Browsing by Author "Pinho, C."
Now showing 1 - 5 of 5
Results Per Page
Sort Options
- Geoquímica de sedimentos lacustres em sistemas com elevadas taxas de sedimentação por eventos climáticos extremos: estudos de caso na República DominicanaPublication . Fonseca Araújo, Joana; Nogueira, Pedro; Fonseca, Rita; Pinho, C.; Araujo, A.Resumo: As condições climáticas da República Dominicana são propícias à ocorrência de elevadas taxas de erosão e, consequentemente, a elevadas taxas de sedimentação, prejudicando por isso o potencial de armazenamento de água e de produção de energia eléctrica das barragens. Neste estudo, foram abordadas duas barragens, Tavera e Sabana Yegua, nas quais se amostraram os solos das respectivas bacias de drenagem, bem como os sedimentos de fundo. Recorrendo à análise da química total através de ICP-OES, bem como à análise textural e elementar, pretende-se realizar uma caracterização geoquímica quanto aos elementos maiores e em traço, bem como a avaliação da proveniência dos sedimentos, de modo a determinar a real influência de cada sub-bacia de drenagem no processo de sedimentação das barragens.
- Reduced mechanism for combustion of hydrogen and methane with nitrogen chemistryPublication . Azevedo, Pedro; Cabrita, Isabel; Pinho, C.A reduced chemical kinetic reaction mechanism that could be used in computational fluid dynamics (CFD) software was developed to describe the formation of nitrogen oxides and their subsequent destruction in hydrogen and/or hydrocarbon flames with or without seeding of nitrogen compounds. The research work presented here will describe the numerical work done with the application "CHEMKIN" in order to verify the quality of the reduced mechanism. The mechanism was validated through comparisons between computational data from a variety of different sources. In addition, numerical experiments were carried out to examine features of methane combustion in which the detailed mechanisms can be used to compare their response. The proposed reduced mechanism provides reasonable agreement with the studied detailed mechanisms, mainly in the species produced from the hydrocarbon oxidation process. Regarding the produced nitrogen species, the proposed reduced mechanism showed the same tendencies as the detailed mechanisms, but there is a need for a better agreement regarding the quantities.
- Water management in PEMFCPublication . Falcão, D. S.; Rangel, C. M.; Pinho, C.; Pinto, A.M.F.R.The potential of fuel cells for clean and efficient energy conversion is generally recognized. Proton-exchange membrane (PEM) Fuel Cells are among the different types of fuel cells one of the most promising. The water management is a critical problem to overcome in the PEM fuel cell technology. Despite several studies on this topic effective water management is still elusive. Models play an important role in fuel cell development since they enable the understanding of the influence of different parameters on the cell performance allowing a systematic simulation, design and optimization of fuel cells systems. In this work, a model previously developed and validated [1], is used to predict the water transport through the cell. The model takes into account heat and mass transport effects The influence of membrane thickness and transport properties, GDL thickness and structure, reactants pressure and humidification temperatures, on the water content through the membrane and on the cell performance was studied. All these parameters have an important impact in the cell water management. The model predicts the membrane water contents and water concentration profiles along the MEA. This work represents a useful tool to set-up suitable operating conditions and optimized tailored MEAs to produce a better performance of PEM fuel cells.
- Water transport in PEM fuel cellsPublication . Falcão, D. S.; Rangel, C. M.; Pinho, C.; Pinto, A. M. F. R.
- Water transport through a PEM Fuel Cell: a one-dimensional model with heat transfer effectsPublication . Pinto, A. M. F. R.; Oliveira, V. B.; Falcão, D. S.; Pinho, C.; Rangel, C. M.One of the critical problems and design issues of PEM fuel cells is the water management because the membrane’s hydration determines the performance and durability of the cell. In this work, a steady state, one-dimensional model accounting for coupled heat and mass transfer in a single PEM fuel cell is presented. Two-phase flow effects are neglected. The anode and cathode flow channels are treated using the continuous stirred tank reactor (CSTR) approach. The cell voltage expression incorporates the anodic and cathodic overpotentials as well as the ohmic losses across the membrane. The reactions in the catalyst layers are considered as homogeneous. The kinetics of the cathodic oxygen reduction is modelled using the Tafel equation while a modified Tafel expression is used to describe the anode losses. Pressure gradients across the layers are assumed as negligible. Mass transport in the diffusion layers and membrane is described using effective Fick models. Local equilibrium at interfaces is represented by partition functions. Water transport through the membrane is assumed to be a combined effect of diffusion and electro-osmotic drag. It is assumed that the membrane proton conductivity and water diffusivity are a function of , the number of water molecules per ionic group. The heat transport through the gas diffusion layers is assumed as a conduction-dominated process. The thermal conductivity for all the materials is assumed as constant. Heat generation or consumption is considered in the catalyst layers. The analytical solutions for concentration and temperature across the cell are computed. Particular attention is paid to the water distribution across the membrane. The influence of different parameters (such as the current density and the level of humidification of inlet gases) over the water transport and on the cell performance is studied. The model is validated with recent published data and with experimental results obtained with an in-house designed PEMFC (25cm2 of active area). This easily implemented simplified model is suitable to define the optimal hydration conditions of the membrane