The thermal response of a borehole field is often described by non‐dimensional response factors called gfunctions.The g‐function was firstly generated as a numerical solution based on SBM (Superposition BoreholeModel). An analytical approach, the FLS (Finite Line Source), is also accepted for generating the g‐function. In thiswork the potential to numerically produce g‐functions is studied for circular borehole fields using the commercialsoftware COMSOL. The numerical method is flexible and allows the generation of g‐functions for any boreholefield geometry. The approach is partially validated by comparing the solution for a square borehole field containing36 boreholes (6x6) with g‐functions generated with the FLS approach and with the program EED (Earth EnergyDesigner). The latter is based on Eskilsons SBM, one of the first documents where the concept of g‐functions wasintroduced. Once the approach is validated, the square COMSOL model is compared with a circular geometryborehole field developed by the same method, consisting of 3 concentric rings having 6, 12, and 18 boreholes.Finally the influence on the circular geometry g‐function is studied when connecting the boreholes in radial zoneswith different thermal loads. / Den termiska responsen för ett borrhålsfält beskrivs ofta med den dimensionslösa responsfunktionen kallad gfunktion.Responsfunktionen togs först fram som en numerisk lösning med SBM (Superposition Borehole Model).En analytisk metod, FLS (Finite Line Source) är också accepterad för framtagandet av g‐funktioner. I det här arbetetundersöks förutsättningarna att numeriskt ta fram g‐funktioner för cirkulära borrhålsfält genom att använda detkommersiella simuleringsprogrammet COMSOL Multiphysics. Den numeriska metoden är flexibel och kananvändas för alla typer av borrhålsgeometrier. Metoden att använda COMSOL valideras delvis genom att jämföraresultatet för ett kvadratiskt borrhålsfält innehållande 36 borrhål (6x6) med lösningar framtagna med FLS och meddimensioneringsprogrammet EED (Earth Energy Designer). Det senare har sin grund i Eskilsons SBM, ett av deförsta arbeten där begreppet g‐funktion introducerades. När metoden att använda COMSOL verifierats, jämförsden kvadratiska borrhålsmodellen med en cirkulär borrhålskonfiguration, upprättad med samma metod,innehållande 3 koncentriska ringar om vardera 6, 12, 18 borrhål. Slutligen undersöks hur den termiska responsenpåverkas då borrhålen i ett cirkulärt borrhålsfält kopplas samman och grupperas i radiella zoner med olika termiskalaster. / SEEC Scandinavian Energy Efficiency Co.

Thesis (PhD) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: Currently the reduction of the levelised cost of electricity (LCOE) is the main goal of concentrating solar power (CSP) research. Central to a cost reduction strategy proposed by the American Department of Energy is the use of advanced power cycles like supercritical steam Rankine cycles to increase the efficiency of the CSP plant. A supercritical steam cycle requires source temperatures in excess of 620°C, which is above the maximum storage temperature of the current two-tank molten nitrate salt storage, which stores thermal energy at 565°C. Metallic phase change materials (PCM) can store thermal energy at higher temperatures, and do not have the drawbacks of salt based PCMs. A thermal energy storage (TES) concept is developed that uses both metallic PCMs and liquid metal heat transfer fluids (HTF). The concept was proposed in two iterations, one where steam is generated directly from the PCM – direct steam generation (DSG), and another where a separate liquid metal/water heat exchanger is used – indirect steam generation, (ISG). Eutectic aluminium-silicon alloy (AlSi12) was selected as the ideal metallic PCM for research, and eutectic sodium-potassium alloy (NaK) as the most suitable heat transfer fluid. Thermal energy storage in PCMs results in moving boundary heat transfer problems, which has design implications. The heat transfer analysis of the heat transfer surfaces is significantly simplified if quasi-steady state heat transfer analysis can be assumed, and this is true if the Stefan condition is met. To validate the simplifying assumptions and to prove the concept, a prototype heat storage unit was built. During testing, it was shown that the simplifying assumptions are valid, and that the prototype worked, validating the concept. Unfortunately unexpected corrosion issues limited the experimental work, but highlighted an important aspect of metallic PCM TES. Liquid aluminium based alloys are highly corrosive to most materials and this is a topic for future investigation. To demonstrate the practicality of the concept and to come to terms with the control strategy of both proposed concepts, a storage unit was designed for a 100 MW power plant with 15 hours of thermal storage. Only AlSi12 was used in the design, limiting the power cycle to a subcritical power block. This demonstrated some practicalities about the concept and shed some light on control issues regarding the DSG concept. A techno-economic evaluation of metallic PCM storage concluded that metallic PCMs can be used in conjunction with liquid metal heat transfer fluids to achieve high temperature storage and it should be economically viable if the corrosion issues of aluminium alloys can be resolved. The use of advanced power cycles, metallic PCM storage and liquid metal heat transfer is only merited if significant reduction in LCOE in the whole plant is achieved and only forms part of the solution. Cascading of multiple PCMs across a range of temperatures is required to minimize entropy generation. Two-tank molten salt storage can also be used in conjunction with cascaded metallic PCM storage to minimize cost, but this also needs further investigation. / AFRIKAANSE OPSOMMING: Tans is die minimering van die gemiddelde leeftydkoste van elektrisiteit (GLVE) die hoofdoel van gekonsentreerde son-energie navorsing. In die kosteverminderingsplan wat voorgestel is deur die Amerikaanse Departement van Energie, word die gebruik van gevorderde kragsiklusse aanbeveel. 'n Superkritiese stoom-siklus vereis bron temperature hoër as 620 °C, wat bo die 565 °C maksimum stoor temperatuur van die huidige twee-tenk gesmelte nitraatsout termiese energiestoor (TES) is. Metaal fase veranderingsmateriale (FVMe) kan termiese energie stoor by hoër temperature, en het nie die nadele van soutgebaseerde FVMe nie. ʼn TES konsep word ontwikkel wat gebruik maak van metaal FVM en vloeibare metaal warmteoordrag vloeistof. Die konsep is voorgestel in twee iterasies; een waar stoom direk gegenereer word uit die FVM (direkte stoomopwekking (DSO)), en 'n ander waar 'n afsonderlike vloeibare metaal/water warmteruiler gebruik word (indirekte stoomopwekking (ISO)). Eutektiese aluminium-silikon allooi (AlSi12) is gekies as die mees geskikte metaal FVM vir navorsingsdoeleindes, en eutektiese natrium – kalium allooi (NaK) as die mees geskikte warmteoordrag vloeistof. Termiese energie stoor in FVMe lei tot bewegende grens warmteoordrag berekeninge, wat ontwerps-implikasies het. Die warmteoordrag ontleding van die warmteruilers word aansienlik vereenvoudig indien kwasi-bestendige toestand warmteoordrag ontledings gebruik kan word en dit is geldig indien daar aan die Stefan toestand voldoen word. Om vereenvoudigende aannames te bevestig en om die konsep te bewys is 'n prototipe warmte stoor eenheid gebou. Gedurende toetse is daar bewys dat die vereenvoudigende aannames geldig is, dat die prototipe werk en dien as ʼn bevestiging van die konsep. Ongelukkig het onverwagte korrosie die eksperimentele werk kortgeknip, maar dit het klem op 'n belangrike aspek van metaal FVM TES geplaas. Vloeibare aluminium allooie is hoogs korrosief en dit is 'n onderwerp vir toekomstige navorsing. Om die praktiese uitvoerbaarheid van die konsep te demonstreer en om die beheerstrategie van beide voorgestelde konsepte te bevestig is 'n stoor-eenheid ontwerp vir 'n 100 MW kragstasie met 15 uur van 'n TES. Slegs AlSi12 is gebruik in die ontwerp, wat die kragsiklus beperk het tot 'n subkritiese stoomsiklus. Dit het praktiese aspekte van die konsep onderteken, en beheerkwessies rakende die DSO konsep in die kollig geplaas. In 'n tegno-ekonomiese analise van metaal FVM TES word die gevolgtrekking gemaak dat metaal FVMe gebruik kan word in samewerking met 'n vloeibare metaal warmteoordrag vloeistof om hoë temperatuur stoor moontlik te maak en dat dit ekonomies lewensvatbaar is indien die korrosie kwessies van aluminium allooi opgelos kan word. Die gebruik van gevorderde kragsiklusse, metaal FVM stoor en vloeibare metaal warmteoordrag word net geregverdig indien beduidende vermindering in GLVE van die hele kragsentrale bereik is, en dit vorm slegs 'n deel van die oplossing. ʼn Kaskade van verskeie FVMe oor 'n reeks van temperature word vereis om entropie generasie te minimeer. Twee-tenk gesmelte soutstoor kan ook gebruik word in samewerking met kaskade metaal FVM stoor om koste te verminder, maar dit moet ook verder ondersoek word.

Atualmente é de complexa equalização o problema advindo da elevação da demanda energética e das ações antrópicas que corroboram para o aquecimento global e, neste sentido, apesar de o Brasil ser abundante em hidroeletricidade, há ainda um grande espaço para o uso de outras fontes renováveis de energia, como a biomassa residual. Na indústria, projetos de adoção de novos e eficientes processos para a redução da carga térmica, bem como o uso de biomassa e de biogás das estações de tratamentos de efluentes podem ser um diferencial no conjunto de soluções para o dilema energético-ambiental, uma vez vão ao encontro dos objetivos das políticas energéticas globais em vigência, as quais pregam a segurança e sustentabilidade. Porém, verifica-se que tais medidas ainda têm sido desprezadas por muitas empresas, pois os investimentos são ainda muito elevados, ressaltando-se ainda que, talvez por não se entender como esses projetos podem internalizar as externalidades positivas que os acompanham, essas empresas seguem alheias aos benefícios socioambientais e econômicos advindos dos créditos de carbono, que podem compensar os altos investimentos realizados em racionalização energética. Desta maneira, essa dissertação analisa a viabilidade econômica da implantação de projetos de substituição de combustíveis fósseis por biomassa renovável para geração de vapor de processos; de uso de biogás de ETEs para geração de eletricidade e de implementação de tecnologias para a redução do consumo de vapor industrial, com foco em cervejarias, considerando-se nas análises econômico-financeiras os créditos de carbono recebidos pelas reduções de emissões de gases de efeito estufa. Pelas análises de cenários, verificou-se que quando as medidas de eficiência energética reduzirem pelo menos 5% da demanda energética, com um custo de energia de pelo menos R$ 187,50/MWh, bem como reduções de consumo de energia acima de 10%, com custo energético mínimo de R$ 122,50/MWh, e preço de das RCE acima de 5,00, os projetos mencionados são viáveis, e as receitas dos créditos podem internalizar as externalidades positivas desses projetos, compensando os investimentos. / Nowadays it´s quite complex to solve the problem between energy demand growth and the human activities, which have negative, widespread effects on the global climate. In this sense, apart from the fact that Brazil adopts massivelythe hydropower, there is a large potential for the use of renewable energy sources, as biomass. In process industries, techologies for reducing thermal energy consumption associated with the use of the sustainable biomass and biogas from wastewater treatment systems can be one among other solutions for equalizing the energy-environment dilemma, also targeting the prorrogatives of the current global policies on safety and sustainable energy sypply. Anyway, such measures have still been left aside by many industries, because it´s still not properly understood regarding the way these projects can internilize their positive externalities, some enterprises keep distant from the social, economic and environmental beneffits that carbon credit projects can bring up to help them in succeeding and rationalizing energy consumption. This dissertation evaluates and assesses the economic viablitity of projects of fuel switch (from fossil fuels to renewable biomass); use of biogas from industrial wastewater treatment systems and also the implementation of technologies and processes for reducing steam comsumption, focusing on breweries. By means of economic sceneries, it´s shown that the revenues from carbon credits can significantly have positive impacts, while financial incentives, on the decision making process towards the carrying and dissemination of such projects. As demonstrated in this work, the RCE, if required in the sceneries analysed, can bring the cash flows whithin brewery IRR expectations. Hence, the model showed that when measures of energy afficiency achieve at least 5,0% with the price of energy saved is of at least R$187,50/MWh, and for measures above 10% and energy is bought at prices higher then R$ 122,50/MWh, all projects with CER prices above 5,00 viable, and can be conducted. Also, the revenues from carbon credits can make industries wake up for the fact that they can internalize the positive externalities of these projects, once the high investiments can be compensated by their carbon offsets.

Cette thèse présente les résultats de recherche, de modélisation et de simulation d'un système de rafraîchissement solaire au Maroc dans le cadre du projet PRSM (Procédés de Rafraîchissement Solaire au Maroc) financé par l'IRESEN (Institut de Recherche en Energie Solaire et Energies Nouvelles). L'objectif est d'étudier les facteurs concernant l'optimisation d'une machine à absorption solaire (LiBr-H2O) sous les conditions marocaines. De plus, un certain nombre de critères de conception, qui peuvent être utilisés par les concepteurs de systèmes de climatisation et de chauffage solaires, ont été établis en tenant compte de considérations énergétiques et économiques. En conséquence, cette thèse couvre quatre aspects. Le premier aspect présente un aperçu de recherche bibliographique sur les technologies solaires, en mettant l'accent sur les systèmes du froid solaire, les processus pertinents existants, l'état du marché, les développements récents des technologies les plus prometteuses et les principaux indicateurs de performance qui figurent dans la littérature. De plus, l'aspect expérimental de l'installation de climatisation solaire adopté dans le projet PRSM a été décrit pour identifier les caractéristiques techniques importantes de l'installation et les difficultés rencontrées lors de la réalisation du prototype. La deuxième dimension concerne la faisabilité technique d'un système de climatisation solaire en se basant sur des indicateurs énergétiques et économiques et prenant en compte les effets combinés des climats, des catégories de bâtiments et des besoins en climatisation dans les conditions marocaines. Le troisième aspect présente le stockage latent de l'énergie thermique utilisant les matériaux à changement de phase (MCPs). Il porte sur l'étude des méthodes numériques utilisées dans la modélisation des phénomènes de changement de phase et se concentre également sur l'ajout des MCPs dans le système de climatisation solaire intégré à l'intérieur du ballon solaire connecté au générateur de la machine à absorption pour évaluer l'amélioration possible du rendement du système. Le quatrième volet de cette thèse présente l'analyse technico-économique et de sensibilité appliquée au développement d'un procédé solaire combiné d'eau chaude sanitaire, chauffage et climatisation au Maroc. L'analyse globale via une généralisation des résultats au niveau national a été réalisée en complément d'une analyse de sensibilité liée à l'investissement dans ces systèmes afin d'évaluer le potentiel de remplacement des technologies traditionnelles par les systèmes solaires et les gains éventuels liés à leur implantation au Maroc. / This thesis reports the results of research into the modeling and simulation of a solar air-conditioning system for Morocco in the framework of the project SCPM (Solar Cooling Process in Morocco) funded by IRESEN (Research Institute for Solar Energy and New Energies). The aim is to investigate the factors concerning the optimization of a LiBr-H2O solar absorption chiller under Moroccan conditions. Further, a number of design criteria, which can be used by designers of solar cooling and heating systems, have been established using energy and economic considerations. Accordingly, this thesis covers four aspects. The first overviews the literature survey on solar technologies with a focus on solar cooling systems which reports the relevant processes, summarizes the market status, presents the recent developments of the most promising technologies and describes the main performance indicators figuring in the literature. Moreover, the experimental aspect of the solar air-conditioning installation adopted in the SCPM project was described to identify the important technical characteristics of the installation and the difficulties encountered during the realization of the prototype. The second dimension concerns the technical feasibility of solar air-conditioning system using energy and economic indicators taking into account the combined effects of climates, building categories and cooling demands under Moroccan conditions. The third aspect presents the latent thermal energy storage using Phase Change Materials (PCMs). It concerns the investigation of numerical methods used in the modeling of phase change phenomena and also focuses on PCMs addition in the solar cooling process integrated inside solar storage tank connected to the generator of the absorption chiller to evaluate the possible enhancement in the system efficiency. The fourth aspect of this thesis outlines the technico-economic and sensitivity analysis applied to the development of a combined processes of solar DHW, heating and air-conditioning in Morocco. The overall analysis via a generalization of the results to the national level was carried out in addition to a sensitivity analysis related to the investment in these systems in order to assess the potential of replacing traditional technologies with the solar systems and the possible earnings related to their implementation in Morocco.

Le couple zéolite/H2O, qui présente une densité énergétique importante et remplit les conditions d’innocuité requises pour un système de stockage de chaleur pour l’habitat, est mis en œuvre dans réacteur modulaire à lit fixe. Un modèle monodimensionnel de transferts couplés de masse et de chaleur dans un lit fixe de grains de zéolite parcourus par un flux d'air humide été élaboré. Ce dernier a été conçu de façon à pouvoir intégrer rapidement des données sur de nouvelles générations de matériaux et coupler le réacteur à d’autres modèles : bâtiment/sous-station/quartier. L'étape de validation expérimentale montre que le modèle permet une estimation satisfaisante de l'autonomie, la durée d'amorçage et la puissance moyenne fournie en phase de décharge ainsi que la durée de charge. Ce modèle est donc un bon outil de dimensionnement et de pilotage du réacteur. L'analyse de sensibilité a montré que l'amélioration des prévisions du modèle requiert une évaluation plus précise de la chaleur complémentaire de sorption et de la porosité du lit. Après avoir estimé les besoins de chauffage d'une maison BBC deux dimensionnements ont été proposés afin d'effacer soit l'hyper-pointe de 18h - 20h soit la semaine la plus froide. Si la première stratégie aboutit à un système de stockage plus compact, la seconde permet de réduire le nombre de cycles marche/arrêt. Pour un îlot de 50 maisons BBC, la notion de foisonnement est considérée lors de l'estimation des besoins en chauffage pendant la semaine la plus froide. La phase de charge du système de stockage se ferait par le biais de la chaleur fatale récupérée dans l'industrie. Pour des stratégies d'effacement similaires (semaine la plus froide en hiver), un volume équivalent de 544 litres par maison dans l'îlot suffit pour répondre aux besoins de chauffage à Nancy contre 580 litres pour une maison BBC seule. / Heat storage systems for residential house heating could contribute to smoothing the load curve and would help prevent the use of the most polluting power plants or electricity imports during consumption peaks. Thermochemical heat storage systems are suitable for the intended application since they have high energy densities and low thermal losses. This thesis focuses on the design of an adsorption heat storage system that would be used to shed the load curve of the heating device of a house or residential district during the winter peak consumption periods. The zeolite/H2O pair, which has interesting features such as a high energy density and meets the conditions of safety required for a heat storage system for housing, is implemented in a modular fixed bed reactor. A 1D pseudo-homogeneous model was developed in order to simulate the performance of a fixed bed of zeolite during the adsorption and desorption of water. The latter was designed so as to facilitate the integration of data on new generations of materials and model couplings. The need to obtain data on the sorption properties of the zeolite/H2O pair to have reliable simulation results has been demonstrated, particularly at low partial pressures of water vapor and under the operating conditions selected. The experimental validation phase shows that the pseudo-homogeneous model provides a satisfactory estimate of criteria such as the autonomy, the responsiveness and the average power delivered during the discharging phase and the charging time. The model is thus a good sizing and management tool of the reactor. A sensitivity analysis, with the method of Morris, showed that improved model estimates require a more accurate assessment of the additional heat of sorption and porosity of the bed. After assessing the heating needs of the LEB house with a thermal model of the latter in cold climate conditions, two heat storage reactors were sized in order to shed the heating system's load curve either between 6 and 8pm or during the coldest week of the year. While the first strategy results in a more compact storage system, the second makes it possible to reduce the number of on/off cycles. The need for predictive control for monitoring the storage system was highlighted. As for the residential district of 50 LEB houses, diversity is considered when estimating the heating needs of the latter during the coldest week in Nancy. The heat source during the charging phase of the container would be industrial waste heat. During the coldest week, two sizings are suggested. For similar load shedding strategies, the comparison of the equivalent storage volume per house in the district with the storage volume for a single house serves highlights the importance of taking into account diversity. In order to meet the heating needs in Nancy, an equivalent volume of 544 liters per house in the district is sufficient whereas 580 liters are needed for a LEB house.

Made available in DSpace on 2017-07-21T19:25:52Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-03-10 / This work aimed at study the correlation of variables in a plasma immersion ion implantation (PIII) system, as well as their synergistic combination for the nitriding of the UNS S32750 super duplex stainless steel ( SD 2507). The research comprised two phases, as follows. (i) Study of the system. The interconnection of variables, namely voltage (V), pulse width (L), frequency (f) and current (I), were systematically analyzed with respect to the cathode heating. A mathematical formulation was proposed for the ion average energy and the substrate temperature, which took into consideration the energy conservation in the system, and the basic theories for plasma and sheaths and the ion interaction with matter. Hereafter, such model is thought to be experimentally demonstrated, allowing inferring the actual PIII fraction of energy that is converted to heat. (ii) N-PIII of the SD. Mirror-like samples were nitrided under different V, f and L combinations, leading to the temperatures 295, 325, 355 and 400 oC. The surface characterization methods were the optical, field emission electron, and atomic force microscopies, X-ray diffraction, energy dispersive X-ray spectroscopy, backscattered electron diffraction, and instrumented indentation. The austenite and ferrite fraction in the as received material amounted to 43,7 % and 56,3 %, respectively. After nitriding, the modified layers were 0,5-1,5 m thick. Up to 355 ºC, the expanded phase N was produced in originally austenite grains, whereas Fe2-3N e Fe4N precipitates were formed in ferrite grains. The hardness profiles were similar among different temperatures and between the two phases in the same sample. However, in ferritic regions, the mechanism for plastic deformation changed from ductile to brittle. In the 400 ºC treatments, only N was formed. Finally, a correlation for the production of the expanded phase in PIII and the mean pulse energy Ei was attained, given by and . Where IN and I are the integrated intensities of diffraction peaks for austenite and expanded austenite, respectively. / O objetivo deste trabalho foi estudar o comportamento de um sistema de implantação iônica por imersão em plasma (PIII: “plasma immersion ion implantation”), em função de suas variáveis, bem como a influência destas na nitretação de superfícies do aço super duplex UNS S32750 (ou SD 2507). O trabalho foi dividido em dois momentos, como segue. (i) Estudo do sistema. O comportamento das variáveis associadas à implantação iônica, especificamente tensão (V), largura de pulsos (L), frequência (f) e corrente (I), foi sistematicamente analisado com relação ao aquecimento do cátodo. Com base na conservação de energia, física de plasmas e bainhas catódicas e interação de íons com a matéria, propôs-se uma formulação matemática relacionado a energia média dos íons à temperatura do substrato, a qual poderá, futuramente, ser posta à prova experimental, mensurando-se a fração de energia que é, de fato, transformada em calor. (ii) Nitretação por PIII do SD. Amostras com superfície especular foram nitretadas sob diferentes combinações de V, f e L, em temperaturas de 295, 325, 355 e 400 oC. As superfícies foram caracterizadas por métodos de microscopia (ótica, eletrônica com efeito de campo, de força atômica), difração de raios X, espectroscopia de raios X por energia dispersiva, difração de elétrons retroespalhados, e indentação instrumentada. O SD apresenta estrutura cristalina de austenita e ferrita na proporção de 43,7/56,3. A nitretação produziu camadas modificadas com espessura de 0,5 a 1,5 m. Observou-se, nos tratamentos até 355 ºC, a formação da fase expandida N nos grãos que originalmente eram austenita, e de precipitados de nitretos -Fe2-3N e -Fe4N em grãos de ferrita. Embora não houve diferenças significativas nos perfis de dureza, tanto entre as temperaturas quanto entre as fases em uma mesma amostra, o mecanismo de deformação plástica nas regiões ferríticas transitou de dúctil para frágil. Nas nitretações em 400 ºC, houve apenas a formação de N. Finalmente, determinou-se que a obtenção da fase expandida por PIII no SD se relaciona com a energia média por pulso Ei por e . Onde I e I são as intensidades integradas dos picos de difração da austenita expandida e da austenita, respectivamente.

Le travail présenté dans ce manuscrit concerne le développement d’un système de stockage thermique par chaleur latente pour les centrales solaires à concentration utilisant la génération directe de vapeur, et s’attache plus particulièrement la sélection et l’étude du matériau à changement de phase (MCP). Cette thèse a été réalisée dans le cadre du projet Stockage Thermique Appliqué à l’extension de pRoduction d’énergie Solaire thermodynamique (STARS) porté par le consortium composé d’AREVA Renouvelables, la société Hamon d’Hondt, l’institut CEA liten et les laboratoires IPNO, LPCS et LaTEP. Ce projet est accompagné par l’ADEME dans le cadre du programme énergies décarbonnées des investissements d’avenir.Le premier chapitre de ce manuscrit situe le contexte de l’étude en dressant un état de l’art des différents systèmes solaires à concentration existants et des différents moyens de stocker l’énergie pour ce type de technologie. Le projet STARS est ensuite présenté. Ce chapitre se termine par un descriptif des objectifs du travail de thèse. L’intégralité du processus de sélection du MCP, incluant le recensement des matériaux dans la littérature, la définition des critères de sélection et la caractérisation par calorimétrie différentielle à balayage des candidats les plus pertinents, est détaillée dans le chapitre II. À l’issue de ce travail, le choix du consortium se porte sur le nitrate de sodium, un sel inorganique possédant une température de fusion adaptée à la technologie d’AREVA et une densité de stockage importante. La poursuite de l’étude, concernant la stabilité thermique du MCP durant son utilisation en conditions industrielles, fait l’objet du chapitre III. Cette étude comporte une partie bibliographique permettant de mettre en évidence les problématiques liées à la dégradation thermique du matériau et à son comportement vis-à-vis des matériaux métalliques avec lesquels il sera amené à être en contact (échangeur de chaleur, cuve de stockage). La principale conséquence des phénomènes mis en évidence étant la réduction du nitrate de sodium en nitrite de sodium, l’étude de l’impact du taux de nitrite de sodium sur les propriétés thermiques du MCP a été réalisée. Les résultats de cette campagne expérimentale ont montré une diminution significative de la température de fusion et de la chaleur latente du MCP lorsque la proportion de nitrite de sodium croît. Afin d’étudier l’évolution de composition du MCP dans des conditions réelles de fonctionnement, un dispositif a été conçu spécifiquement pour reproduire des conditions de cyclage thermique en présence de métaux. L’étude menée à l’aide de ce dispositif a permis d’analyser la cinétique de réduction du nitrate de sodium en nitrite de sodium. Les résultats montrent que l’évolution de composition du MCP dans les conditions opératoires du projet est négligeable, garantissant la stabilité des propriétés thermiques de celui-ci au cours de son utilisation.Enfin, le dernier chapitre est consacré à l’étude de l’amélioration des transferts thermiques au sein du MCP. En effet, le nitrate de sodium possède une conductivité thermique faible, pouvant limiter la puissance des échanges de chaleur dans le système de stockage. En premier lieu, un état de l’art des solutions d’intensification des transferts dans le domaine du stockage par chaleur latente est dressé. Ce travail a permis de mettre en évidence que l’utilisation de composites à base de mousses métalliques constitue une voie pertinente d’amélioration des transferts. Ainsi une campagne expérimentale visant à évaluer les performances de tels composites a permis de mettre en évidence le potentiel de ce type de configuration. / The work presented in this manuscript concerns the development of a latent heat thermal energy storage system adapted to concentrated solar power plant using direct steam generation, and more particularly on the selection and the study of the Phase Change Material (PCM) used in this system. This thesis was performed within the framework of the STARS project (Stockage Thermique Appliqué à l’extension de pRoduction d’énergie Solaire thermodynamique) carried by the consortium of AREVA Renouvelables, Hamon d’Hondt company, CEA institute liten and laboratories IPNO, LPCS and LaTEP. This project is accompanied by ADEME under the énergies décarbonnées des investissements d’avenir program. The first chapter of this manuscript sets up the context of this study by drawing a state of art of different existing CSP technologies and various ways to store energy for this kind of systems. The STARS project is then described. This chapter ends with a description of the thesis objectives. The entire PCM selection process, including identification of materials in literature, definition of various criteria and thermal characterization by differential scanning calorimetry (DSC) of the most relevant candidates, is detailed in chapter II. This work leads to the selection of sodium nitrate by the consortium, an inorganic salt with a suitable melting temperature considering AREVA’s technology and a large storage density. The following work, concerning the thermal stability of the PCM under thermal cycling, is then presented in chapter III. This part includes a bibliographic study allowing to highlight issues related to thermal degradation of the PCM and its behavior regarding to metallic material with which it will have to be in contact (heat exchanger, storage tank). The main consequence of these phenomena is the reduction of sodium nitrate into sodium nitrite, and thus the impact of sodium nitrite fraction on the thermal properties of the PCM was studied. The results of this experimental work shows a significant reduction of the melting temperature and the latent heat as the fraction in sodium nitrite increases. To study the evolution of the PCM composition under real operating situation, a specific device was designed to replicate thermal cycling conditions in the presence of metals. This device was used to analyze the kinetics of reducing sodium nitrate into sodium nitrite. The results show that the changes in composition of the PCM in the project’s operating conditions are negligible, ensuring the stability of its thermal properties during its lifetime. The last chapter is devoted to the improvement of heat transfers within the PCM. Indeed, sodium nitrate has a low thermal conductivity which may limit the power of the heat exchange in the storage system. A state of art of available solutions for the intensification of thermal transfers concerning latent heat storage was done. This study highlighted that the use of composites based on metallic foams constitutes an effective way of improvement. Thus an experimental campaign was conducted to evaluate the performances of such composites, allowing to show the potential of this kind of configuration.

Made available in DSpace on 2017-07-10T15:14:37Z (GMT). No. of bitstreams: 1 _Anderson_Lenz.pdf: 3725618 bytes, checksum: 39203aa64331d0ed552c80b97130d676 (MD5) Previous issue date: 2016-02-15 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Considering that the energy consumption of residential water heating systems by showers represents 24% of household electricity consumption, and households account for 27% of total electricity consumption in Brazil in order to minimize this consumption, one of the most sustainable alternatives is the use of heating systems using thermosolar plates. This work aimed to evaluate during the period of one year performance of a thermosolar heating system of 1 m² in size, using commonly found materials in civil construction. The unit of measurement used to measure the amount of energy absorbed by the system is the W (watt), the same unit of consumption of the showers to facilitate your sizing. inside the results it can be observed that along one year, the monthly average efficiency ranged from 33.7% will be 53.54%, and average efficiency was 45.9%, and over this period the system absorbed 695 394 Wh Thermal energy, indicating the amount of electric energy that can be saved by using a thermosolar water heating system instead of showers. The system was considered suitable for use in water heating in residences because their efficiency was within the same levels obtained with plates manufactured industrially. Photovoltaic solar panels can be used both for rural electrification in isolated systems, as they are used connected to the power grid. In both cases one of the factors that most limits the overall efficiency is the panel temperature, because it increases its internal resistance and therefore generates energy losses. To minimize this effect was mounted a cooling system in the bottom of the panel with water spray, to assess the cooling effect on the panel performance characteristics as current, voltage, power and efficiency. The performance of the panel was monitored in three different periods, the 1st with intermittent cooling, without cooling the 2nd and 3rd with cooling continued in the hottest hours of the day. The analyzes were performed on two levels of irradiation, the high level with respect to levels closer to the maximum occurring on a clear day, around 1000 W / m², and the lower level was set to 700 W / m² that it is one of the largest occurrence levels. Within the analysis of the data it was observed that the use of cooling for a high level of solar irradiation power increased by 12.26% and 12.17% efficiency at not cooled, and the low irradiation power increased by 8.48% and 9.09% efficiency compared to not be cooled. It is concluded that the system was effective in boosting the performance of the panel and can be used to increase efficiency in isolated systems as in the network connected systems. In this work we studied the technical performance of two solar energy conversion technologies into useful energy, thermal energy in the case of thermosolar panels and electric energy with photovoltaic panels, which can be used to help supply the energy needs of a single family residence rural as well as urban households. The collected performance technical information can provide an incentive for new ventures. / Tendo em vista que o consumo energético dos sistemas de aquecimento de água residenciais por chuveiros representa 24% do consumo de energia elétrica residencial, e que as residências correspondem a 27% do consumo de energia elétrica total no Brasil, visando minimizar este consumo, uma das alternativas mais sustentáveis é o uso de sistemas de aquecimento utilizando placas termossolares. Neste trabalho buscou-se avaliar durante o período de um ano desempenho de um sistema de aquecimento termossolar de 1 m² de área, utilizando materiais comumente encontrados em construção civil. A unidade de medida utilizada para mensurar a quantia de energia absorvida pelo sistema foi o W(watt), mesma unidade de consumo dos chuveiros visando facilitar o seu dimensionamento. Dentro dos resultados observa-se que ao longo de um ano a eficiência média mensal variou de 33,7% á 53,54%, e eficiência média ficou em 45,9%, e ao longo deste período o sistema absorveu 695.394 Wh de energia térmica, indicando o montante de energia elétrica que pode ser economizada ao utilizar um sistema de aquecimento de água termossolar em vez de chuveiros. O sistema foi considerado adequado para o uso de aquecimento de água em residências, pois a sua eficiência ficou dentro dos mesmos níveis obtidos com placas fabricadas industrialmente. Painéis solares fotovoltaicos podem ser utilizados tanto para eletrificação rural em sistemas isolados, quanto serem usados conectados a rede de energia elétrica. Em ambos os casos um dos fatores que mais limita a eficiência do conjunto é a temperatura do painel, pois aumenta a sua resistência interna e por consequência gera perdas de energia. Visando minimizar este efeito montou-se um sistema de resfriamento na parte inferior do painel com aspersão de água, para avaliar o efeito do resfriamento sobre as características de desempenho do painel como corrente, tensão, potência e eficiência. O desempenho do painel foi monitorado em três períodos distintos, o 1° com resfriamento intermitente, o 2° sem resfriamento e o 3° com resfriamento continuo nas horas mais quentes do dia. As análises foram feitas sobre dois níveis de irradiação, o nível alto diz respeito aos níveis mais próximos do máximo que ocorre em um dia de céu limpo, em torno de 1000 W/m², e o nível baixo foi definido como 700 W/m² que é um dos níveis de maior ocorrência. Dentro da análise dos dados observou-se que o uso do resfriamento para um nível alto de irradiação solar a potência aumentou 12,26% e a eficiência 12,17% em relação ao não resfriado, e para o nível baixo de irradiação a potência aumentou 8,48% e a eficiência 9,09% em relação ao não resfriado. Conclui-se que o sistema foi eficaz em aumentar o desempenho do painel e que pode ser utilizado para incrementar a eficiência em sistemas isolados como em sistemas conectados a rede. Neste trabalho estudou-se o desempenho técnico de duas tecnologias de conversão de energia solar em energia útil, energia térmica no caso dos painéis termossolares, e energia elétrica com painéis fotovoltaicos, que podem ser utilizadas para auxiliar o suprimento das necessidades energéticas de uma residência unifamiliar rural bem como em residências urbanas. As informações técnicas de desempenho coletadas podem servir de incentivo para novos empreendimentos.

Ces travaux consistent en l’étude expérimentale et numérique des performances énergétiques d’un prototype de micro-cogénération solaire. L’installation, située sur le campus de l’Université de la Rochelle, fonctionne grâce au couplage d’un champ de capteur solaire cylindro-parabolique de 46,5 m² avec un moteur à vapeur à piston non lubrifié fonctionnant selon le cycle thermodynamique de Hirn. Le système de suivi solaire s’effectue selon deux axes et l’eau est directement évaporée au sein de l’absorbeur des capteurs cylindro-paraboliques. La génération d’électricité est assurée par une génératrice et la récupération des chaleurs fatales doit permettre d’assurer les besoins en chauffage et eau chaude sanitaire d’un bâtiment. La première partie de ces travaux présente les essais réalisés. L’objectif est de réaliser des essais complémentaires pour caractériser le concentrateur solaire, d’étudier les conditions de surchauffe de la vapeur, ainsi que le fonctionnement de l’installation complète en hiver. Ce travail a permis le développement de modèles pour le capteur cylindro-paraboliques, les essais en régime surchauffé ont montré la nécessité d’un appoint pour le fonctionnement d’une telle installation tandis que les essais avec moteur présentent des productions compatibles avec les consommations en électricité et chaleur d’un bâtiment résidentiel. La seconde partie concerne la modélisation des éléments constituant le micro-cogénérateur ainsi que l’intégration de cette installation au bâtiment à l’aide d’un logiciel de simulation thermique dynamique (TRNSYS©). Cette étude propose deux options d’intégration selon le positionnement de l’appoint de chaleur. Pour les deux configurations, des bilans hebdomadaires et annuels sont présentés permettant de discuter les avantages/inconvénients de chaque disposition. Il apparaît que le positionnement de l’appoint sur le circuit primaire permet de piloter la production électrique. L’ajout de l’appoint sur la distribution semble plus facilement réalisable mais empêche le contrôle de la production électrique. / This work consists of the experimental and numerical study of the energy performance of a prototype of solar micro-cogeneration. The facility, located on the campus of the University of La Rochelle, operates by coupling a 46.5 m² parabolic trough solar collector field with an oil-free piston steam engine operating according to the Hirn thermodynamic cycle. The solar tracking system is carried out in two axes and the water is evaporated directly into the absorber of the parabolic trough collectors. Electricity generation is provided by a generator and the recovery of fatal heat must make it possible to meet the heating and domestic hot water needs of a building. The first part of this work presents the tests performed. The objective is to carry out additional tests to characterize the solar concentrator, to study the conditions of steam overheating, as well as the operation of the complete installation in winter. This work has allowed the development of models for the parabolic trough sensor, the tests in overheated mode have shown the need for an extra charge for the operation of such an installation while the tests with motor present productions compatible with the electricity and heat consumption of a residential building. The second part concerns the modelling of the elements constituting the micro-cogenerator as well as the integration of this installation into the building using dynamic thermal simulation software (TRNSYS©). This study proposes two integration options depending on the positioning of the auxiliary heater. For both configurations, weekly and annual reviews are presented to discuss the advantages/disadvantages of each provision. It appears that the positioning of the auxiliary on the primary circuit makes it possible to control the electrical production. The addition of back-up boiler on the distribution seems more easily achievable but prevents the control of power generation.

Ce travail porte sur le développement d’un système de stockage de chaleur en vue d’assurer le confort thermique de l’habitacle d’un véhicule électrique. Ce dispositif, appelé batterie thermique, se présente comme un réservoir composé d’un lit fixe de matériaux à changement de phase (MCP). Ce type de matériau a la propriété d’emmagasiner de fortes quantités de chaleur (latente) sous de faibles volumes, permettant d’envisager un système très compact. A l’échelle du matériau, une investigation sur la cinétique des transferts thermiques au sein de plusieurs MCPs a été évaluée. Une expression phénoménologique décrivant l’évolution temporelle de la température d’un MCP en phase de solidification a été proposée. Elle permet d’estimer la durée de solidification du matériau en fonction de ses caractéristiques géométriques et thermiques. A l’échelle du système, un prototype de batterie thermique a été réalisé et la dynamique des transferts en phase de stockage et déstockage a été étudiée. Les durées de stockage et déstockage suivent des lois de puissance avec le débit imposé ; les pertes de charges s’avèrent insignifiantes. En parallèle, un modèle numérique simulant le comportement dynamique et thermique d’un lit fixe de particules de MCP a été développé et validé sur les données expérimentales. Il pourra être utilisé pour le dimensionnement du futur prototype et servira également d’outil pour optimiser les performances de la batterie en ajustant les paramètres de contrôle / This study focuses on the development of a heat storage system used to ensure passenger compartment thermal comfort in an electric vehicle. This device, called a thermal battery, is a packed bed latent heat tank filled with phase change materials (PCM). This type of material has the property of storing large amounts of latent heat in small volumes, allowing a very compact system. At the material scale, an investigation on heat transfer dynamics within several PCM was studied. A phenomenological expression which depicts the temporal evolution of the PCM temperature for a solidification phase was suggested. This allows the estimation of the material solidification duration in terms of geometric and thermal characteristics. At the system scale, a thermal battery prototype was set up and the thermal transfer dynamics during the charging and discharging phases were studied. The charging and discharging durations are fitted by power laws in terms of the flow rate; the pressure drops are insignificant. Simultaneously, a numerical model which simulates the dynamic and thermal behavior of a PCM particle fixed bed was developed and validated with the experimental data. It can be used for future prototype sizing and will also serve as a tool to optimize the performance of the battery by setting the control parameters