Estudo teórico experimental de sistemas de aquecimento de água usando coletores solares para uso residencial / Theoretical and experimental study of water heating systems using solar collectors for residential use

O aquecimento solar de água representa uma tecnologia ambiental que utiliza uma energia limpa, abundante, permanente, renovável, e não poluente. Este estudo, testou dois sistemas de aquecimento de água unifamiliares e um sistema híbrido solar/gás multifamiliar. O primeiro sistema utilizou 2 ou 3 coletores solares planos e 1 reservatório térmico de 200 litros, e o segundo sistema utilizou 1 ou 2 coletores solares tubulares evacuados e 1 reservatório térmico de 300 litros. Os resultados mostraram que os coletores evacuados ocupam uma área menor de captação de energia solar com custo superior e devido ajuste na inclinação dos coletores para obter um maior desempenho. No sistema híbrido foi realizada uma análise técnica comparando duas configurações: com recirculação (2012-2013) e sem recirculação (2018-2019). Os resultados mostraram que o desempenho do sistema atual diminuiu, provocando um maior consumo de água quente nos apartamentos com maior consumo de gás, mas com menor custo devido o gás natural ser mais barato que o gás liquefeito do petróleo. Concluiu-se que é muito importante avaliar o desempenho dos sistemas periodicamente, para evitar perdas de energia com consequências econômicas e ambientais. A tecnologia solar é viável desde que seja utilizada com responsabilidade e conhecimento técnico garantindo a sustentabilidade

Análise termoquímica de reformador de etanol: produção de hidrogênio para acionamento de uma célula combustível do tipo PEM de 1 KW

Este trabalho estuda os diversos parâmetros termoquímicos associados à reforma a vapor, visando o dimensionamento de dois protótipos de reformadores de etanol com capacidade de produzir hidrogênio suficiente para acionar uma célula a combustível do tipo PEM (Proton Exchange Menbrane Fuel Cell) de 1 KW. As condições de operação analisadas foram os níveis de temperatura e de pressão na composição de equilíbrio dos reagentes e dos produtos, e os tipos de catalisadores para o sistema de reforma a vapor de etanol. Também foram estudados os produtos das reações catalíticas do reformador de etanol e as concentrações dos gases presentes no fluxo de gases de síntese da reforma para o dimensionamento do reator de troca água-gás, o qual remove parte do CO e propicia uma produção adicional de hidrogênio para o processo. Na etapa de dimensionamento, foram estudadas as condições de operação, os tipos e as quantidades de catalisadores necessários para produzir hidrogênio suficiente para acionar uma célula a combustível do tipo PEM de 1 KW. A determinação das concetrações dos produtos do sistema de reforma a vapor de etanol foi realizada através de métodos de análises de cromatografia gasosa. Os resultados obtidos no primeiro reformador protótipo I, foram utilizados para o dimensionamento do sistema de reforma a vapor de etanol do reformador final de etanol protótipo II. POde-se concluir que a utilização do etanol para a produção de hidrogênio é tecnicamente viável através do processo termoquímico de reforma a vapor, o qual consiste numa importante rota para obtenção de um bio-hidrogênio, insumo energético alternativo e renovável para o país.This work presents thermochemical analysis, based on the study of the several parameters associated to steam reforming system, for the dimensioning of two ethanol reformers with enough capacity to hydrogen produce to operating a PEMFC (Proton Exchange Membrane Fuel Cell) of 1 KW. In the analysis of the steam reforming system the operation conditions studied, the were the influences of the temperature and pressure in the composition of balance of the reactants, products and the types of catalysts for the ethanol steam reforming system. It was studied the products of the catalytic reactions of the ethanol reformer and the concentrations of the present gases in the flow of gases of synthesis of the reformer for dimensioning of the water-gas shift reactor, wich removes part of CO and it hydrogen additional production for the process. In the dimensioning stage studied the operation conditions, the types and the amounts necessary of catalysts to produce enough hydrogen to operating of PEMFC of 1 KW. The determination of the concentrations of the products of ethanol steam reforming system was accomplished through methods for gas chromatography analysis. The results obtained in the first reformer prototype I, they were used for the dimensioning of the ethanol steam reformin system of the final ethanol reformer prototype II. It can be concluded that the use of the ethanol for the production of hydrogen, is technically feasible, through the Termochemical process of steam reforming wich consists of a route important for obtainin of the bio-hydrogen alternative and renewable energy raw material input for country

Thermodynamic analysis of direct steam reforming of ethanol in molten carbonate fuel cell

Fuel cell as MCFC (molten carbonate fuel cell) operate at high temperatures, and due to this issue, cogeneration processes may be performed, sending heat for own process or other purposes as steam generation in an industry. The use of ethanol for this purpose is one of the best options because this is a renewable and less environmentally offensive fuel, and cheaper than oil-derived hydrocarbons (in the case of Brazil). In the same country, because of technical, environmental and economic advantages, the use of ethanol by steam reforming process have been the most investigated process. The objective of this study is to show a thermodynamic analysis of steam reforming of ethanol, to determine the best thermodynamic conditions where are produced the highest volumes of products, making possible a higher production of energy, that is, a most-efficient use of resources. To attain this objective, mass and energy balances are performed. Equilibrium constants and advance degrees are calculated to get the best thermodynamic conditions to attain higher reforming efficiency and, hence, higher electric efficiency, using the Nernst equation. The advance degree of reforming increases when the operation temperature also increases and when the operation pressure decreases. But at atmospheric pressure (1 atm), the advance degree tends to the stability in temperatures above 700°C, that is, the volume of supplemental production of reforming products is very small for the high use of energy resources necessary. Reactants and products of the steam-reforming of ethanol that weren't used may be used for the reforming. The use of non-used ethanol is also suggested for heating of reactants before reforming. The results show the behavior of MCFC. The current density, at same tension, is higher at 700°C than other studied temperatures as 600 and 650°C. This fact occurs due to smaller use of hydrogen at lower temperatures that varies between 46.8 and 58.9% in temperatures between 600 and 700°C. The higher calculated current density is 280 mA/cm 2. The power density increases when the volume of ethanol to be used also increases due to higher production of hydrogen. The highest produced power at 190 mW/cm 2 is 99.8, 109.8 and 113.7 mW/cm2 for 873, 923 and 973K, respectively. The thermodynamic efficiency has the objective to show the connection among operational conditions and energetic factors, which are some parameters that describes a process of internal steam reforming of ethanol

Thermodynamic analysis of direct steam reforming of ethanol in molten carbonate fuel cell

Fuel cell as molten carbonate fuel cell (MCFC) operates at high temperatures. Thus, cogeneration processes may be performed, generating heat for its own process or for other purposes of steam generation in the industry. The use of ethanol is one of the best options because this is a renewable and less environmentally offensive fuel, and is cheaper than oil-derived hydrocarbons, as in the case of Brazil. In that country, because of technical, environmental, and economic advantages, the use of ethanol by steam reforming process has been the most investigated process. The objective of this study is to show a thermodynamic analysis of steam reforming of ethanol, to determine the best thermodynamic conditions where the highest volumes of products are produced, making possible a higher production of energy, that is, a more efficient use of resources. To attain this objective, mass and energy balances were performed. Equilibrium constants and advance degrees were calculated to get the best thermodynamic conditions to attain higher reforming efficiency and, hence, higher electric efficiency, using the Nernst equation. The advance degree (according to Castellan 1986, Fundamentos da Fisica/Quimica, Editora LTC, Rio de Janeiro, p. 529, in Portuguese) is a coefficient that indicates the evolution of a reaction, achieving a maximum value when all the reactants' content is used of reforming increases when the operation temperature also increases and when the operation pressure decreases. However, at atmospheric pressure (1 atm), the advance degree tends to stabilize in temperatures above 700 degrees C; that is, the volume of supplemental production of reforming products is very small with respect to high use of energy resources necessary. The use of unused ethanol is also suggested for heating of reactants before reforming. The results show the behavior of MCFC. The current density, at the same tension, is higher at 700 degrees C than other studied temperatures such as 600 and 650 degrees C. This fact occurs due to smaller use of hydrogen at lower temperatures that varies between 46.8% and 58.9% in temperatures between 600 and 700 degrees C. The higher calculated current density is 280 mA/cm(2). The power density increases when the volume of ethanol to be used also increases due to higher production of hydrogen. The highest produced powers at 190 mA/cm(2) are 99.8, 109.8, and 113.7 mW/cm(2) for 873, 923, and 973 K, respectively. The thermodynamic efficiency has the objective to show the connection among operational conditions and energetic factors, which are some parameters that describe a process of internal steam reforming of ethanol

Can Unmanned Aerial Vehicle Images Be Used to Estimate Forage Production Parameters in Agroforestry Systems in the Caatinga?

The environmental changes in the Caatinga biome have already resulted in it reaching levels of approximately 50% of its original vegetation, making it the third most degraded biome in Brazil, due to inadequate grazing practices that are driven by the difficulty of monitoring and estimating the yield parameters of forage plants, especially in agroforestry systems (AFS) in this biome. This study aimed to compare the predictive ability of different indexes with regard to the biomass and leaf area index of forage crops (bushveld signal grass and buffel grass) in AFS in the Caatinga biome and to evaluate the influence of removing system components on model performance. The normalized green red difference index (NGRDI) and the visible atmospherically resistant index (VARI) showed higher correlations (p < 0.05) with the variables. In addition, removing trees from the orthomosaics was the approach that most favored the correlation values. The models based on classification and regression trees (CARTs) showed lower RMSE values, presenting values of 3020.86, 1201.75, and 0.20 for FB, DB, and LAI, respectively, as well as higher CCC values (0.94). Using NGRDI and VARI, removing trees from the images, and using CART are recommended in estimating biomass and leaf area index in agroforestry systems in the Caatinga biome

Bioenergia: desenvolvimento, pesquisa e inovação

Com 27 trabalhos produzidos por pesquisadores do Instituto de Pesquisa em Bioenergia (Bioen), da Unesp, este livro oferece uma ampla visão sobre as áreas que compõem o segmento. Seu principal objetivo é contribuir para melhorar a compreensão dos vários aspectos da bioenergia, em especial no Brasil, que figura entre os países com maior nível de desenvolvimento tecnológico no setor. Os artigos abordam uma série abrangente de questões relacionadas à bioenergia, como a construção genética das plantas de cana-de-açúcar visando ao aumento de produtividade, a disseminação de sementes para estimular a propagação de espécies com potencial energético, etapas de produção de bioenergia, usos do combustível e seus efeitos nos diversos tipos de motores. Agrupados por assunto, os textos estão distribuídos em cinco partes: Biomassa para bioenergia; Produção de biocombustíveis; Utilização de bioenergia; Biorrefinaria, alcoolquímica e oleoquímica e Sustentabilidade dos biocombustíveis