Thesis (Ph. D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references (leaves 181-189). Also available on the Internet.

Orientador: Teófilo Miguel de Souza / Banca: Osiris Canciglieri Junior / Banca: Rubens Alves Dias / Resumo: Este aquecedor solar foi construído em uma estrutura metálica, que tem um revestimento de polietileno reflexivo parabólico cilíndrico, onde no foco da parábola passa uma serpentina com sete tubos em cobre de 9,5 mm e o projeto foi desenvolvido para obter temperaturas mais elevadas do que os aquecedores planos. O objetivo desta dissertação foi atingir temperaturas mais altas na fase líquida. As temperaturas alcançadas foram obtidas utilizando uma densidade de potência solar que variou entre (1.000±10) W/m2, nas vazões de: 66, 54, 42, 30, 27, 24, 21, 18, 15, 12 e 9 litros por hora. A máxima temperatura atingida utilizando-se a vazão de nove litros por hora foi de 71°C, permitindo uma diferença de temperatura, em relação a temperatura ambiente de 43°C. A máxima vazão utilizada no aquecedor solar parabólico cilíndrico foi de 66 litros por hora e obteve-se uma temperatura de 38°C, sendo a diferença em relação à temperatura ambiente de 6°C. Assim com o desenvolvimento do aquecedor solar parabólico cilíndrico obtiveram-se temperaturas maiores em uma área de captação menor, do que em aquecedor convencionais planos e com rendimentos superiores a 70% em sua maior faixa de operação / Abstract: This solar heater is constructed of a metallic structure, which has a polyethylene coating reflective parabolic cylindrical, where the focus of the parable is a serpentine seven copper pipes of 9.5 mm and the project was designed to obtain higher temperatures than the heaters plans and the objective of this thesis was to reach higher temperatures in the liquid phase. The temperatures reached were obtained using a solar power density ranged from (1000±10) W/m2, the flow rates: 66, 54, 42, 30, 27, 24, 21, 18, 15, 12 and 9 liters per hour. The maximum temperature reached by using the flow of nine liters per hour was 71°C, allowing a temperature difference in relation to ambient temperature of 43°C. The maximum flow rate used in the cylindrical parabolic solar heater was 66 liters per hour and obtained a temperature of 38°C, and the difference in the ambient temperature of 6°C. So with the development of a cylindrical parabolic solar heater temperatures were obtained in a larger area smaller than in conventional heating plans and with performance up to 70% on the higher range of operation / Mestre

The insight that the fossil fuel reserves are limited, together with concerns over security of supply (i.e. the oil crises), initiated the first raise of interest in biomass and all other renewable energy forms. However, the concern grew that global warming and the resulting climate change were enhanced by carbon dioxide (CO2) emissions resulting from fossil fuel consumption. Meanwhile, biomass energy is thought to account for 14–15% of total world energy consumption. Hence, the exploitation and utilization of biomass energy are effective and necessary for relieving the pressures caused by environmental pollution and fossil fuel shortage (Lv et al., 2010). Recently, extensive research aimed at converting biomass to useful energy have been carried out, especially pyrolysis and gasification, which are particularly suitable for the effective and efficient utilization of biomass. Sugarcane bagasse is the main byproduct of sugarcane mill, ready available at the production site so that it may be a suitable raw material for the production of biofuels, chemicals, and electricity. Among the methods that have been previously studied, is this particular study we explore thermochemical process, gasification. The properties of sugarcane bagasse relevant to gasification are briefly reviewed. The compositions of the bagasse as a fuel are variable, especially with respect to inorganic constituents important to the critical problems of sintering, fouling and slagging. Alkali and alkaline earth metals, in combination with other fuel elements such as silica and sulfur, are responsible for many undesirable reactions in a gasifier system.

Orientador: Oscar Armando Maldonado Astorga / Banca: Durval Luiz Silva Ricciulli / Banca: George Alves Soares / Resumo: No Brasil, devido ao forte crescimento da demanda de energia elétrica nas últimas décadas e com a necessidade de atender a esta procura, torna-se indispensável a inclusão no sistema elétrico brasileiro de programas de eficiência energética e a utilização de fontes alternativas de energia, pois com a construção de novas hidrelétricas e termoelétricas para atender o consumidor, ocorre inundações de grandes áreas e diminuição da emissão de gases para a atmosfera, o que causa fortes impactos ambientais. O uso de fontes alternativas também diminui a dependência do Brasil de combustíveis fósseis, pois futuramente ocorrerá o esgotamento de reservas naturais no país, tendo a necessidade de importar energia, o que elevará os preços das tarifas de energia elétrica. Para que haja a conservação de energia proveniente de fontes tradicionais e incentivar a implantação de energia solar no sistema elétrico brasileiro, desenvolveu-se um programa que analisa a viabilidade técnico-econômica de inclusão do sistema fotovoltaico e fototérmico ao sistema tradicional de distribuição de energia nas diversas regiões do Brasil em residências, pois é o setor que possui um maior potencial de economia de energia. O programa é uma ferramenta de fácil manuseio, de acesso rápido que permitem tomadas de decisões rápidas e seguras quanto à implantação de energia solar por parte do consumidor, além de fornecer em qual região é mais viável essa implantação. / Abstract: In Brazil, due to a solid increasing in electrical energy demand at the last decades and due to the need to comply with this demand, became essential the inclusion of energetic efficiency programs and use of alternative energy resources in the Brazilian electrical supply system. However, the new hydro and thermo electrical power plants construction to attend the consumer cause strong environmental impacts, since they need big flooded lakes and eliminate theirs pollutants in the atmosphere, respectively. Moreover, the use of alternative energy resources decreases Brazil dependency of fossil fuels, besides it prevents the breakdown of the natural reserves and the need of energy importation, what would increase the charge for the electrical energy. To the energy conservation provided by traditional resources and to encourage the implementation of a solar energy based system in Brazil, it was developed a software that analyzes technical and economic feasibility of the photovoltaic and photothermical systems introduction in the traditional supply system on the several regions of Brazil to residential use, because this is a sector that has an elevated potential of energy saving. The software has a friendly interface, with quick access that allows the user to take quick and safe decisions, regarding to the solar energy implementation by consumers, and evaluate which area of the country is the most interesting to the implementation. / Mestre

Made available in DSpace on 2014-06-11T19:29:53Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-07-07Bitstream added on 2014-06-13T18:47:28Z : No. of bitstreams: 1 santos_rs_me_guara.pdf: 3310410 bytes, checksum: dbdc747497f7d936a9a108f561ec367f (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / No Brasil, devido ao forte crescimento da demanda de energia elétrica nas últimas décadas e com a necessidade de atender a esta procura, torna-se indispensável a inclusão no sistema elétrico brasileiro de programas de eficiência energética e a utilização de fontes alternativas de energia, pois com a construção de novas hidrelétricas e termoelétricas para atender o consumidor, ocorre inundações de grandes áreas e diminuição da emissão de gases para a atmosfera, o que causa fortes impactos ambientais. O uso de fontes alternativas também diminui a dependência do Brasil de combustíveis fósseis, pois futuramente ocorrerá o esgotamento de reservas naturais no país, tendo a necessidade de importar energia, o que elevará os preços das tarifas de energia elétrica. Para que haja a conservação de energia proveniente de fontes tradicionais e incentivar a implantação de energia solar no sistema elétrico brasileiro, desenvolveu-se um programa que analisa a viabilidade técnico-econômica de inclusão do sistema fotovoltaico e fototérmico ao sistema tradicional de distribuição de energia nas diversas regiões do Brasil em residências, pois é o setor que possui um maior potencial de economia de energia. O programa é uma ferramenta de fácil manuseio, de acesso rápido que permitem tomadas de decisões rápidas e seguras quanto à implantação de energia solar por parte do consumidor, além de fornecer em qual região é mais viável essa implantação. / In Brazil, due to a solid increasing in electrical energy demand at the last decades and due to the need to comply with this demand, became essential the inclusion of energetic efficiency programs and use of alternative energy resources in the Brazilian electrical supply system. However, the new hydro and thermo electrical power plants construction to attend the consumer cause strong environmental impacts, since they need big flooded lakes and eliminate theirs pollutants in the atmosphere, respectively. Moreover, the use of alternative energy resources decreases Brazil dependency of fossil fuels, besides it prevents the breakdown of the natural reserves and the need of energy importation, what would increase the charge for the electrical energy. To the energy conservation provided by traditional resources and to encourage the implementation of a solar energy based system in Brazil, it was developed a software that analyzes technical and economic feasibility of the photovoltaic and photothermical systems introduction in the traditional supply system on the several regions of Brazil to residential use, because this is a sector that has an elevated potential of energy saving. The software has a friendly interface, with quick access that allows the user to take quick and safe decisions, regarding to the solar energy implementation by consumers, and evaluate which area of the country is the most interesting to the implementation.

Made available in DSpace on 2014-06-11T19:30:09Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-02-09Bitstream added on 2014-06-13T20:39:45Z : No. of bitstreams: 1 mattos_sr_me_guara.pdf: 1275419 bytes, checksum: 6a6b8796ddc4c875ee2155aa72412e97 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este aquecedor solar foi construído em uma estrutura metálica, que tem um revestimento de polietileno reflexivo parabólico cilíndrico, onde no foco da parábola passa uma serpentina com sete tubos em cobre de 9,5 mm e o projeto foi desenvolvido para obter temperaturas mais elevadas do que os aquecedores planos. O objetivo desta dissertação foi atingir temperaturas mais altas na fase líquida. As temperaturas alcançadas foram obtidas utilizando uma densidade de potência solar que variou entre (1.000±10) W/m2, nas vazões de: 66, 54, 42, 30, 27, 24, 21, 18, 15, 12 e 9 litros por hora. A máxima temperatura atingida utilizando-se a vazão de nove litros por hora foi de 71°C, permitindo uma diferença de temperatura, em relação a temperatura ambiente de 43°C. A máxima vazão utilizada no aquecedor solar parabólico cilíndrico foi de 66 litros por hora e obteve-se uma temperatura de 38°C, sendo a diferença em relação à temperatura ambiente de 6°C. Assim com o desenvolvimento do aquecedor solar parabólico cilíndrico obtiveram-se temperaturas maiores em uma área de captação menor, do que em aquecedor convencionais planos e com rendimentos superiores a 70% em sua maior faixa de operação / This solar heater is constructed of a metallic structure, which has a polyethylene coating reflective parabolic cylindrical, where the focus of the parable is a serpentine seven copper pipes of 9.5 mm and the project was designed to obtain higher temperatures than the heaters plans and the objective of this thesis was to reach higher temperatures in the liquid phase. The temperatures reached were obtained using a solar power density ranged from (1000±10) W/m2, the flow rates: 66, 54, 42, 30, 27, 24, 21, 18, 15, 12 and 9 liters per hour. The maximum temperature reached by using the flow of nine liters per hour was 71°C, allowing a temperature difference in relation to ambient temperature of 43°C. The maximum flow rate used in the cylindrical parabolic solar heater was 66 liters per hour and obtained a temperature of 38°C, and the difference in the ambient temperature of 6°C. So with the development of a cylindrical parabolic solar heater temperatures were obtained in a larger area smaller than in conventional heating plans and with performance up to 70% on the higher range of operation

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Water electrolysis conjugated with renewable energy sources potentially realizes a sustainable society. Although the current electrolyzers operate at extreme pH to maximize the electrolysis efficiency, near-neutral pH conditions may optimize the overall system operation when conjugated with renewable energy sources. In this context, a study on the electrolysis in the mild conditions is essential. The dissertation investigates the water electrolysis in various conditions, with a particular focus placed on milder conditions, to rationalize and improve its performance. Microkinetic analysis was performed for the cathodic half-reaction in conjugation with mass transport evaluation using various electrode materials. The analysis revealed a significant universal influence of electrolyte properties on the reaction performances at near-neutral pH. Investigation of the associated electrolyte properties (ion size, viscosity and activity/fugacity) rationally optimized the reaction conditions. Together with the separately performed studies on the anodic half-reaction and system configurations, the finding was successfully transferred to electrocatalytic and solar-driven water splitting systems. The presented herein is a fundamental yet crucial aspect of water electrolysis, which can advance the water electrolysis for the future.

Along with many other solar energy conversion processes, research on photocatalytic water splitting to generate hydrogen and oxygen has experienced rapid major development over the past years. Developing an efficient visible-light-responsive photocatalyst has been one of the targets of such research efforts. In this regard, nitride materials, particularly Ta3N5, have been the subject of investigation due to their promising properties. This dissertation focuses on the fundamental parameters involved in the photocatalytic processes targeting overall water splitting using Ta3N5 as a model photocatalyst. The discussion primarily focuses on relevant parameters that are involved in photon absorption, exciton separation, carrier diffusion, carrier transport, and catalytic efficiency. A collection of theoretical and experimental studies of properties associated with Ta3N5 have been utilized to obtain a comprehensive understanding of this material. The fundamental structural and optoelectronic properties of Ta3N5 have been addressed. From the electronic properties, the dielectric constant and effective masses have been calculated. Because of its high dielectric constant and relatively low effective masses, Ta3N5 is promising for photocatalytic reaction applications. Studies of lattice dynamics, optical properties, and band positions have been able to clearly show that the synthesized Ta3N5 is essentially non-stoichiometric and that a truly pure phase of Ta3N5 has never been achieved, even though XRD has shown a pure phase sample. The photophysical properties of Ta3N5, such as the absorption coefficient, carrier mobility, and carrier lifetime, have been experimentally measured by synthesizing Ta3N5 thin films. Very low kinetic properties with very low transport properties and fast carrier recombination explained why overall water splitting has never been achieved with Ta3N5 as a photocatalyst to date. The extent to which the surface states of Ta3N5 photocatalysts affect photocatalytic performance has been investigated. The surface topmost layer is demonstrated to play a critical role in the photocatalytic activity of Ta3N5; further research on the surface properties of Ta3N5 should be conducted to understand and improve charge separation and the resulting photocatalytic activity. Finally, a remarkable improvement in the photocatalytic OER has been achieved with the addition of cobalt as a cocatalyst. There is a trade-off between the optimum contact of hole transfer from bulk Ta3N5 to the surface of the cobalt cocatalyst and providing active sites for the electrochemical reaction. Knowing the characteristics of cobalt on the Ta3N5 surface, further improvement was attempted by adding a noble metal to the CoOx/Ta3N5 photocatalyst system, where a synergetic effect of CoOx and noble metals was observed.