Browsing by Author "Luz, Paulo P. da"
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- Comportamento electroquímico do aço galvanizado em estruturas de suporte de mastros treliçados utilizados na avaliação de recursos eólicosPublication . Nogueira, R.; Rangel, C. M.; Luz, Paulo P. da; Estanqueiro, AnaO reconhecimento do potencial da energia eólica como fonte de electricidade limpa e de baixo custo, tem criado a necessidade de reavaliar materiais candidatos a integrar em estruturas para a medição da velocidade e direcção do vento. Neste trabalho, o comportamento electroquímico de aço galvanizado à quente utilizado em estruturas metálicas utilizadas para avaliar potencial eólico foi avaliado em ambientes contendo iões cloretos. Foi também conduzida uma análise de falha de componentes de estruturas de suporte de mastros anemométricos treliçados, convenientemente expostos à atmosfera. O potencial em circuito aberto de sistemas aço galvanizado/NaCl (soluções 10-3 a 10-1 M) foi medido durante tempos suficientemente longos para obter resultados significativos para a identificação de diferentes fases do processo corrosivo até se atingir o substrato. A espectroscopia de impedância electroquímica associada revelou a complexidade dos processos que ocorrem sob a camada porosa de produtos de corrosão gerados. Evidenciaram-se três fases, dissolução inicial de zinco; exposição da liga Fe-Zn e inibição do processo anódico; exposição do substrato com a formação de produtos de corrosão contendo Fe+2 e Fe+. Os resultados obtidos foram complementados mediante a análise de secções transversais das amostras, observadas ao microscópio óptico e electrónico de varrimento O mecanismo de degradação em condições de imersão contínua é comparado com o observado em condições de imersão alternada em ambientes contendo iões cloreto. A análise de falha de componentes expostos à atmosfera confirma o mecanismo proposto.
- EIS diagnostics of aged Li-ion batteriesPublication . Plancha, Maria João; Luz, Paulo P. da; Rangel, C. M.High-power batteries with long cycling life and adequate storage behaviour are needed as energy sources devices for (hybrid) electric vehicles and lithium-ion rechargeable cells are the most promising candidates. In this work, Li-ion cells with a nominal capacity of 10 Ah were studied. Electrochemical impedance spectroscopy (EIS) was used for studying the cycling ageing effect on discharge capacity fade. EIS measurements were conducted in a galvanostatic mode, by means of a Solartron Electrochemical Interface 1286 and a Solartron FRA 1250 controlled by Zplot from Scribner Associates. Scanning frequency ranged from 600 Hz to 0.005 Hz and the ac amplitude was set to 100 mA. An equivalent circuit complex non-linear least squares fitting procedure was used for spectra analyses. Cell charge transfer and film resistances were estimated at several cycle life stages and its evolution on cycle number was analysed. Capacity losses were estimated after 300, 600 and 1200 cycles at C/1 discharge rate and were found to be 5.8, 7.5 and 16.8% of the initial capacity, respectively. EIS data revealed that the major factor responsible for the observed capacity fade was the cell’s charge transfer resistance (Rct) increase following the opposite tendency of the discharge capacity values with cycle number. Very little change can be attributed to film resistances as a result of ageing by cycling. The SEI layer thickness appeared to increase from 0 to 300 cycles remaining almost constant up to 1200 cycles. The effect of a high storage temperature on the performance of the sealed commercial batteries was evaluated by means of discharge capacity measurements and impedance behaviour. The thermal ageing conditions were applied over time and the results were interpreted taking into account the cell’s state of charge (SOC). Before storage at 45 oC, in an open circuit state, cells were fully charged (100% SOC). At defined intervals, cells were cooled to ambient temperature and capacities were determined by a discharge step. As the cells aged up to 25 weeks at 45 oC, the C/1 capacity slowly fades, at first, with a capacity retention of about 95% after 16 weeks of storage. However, the value of discharge capacity loss reached 10.9%, after 25 weeks (Fig. 1). Impedance data were fit to an equivalent circuit with a high frequency arc associated to the SEI film resistance (R sei) and a second arc at medium frequencies to Rct.
- Environmental impact assessment of the penetration of hydrogen technologies in Portugal's road transportPublication . Travassos, Maria Antónia; Sá, A.I. De; Luz, Paulo P. da; Rangel, C. M.Road traffic is one of the transportation sectors with faster growth and also one of the most important emitters of greenhouse gases (GHGs). In this work, an analysis of the environmental benefits resulting from the introduction of hydrogen on road transport in Portugal is made. Impact is analyzed mainly looking at the pollutant emissions provided by road transport at the point of use. Emissions associated to road transport have been estimated using the software COPERT (version 4), since it provides a detailed methodology for each specific pollutant related to the vehicle fleet of a region or country, as well as the driving conditions and fuel consumption. Passenger cars, light duty vehicles and public transport buses are the vehicles categories in which the hydrogen technology is foreseen. The hydrogen penetration rates (moderate and high) are extracted from the European Project HYWAYS. Two trends are then considered, which give penetration rates of 40.0 % and 74.5 % in 2050 for the moderate and high scenarios respectively.
- Fuel cell and hydrogen storage development for a wheel chairPublication . Rangel, C. M.; Silva, V.; Luz, Paulo P. da; Franco, Alexandra; Azevedo, F.; Bosukov, L.In this paper are presented, the recent advances of a demonstration project that focuses on the implementation of a hybrid system for a wheel chair incorporating a fuel cell and a metal hydride hydrogen storage system. Advantages regarding weight reduction and greater autonomy are emphasized, apart from the use of clean energy and the drastic reduction in charging time, when compared with the system before conversion.
- Penetration of hydrogen technologies: study on the environmental impact of road transport in PortugalPublication . Travassos, Maria Antónia; Sá, A.I. De; Luz, Paulo P. da; Rangel, C. M.Road traffic is one of the transportation sectors with faster growth and also one of the most important emitters of greenhouse gases (GHGs). In this work, an analysis of the environmental benefits resulting from the introduction of hydrogen on road transport in Portugal is made. Impact is analyzed mainly looking at the pollutant emissions provided by road transport at the point of use. Emissions associated to road transport have been estimated using the software COPERT (version 4), since it provides a detailed methodology for each specific pollutant related to the vehicle fleet of a region or country, as well as the driving conditions and fuel consumption. Passenger cars, light duty vehicles and public transport buses are the vehicles categories in which the hydrogen technology is foreseen. The hydrogen penetration rates (moderate and high) are extracted from the European Project HYWAYS. Two trends are then considered, which give penetration rates of 40.0 % and 74.5 % in 2050 for the moderate and high scenarios respectively.