microstructure and colour of FCOJ, as well as the pulp sedimentation stability of the reconstituted product, the turbidity and colour were also evaluated. The influence of the number of HPH cycles, on rheological behaviour (steady-state) e on particle size distribution of FCOJ was also verified. HPH decreased the consistency of FCOJ as the pressure increased from 0 to 150MPa. At 150MPa the apparent viscosity was decreased to approximately half its original value. The thixotropy and viscoelasticity of the concentrated juice were also reduced during HPH, and the value of the Arhenius activation energy had its value increased, indicating that a minor change in temperature produces a significant change in consistency. The particle size was reduced, and the particle distribution changed, showing a higher ratio of small particles over larger ones. These changes could be observed from the microstructure. The FCOJ or diluted product showed no difference in colour, neither due to affect by the homogenization nor for the storage time. HPH slighty decreased the viscosity of the RTD-juice. None of the above mentioned parameters changed during the storage time. The pulp sedimentation behaviour was not affected by HPH. Multiple HPH cycles at lower pressures are an alternative to a single HPH at higher pressure / Mestrado / Tecnologia de Alimentos / Mestre em Tecnologia de Alimentos
193

A transição para uma matriz energética limpa : os avanços na tecnologia solar / The transition towards a clean energy matrix : the advances in solar technology

Suzigan, Kelly Rosana, 1983- 27 August 2018 (has links)
Orientador: Ademar Ribeiro Romeiro / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Economia / Made available in DSpace on 2018-08-27T14:56:12Z (GMT). No. of bitstreams: 1 Suzigan_KellyRosana_M.pdf: 3841622 bytes, checksum: f6215a3e1341048e3689f5c380771993 (MD5) Previous issue date: 2015 / Resumo: As reservas mundiais de petróleo, carvão e gás natural podem acomodar maior crescimento no uso destas fontes de energia sobre as próximas décadas, mas agrava os enormes desafios colocados pelas alterações climáticas. A produção e o consumo energético de energia têm grande impacto na sociedade e na natureza, e o uso dos combustíveis fósseis é claramente insustentável com consequências potencialmente catastróficas. Desta forma, a necessidade de transição para uma matriz energética mais limpa é evidente, podendo ser observada através do redirecionamento da política energética de algumas das nações líderes do mundo. Dentre as tecnologias energéticas limpas, a tecnologia solar tem se destacado no cenário mundial, e por hipótese a energia solar deverá ser a principal fonte para geração de eletricidade no futuro. Esta dissertação pretende contribuir com a investigação acerca do desenvolvimento e perspectivas da energia solar no mundo, trazendo alguma luz à controvérsia sobre a possibilidade de superação do paradigma energético baseado na combustão de fósseis a tempo de se evitar um possível desastre ambiental. O presente trabalho divide-se em três partes. A primeira parte trata da necessidade da transição da matriz energética baseada em uso de combustíveis fósseis para uma baseada em energia limpa, essencial em decorrência das já comprovadas limitações ambientais, que se agravará futuramente diante da expectativa de largo aumento na demanda de energia para acompanhar o crescimento econômico futuro. A segunda parte faz uma breve discussão acerca de algumas questões relativas à construção de um novo paradigma energético e da inovação em tecnologias de energia de baixo carbono, além de salientar especificidades da tecnologia solar. Por fim, na terceira parte traça-se um panorama do cenário atual mundial com relação ao setor de energia solar a partir dos principais países que investem na tecnologia: Estados Unidos, Alemanha, Japão e China. Neste capítulo será analisado o progresso do setor solar em cada país, apontando as políticas de incentivo, desenvolvimento da indústria solar, evolução do mercado e perspectivas futuras da energia solar / Abstract: The world reserves of oil, coal and natural gas can accommodate further growth in energy use over the next few decades, but aggravates the great challenges posed by climate change. The production and consumption of energy have been creating great impact in our society and nature, and the consumption of fossil fuels is clearly unsustainable with potentially catastrophic consequences. Thus, the importance of renewable forms of energy is growing robustly, which can be observed by the energy policies of some of the leading nations in the world. Among the renewable forms of energy, solar power generation is becoming mainstream and by hypothesis is likely to become the world¿s most important source for electricity generation in the future. This thesis aims to contribute on the research concerning the development and prospects of solar energy in the world, bringing some light to the controversy about the possibility of overcoming the energy paradigm based on the combustion of fossil in time to prevent a possible environmental disaster. This paper is divided into three parts. The first one highlight the need for a transition from a fossil fuel-based society to one based on renewable energy, enabling a more sustainable growth. The second part is a brief discussion regarding the construction of a new energy paradigm and the innovations in the in low-carbon energy technologies, highlighting specific characteristics of the solar technology. Finally, the third part makes an overview of the current scenario, especially the one regarding the solar industry in the most advanced countries in the development of solar energy (United States, Germany, Japan and China). In this chapter an analysis is made about the progress of the solar energy in each country, pointing out government subsidies, industry and market development and future prospects of solar energy / Mestrado / Desenvolvimento Economico, Espaço e Meio Ambiente / Mestra em Desenvolvimento Econômico
194

An examination of the applicability of implementing Canada's immersion model in a language minority educational setting in the United States

Simmers, Lisa Anne 01 January 1996 (has links)
No description available.
195

Studie chování vyztuženého zeminového bloku pod koncetrovaným zatížením / The study the behavior of the reinforced soil block under the concentrated load

Prechtlová, Kateřina January 2016 (has links)
This thesis deals with numerical 3D modeling of reinforced earth block under concentrated wheel load. This is a parametric study, which varies entering face and load position and even his own task. And either by simplification of the CSN 73 0037 or directly. At the beginning briefly describes the construction of reinforced soil in terms of history, application, construction, and properties of materials from which the structure is formed. Attention is also paid to static action and methods of spreading of a concentrated load to earth block. structural design using analytical methods is also part of the thesis
196

Experimentelle Untersuchungen zum Einfluss physikalischer Bodeneigenschaften auf die Rillenerosion

Hieke, Falk 29 January 2010 (has links)
Der Einfluss bodenspezifischer Größen auf die Rillenerosion wurde in Überströmungsversuchen in einem eigens dafür konstruiertem Kleingerinne untersucht. Die Neigung des 2 m langen und 0,1 m breiten Gerinnes wurde dafür zwischen 2, 4 und 6 % variiert. Im Gerinne wurden zum einen natürliche Böden, zum anderen künstliche, aus Schluff und Sand gemischte Substrate mit 0,060 l*s-1, 0,125 l*s-1 und 0,300 l*s-1 überströmt. Die Körnung der natürlichen Böden reichte von stark schluffig bis sandig-lehmig, die der künstlichen Substrate von stark schluffig bis sandig. Die künstlichen Substrate wiesen im Gegensatz zu den natürlichen Böden keine Aggregierung auf und waren frei von organischer Substanz. Zu Beginn der Versuche wird der Boden zunächst flächig überströmt. Währenddessen bilden sich Mikrorillen auf der Gerinnesohle aus. Selektiver Sedimenttransport bewirkt die Akkumulation der nicht transportablen Fraktion auf der Bodenoberfläche, wodurch sich Rippel bilden. Über den Rippeln formen sich stehende Wellen im Abfluss. Die stehenden Wellen erzeugen Sohlschubspannungsspitzen auf die Gerinnesohle, welche zu verstärkter lokaler Erosion, zur Ausbildung von Mikrodepressionen und im weiteren zur Entstehung von Rillenköpfen führen. Die Rillenköpfe wandern entgegen dem Gefälle und hinterlassen Rillen, in denen sich der Abfluss konzentriert. In den Rillen können weitere Rillenköpfe entstehen. Anhand des Beginns der Rillenerosion, der Rillenkopfneubildungsrate, dem Erosionsfortschritt der Rillenköpfe, der Bestandsdauer der Rillenköpfe und der Sedimentkonzentration im Abfluss kann das Phänomen „Rillenerosion“ erfasst und quantifiziert werden. Diese erosionsspezifischen Kennwerte zeigen sich dabei in Abhängigkeit von bodenspezifischen Größen, wie der Lagerungsdichte, der Korngrößenzusammensetzung sowie der Aggregatgrößenverteilung und –stabilität. Aus den Korrelationsanalysen zwischen den bodenspezifischen Größen und den spezifischen Kennwerten der Rillenerosion leiten sich empirische Beziehungen ab. Diese Beziehungen sind nicht-linearerer und nicht-stetiger Natur. Parallel zu den Versuchen im Kleingerinne wurden Überströmungs- und Beregnungsversuche in einem Großgerinne durchgeführt. Die Projektion der laborativen Ergebnisse des Kleingerinnes auf das naturnahere Großgerinne zeigte dabei Parallelen.
197

Aufbau und Inbetriebahme eines Teststandes mit bewegtem Reaktionsbett zur thermochemischen Wärmespeicherung

Ramm, Nico 26 May 2015 (has links)
Für den ökonomischen Erfolg konzentrierender Solarkraftwerke und für die Effizienz-steigerung der Industrie durch Weiterverwendung von Abwärme sind skalierbare Hochtemperatur-Wärmespeicher zu vertretbaren Kosten unabdingbar. Bisher sind für dieses Anwendungsgebiet nur sensible Speicher kommerziell verfügbar. Denen gegenüber besitzen chemische Speicher zahlreiche Vorteile. Sie bieten höhere Speicherdichten, geringere Wärmeverluste, die Möglichkeit zur Wärmetransformation durch Variation des Reaktionsdrucks und eine Vielzahl von Reaktionssystemen für eine optimale Prozess-integration. Jedoch befinden sie sich noch in der Entwicklungsphase. Die reversible Gas-/Feststoffreaktion von Calciumoxid und Wasserdampf zu Calcium-hydroxid geschieht bei Temperaturen von 400 – 600 °C und ist damit optimal für solarthermische Anwendungen geeignet. Für die Entwicklung eines Speichers ist neben der thermochemischen Charakterisierung des Speichermaterials ein effizientes, skalierbares Reaktorkonzept nötig. Ein Reaktor mit bewegtem Reaktionsbett ermöglicht die Trennung der zwei charakteristischen Speichergrößen Leistung und Kapazität und stellt damit einen wirtschaftlichen Speicher in Aussicht. Die vorliegende Arbeit befasst sich mit Aufbau und Inbetriebnahme eines neuen Teststandes, in welchem ein innovatives Reaktordesign erprobt werden soll. Sie beschreibt die Auslegung einer planaren Reaktorgeometrie, die einen Schwerkraftfluss des Bettes und die Modularisierung für größere Anlagen gewährleistet. Bei Vorversuchen stellt sich die homo-gene Bewegung des Reaktionsbettes aufgrund dessen Kompressibilität als schwierig heraus. Der angestrebte homogene Massenfluss des Reaktionsmaterials kann durch die ursprünglich eingesetzten Feindosiereinheiten nicht erzielt werden. Sie zeigen sich jedoch für die Temperierung des Speichermediums und die Gasdichtheit des Reaktionsraumes als geeignet. Das homogene Ausfließen wird einer separaten Austragshilfe zugeteilt, welche konstruiert und umgesetzt wird. Experimente mit einem Schaureaktor identifizieren eine Zahnwelle als beste Option. Für einen kommerziellen Speicher wird ein Schlitzschieber empfohlen. Ebenso erfolgen Auslegung und Errichtung der peripheren Anlagenteile, wie z.B. die Fertigung eines Druckhalters zur Steuerung der Reaktionstemperatur. Am Teststand werden somit alle Vorbereitungen abgeschlossen, um Heißversuche bei Reaktionstemperatur durchzuführen.:Kurzfassung.....................................................................II Aufgabenstellung ..............................................................III Inhaltsverzeichnis ..............................................................V Nomenklatur ...................................................................VII Abbildungs- und Tabellenverzeichnis ............................................IX Vorwort ........................................................................XI 1 Einleitung ................................................................... 1 2 Theorie thermischer Energiespeicher .......................................... 3 2.1 Beschreibung von Wärmespeichern ............................................ 3 2.2 Sensible Wärmespeicher ..................................................... 4 2.3 Latente Wärmespeicher....................................................... 9 2.4 Sorptive Wärmespeicher .....................................................12 2.5 Chemische Wärmespeicher ....................................................14 3 Spezifikation des thermochemischen Speichersystems ...........................17 3.1 Thermochemische Grundlagen .................................................17 3.2 Motivation der Aufgabenstellung ............................................20 3.3 Charakterisierung des Reaktionssystems .....................................21 4 Systembeschreibung des Speicherkonzepts ......................................26 4.1 Kurzdarstellung der Ausgangssituation ......................................26 4.2 Weiterentwicklung zum bewegten Reaktionsbett ...............................27 4.2.1 Theorie des bewegten Reaktionsbettes .....................................27 4.2.2 Konstruktion des Reaktors ................................................28 4.2.3 Förderung des Speichermaterials ..........................................31 4.3 Periphere Anlagenteile .....................................................33 4.3.1 Anlagenschema ............................................................33 4.3.2 Entwurf des Druckhalters .................................................35 INHALTSVERZEICHNIS VI 4.3.3 Ausführung der Elektro- und Messtechnik ..................................37 5 Experimentelle Untersuchungen ................................................39 5.1 Versuchsdurchführung .......................................................39 5.2 Betrieb der Fördereinheiten ................................................40 5.3 Optimierung der Fördereinheiten ............................................44 5.3.1 Inaktive Mischpaddel .....................................................44 5.3.2 Modifizierte Mischpaddel .................................................47 5.4 Erkenntnisse ...............................................................49 6 Finales Konzept des Versuchsstandes ..........................................50 6.1 Lösungsansätze für den Massenfluss .........................................50 6.2 Gestaltung der Austragshilfe ...............................................54 7 Zusammenfassung und Ausblick .................................................57 Eidesstattliche Erklärung ......................................................59 Literatur- und Quellenverzeichnis ..............................................60 Anlagen ........................................................................63 A.1. Parametrierung des Temperaturwächters (Kapitel 4.3.3) .....................63 A.2. Inhalt des beigelegten Datenträgers (Einband) .............................63 A.3. Berechnung der Aufheizstrecke des Stickstoffstroms (Kapitel 4.3.1) ........64 A.4. Konstruktionszeichnung des Druckhalters (Kapitel 4.3.2) ...................65 A.5. Dampftafel: Sättigungsdampfdruck von Wasserdampf (Kapitel 4.3.2) ..........66 A.6. Stromlaufpläne und Baugruppenliste des Teststandes (Kapitel 4.3.3) ... ....67 A.7. Ermittlung der Kabelquerschnitte für Stromlaufplan (Kapitel 4.3.3) ........73 A.8. Parametrierung der Frequenzumrichter (Kapitel 5.1) ....................... 74 A.9. Ergebnisse der Kalibiermessungen (Kapitel 5.2) ............................75 A.10. Berechnungen zur Dynamik des Schlitzschiebers (Kapitel 6.1) ............. 76 A.11. Konstruktionszeichnungen der Austragshilfe (Kapitel 6.2) .................77
198

Solar fuels production from thermochemical gasification and reforming of carbonaceous feedstocks / Production de combustibles solaires par voie thermochimique à partir de gazéification et reformage de ressources hydrocarbonées

Chuayboon, Srirat 29 November 2019 (has links)
Les procédés thermochimiques solaires étudiés concernent la conversion de charges hydrocarbonées solides ou gazeuses en syngas, ainsi que la réduction d’oxydes en métaux en utilisant l’énergie solaire concentrée pour effectuer les réactions endothermiques, permettant ainsi le stockage de l’énergie solaire intermittente en carburants sans émissions de CO2. Ce travail a pour objectif l’étude expérimentale de trois procédés solaires incluant la gazéification de biomasse, le reformage de méthane en boucle chimique, et la carboréduction de ZnO et MgO. La gazéification et le reformage permettent la valorisation de biomasse bois et de méthane en syngas, tandis que la carboréduction permet de produire Zn et Mg à partir de ZnO et MgO. Ces procédés ont été étudiés dans des réacteurs solaires de 1.5 kWth, en utilisant le rayonnement concentré fourni par des systèmes à concentration du laboratoire PROMES, Odeillo, France. L’impact des paramètres opératoires de chaque procédé sur les mécanismes réactionnels, conversion, rendement, et performances énergétiques a été évalué en détail. Ces procédés ont permis d’améliorer la conversion chimique, les rendements en syngas, les efficacités énergétiques tout en permettant un stockage de l’énergie solaire en combustibles transportables, avec des performances globales supérieures aux procédés conventionnels. De plus, leur faisabilité, fiabilité et robustesse pour la conversion de méthane et biomasse en syngas et la production de Mg et Zn en fonctionnement batch ou continu sous pression réduite ou atmosphérique en conditions solaires réelles ont été démontrés. / The investigated solar thermochemical processes consist of the thermochemical conversion of solid and gaseous carbonaceous feedstocks into syngas as well as metal oxides reduction into metal commodities utilizing concentrated solar energy to drive endothermic chemical reactions, thereby enabling intermittent solar energy storage into solar fuels and avoiding CO2 emissions. This work aims to experimentally investigate three key solar thermochemical conversion approaches regarding biomass gasification, chemical looping reforming of methane, and carbothermal reduction of ZnO and MgO. Solar gasification and solar chemical looping reforming allowed valorizing wood biomass and methane into syngas, while solar carbothermal reduction was applied to produce Zn and Mg from ZnO and MgO. Such solar thermochemical processes were performed in 1.5 kWth prototype solar chemical reactors, utilizing highly concentrated sunlight provided by a solar concentrator at PROMES laboratory, Odeillo, France. The impact of controlling parameters of each process on the reaction mechanism, conversion, yields, and process performance, during on-sun testing was investigated and evaluated thoroughly. Such processes were proved to significantly improve the chemical conversion, syngas yields, energy efficiency, with solar energy storage into transportable fuels, thereby outperforming the conventional processes. Moreover, their feasibility, reliability, and robustness in converting both methane and biomass feedstocks to syngas as well as producing Mg and Zn metals in batch and continuous operation under vacuum and atmospheric conditions during on-sun operation were successfully demonstrated.
199

Propriétés d'écoulement de suspensions concentrées de particules de PVC et leur lien avec la physico-chimie du système / Flow properties of PVC-particles concentrated suspensions and their relation to physico-chemistry of the system

Chatté, Guillaume 18 September 2017 (has links)
Nous étudions des suspensions concentrées de particules non-colloïdales de PVC. Ces suspensions, appelées plastisols, sont utilisées principalement pour la fabrication de revêtements de sols.Elles présentent notamment un phénomène de rhéoépaississement (hausse de la viscosité en cisaillant). Nous montrons que cela provient des forces de frottement entre particules. En effet, à l’aide d’un microscope à force atomique, nous sommes pour la 1ère fois capable de relier directement la contrainte macroscopique d’apparition du rhéo-épaississement à la contrainte microscopique d’apparition de la friction solide entre particules.Nous caractérisons la viscosité de la suspension jusqu’à 100 000 s-1 et nous observons qu’une plus grande polydispersité limite le rhéoépaississement. Les différences de contraintes normales N1 et N2 sont aussi mesurées. Par ailleurs, des mesures à l’aide de rayons X ou d’ultrasons ne montrent aucune migration de particules sous cisaillement.Nous montrons également que la géométrie a un fort impact sur l’écoulement de la suspension concentrée. Un entrefer plus petit provoque une baisse de la viscosité et retarde le rhéoépaississement. Une approche non-locale permet de rationaliser les résultats.La substitution de particules de PVC par des particules de CaCO3 modifie profondément la viscosité et la densité d’empilement maximum. Nous développons alors des modèles simples pour modéliser ces effets. En outre, nous mesurons l’impact sur la rhéologie d’un éventuel surfactant à la surface des particules.Nous avons pu finalement étudier des instabilités observées en étalant ces suspensions à haute vitesse. Une instabilité de surface est d’abord observée. A plus haute vitesse, un dépôt se forme en aval sur le couteau. Nous corrélons ces instabilités avec l’apparition de différences de contraintes normales. / Highly concentrated and non-colloidal suspensions consisting of micrometric PVC particles dispersed in a liquid phase, were studied. These suspensions, called plastisol, are mostly used in vinyl flooring manufacture.A key feature of these suspensions is shear-thickening, since viscosity greatly increases as a function of the applied shear rate. This phenomenon is explained as being related to frictional forces between particles. Indeed, using an Atomic Force Microscope, we were able, for the first time, to link the macroscopic stress, at which shear-thickening appears, with the microscopic stress needed to enter a frictional regime.We then characterize the suspension viscosity up to 100 000 s-1. We observed that shear thickening is lowered with a more polydisperse powder. Large normal stress differences N1 and N2 were also measured, along with shear thickening. In addition, using both X-ray radiography and ultrasound, no particle migration in the sheared suspension could be detected.We also found that geometry plays a major role in the features of the flow of concentrated suspensions. For a smaller gap, the viscosity is lower and shear-thickening is pushed to higher shear rates. A non-local approach accounts for our experimental results.Replacing a number of PVC particles with CaCO3 particles changes both the viscosity and the maximum packing fraction quite dramatically. For both of these, we developed simple models that matched quite well with the experimental data. Moreover, we elucidate the rheological changes resulting from adding surfactant at the surface of each particle type.Finally, we investigated some instabilities observed while coating at high speed. At a moderate speed, a ribbing phenomenon appears. At a higher speed, a deposit is formed on the knife (downstream). The appearance of these instabilities correlates with normal stress differences
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Modeling of a PMSynRel stator with concentrated windings using FEM and non-linear reluctance networks

Pablos Rabano, Alejandro January 2013 (has links)
Permanent magnets synchronous reluctance (PMSynRel) motors are attractive due to their high torque density and because a lower quantity of permanent magnets is necessary in comparison with other permanent magnet machines. This thesis deals with the analysis of PMSynRel machines using a finite element method (FEM) and reluctance networks. First, a PMSynRel machine model is built in order to carry out simulations using a finite element method package. The effect of different design parameters such as the combination of the number of poles and slots, the number of flux barriers or the number of magnets can be studied since the implementation provides the possibility to change those variables. Next, a reluctance networks model, aimed to enable lower computation times than corresponding finite element models, is implemented for analysing the flux density distributions along the air gap of the machine disregarding the magnetic influence of the rotor. Finally, the results are compared with FEM simulations. It is concluded that the agreement reached is satisfactory in most of the cases analysed.

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