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- Fluid flow and structural numerical analysis of a cerebral aneurysm modelPublication . Souza, Maria Sabrina; Souza, Andrews Victor Almeida; Carvalho, Violeta Meneses; Teixeira, Senhorinha F.C.F.; Fernandes, Carla S.; Lima, Rui A.; Ribeiro, J.E.Intracranial aneurysms (IA) are dilations of the cerebral arteries and, in most cases, have no symptoms. However, it is a very serious pathology, with a high mortality rate after rupture. Several studies have been focused only on the hemodynamics of the flow within the IA. However, besides the effect of the flow, the development and rupture of the IA are also associated with a combination of other factors such as the wall mechanical behavior. Thus, the objective of this work was to analyze, in addition to the flow behavior, the biomechanical behavior of the aneurysm wall. For this, CFD simulations were performed for different Reynolds numbers (1, 100, 500 and 1000) and for two different rheological models (Newtonian and Carreau). Subsequently, the pressure values of the fluid simulations were exported to the structural simulations in order to qualitatively observe the deformations, strains, normal stresses and shear stress generated in the channel wall. For the structural simulations, a hyperelastic constitutive model (5-parameter Mooney–Rivlin) was used. The results show that with the increase in the Reynolds number (Re), the recirculation phenomenon is more pronounced, which is not seen for Re = 1. The higher the Re, the higher the strain, displacement, normal and shear stresses values.
- Laminar flow in chevron-type plate heat exchangers: CFD analysis of tortuosity, shape factor and friction factorPublication . Fernandes, Carla S.; Dias, Ricardo P.; Nóbrega, João M.; Maia, João M.Liquid foodstuffs with high viscosity are usually processed in plate heat exchangers (PHEs) at laminar or low Reynolds numbers, Re, flows. The tortuosity coefficient is used by the manufacturers for the design and optimization of PHE geometries. Using the finite-element computational fluid dynamics program POLYFLOW®, fully developed laminar flows in double-sine chevron-type PHEs passages are analysed in this work. The corrugation angle and channel aspect ratio of the passages vary in a broad range, PHEs with common area enlargement factors and with high area density being studied. The tortuosity coefficient and the coefficient K (Kozeny´s coefficient in granular beds) from the friction factor correlations increase with the increase of the channels aspect ratio and the decrease of the chevron angle. The shape factor from the PHEs passages also increases with the decrease of the chevron angle and is weakly influenced by the channel aspect ratio. In this paper, relations to predict the tortuosity coefficient and shape factor are proposed, the coefficient K being predicted resorting to the tortuosity coefficient and shape factor. The coefficient K compares well with literature data in the region of common chevron angles, channel aspect ratio and area enlargement factor.
- Micro-flow visualization of in vitro blood through a microchannel with a bifurcation and confluencePublication . Cidre, Diana; Lima, Rui A.; Fernandes, Carla S.; Dias, Ricardo P.; Ishikawa, Takuji; Imai, Yohsuke; Yamaguchi, TakamiMicro-visualization techniques have been used to investigate the in vitro blood flow through straight glass capillaries. Although the glass microchannels present certain similarities to in vivo microcirculation, it is also clear that these kind of in vitro experiments differ from microvessels in several respects, such as: elasticity of microvessels, effect of the endothelial surface layer and microvascular networks composed with short irregular vessel segments which are linked by numerous bifurcations and convergences. Thus it was not surprising that several studies on blood flow in glass microtubes and in microvessels have yielded conflicting results with respect to blood viscosity and flow resistance. The main purpose of this work is to improve our understanding about the effect of a bifurcation and convergence on the rheological properties of in vitro blood. The microchannel containing a bifurcation and confluence will be fabricated in PDMS by using a soft lithography technique. The flow behaviour of both pure water (PW) and dextran 40 (Dx40) containing about 14% (14Hct) of human red blood cells (RBCs) will be investigated by means of a confocal micro-PTV system. Additionally, the experimental measurements obtained with PW will be also compared numerically by using the commercial finite element software package POLYFLOW®.
- Laminar blood flow in stenotic microchannelsPublication . Calejo, Joana A.C.; Garcia, Valdemar; Fernandes, Carla S.In this work, Newtonian and non-Newtonian laminar blood flow in rectangular microchannels with symmetric and asymmetric atheroma were numerically studied. It was observed that the impact of symmetry of the atheroma is almost negligible and the non-Newtonian properties of blood leads to higher pressure drops and wall shear stresses than the ones obtained for Newtonian flows.
- Método semi-automático em MatLab para calcular o coeficiente de dispersão de eritrócitos em microcanaisPublication . Curralo, Ana; Pereira, Ana I.; Lima, Rui A.; Fernandes, Carla S.O sangue é um fluido fisiológico de elevada importância para o normal funcionamento do organismo humano pois desempenha funções essenciais à vida. Um ser humano possui cerca de 5 litros de volume sanguíneo no organismo onde, aproximadamente, metade desse volume é composto por eritrócitos e estes influenciam fortemente as propriedades do escoamento sanguíneo. A microcirculação tem uma função muito importante na circulação sanguínea pois é nesta que ocorre a maioria das trocas de substâncias entre o sangue e os tecidos vizinhos. O estudo do comportamento dos eritrócitos apresenta uma elevada importância na avaliação precoce de alterações comportamentais dos mesmos evitando o aparecimento e a evolução de patologias no organismo. Neste estudo, com o auxílio do MatLab, foi desenvolvido um método semi-automático para o cálculo do Coeficiente de dispersão de eritrócitos em microcanais. O algoritmo desenvolvido em MatLab foi validado através da comparação com um método manual e foi testado em vários elementos selecionados e seguidos em segmentos de imagens, obtidos por um sistema de micoscopia confocal (Leble et al., 2011, Lima et al., 2006, 2008). Os resultados obtidos foram bastante satisfatórios. A validação do método automático foi positiva, apresentando um erro despresável em comparação com o método manual. Os resultados obtidos no cálculo do coeficiente de dispersão através do método semi-automático aproximaram-se dos valores teóricos esperados.
- Optimização do projecto e desempenho de permutadores de calor de placas para fluidos alimentaresPublication . Fernandes, Carla S.; Maia, João Manuel; Pinho, Fernando Tavares deNeste trabalho estudou-se numericamente o desempenho térmico e hidráulico de canais de permutadores de calor de placas do tipo chevron com diferentes propriedades geométricas utilizando o software de mecânica de fluidos computacional POLYFLOW®. Foi analisado o escoamento laminar de fluidos newtonianos e não-newtonianos nos referidos canais, tendo o comportamento reológico dos últimos sido descrito pela lei de potência. Inicialmente estudou-se o arrefecimento de iogurte num permutador de calor de placas do tipo chevron de pequeno comprimento, onde os efeitos de entrada influenciam significativamente os números de Nusselt obtidos. O domínio computacional deste problema consistiu numa unidade tridimensional que representava metade de um canal do permutador de calor em causa. Apesar desta simplificação, encontrou-se uma boa concordância entre os resultados numéricos do número de Nusselt, Nu, e dados experimentais da literatura. Os trabalhos iniciais com o iogurte permitiram observar a existência de periodicidades adicionais do escoamento ao longo da largura do canal, o que permitiu desenvolver uma célula periódica. Usando esta célula periódica, estudaram-se então escoamentos laminares totalmente desenvolvidos de fluidos newtonianos e não-newtonianos genéricos em canais com propriedades geométricas bastante distintas. Para a obtenção de escoamentos completamente desenvolvidos térmica e hidraulicamente foi necessário utilizar canais constituídos por sete unidades periódicas consecutivas, também designadas por células unitárias.
- Visualization and measurement of red blood cells flowing in microfluidic devicesPublication . Rodrigues, Raquel Oliveira; Pinho, Diana; Faustino, Vera; Yaginuma, Tomoko; Bento, David; Fernandes, Carla S.; Garcia, Valdemar; Lima, Rui A.Several experimental techniques were performed in the past years using in vitro environments, in an attempt to not only understand the blood flow behaviour in microcirculation but also develop microfluidic devices as an alternative clinical methodology to detect blood diseases. Hence, the visualization and measurement of red blood cells (RBCs) flowing in a microfluidic device are important to provide not only essential information about hydrodynamic characteristics of the blood but also vital information to diagnose the initial symptoms of diseases during clinical investigations. For instance, RBC rigidity has been correlated with myocardial infarction, diabetes mellitus, hypertension, and also other haematological disorders and diseases that affect RBC deformation more directly, such as, hereditary spherocytosis, sickle cell anaemia and malaria. Regarding a better understanding of the RBCs deformation and motion, we present in this paper a compilation of studies made in our research group, using several microfluidic devices with different microchannel geometries and fabrication techniques (i.e., soft-lithography, xurography and hybrids) that focus in the shear and extensional flow behaviour, either in healthy or chemically stiffed RBCs.
- Simulação do escoamento não isotérmico de fluidos não-newtonianos em canais convergentes/divergentesPublication . Fernandes, Carla S.Este trabalho teve como objectivo simular numericamente o escoamento em estado estacionário de iogurte no interior de um canal pertencente a um permutador de placas. A simulação consistiu na resolução simultânea de três problemas: dois de condução de calor através das placas em aço inox e um de fluxo não-isotérmico do iogurte no canal referido. A simulação foi efectuada recorrendo ao software POLYFLOW, utilizando este o método de elementos finitos na resolução das equações de Navier-Stokes. Na fase inicial do trabalho construiu-se o domínio geométrico do problema, sendo este constituído por três elementos tridimensionais: placa superior, placa inferior e canal por elas delimitado. As placas apresentavam um conjunto de corrugações, tendo-se definido a sua geometria recorrendo a uma função sinusoidal. Posteriormente, efectuou-se a discretização do domínio, obtendo-se uma malha com um total de 161474 elementos (tetraédricos, hexaédricos, prismas e pirâmides) e 34373 nós. O iogurte apresentava um comportamento Não-Newtoniano, sendo a sua viscosidade descrita pelo produto da lei da potência e lei de Arrhenius. Devido ao baixo valor do índice de fluxo e alto valor da energia de activação, estes parâmetros conduziam a dificuldades na convergência das simulações efectuadas. Para a resolução das dificuldades de convergência citadas, utilizou-se o método das iterações de Picard no respeitante ao índice de fluxo e um processo evolutivo na energia de activação. Foi utilizada como condição de fronteira um fluxo de calor variável ao longo das placas para descrever o calor perdido pelo iogurte ao longo das mesmas. Esta condição fronteira foi deduzida recorrendo a dados experimentais. Os dados experimentais disponíveis, nomeadamente temperatura do iogurte à saída do canal, permitiram verificar a validade dos pressupostos considerados nas simulações.
- Blood flow of bubbles moving in microchannels with bifurcationsPublication . Bento, David; Lopes, Sara Helena Carvalho; Maia, Inês; Pereira, Ana I.; Fernandes, Carla S.; Miranda, João Mário; Lima, Rui A.The gas embolism is a well-known phenomenon. Previous studies have been performed to understand the formation, the behavior and the influence of air bubbles in microcirculation. This study aims to investigate the flow of bubbles in a microchannel network with bifurcations. For that purpose, a microchannel network was fabricated by soft lithography. The working fluids used were composed by sheep red blood cells (RBCs) suspended in dextran 40 and two different hematocrits were studied, 5% and 10%. The in vitro blood flow was analyzed for a flow rate of lO ~-tllmin, by using an inverted microscope and a high-speed camera. It was possible to visualize the formation of the bubbles and their behavior along the network. The results show that the passage of air bubbles influences the cells local concentration, since a higher concentration of cells was seen upstream to the bubble and lower concentrations downstream to the bubble.
- CIEEMAT 2022 - VII Ibero-American Congress on Entrepreneurship, Energy, Environment and Technology: book of abstractsPublication . Ferreira, Ângela P. (Ed.); Fernandes, Carla S. (Ed.); Fernandes, Florbela P. (Ed.); Pais, Luís S. (Ed.)The VII Ibero-American Congress on Entrepreneurship, Energy, Environment and Technology (VII CIEEMAT), coordinated by the Federal Centre of Technological Education from Rio de Janeiro (CEFET/RJ), was held for the third time in Portugal, and for the second time in the city of Bragança, under the organization of the Polytechnic Institute of Bragança (IPB), the Research Centre in Digitalization and Intelligent Robotics (CeDRI), the Mountain Research Centre (CIMO) and the Associated Laboratory for Sustainability and Technology in Inland Regions (SusTEC). The event aims to consolidate the Luso- Brazilian and Ibero-American cooperation in those areas, gathering the multinational contribution and enhancing collaboration in academic and scientific fields. The VII CIEEMAT took place on July 6-8, 2022 and had the Energy Transition as its specific theme. The current energy context and the transition of energy generation and consumption typologies are unavoidable in defining the profiles of national and international societies and energy policies. The dynamism to which the energy sector is currently subjected is imposed by environmental and safety concerns, the fluctuation of the fossil fuels price and shifting technologies, which translates into challenges and opportunities across various sectors as research and innovation, education, policy and environmental governance. The opportunities and challenges of the energy transition are outlined, for instance, in the exploitation of natural assets, the decarbonisation of the economy and the transport sector and the flexibility of energy infrastructure through smart grids. The VII CIEEMAT followed a program addressing various perspectives of action of higher education institutions and R&D units and their cooperation with society: i) the academic perspective (why, what and how to teach the challenges of energy transition); ii) the perspective of international cooperation, defining new cooperation programs between Portugal and Brazil in the energy field, with emphasis on the Brazilian EnergIF program and its potential for international cooperation with Portugal; iii) and the research and innovation perspective, with the contribution of academic experts and the business sector regarding the challenges that the necessary and emerging energy transition poses. At the same time, the VII CIEEMAT provided also a forum to disseminate and share ongoing research in various academic and scientific institutions, through oral communications in the areas of sustainable urban mobility, energy generation and self-consumption, environmental challenges, decarbonisation and climate change.