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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., The authors acknowledge the financial support from the project EXPL/EME-EME/0732/2021, funded by the NORTE 2020 Portugal Regional Operational Programme, under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (FEDER) and by Fundação para a Ciência e Tecnologia (FCT). This work was also supported by Fundação para a Ciência e a Tecnologia (FCT) under the strategic grants UIDB/04077/2020, UIDB/04436/2020, UIDB/00319/2020 and UIDB/00532/2020. Andrews Souza and Violeta Carvalho also acknowledge the financial support by FCT through the individual research grants 2021.07961.BD and UI/BD/151028/2021, respectively

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. info:eu-repo/semantics/publishedVersion

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A malária mata mais de um milhão de pessoas por ano e é uma das principais causas de morte em regiões subdesenvolvidas. Assim, o desenvolvimento de técnicas de diagnóstico rápidas, eficientes e competitivas é essencial. Este trabalho focou-se no estudo da deformabilidade dos glóbulos vermelhos (GVs) como biomarcador de malária, visto que esta propriedade do sangue está diretamente relacionada com as alterações que o parasita provoca ao longo da evolução da doença. Sistemas microfluídicos com estreitamentos abruptos juntamente com técnicas de processamento de imagem permitem determinar parâmetros como a velocidade de escoamento e a deformabilidade dos GVs. Assim, utilizando microcanais poliméricos com estreitamentos de 6 µm a 10 µm, efetuou-se um estudo comparativo entre GVs saudáveis e GVs quimicamente modificados para aumentar a sua rigidez e mimetizar o comportamento do parasita da malária. Os resultados obtidos mostram que os GVs saudáveis se deformam naturalmente para atravessar estreitamentos e recuperam rapidamente a sua forma original após o estreitamento. Em contrapartida, nas amostras modificadas com maiores percentagens de químicos o mesmo não se verificou, ocorrendo várias oclusões. Conclui-se assim que o aumento da rigidez dos GVs provoca a diminuição da velocidade de escoamento, da deformabilidade e da capacidade de recuperação de forma das células. Este trabalho assume-se como um contributo para o desenvolvimento de novos sistemas de diagnóstico. Tendo em conta as microtecnologias existentes, será possível integrar, num chip, sensores, microeletrónica e plataformas microfluídicas, de forma a criar um método de diagnóstico simples, rápido, preciso e barato para deteção precoce da malária. info:eu-repo/semantics/publishedVersion

Os estudos relacionados com o escoamento de fluidos em microcanais têm assumido um lugar de destaque na área da biomédica, uma vez que permitem estudar o escoamento sanguíneo e algumas patologias que o afetam, tal como as embolias gasosas, evitando questões de ética. As embolias gasosas ocorrem quando bolhas gasosas circulam na corrente sanguínea e é importante o seu estudo pois as bolhas podem obstruir os vasos sanguíneos e provocar deterioração dos tecidos. O objetivo deste trabalho é estudar o escoamento de fluidos em microcanais com bifurcações, capazes de produzirem bolhas. Para tal, fabricaram-se microcanais por litografia suave e posteriormente analisou-se o escoamento de fluídos newtonianos e de sangue de ovino com 5 e 10% de hematócrito em dextrano 40, para vários caudais e para pressões diferentes, com o auxílio de um microscópio invertido e uma camara de alta velocidade. Nestes escoamentos foi possível visualizar a formação das bolhas e o seu comportamento ao longo do microcanal e possibilitou a análise de vários parâmetros: a velocidade das bolhas e a sua frequência, o tempo entre bolhas, o entupimento dos microcanais e o efeito das bolhas no hematócrito. Os resultados obtidos demonstraram que a velocidade das bolhas aumenta com o aumento dos caudais e pressões utilizadas, sendo que para caudais e pressões baixas os microcanais têm tendência a ficarem obstruídos. Também demonstraram que a passagem das bolhas de ar influenciam a quantidade de células, existindo uma maior concentração das células antes da passagem das bolhas. info:eu-repo/semantics/publishedVersion

Os biomodelos virtuais e físicos estão a tornar-se cada vez mais úteis no diagnóstico precoce de doenças, bem como no planeamento detalhado e simulação de intervenções cirúrgicas complexas. Para complementar este avanço, a simulação numérica de in vivo ou in vitro biomodelos e simulação numérica para prever propriedades do escoamento sanguíneo num aneurisma cerebral. info:eu-repo/semantics/publishedVersion

Neste trabalho estudaram-se escoamentos sanguíneos laminares em estado estacionário num aneurisma cerebral obtido por imagiologia médica. Nas simulações realizadas o sangue foi considerado um fluido Newtoniano, assim como não-Newtoniano, tendo-se verificado que, para as condições de operação estabelecidas, as propriedades não-Newtonianas não influenciaram propriedades como a tensão de corte na parede e as quedas de pressão. info:eu-repo/semantics/publishedVersion

O interesse nos estudos relacionados com o escoamento de fluidos em microcanais tem assumido um lugar de destaque na área de biomédica, uma vez que que estes estudos permitem analisar escoamentos sanguíneos evitando questões de ética que se colocam quando se trabalha fisicamente com o sangue. Numa primeira fase deste trabalho foram fabricados modelos anatómicos tridimensionais, mais concretamente canais circulares, um sem patologia e dois com ateromas de alturas diferentes, onde foram efetuadas medições de quedas de pressão. Com os resultados obtidos foi possível concluir que a presença de ateromas influencia o escoamento sanguíneo, verificando-se que as quedas de pressão aumentam com o aumento do grau da estenose. Numa segunda fase os escoamentos estudados experimentalmente foram alvo de um estudo numérico com o objetivo de comparar os resultados da simulação com os obtidos experimentalmente. As simulações numéricas foram efetuadas recorrendo a um software comercial que implementa o método dos volumes finitos e os resultados obtidos revelaram-se concordantes com os obtidos experimentalmente, o que permitiu concluir que a dinâmica de fluidos computacional é de facto uma boa estratégia a ser utilizada. Na fase final do trabalho, procedeu-se à identificação da melhor modelação matemática para caracterizar a diferença de valores obtidos nos estudos experimental e numérico. Após diversas estratégias conclui-se que a diferença de valores pode ser caracterizada por uma função polinomial.

Nas últimas décadas o interesse nos estudos da aterosclerose tem assumido um lugar de destaque na área da medicina pois, devido ao estilo de vida adotado pela sociedade moderna, esta patologia do sistema cardiovascular tornou-se numa das maiores causas de morte. Os estudos de escoamentos sanguíneos in vivo, e mesmo in vitro, levantam por vezes problemas por questões éticas, pelo que ferramentas numéricas têm vindo a ganhar espaço na área da hemodinâmica. Neste trabalho recorreu-se à dinâmica de fluidos computacional para simular escoamentos newtonianos e não-newtonianos em microcanais com estenose simétrica. Para tal foram realizadas simulações em canais de secção retangular com graus de estenose distintos, o que permitiu estudar a influência do grau de contração nas propriedades do escoamento sanguíneo. Para descrever o comportamento não-newtoniano do sangue utilizou-se o modelo de Carreau, sendo os resultados obtidos considerando este modelo comparados com os obtidos para fluido newtoniano, o que permitiu avaliar o impacto das propriedades não-newtonianos nos escoamentos estudados. Com este estudo, verificou-se que a existência de ateroma no microcanal altera os perfis típicos de queda de pressão e velocidade, verificando-se um aumento da queda de pressão e velocidade máxima com o aumento do grau de estenose. No que diz respeito à influência das propriedades não-newtonianas do sangue, constatou-se que estas não têm grande impacto nos perfis de velocidade, não se verificando o mesmo no que diz respeito às quedas de pressão pois estas assumem valores mais elevados quando se admitiu o modelo de Carreau para descrever a reologia do sangue. Os autores agradecem à FCT, COMPETE, QREN e União Europeia (FEDER) no âmbito do Projeto EXPL/EMS-SIS/2215/2013.

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. The authors acknowledge the financial support provided by: EXPL/EMS-SIS/2215/2013 and PTDC/SAU-ENB/116929/2010 from FCT (Science and Technology Foundation), COMPETE, QREN and FEDER.

Brain aneurysms are pathological dilatations of cerebral arteries and are known as one of the most common and serious cerebrovascular events. Most cerebral aneurysms do not cause symptoms until they become large, beginning to break up. This study's main objective is the numerical characterization of biomechanical behavior of aneurysms, taking into ac-count different geometric and physiological parameters, in order to analyze the blood vessel wall behavior during the formation of an aneurysm in order to understand what leads to its formation and where are most conducive to its rupture zones. Simulation of the Newtonian fluid flow (glycerin, with well-known properties and sufficient viscosity to measure the pressure drops) was performed using the commercial finite method package Ansys® - Fluent, and pressure along the channel was determined. These pressures were imported into the channel, in the Ansys®- Static Structural, in order to be able to evaluate and analyse the deformations and stresses in the channel wall, caused by internal pressure induced by the fluid flow. To do this, the most known hyper-elastic constitutive models were used. and it was concluded that any constitutive model can be applied to this kind of studies, allowing to visualize where pressure achieve maximums and consequently, the most favorable areas to the rupture.

A few detailed studies have been performed in complex in vitro microvascular networks composed by bifurcations and confluences. The main purpose of the present work is to numerically simulate the flow of two distinct fluids through bifurcation and confluence geometries, i. e red blood cells (RBCs)suspended in Dextran40 with about 14% of heamatocrit and pure water. The simulations of pure water and RBCs flows were performed resorting to the commercial finite volume software package FLUENT. A well known hemodynamic phenomenon, known as Fahraeus-Lindqvist effect, observed in both in vivo and in vitro studies, results in the formation of a marginal cell-free layer (CFL) at regions adjacent to the wall. Recently, studies have shown that the formation of the CFL is affected by the geometry of the microchannel and for the case of the confluences a CFL tend to appear in the middle of the microchannel after the apex of the confluence. By using the CFL experimental data, the main objective of this work is to implement a CFL in the numerical simulations in order to obtain a better understanding of the effect of this layer on the velocity profiles.

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. The authors acknowledge the financial support provided by 2007 Global COE Program “Global Nano-Biomedical Engineering Education and Research Network”, Japan and grant-in-Aid for Science and Technology, PTDC/SAU-BEB/105650/2008, PTDC/EME-MFE/099109/2008, PTDC/SAUENB/116929/2010, EXPL/EMS-SIS/2215/2013, scholarship SFRH/BD/91192/2012 and scholarship SFRH/BD/89077/2012 from FCT (Science and Technology Foundation), COMPETE, QREN and European Union (FEDER). The authors are also very grateful to Dr. Mónica Oliveira (Strathclyde University), Professor Takuji Ishikawa and Professor Takami Yamaguchi (Tohoku University) for their suggestions and support to this research work.

A few detailed studies have been performed in complex in vitro microvascular networks composed by bifurcations and confluences. The main purpose of the present work is to numerically simulate the flow of two distinct fluids through bifurcation and confluence geometries, i. e red blood cells (RBCs) suspended in Dextran40 with about 14% of heamatocrit and pure water. The simulations of pure water and RBCs flows were performed resorting to the commercial finite volume software package FLUENT. A well known hemodynamic phenomenon, known as Fahraeus-Lindqvist effect [1, 2], observed in both in vivo and in vitro studies, results in the formation of a marginal cell-free layer (CFL) at regions adjacent to the wall [3]. Recently, studies have shown that the formation of the CFL is affected by the geometry of the microchannel and for the case of the confluences a CFL tend to appear in the middle of the microchannel after the apex of the confluence [4, 5]. By using the CFL experimental data, the main objective of this work is to implement a CFL in the numerical simulations in order to obtain a better understanding of the effect of this layer on the velocity profiles.

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.

O artigo deve também estar associado ao Departamento de Electrotécnia, Tecnologia Mecânica e Química In the present work, in vitro blood flowing through a bifurcation microchannel was studied. The aim was to measure the Trajectories of the cell-free layer (CFL) by using different methods, i. e., a manual and two automatic methods. The authors acknowledge the financial support provided by: PTDC/ SAU-BEB/108728/2008, PTDC/SAU-BEB/ 105650/2008, PTDC/EMEMFE/099109/2008 and PTDC/SAU ENB/116929/2010 from the FCT (Science and Technology Foundation) and COMPETE, Portugal.

Human blood is a multiphase biofluid primarily composed by the deformable red blood cells (RBCs) suspended in plasma. Because the complex structure of RBCs, blood exhibits unique flow characteristics on micro-scale level, due to their complex biochemical mechanisms and their response to both shear and extensional flow, which influence the rheological properties and flow behaviour of blood [1,2]. In the past years in vitro blood studies have been extensively performed and some important physiological phenomena, such as Fahraeus and Fahraeus-Lindqvist effect, were revealed [1,3]. This pioneer studies performed by Fahraeus and Fahraeus-Lindqvist in straight glass microchannels [4] revealed that for narrow tubes (diameter

Over the years micro-visualization techniques have been used to investigate in vitro blood flow through straight microchannels with dimensions close to in vivo capillaries. However, a few detailed studies have been performed in complex in vitro microvascular networks composed by diverging and converging bifurcations. The main purpose of present work is to show the application of a confocal micro-PTV system to track both flourescent particles and red blood cells (RBCs) through a rectangular polydimethysiloxane (PDMS) microchannel with a confluence. The measurements of the flow behaviour of trace particles suspended in pure water and RBCs in concentrated suspensions were performed in the surroundings of a confluence. After performing simulations with the commercial finite element software package POLYFLOW®, some experimental results were compared with the numerical ones. Experimental results for pure water were in a good agreement with numerical results. Overall, the RBCs velocities were higher than those for fluorescent particles which suggest that RBC deformability and cell-free layer formation around the apex of the confluence may play an important role on the observed deviations The authors acknowledge the financial support provided by: PTDC/SAU-BEB/108728/2008 and PTDC/EME-MFE/099109/2008 from the FCT (Science and Technology Foundation) and COMPETE, Portugal.

Arthrosclerosis means literally “arteries hardening”. However, arthrosclerosis it is a generic term that is related with three patterns of vascular diseases, which have the hardening and loss of elasticity of the arteries walls as a common factor [1]. The dominant pattern is atherosclerosis, characterized by the formation of atheroma, which is comprised by fibrous plaques that generally exhibit a centre rich in lipids. In the present work, the flow of blood in a cylindrical channel, containing an atheroma at the walls, has been numerically studied using the finite-element software package POLYFLOW®. In the simulations, blood was considered an incompressible homogenous fluid and the flow regime was the laminar regime. The rheology of the mentioned fluid was described by distinct constitutive equations [2] - constant viscosity, power-law model and Carreau model. The local behaviour of properties such as pressure, interstitial velocities, shear rate and shear stress was explored in the present investigation. The local behaviour of these properties can help to understand the formation and detachment of thrombi.

Wall shear rates and pressure developed in circulatory system play an important role on the development of some clinical problems such as atherosclerosis and thrombosis. In the present work, blood flow behaviour was numerically studied in simplified domains and several relevant local properties were determined. The stenosis degree was varied in the distinct studied channels and blood rheology was described by three different models – constant viscosity, power-law model and Carreau model. Pressure attains maximum values in the wall of the atheroma and shear rates achieved maximum values in the top of the atheroma. It was also observed that, with the studied flows, the predictions for velocity and shear rate using non-Newtonian models were very similar. This observation can be explained by the magnitude of the obtained shear rates. The authors acknowledge the financial support provided by: PTDC/ SAU-BEB/108728/2008 and PTDC/SAU-BEB/105650/2008 from the FCT (Science and Technology Foundation) and COMPETE, Portugal.

This paper presents microflow visualizations of both pure water and red blood cells (RBCs) in a converging bifurcation. The visualizations are a combination of results obtained from a confocal micro-PTV system and an image analysis technique known as “Zproject” from ImageJ. Our preliminary qualitative results suggest that the cell-free layer that is formed in middle of the microchannel (after confluence apex) may play an important role on RBCs trajectories. The authors acknowledge the financial support provided by: 2007 GlobalCOE Program, Japan; PTDC/SAU-BEB/108728/2008, PTDC/SAU-BEB/105650/2008 and PTDC/EME-MFE/099109/2008 from the FCT (Science and Technology Foundation) and COMPETE, Portugal.

The blood flow dynamics in microcirculation depends strongly on the microvascular networks composed with short irregular vessel segments which are linked by numerous bifurcations. This paper presents the application of a confocal micro-PTV system to track RBCs through a rectangular polydimethysiloxane (PDMS) microchannel with a bifurcation. By using a confocal micro-PTV system, we have measured the effect of bifurcation on the flow behaviour of both fluorescent particles diluted in pure water and RBCs in concentrated suspensions. After performing simulations with the commercial finite element software package POLYFLOW, some experimental results were compared with the numerical results and the limitations of these simulations were outlined. This study was supported in part by the following grants: Grant-in-Aid for Science and Technology (BII/UNI/0532/EME/2008, PTDC/SAU-BEB/108728/2008, PTDC/SAUBEB/ 105650/2008 and PTDC/EME-MFE/099109/2008) from the Science and Technology Foundation (FCT) and COMPETE, Portugal and Grant-in-Aid for Scientific Research (S) from the Japan Society for the Promotion of Science (JSPS; No.19100008). We also acknowledge the support from the 2007 Global COE Program “Global Nano-Biomedical Engineering Education and Research Network”. The authors would like also to thank Dr. C. Balsa for his valuable assistance and support for the MATLAB numerical calculations and Ms. B. Oliveira, Ms. D. Cidre and Mr. M. Lagoela for their valuable technical assistance in this research work.

Micro-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®.

Vários estudos revelaram que a informação obtida sobre as propriedades reológicas do sangue em capilares de vidro difere da situação in vivo (Pries et al. 1994). As principais causas potenciais para estas discrepâncias podem ser devidas à camada superficial formada por células endoteliais e às redes microvasculares compostas por segmentos de vasos irregulares e curtos que estão ligados por numerosas bifurcações e convergências (Maeda 1996).O principal objectivo deste trabalho é analisar as propriedades não-Newtonianas do sangue durante o escoamento em modelos microvasculares. Neste estudo foi utilizado o método de litografia suave para fabricar microcanais bifurcados com secção rectangular em polidimetisiloxano (PDMS). Usando um sistema “confocal micro-PTV” (Lima et al. 2008), mediu-se o efeito da bifurcação no escoamento de partículas fluorescentes diluídas em água pura e em suspensões concentradas de eritrócitos. Os resultados experimentais obtidos pelo sistema “confocal micro-PTV” foram complementados por modelos hemodinâmicos computacionais. Após a execução de várias simulações com o software comercial de elementos finitos POLYFLOW®, compararam-se alguns resultados experimentais com resultados numéricos. Os resultados preliminares sugerem que as trajectórias dos eritrócitos podem sofrer alterações na direcção transversal ao escoamento devido à colisão com os eritrócitos que se encontram na vizinhança do ponto de divergência da bifurcação (Brigitte et al. 2009).

Neste trabalho estudou-se numericamente o escoamento isotérmico laminar completamente desenvolvido de fluidos Newtonianos e não-Newtonianos em canais de permutadores de calor de placas do tipo chevron com ângulo de corrugação igual a zero (canais do tipo sinusoidal). Este estudo foi efectuado recorrendo ao software de dinâmica de fluidos computacional, baseado no método de elementos finitos, POLYFLOW®. Para cada uma das geometrias estudadas (com valores de razão de aspecto de canal entre 0 e 1), estudaram-se os factores de fricção de Fanning, f, tendo sido determinadas, para cada um dos canais, curvas de fricção únicas (f Reg = K) para os fluidos Newtoniano e não-Newtonianos. Para os fluidos Newtonianos, o coeficiente K foi modelado através de uma função da razão de aspecto de canal e, uma vez que K depende do factor de forma K0 e da tortuosidade, τ, através da expressão K = K0τ2, propuseram-se também relações entre K0 e τ com a razão de aspecto de canal.

Food fluids are frequently processed in plate heat exchangers (PHEs) and usually behave as non-Newtonian fluids, this behaviour being scarcely considered for PHEs design purposes. Moreover, many food fluids processed in PHEs have a high viscosity and, therefore, data obtained in laminar flow regime is useful to practical applications. The thermal-hydraulic performance of PHEs is strongly dependent on the physical properties of the fluid and on the geometrical properties of the plates namely, on the corrugation angle and on the channel aspect ratio. The mostly widely used PHEs have corrugations of the chevron type with an area enlargement factor defined as the ratio between the effective plate area and projected plate area close to 1.17. In the present work non-isothermal laminar flows of Newtonian and power-law fluids through cross-corrugated chevron-type plate heat exchangers are studied numerically in terms of the geometry of the channels. The plates area enlargement factor was a typical one (1.17), the corrugation angle varied between 30º and 60º and the flow index behaviour, n, between 0.25 and 1. The numerical calculations were performed using the commercial finite element software package POLYFLOW®. The equations solved were the conservation of mass, momentum and energy equations for laminar incompressible flow of Newtonian and power-law fluids. The simulations were performed using channels containing seven consecutive unitary cells, since thermal and hydraulic fully developed flows were achieved in the fifth or sixth consecutive cell, as described in previous works. Coefficient K from the friction curves fRe = K compares very well with experimental and semi-theoretical data for all (seven) values of corrugation angle. Nusselt number reaches a maximum in the interior of the studied corrugation angle range, for a fixed Reynolds, Re, number. Shear thinning effects greatly affect the thermal-hydraulic performance of the plate heat exchangers

Os fluidos alimentares com viscosidade elevada são frequentemente processados em permutadores de calor de placas (PCPs) em regime laminar. O desempenho termo-hidráulico dos PCPs do tipo chevron depende das características geométricas dos mesmos, nomeadamente do ângulo das corrugações sinusoidais das placas, do espaçamento entre placas e do factor de incremento de área, definido como a razão entre a área real das placas e a sua área projectada. Apesar desta dependência ser consensualmente reconhecida, as correlações termo-hidráulicas existentes na literatura para este tipo de equipamentos não incluem todos os parâmetros geométricos. Neste trabalho é apresentado um estudo sobre a influência dos parâmetros geométricos das placas e das propriedades físicas do fluido no desempenho dos PCPs, sendo os valores obtidos comparados com dados experimentais da literatura. O estudo numérico é efectuado utilizando o software comercial de mecânica de fluidos computacional baseado no método de elementos finitos POLYFLOW®, sendo resolvidas as equações de conservação de massa, momento e energia para fluxos laminares incompressíveis. Sendo este um problema não linear, a sua resolução passa por um processo iterativo, baseando-se o critério de convergência no erro relativo cometido em cada iteração nos campos de velocidade e temperatura. A resolução numérica do problema foi efectuada num computador Dell Workstation PWS530 com 1GB de RAM. A validação do modelo usado na resolução deste problema foi efectuada recorrendo a um caso limite existente nos PCPs - ângulo de corrugação = 90º - para o qual estão disponíveis na literatura soluções analíticas. A diferença máxima obtida, entre os valores numéricos e analíticos, foi de 0.2%.

Afectar ao Departamento de Tecnologia Química e Biológica - Docente Ricardo Dias e ao docente Carlos Balsa do Departamento de Matemática Utilizando o software comercial de mecânica de fluidos computacional POLYFLOW® estudou-se o escoamento laminar isotérmico de um fluido Newtoniano com propriedades físicas constantes no interior de canais de permutadores de calor de placas corrugadas. Foi estudada a dependência da tortuosidade e factor de forma dos canais com o ângulo de corrugação e factor de incremento de área. O coeficiente das relações f-Re foi bem descrito por correlações da literatura para valores de factor de incremento de área usuais. A tortuosidade é utilizada por fabricantes destes equipamentos na determinação de perdas de carga e coeficientes convectivos de transferência de calor.

Physical processing brings about irreversible textural and sensorial properties of nearly all the fluids on the food industry. In liquid food processing, plate heat exchangers (PHEs) are commonly used in the heating or cooling stages due to their advantages, such as high efficiency, ease of maintenance and cleaning and flexibility on account of the modular design. Although, laminar or low Reynolds number flows are usually obtained when liquid foods are processed in PHEs, the behaviour is strongly dependent on the geometrical properties of the chevron plates, namely on the corrugation angle and channel aspect ratio. Fanning friction factor correlations can be helpful on the calculation of wall shear rates developed during the flow of Newtonian or power law fluids inside the PHE channels, which then allows the viscosity evolution of the liquids to be predicted. This is important because most food stuffs exhibit a complex rheological behaviour, the thermal-hydraulic performance of PHEs being greatly dependent on the shear thinning or thickening properties of the processed fluids. The aim of this work is to study the influence of geometrical properties of chevron plates on the behaviour of power-law fluids during thermal treatment. In order to do so, numerical simulations were performed using 3D geometries, with different geometric properties, that represent a channel of chevron-type PHE. In a first step, the numerical results obtained with Newtonian fluids were compared with data from the literature and a good agreement was found. For thermal and hydraulic fully developed non-Newtonian flows, Nusselt numbers and Fanning friction factors were estimated and the impact of the geometrical properties and flow behaviour index on the wall shear rates was also studied. The values of the flow behaviour index and geometrical properties play an important role on the maximum observed for the ratio between the Nusselt number and Fanning friction factor.

Associar ao Dep. de Tecnologia Química e Biológica - docente Ricardo Dias. Este artigo não pode estar disponível para ninguém uma vez que ainda é um trabalho em curso associado ao meu doutoramento (não sei se colocar restricted acess é suficiente para ti...) Thermal-hydraulic performance of plate heat exchanger is strongly dependent on their geometrical properties and variable viscosity effects. On the laminar region, numerical simulations with power-law fluids were performed in order to understand the influence of corrugation angle, shear thinning and thickening effects on the performance of these equipments. Corrugation angles of plate heat exchangers passages were varied between 15º and 85º and the flow index behaviour of power-law fluids between 0.85 and 1.5. The thermal-hydraulic performance of the different passages was analysed resorting to the area goodness factor. Maximum area goodness factors were obtained on corrugation angles close to 59º or 75º, depending on the flow index behaviour of the fluid. Due to the high shear rates developed on the complex passages of plate heat exchangers, shear thinning effects greatly enhances the performance of this equipments.

Plate heat exchangers (pHE's) are widely used in chemical, pharmaceutical, biochemical processing, food, and dairy industries, offering this type of equipments several advantages like the low space requirement, high efficiency, easy cleaning and maintenance, low fouling tendency and high flexibility (Reppich, 1999). Heat transfer in a PRE is strongly dependent on geometrical properties of the chevron plates, namely on corrugation angle, area enlargement factor and channel aspect ratio. Besides tilese factors, heat transfer is also influenced by the local variation of temperature dependent physical properues and especially the variable viscosity effects (Kaka, and Liu, 2002; Manglik and Ding, 1997). The design of this heat exchange equipment involve the determination of optimum pressure drops being referenced in the literature several studies directed to this subject (Bassiouny and Martin, 1984; Leuliet et aI., 1990; Stasiek et aI., 1996; Mehrabian and Poulter, 2000).

In this study, CFD calculations were made in order to analyze the thermal behaviour of a power-law fluid in the channels of plate heat exchangers with corrugation angles of 30º and 60º. For the observed laminar flow, the numerical results show the absence of a typical local temperature profile in the 3D channel. Local Nusselt numbers and transversal variations of viscosity along the plate heat exchangers were studied and simulations considering and discarding the influence of temperature on the non-Newtonian fluid viscosity were performed for the two geometries and the impact of these variations on the thermal correlations was analyzed., info:eu-repo/semantics/publishedVersion

Thermal processing is widely used in the food industry mainly to improve quality and safety of food products. The investigation of heat transfer problems of non-Newtonian fluids during heating and cooling in heat exchangers is of major interest since the main factor limiting heat transfer is the viscous behaviour of these fluids. Therefore, the knowledge of the interface heat transfer coefficients is important in the design of food processes and processing equipment. In the present work, simulations of stirred yoghurt cooling in a plate heat exchanger were performed using computational fluid dynamics (CFD) calculations and the obtained results were compared with experimental data. Simulations were carried out using the commercial finite element method package POLYFLOW, being the geometrical domain the representation of a single 3D channel of the plate heat exchanger with a 30º corrugation angle. The correlation obtained numerically was compared to the one obtained from previous experimental work and they were found to be very similar to the experimental one. The constitutive model, under the assumptions used, was found to be a very good approximation for predicting the convective coefficients of stirred yoghurt during cooling in a plate heat exchanger.

Research on heat transfer of non-Newtonian fluids during thermal processing is useful to optimise the heat exchanger design, as well as to define quality levels of the final product. In the present study, a nonisothermal and non-Newtonian flow in plate heat exchangers was simulated numerically, in order to evaluate the influence of corrugation angle on the thermal and hydrodynamics characteristics of yoghurt during cooling in a plate heat exchanger (PHE). Cooling treatment of stirred yoghurt is usually carried out in PHEs since these equipments are suitable for liquid-liquid heat transfer duties that require uniform and rapid cooling or heating. In this operation, two mechanisms of heat transfer occur: conduction, in the plates, and convection inside the channels. The set of equations that describe mathematically the problem were the Navier-Stokes equations, for incompressible and stationary flow, and Fourier’s law for the conduction problems. Additionally, a constitutive model that describes the rheological properties of yoghurt under the cooling conditions has to be established in order to define totally the problem. The used model was proposed by Afonso et al. (2003) and takes into account the influence of shear rate and temperature

Thermal processing and manufacturing in the food industry involves heating and cooling of highly viscous fluids. In general, these fluids exhibit complex flow patterns and are dependent on temperature, shear rate, duration of shear and elastic properties. Since the main factor limiting heat transfer is the viscous behaviour of the fluids, models that can capture this are of major interest to optimize heat exchanger design and to proper control of the manufacturing processes. A typical non-Newtonian food fluid is yoghurt, the rheological properties of which are influenced by several factors related with the physical nature of yoghurt and the processing conditions. Rheologically, stirred yoghurt shows a typical Herschel-Bulkley-type behaviour, with a yield stress at low shear rates and a power-law behaviour at higher stresses. Also, its viscosity varies from being highly temperature dependent to being almost temperature independent, depending whether it is being processed at temperatures above or below 22 ºC, respectively. The aim of the first part of this work is to simulate the non-isothermal flow of stirred yoghurt in a plate heat-exchanger. In order to do so, three problems were solved simultaneously: two of heat conduction in the plates and one on non-isothermal flow in the channel. The simulation was carried out using POLYFLOW, the geometrical domain being constituted by three three-dimensional components: superior and inferior plates and the flow channel. The corrugation of the plates was assumed to have a sinusoidal variation along the heat-exchanger.

Thermal processing and manufacturing in the food industry involves heating and cooling of highly viscous fluids. In general, these fluids exhibit complex flow patterns and are dependent on temperature, shear rate, duration of shear and elastic properties. Since the main factor limiting heat transfer is the viscous behaviour of the fluids, models that can capture this are of major interest to optimize heat exchanger design and to proper control of the manufacturing processes. A typical non-Newtonian food fluid is yoghurt, the rheological properties of which are influenced by several factors related with the physical nature of yoghurt and the processing conditions. Rheologically, stirred yoghurt shows a typical Herschel-Bulkley-type behaviour, with a yield stress at low shear rates and a power-law behaviour at higher stresses. Also, its viscosity varies from being highly temperature dependent to being almost temperature independent, depending whether it is being processed at temperatures above or below 22 ºC, respectively. The aim of the second part of this work is to compare the correlations concerning stirred yoghurt convective heat transfer, obtained from numerical approaches, to the ones obtained from previous experimental work carried out in a plate heat exchanger during the cooling stage. These correlations included both rheological and thermal aspects, taking into account the complex flow behaviour of stirred yoghurt.