Browsing by Issue Date, starting with "2011-11"
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- A água subterrânea como fonte térmica na climatização de edifícios : situação em Portugal e perspectivas futurasPublication . Costa, Augusto Marques da; Amaral, Helena; Coelho, Luís
- Iberian Pyrite Belt Geosites - valorisation of the geodiversity based in the geological parks modelPublication . Matos, João Xavier; Pereira, Zélia; Oliveira, José Tomás
- O Trilho Geológico no Jardim Público de BejaPublication . Matos, João Xavier; Piçarra, José Manuel; Pereira, Zélia; Dias, Ruben Pereira; Preteseille, S.
- A água subterrânea como fonte térmica na climatização de edifícios : situação em Portugal e perspectivas futurasPublication . Costa, Augusto Marques da; Amaral, Helena; Coelho, Luís
- The Beja Public Geological Trail - geology in the gardenPublication . Matos, João Xavier; Piçarra, José Manuel; Pereira, Zélia; Dias, Ruben Pereira; Preteseille, S.
- Geologia do Portinho da ArrábidaPublication . Brito, Pedro Oliveira; Rebêlo, Luís Pina
- Three dimensional model of a high temperature PEMFC using PBI doped phosphoric acid membranes. Study of the flow field effect on performancePublication . Sousa, T.; Mamlouk, M.; Rangel, C. M.; Scott, K.A three-dimensional isothermal model of a high temperature polymer membrane fuel cell equipped with polybenzimidazole (PBI) membrane is described. All major transport phenomena were taken into account except the species cross-over thought the membrane. The cathode catalyst layer was treated as spherical catalyst agglomerates with porous inter-agglomerate spaces. The inter-agglomerate spaces were filled with a mixture of electrolyte (hot phosphoric acid) and polytetrafluoroethylene (PTFE). This approach proved to be an essential requirement for accurate simulation. In this particular paper the influence of different flow field designs and dimensions on performance was intensely study. Traditional configurations were tested (straight, serpentine, pin-in and interdigitated), and a new designs were proposed. With these new designs we tried to maximize performance by providing homogeneous reactants distribution over the active area keeping low pressure drop and relatively high velocity. The dimension and position of the inlet and outlet manifolds were also analysed. From the obtained results was observed a massive influence of the manifolds position and dimension on performance. This fact leaded to an optimization of the manifolds which can give important guidelines for future bipolar plates production.
- The effect of NaOH on the kinetics of Hydrogen production from sodium borohydride using Ni-based catalysts doped with RutheniumPublication . Fernandes, Vitor; Ferreira, M. J.; Pinto, A. M. F. R.; Rangel, C. M.Previous work by the authors has demonstrated a high rate and high yield hydrolysis of sodium borohydride in the presence of a Ni-Ru catalyst synthesized by wet chemistry. The catalyst has been fully characterized and utilized more than 300 times, exhibiting high stability and durability. In this work, the effect of temperature on the reaction rate was studied and the activation energy of the process estimated for temperatures up to 65 ºC. Typical data in the form of an Arrhenius type relationship showed two slope regions suggesting a change of mechanism that lead to a more accentuated role of ruthenium for temperatures higher than 45 ºC. This effect is maintained with increasing Ru doping of the catalyst. The effect of NaOH as a stabilizer was also studied and the role of Ni and Ru in the hydrolysis of sodium borohydride is under study on the basis of data obtained for various Ru concentrations and data for 100% Ni and 100% Ru as catalysts. An increase in the concentration of Ruthenium in the catalyst allowed effective utilization of the catalyst without the need for the stabilizer, minimizing the induction reaction time. Excellent catalytic activity and catalyst minimal deactivation for sodium borohydride hydrolysis are characteristic of the series of Ni-Ru catalyst synthesized by wet chemistry used in this work.
- MEA degradation in PEM Fuel Cell : a joint SEM and TEM studyPublication . Silva, R. A.; Hashimoto, T.; Thompson, G. E.; Rangel, C. M.One of the important factors determining the lifetime of polymer electrolyte membrane fuel cells (PEMFCs) is membrane electrode assembly (MEA) degradation and failure. The lack of effective mitigation methods is largely due to the currently very limited understanding of the underlying mechanisms for mechanical and chemical degradations of fuel cell MEAs. This work reports on the effect of 1500 h operation of an eight-cell stack Portuguese prototype low power fuel cell. A performance decrease of 34%, in terms of maximum power, was found at the end of testing period. A post-mortem analysis by SEM and TEM was done for most cells of the fuel cell. Loss of the PTFE ionomer in the anode and cathode catalytic layers; morphological changes in the catalyst surfaces such as loss of porosity and platinum aggregation, deformation on the MEA components (anode, cathode and membrane) were identified. Others, like delamination and cracking were also detected. Catalyst migration and agglomeration on the interface of the electrodes was observed at cells 2, 4, 6 and 7. A platinum band was also detected on the membrane at 2 μm apart from the anode of cell 4. In some cases, dissolution occurred with re-deposition of the platinum particles with facet
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