ISEL - Engenharia Mecânica
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Browsing ISEL - Engenharia Mecânica by Field of Science and Technology (FOS) "Engenharia e Tecnologia::Engenharia Mecânica"
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- Assessment of influential operational parameters in the mitigation of CO2 emissions in a power plant: case study in PortugalPublication . Balanuta, Vítor; Baptista, Patricia; Neves da Fonseca Cardoso Carreira, Fernando Paulo; Duarte, Gonçalo; Casaca, Cláudia Sofia Séneca da LuzThe European decarbonization goals and requirement for energy independence are mostly relying on intermittent renewable energy sources for electrification. A numerical model was developed to simulate the operation of a steam generator, allowing a study of the potential impacts of retrofitting existing coal-fired power plants to operate with biomass or coal–biomass mixtures on combustion parameters and CO2 emissions. The results obtained using the operational parameters of the Sines power plant indicate that a mixture of 25% coal and 75% pine sawdust allow operation at λ = 1.8, demonstrating that a small amount of coal allows operation near the coal combustion parameters (λ = 1.9). These conditions have the drawback of a reduction of 8.7% in adiabatic flame temperature but a significant reduction of 57.5% in CO2 emissions, considering the biomass as carbon-neutral.
- Color evaluation of pre-shaded monolithic zirconia restorations on different substrates and resin cementsPublication . Fonseca, Vanessa; Neves, Cristina Bettencourt; Portugal, Jaime; Anes, Vitor; Chasqueira, Filipa; Roque, Joao CarlosThis study evaluated if the material, the substrate, and the cement have no influence on the color of pre-shaded monolithic zirconia crowns. The specific effect of the cement over each substrate/brand group was also studied. Two commercial brands of zirconia, Amann Girrbach (AG) and Zirkonzahn (ZZ), were used to produce crowns that were placed over three substrates (natural tooth, zirconia, metal) using two different resin cements (Ivoclar AG (Shaan, Liechtenstein) Neutral and Light) or glycerol (as the control) (n = 10). Lightness (L*), chroma (C*), hue (h*), and color difference (ΔE) of each crown were measured using a VITA Easyshade V® spectrophotometer (VITA Zahnfabrik, Bad Säckingen, Germany), following the standardized reference. Since normality was not verified by the Shapiro–Wilk test, data were statistically analyzed using the Kruskal–Wallis test for group comparisons and Tukey’s post-hoc test for multifactorial variance analysis (α = 0.05). ΔE medians ranged between 1.3 in the AG/zirconia substrate/glycerol group and 8.0 in the ZZ/metal substrate/light cement group. In general, lower values of ΔE were recorded in AG restorations compared to ZZ (p < 0.05), zirconia, and natural tooth substrates compared to metal (p < 0.001) and neutral compared to light cements (p < 0.05). Specifically, over the metal substrate, AG crowns with neutral cement and ZZ crowns with neutral cement and glycerol showed lower ΔE values (p < 0.05). Over the zirconia substrate, light cement presented higher ΔE values than glycerol in both brands but similar to neutral cement. Over the natural tooth, no significant differences were observed between cements (p > 0.05) in the AG brand, while in the ZZ group, light cement showed higher ΔE values (p < 0.05). The final color of the restorations was significantly influenced by the zirconia brand, substrate type, and resin cement. Light cement led to greater color variations, particularly in ZZ restorations. These findings highlight the importance of material selection in achieving esthetically pleasing zirconia restorations.
- Energy production from landfill gas: short-term managementPublication . Domingues, Nuno SoaresAn increasing lack of raw materials, resource depletion, environmental impacts and other concerns have changed the way the population faces garbage disposal and municipalities implement waste management strategies. The aggravated global rise in municipal solid waste (MSW) generation has led to a new stage in full development, with objectives and targets set by the European Union regarding reducing the production of MSW. The targets also include the increasing selective collection, reuse, recycling and recovery (organic and energetic) of the waste produced. At the same time, the European Union has also set caps for the greenhouse gas emissions and for increasing the use of alternative renewable energy sources. In this context, one of the sources of renewable energy that is beginning to be used to produce electricity in our country is biogas. Finally, AD promotes the development of a circular economy. The present study introduces the formalism for a computer application that simulates the technical-economic behaviour of the short-term management of biogas for the conversion of electricity, and the mathematical model is formulated as a mathematical programming problem with constraints. A simulation for a case study of short-term management is given using the real landfill data available. The case study proves the ability of the LandGEM, despite some authors' support that the Tabasaran-Rettenberger model provided a more reliable estimate, especially when compared to actual landfill data. The present paper is a contribution to the optimisation of the management of electricity from the use of biogas, namely the second phase of the Strategic Plan for Urban Waste. In addition to complying with the legislation in force, the use of biogas to produce electricity is an added value for the concessionaires of waste treatment and final destination units, as this alternative energy source can provide not only self-sufficiency in electricity for these units but also the export of surplus energy to the National Electricity Grid, thus contributing to the self-sustaining management and energy flexibility that is intended for these infrastructures.
- Natural gas–hydrogen blends to power: equipment adaptation and experimental studyPublication . Valente, Ruben; Costa, Jorge M.; Soares Domingues, Nuno AlexandreAn experimental study was devised to assess the technical, environmental, and economic impact of incorporating hydrogen into natural gas. The experimental tests were conducted on a GUNT ET 792 demonstration unit, characterized by operating on a gas cycle in a twin-shaft configuration. The equipment was adapted to accommodate natural gas and mixtures of natural gas with hydrogen in volumetric fractions of 5%, 10%, and 20%. The tests carried out ensured the viability of using these mixtures from a safety perspective. On the other hand, it was possible to evaluate the main differences in the use of these fuel gases in terms of the temperatures and pressures that characterize the main points of the gas cycle, fuel injection pressures, air/fuel ratios, excess air, power output, overall cycle efficiencies, NOX and CO2 emissions, and operational cost.
- Projeto de sistema de lavagem para tanques de armazenamento de produtos alimentaresPublication . Lomelino, Pedro Miguel Alves; Carreira, Fernando Paulo Neves da Fonseca Cardoso; Campos, Francisco Mateus Marnoto OliveiraAs alterações climáticas são um tema, nos dias que correm, cada vez mais relevante e que suscita preocupação na realidade das empresas e dos consumidores. Neste contexto, é importante procurar substituir os métodos tradicionais quando existirem soluções tecnológicas mais avançadas e com menor impacto ambiental. Estas devem reduzir a utilização de recursos e aumentar a eficácia dos processos. Desta forma, para além dos benefícios ambientais, as empresas tornar-se-ão mais competitivas no mercado de que fazem parte. O presente trabalho propõe uma solução tecnológica mais avançada em relação ao mercado da lavagem de tanques de armazenamento de produtos. A presente solução foi idealizada para uma herdade onde os tanques de armazenamento são utilizados para a produção de vinho. Na solução aqui apresentada propõe-se, por um lado, automatizar os processos de lavagem, através de um sistema para lavar sequencialmente vários tanques de armazenamento sem a intervenção dos operadores. Por outro lado, tentou-se reduzir os custos de lavagem, selecionando um elemento terminal de lavagem (cabeça de lavagem rotativa) mais atual relativamente à solução presentemente utilizada na herdade (bola de lavagem fixa). Os resultados obtidos, quando comparadas as duas soluções, mostram que a solução proposta tem efeitos positivos a nível do consumo de recursos (água e detergente) com uma redução em cerca de 30%. Por outro lado, verificou-se que a nível económico, existe retorno do investimento inicial a médio-longo prazo. Concluiu-se então que o sistema desenvolvido apresenta benefícios que podem constituir uma mais-valia na herdade para onde foi dimensionado. De uma forma geral, os estudos realizados sugerem que, para empresas onde exista um maior volume de lavagens de tanques, os benefícios do sistema proposto serão mais acentuados.
- Study of additive manufacturing intrinsic defects on fatigue life of Ti-6Al-4V †Publication . Ribeiro Cardoso Martins Morgado, Teresa Leonor; Alves, João; Pereira, António; Pereira, Manuel; Martins, Rui F.The present work presents a new approach to studying the structural integrity of a Ti-6Al-4V alloy obtained by Selective Laser Melting (SLM). This approach is based on the intrinsic addictive manufacturing defects analysis obtained by nanotomography, the experimental S-N curve, and the small crack growth Murakami and Endo model. Also, two counting methods of 3D manufacturing intrinsic defects were considered. The simulation of S-N curves and the small crack propagation curves were successfully obtained. New models for predicted fatigue limit were developed, one using the (3D) variable area of the defects observed as the total area and the other using the total project area. The 3D total surface area counting method presents more conservative values on crack propagation studies, so it is recommended for integrity studies of Ti6Al4V alloy obtained by SLM.