Thermal Gradient Changes Caused by Water in the Soil

The heat flow density data published in the Geothermal Atlas of Europe (1992) show relatively high values for temperature gradients measured in holes in the SW area (Portugal and Spain) of the Iberian Peninsula. This study tries to explain this fact based in the presence of water at relatively high temperatures outside the holes where the measurements were made, and the inclination of strata, derived from samples taken from the boreholes. We used a two-dimensional numerical model based on the finite volume method. Equations governing the transfer of energy by conduction and advection and fluid flow, were solved. Thermal conductivity values of the rocks and water may vary spatially as well as the porosity. Thermal conductivity values were measured but values of the hydraulic conductivity and porosity are unknown. Due to this fact, the models are tested with different values of these parameters. The heat flow density value considered for the region is 60 mWm-2 and the thermal gradient is calculated using the value of thermal conductivity. The results obtained with the models are compared with those published. Different solutions can be obtained for a given hole

Análise do potencial de biomassa residual no Algarve, Portugal, baseada em SIG

O presente estudo avalia o potencial dos resíduos florestais (azinheira, sobreiro, eucalipto, pinheiro bravo, pinheiro manso e castanheiro), parte dos agrícolas (olival e vinhas) e biomassa proveniente de matos e espécies invasoras na região do Algarve, Portugal, e mapeia sua disponibilidade em um raio de coleta de 30 km em torno de todos os pontos de uma malha de 250 m de tamanho de célula que cobre a região. Foi utilizado um Sistema de Informação Geográfica (ArcGIS), o mapa de uso do solo de Portugal e as produtividades de resíduos das espécies de interesse publicadas por outros autores. Se obteve um potencial total de biomassa residual para o Algarve de 96.905 t seca/ano, das quais 65.543 t seca/ano provêm de florestas, se destacando as florestas de pinheiro manso (25,0%) e de eucalipto (19,5%), e 26.322 t seca/ano (27,2%) de matos. Na região centro-oeste do Algarve foi onde se atingiram valores de biomassa residual acima de 30 kt seca/ano para uma área de coleta de raio de 30 km. A quantidade de resíduos indica, do pondo de vista da disponibilidade de recurso, que é possível abastecer pequenas/médias centrais de valorização energética de biomassa residual a implementar na região

Alterações nos gradientes de temperatura provocadas por circulação de água no solo

Os dados de fluxo de calor publicados no Geothermal Atlas of Europe (1992) mostram valores relativamente elevados, para os gradientes de temperatura medidos em furos, na zona SW (Portugal e Espanha) da Península Ibérica. O presente trabalho tenta explicar este facto baseado na existência de água a temperaturas relativamente elevadas, fora dos furos onde foram feitas as medições e na inclinação dos extratos deduzida a partir das amostras retiradas dos furos. Para isso utilizou-se um modelo numérico bidimensional baseado no método dos volumes finitos. Resolvem-se as equações que governam a transferência de energia por condução e adveção e o escoamento dos fluidos. Os valores da condutividade térmica das rochas e da água variam espacialmente, bem como os da porosidade. Enquanto os valores de condutividade térmica utilizados foram medidos, os valores de condutividade hidráulica e a porosidade são desconhecidos. Tal fato faz com que os modelos sejam testados com diferentes valores destes parâmetros. O valor de fluxo que consideramos válido para a região é de 60 mW m-2, sendo o gradiente de temperatura calculado tendo em conta o valor medido de condutividade térmica. Os resultados obtidos com os modelos são comparados com os publicados, podendo existir diferentes soluções, para um dado furo

Clean Air -London

p. 125-143The influence of the perforated plate characteristics that precedes the flame support layer in a newly designed bilayered porous combustor was numerically assessed. It is shown that a perforated plate with 1 mm diameter holes is able to provide the necessary quenching of the reaction front, leading to the stabilization of the flame within the pores of the flame support layer for all the range of operating conditions and is, thus, an appropriate choice. The influence of the diameter of the holes on the gas and solid temperatures, and on the emissions of pollutants, namely NO and CO, is discussed

Evaluation of the electrical energy potential of woody biomass in the near region of the hydropower plant Tucuruí –Brazil

This paper determines the potential of installing power plants fired with wood residues generated at the sawmills located in the region of a 8 GW hydropower complex in the Amazon. Two different scenarios were considered: i) the residues are converted locally at the mills or ii) transported to a centralized power plant. To evaluate the existing electricity potential, sawmills were contacted and the amount and type of generated residues assessed. The LHV (lower heating value) of wood of native species processed at the mills was experimentally determined. Data from real biomass power plants was fitted to calculate efficiencies versus power. With LHV data and conversion efficiency, the potential of installing micro to large-scale biomass-fired power plants was estimated. In 2004 and 2014, sawmills around the Tucuruí dam generated 404×103 t of wood residues, showing that in the region there is a large untapped potential for energy valorization. If the residues were converted at the mills, 57 GWhe could be produced. The energy production would be around 2 times higher in the centralized scenario. The importance of the efficiency in determining biomass potentials or optimizing biomass supply chains is quantified. Ignoring the dependency of efficiency with power leads to erroneous conclusions

Direct Numerical Simulation of the Pressure Drop through Structured Porous Media

Following the development of an immersed boundary method for the study of flow through porous media [1,2], this paper presents direct numerical simulations for structured porous media composed of equal size staggered square cylinders. Different Reynolds numbers are simulated in order to capture the dependence of the pressure drop and friction factor with the Reynolds number. Results are compared to available and widely used empirical correlations. These correlations assume that the additional pressure drop caused by the entrance and exit flow adjustments is unimportant as compared to the pressure drop imposed by the porous medium core. Following this line of though, many of the studies and books on flow though porous media neglect these entrance and exit effects and at best mention them in passing. Through the representation of the pressure drop per unit length for several Reynolds numbers, the authors obtain for a regular matrix composed of equal size square cylinders, the influence of the porous medium entrance. This influence is a function of the Reynolds number

Numerical and experimental assessment of a downdraft gasifier for electric power in Amazon using açaí seed (Euterpe oleracea Mart.) as a fuel

The Amazon region is characterized by communities isolated from the grid that currently are using Diesel engines to produce electricity and that have residual biomass energy potentials between 60 and 500 kW. In this scenario, gasification appears as an evident choice as far as energy generation is concerned. Other than wood, açaí seed is the biomass residue most wasted in the Pará State and its use in gasification systems is assessed in this study. With this purpose, a cylindrical bodied downdraft gasifier was designed, built and tested, and an equilibrium model implemented. The comparison of the simulation values with the experimental and numerical results of other authors show that they are in-line with the predictions of other equilibrium models. Also, they confirm that this kind of models is a fast and useful tool for a preliminary assessment of the applicability of a specific biomass gasification process for electricity production. Moreover, the deviation between the numerical and experimental results obtained in this study was lower around the equivalence ratio that optimizes the gasification process (in the 2.15-2.3 range). As far as biomass humidity is concerned, the producer gas calorific value and cold gas efficiency decreases with an increase in this parameter

Simulação de um forno de aquecimento de biletes

Neste trabalho apresenta-se uma metodologia desenvolvida no âmbito do projeto “Audit Furnace” para apoiar a indústria transformadora na compreensão das eficiências encontradas nos seus fornos bem como na identificação de estratégias de melhoria contínua dos seus processos. Aliando auditorias feitas a várias unidades industriais com a modelação de mecânica de fluidos computacional, procura-se obter uma representação digital por forma a apoiar o desenvolvimento, calibração e treino de um modelo de ordem reduzida. Este será suportado por modelos de aprendizagem no sentido de se ganhar maior flexibilidade do modelo na sua adaptação a diferentes fornos. No artigo apresentam-se resultados da modelação de mecânica de fluidos computacional de um forno de aquecimento de biletes. Essa modelação é um primeiro passo essencial na metodologia proposta e gerador de resultados que alimentam o modelo de aprendizagem