Submitted by Gustavo Nascimento (gustavo.diniz@ufcg.edu.br) on 2018-02-07T12:18:32Z No. of bitstreams: 1 RAISSA MENEZES DE SOUSA - DISSERTAÇÃO PPGEQ 2016.pdf: 3574277 bytes, checksum: fc3f9b72fefbf347de741a28f9bed6b6 (MD5) / Made available in DSpace on 2018-02-07T12:18:32Z (GMT). No. of bitstreams: 1 RAISSA MENEZES DE SOUSA - DISSERTAÇÃO PPGEQ 2016.pdf: 3574277 bytes, checksum: fc3f9b72fefbf347de741a28f9bed6b6 (MD5) Previous issue date: 2016 / Capes / Diversas tecnologias tem sido utilizadas para tratamento da água produzida (mistura água/óleo). Os processos de separação por membranas (PSM) apresentam vantagens sobre outros métodos tradicionais de separação, contudo alguns problemas operacionais atrelados aos PSM, como polarização por concentração, fouling e formação da camada gel, causam o decréscimo do fluxo permeado com o tempo. Sob condições onde os efeitos da polarização por concentração são mínimas, o escoamento será afetado pela pressão transmembrana. Assim, foi realizado um estudo da fluidodinâmica de uma mistura água/óleo utilizando membrana cerâmica, com auxílio do software ANSYS CFX® Release 15.0. Foi desenvolvido um modelo matemático com um fluido incompressível escoando em regime turbulento. As equações de momento linear, conservação e transporte de massa foram resolvidas com o auxílio de uma malha estruturada. Os resultados da simulação apresentaram os seguintes resultados: a modelagem matemática previu numericamente o processo de filtração tangencial via membrana cerâmica no tratamento de água produzida; observou-se que em vazões muito baixas há uma maior concentração de óleo próximo a membrana enquanto em vazões elevadas, o óleo fica disperso na mistura, onde há a quebra da camada limite; os efeitos viscosos não apresentam diferenças significativas nos perfis de concentração e velocidade. / Several technologies have been used to treat the water produced (water / oil mixture). Membrane separation processes (PSM) have advantages over other traditional methods of separation, however, some operational problems related to PSM, such as polarization by concentration, fouling and formation of the gel layer, cause a decrease in permeate flow over time. Under conditions where the effects of concentration polarization are minimal, the flow will be affected by transmembrane pressure. Thus, a study of the fluid dynamics of a water / oil mixture using ceramic membrane was carried out with the help of ANSYS CFX® Release 15.0 software. A mathematical model was developed with an incompressible fluid flowing in a turbulent regime. The equations of linear momentum, conservation and mass transport were solved with the aid of a structured mesh. The results of the simulation presented the following results: mathematical modeling numerically predicted the process of tangential filtration via the ceramic membrane in the treatment of produced water; it was observed that in very low flows there is a higher concentration of oil near the membrane while at high flow rates the oil is dispersed in the mixture, where the boundary layer is broken; the viscous effects do not present significant differences in the concentration and velocity profiles.

Submitted by Maria Medeiros (maria.dilva1@ufcg.edu.br) on 2018-09-13T15:23:53Z No. of bitstreams: 1 JOSEDITE SARAIVA DE SOUZA - TESE (PPGEP) 2014.pdf: 5001055 bytes, checksum: b013c909ca0b39d1d6548d97afc484ce (MD5) / Made available in DSpace on 2018-09-13T15:23:53Z (GMT). No. of bitstreams: 1 JOSEDITE SARAIVA DE SOUZA - TESE (PPGEP) 2014.pdf: 5001055 bytes, checksum: b013c909ca0b39d1d6548d97afc484ce (MD5) Previous issue date: 2014-02-24 / Tecnologias inovadoras são necessárias para atender as normas de tratamento de águas produzidas cada vez mais rígidas, visto que a maioria dos processos de separação é limitada a partículas superiores a 10 m. Os processos de separação utilizando membranas cerâmicas veem despertando grande interesse da comunidade acadêmica e industrial. Mesmo assim, têm sido reportados poucos estudos, especialmente numéricos, referentes à aplicação de membranas inorgânicas na separação água/óleo. Nesse sentido, realizou-se um estudo da fluidodinâmica do escoamento de fluidos em tubos permeáveis (membrana cerâmica porosa tubular), em regime laminar. As equações de conservação de massa, momento linear e transporte de massa foram resolvidas com auxilio de uma malha estruturada usando o pacote comercial ANSYS CFX 12. A velocidade de permeação local foi determinada usando o modelo das resistências em série. A resistência específica da camada polarizada foi obtida pela equação de Carman-Kozeny. Os resultados numéricos foram comparados e avaliados utilizando-se de resultados analíticos e numéricos disponíveis na literatura apresentando boa concordância entre si. Os resultados numéricos indicam que, ao se utilizar o módulo de separação casco/membrana tubular proposto, há um favorecimento da transferência de massa e uma redução da espessura da camada limite polarizada. / Innovative technologies are needed to attend the requirements increasingly strict for produced waters treatment, whereas the most separation processes are limited to particles larger than 10 μm. Separation processes using ceramic membranes is attracting great interest from academic and industrial community. Nevertheless, it has been reported few studies, especially numerical, regarding the inorganic membranes application in the separation water/petroleum. Accordingly, a study of fluid-flow dynamics in porous tubes (tubular porous ceramic membrane) was performed, in a laminar regime. The mass, momentum and mass transport conservation equations were solved with the aid of a structured mesh using ANSYS commercial package CFX 12. The permeation velocity local was determined by using the resistance in series model. The specific resistance of the polarized layer was obtained by Carman-Kozeny equation. The numerical results were compared and evaluated using analytical and numerical results available in the literature presenting good agreement with each other. The numerical results indicate that, using the proposed separation module (shell / tube membrane), there is a mass transfer favoring and a reduction in the thickness boundary layer polarized.

Este trabalho trata de um estudo experimental da transferência de calor e de massa de um condensador evaporativo, bem como, da relação existente entre as grandezas envolvidas durante a sua operação. Para o desenvolvimento da pesquisa foi construído um condensador evaporativo de pequeno porte com dimensões proporcionais a condensadores comercialmente fabricados no Brasil para operar com R-22 como fluido refrigerante. Este condensador tem 35 colunas e 12 fileiras de tubos de cobre de 6,35 mm de externo e opera junto a uma instalação que proporciona o escoamento de R-22 por termossifao. O distribuidor de água também foi construído em cobre e o eliminador de gotas em alumínio, assim como a estrutura do condensador. As laterais e a bandeja de recolhimento de água foram construídas em vidro para permitir a visualização do escoamento da água que e aspergida sobre os tubos. A fim de variar as condições operacionais, este condensador foi acoplado a um ventilador centrifugo acionado por um conversor de freqüência e a um circuito que permitiu a variação da vazão de água aspergida sobre os tubos. Dos ensaios resultaram 79 amostras de medição, que serviram para verificar a relação existente entre grandezas, bem como avaliar os coeficientes de transferência de calor e massa. Foram determinados os coeficientes de transferência de calor médio e local para o R-22. Alem disso, foram verificadas as regiões onde ocorrem o dessuperaquecimento, a mudança de fase e o subresfriamento do fluido refrigerante, e foram confrontados os coeficientes globais de transferência de calor obtidos a partir dos dados experimentais com aqueles obtidos por correlações para as regiões de condensação e subresfriamento. Destas investigações, resultou uma correlação para o coeficiente global de transferência de calor que visa determinar esta grandeza através das condições operacionais e das características geométricas do condensador. O Maximo desvio encontrado entre os valores provenientes dos dados experimentais e aqueles calculados pela correlação foi inferior a 10%. / This work presents an experimental heat and mass transfer study of an evaporative condenser, as well as, the relationship between measured quantities obtained during its operation. A small scale evaporative condenser was built in agreement to the real size equipment geometric similarity. The small scale condenser has a bundle of 210 copper tubes, with the outer diameter equal to ¼ inch, which were arranged in 35 columns and 6 rows and operating connected to the thermosifon facility that promote R-22 flow. The spray water distributor is also built on copper and the drift eliminator on aluminum, as well as the evaporative condenser structure. This condenser bounds were constructed as a glass enclosure to allow for the spray water flow visualization. To evaluate the operational conditions, the equipment was attached to a centrifugal fan controlled by a frequency inverter and a spray water circuit which allows for water quantity changing. From the carried out tests, 79 measuring samples were obtained and used to verify the quantities relationship, as well as, to evaluate the heat and mass transfer coefficients For the R-22 were determined the local and average heat transfer coefficients. Furthermore, the dessuperheating, condensation and subcooling regions were verified and compared both, the experimental overall heat transfer coefficient and those calculated by correlations at condensation and subcooling zones. From these investigations a correlation for the overall heat transfer coefficient is proposed. Its application allows determining the coefficient using the operational conditions and the geometric condenser features. The higher deviation found between the experimental data and the presented correlation is lower to 10%.

Este trabalho apresenta o desenvolvimento e implementação computacional de técnicas de otimização de topologia para problemas governados pela equação de Poisson. O método numérico utilizado para solução numérica das equações foi o método dos elementos de contorno (MEC). Para tanto, três metodologias foram desenvolvidas. A primeira é direcionada à aplicação de algoritmos genéticos (AG) para investigar como um domínio inicialmente preenchido com cavidades aleatórias evolui durante um processo de otimização e verificar a possibilidade de se extrair topologias ótimas a partir da interpretação da solução encontrada. Os contornos externos permanecem fixos enquanto as posições e as dimensões das cavidades são otimizadas com o objetivo extremizar uma função custo especificada. O desempenho do algoritmo proposto é ilustrada com uma série de exemplos e os resultados são discutidos. A segunda metodologia apresenta um algoritmo numérico para otimização topológica baseado na avaliação da derivada topológica (DT), adotando a energia potencial total como função custo. Este procedimento é uma alternativa às tradicionais técnicas de otimização, evitando assim soluções de projeto com densidade de material intermediária. Sólidos com comportamento anisotrópico são estudados sob condições de contorno de Robin, Neumann e Dirichlet. Uma transformação linear de coordenadas é utilizada para mapear o problema original e suas condições de contorno para um novo domínio equivalente isotrópico, onde o procedimento de otimização é aplicado. A solução otimizada é então transformada de volta ao domínio original. A metodologia proposta mostrou-se particularmente atrativa para resolver esta classe de problemas já que o MEC dispensa o uso de malha no domínio, reduzindo significantemente o custo computacional. Na última parte deste trabalho foi implementada uma formulação de sensibilidade topológica para problemas de otimização de transferência de calor e massa simultâneos. Como as sensibilidades para cada equação diferencial são diferentes, utiliza-se um coeficiente de ponderação para compor a sensibilidade do problema acoplado. Isto permite a imposição de distintos fatores para cada problema, de acordo com uma prioridade especificada. Diversos exemplos são apresentados e seus resultados comparados com os da literatura, quando disponíveis, a fim de validar as formulações propostas. / This work presents the computational development and implementation of topology optimization techniques for problems governed by the Poisson equation. The boundary element method was the numerical technique chosen to solve the equations. Three different methodologies were developed aiming this objective. The first methodology is directed to the application of genetic algorithms to investigate how a domain previously populated with randomly placed cavities evolves during the optimization process, and to verify the resemblance of the final solution with a optimal design. The external boundaries remain fixed during the process, while the location and dimension of the cavities are optimized in order to extremize a given cost function. The performance of the proposed algorithm is verified with a number of examples and the results are discussed. The second methodology presents a numerical algorithm for topology optimization based on the evaluation of topological derivatives, using the total potential energy as the cost function. This procedure is an alternative to the traditional optimization techniques, avoiding design solutions containing intermediary material densities. Solids with anisotropic constitutive behavior are studied under Robin, Neumann and Dirichlet boundary conditions. A linear coordinate transformation approach is used to map the original problem into an isotropic one, where the optimization is carried out. The final solution is then mapped back to the original coordinate system. The proposed method was found to be an attractive way to solve this class of problems, since no interior mesh is necessary, which reduces significantly the computational cost of the analysis. In the last part of the present work the topological derivative approach was further developed to deal with the optimization of problems under simultaneous heat and mass transfer. Since the sensitivities for each differential equation are different, a weighting factor was used to evaluate the final sensitivities of the coupled problem. This allows the imposition of different priorities for each problem Several examples are presented and their results are compared with the literature, when available, in order to validate the proposed formulations.

Afin de prédire l’évolution de la composition chimique du laitier dans différents procédés sidérurgiques, un modèle CFD a été développé. Les coefficients de transfert de masse sont estimés à partir des modèles basés sur les paramètres physico-chimiques et hydrodynamiques, comme par exemple la diffusivité des espèces chimiques et la divergence de l’interface. Ces modèles ont été développé pour la prédiction du transfert gaz-liquide où le les nombres de Schmidt (Sc=ν⁄D) sont relativement faible (Sc≈200). Par contre, les procédés industriels ont un nombre de Sc considérablement plus importante, de l’ordre de 103 à 104. Pour évaluer la pertinence de ces modèles, l’hydrodynamique au voisinage d’une interface liquide-liquide a été étudiée. Un modèle CFD et des mesures par l’anémométrie laser (LDA) ont été utilisés pour calculer et valider les champs de vitesse d’une maquette à eau d’une lingotière de coulée continue (CC).Le modèle de transfert de masse d’une lingotière de coulée continu industriel nous a montré que les coefficients de transfert de masse ne sont pas distribués de manière homogène, et les propriétés physiques du laitier ne doivent pas y être non plus. Cette distribution non-homogène a été confirmée par des essais physiques. Les écoulements calculés numériquement ont été utilisé pour prédire les coefficients de transfert de masse entre les deux phases liquide. Ces paramètres seront utilisés comme donnée d’entré pour un modèle de thermodynamique afin de prédire l’évolution de la composition chimique du laitier. / In order to characterize the mass transfer coefficients (MTC) of different species across liquid steel/slag interface, a multiphase Computational Fluid Dynamic (CFD) model was developed. MTC’s are estimated from models based on physicochemical and hydrodynamic parameters, such as mass diffusivity, interface shear and divergence strength. These models were developed for gas-liquid interactions with relative low Schmidt (Sc=ν⁄D) numbers (Sc≈200). However, the industrial processes involve mass transfer of chemical species with Sc number ranging from 103 to 104. To evaluate the applicability of these existing models, the fluid flow in the vicinity of a liquid/liquid interface is investigated. Computational Fluid Dynamic (CFD) and Laser Doppler Anemometry (LDA) were used to calculate and measure the velocity field on a continuous casting (CC) water model configuration. The work provides new insights and original measures to understand the fluid flow near liquid-liquid interfaces.The mass transfer model of an industrial continuous casting mold showed that the mass transfer coefficients are not homogeneously distributed, and slag properties should follow this trend. This non-homogeneity was confirmed by physical experiments performed with a water model of a CC configuration and its CFD representation. The calculated flow was used to predict the MTC and the interface area between phases, since the interface is constantly moving. These parameters will be the input of thermodynamic models to predict slag composition and viscosity. This methodology is currently under validation, and it will also be applied to improve steel plant performance in the desulphurization process.

Les performances des bassins de stations d'épuration sont directement liées au transfert d'oxygène de bulles d'air généralement insufflées par des aérateurs vers des micro-organismes capables de détériorer certains polluants des eaux usées. Une prédiction précise du transfert de matière de l'oxygène dans ces bassins reste toutefois encore délicate. L'objectif de cette thèse est de développer des outils d'analyse aux interfaces afin de mieux appréhender localement les différents mécanismes régissant le transfert de matière gaz/liquide. Cette simplification se base sur l'étude du transfert d'oxygène : (i) pour une bulle millimétrique isolée, (ii) dans un liquide au repos, (iii) sans particules solides (système diphasique). À l'aide de techniques de visualisation, il est possible d'évaluer l'influence de la composition de la phase liquide sur le coefficient de transfert côté́ liquide par PLIF (Fluorescence Induite par un Plan Laser) et sur le comportement hydrodynamique de la bulle (diamètre, vitesse, forme) par caméra rapide. L'influence du diamètre de la bulle sur le transfert de matière visualisé est également évaluée. Le coefficient de transfert côté liquide n'étant pas le seul paramètre représentatif du transfert de matière, des techniques expérimentales spécifiques sont développées afin d'estimer avec précision le coefficient de diffusion de l'oxygène dans la phase liquide d'intérêt ainsi que sa concentration à saturation au travers d'une interface gaz/liquide plane en cellule de Hele-Shaw. Via ces différentes techniques expérimentales développées durant la thèse, une cartographie précise de l'influence de la phase liquide sur le transfert d'oxygène est établie en évaluant dans un premier temps l'influence de certains composants isolés (sel, glucose, alcool, tensio-actifs, médicaments, etc.). Ainsi, il sera observé que certains composants, comme les tensio-actifs, peuvent fortement diminuer le transfert de matière. Les corrélations généralement utilisées afin de caractériser ce transfert de matière ne parvenant pas toujours à représenter de telles diminutions, ces résultats seront par la suite comparés à ceux obtenus dans des eaux de stations d'épuration afin d'approfondir la compréhension des différents mécanismes limitant ce transfert d'oxygène / The performance of tanks in sewage treatment plants is highly related to the oxygen transfer from air bubbles, usually injected through di��users, to microorganisms able to degrade pollutants contained in wastewaters. However, characterizing accurately the oxygen mass transfer in such processes is still a challenging issue mainly because of the liquid phase complexity. The aim of this PhD manuscript is to develop specific techniques to better understand the various mechanisms that locally govern the gas/liquid mass transfer process. This study focuses on the oxygen mass transfer, (i) from a single bubble, (ii) rising in a stagnant liquid, (iii) free from solid particles (biphasic system). Efficient visualization techniques allow the impact of the liquid phase composition on the liquid- side mass transfer coefficient (using PLIF (Planar Laser-Induced Fluorescence)) and on the bubble hydrodynamic behavior (bubble diameter, shape, velocity) using high-speed cameras to be evaluated. Moreover, the impact of the bubble diameter on the mass transfer visualized is considered. Since the liquid-side mass transfer coefficient is often not sufficient to fully characterize mass transfer, specific experimental techniques, based on planar gas/liquid interfaces in Hele-Shaw cells, are proposed to estimate the diffusion coefficient of oxygen and the oxygen saturation concentration in several liquids of interest. Using the visualization techniques developed during this PhD thesis, the impact of the liquid phase on the oxygen mass transfer is evaluated by introducing different compounds in the liquid phase (salts, glucose, alcohol, surfactants, drugs, etc.). It is interesting to note that some compounds, such as surfactants, can drastically bother the oxygen mass transfer. Since the correlations classically used to characterize mass transfer cannot explain such performance degradation, the results obtained (with liquids whose composition is known) are finally compared to those obtained with wastewater from sewage treatment plants to better understand the factors that can alter the oxygen mass transfer

Malgré une longue histoire de développement, l'hémodialyse (rein artificiel) possède encore quelques limitations, telles que la perte des propriétés initiales de la membrane en cours de traitement à cause du colmatage et la mauvaise élimination des toxines urémiques de taille moyenne. La présente étude fait partie d'un projet européen nommé BioArt dont le but est d'apporter des solutions à ces limites. Dans cet objectif, l'un des partenaires du projet a proposé le développement d'un nouveau concept de membrane double couche au sein de laquelle sont incorporées des particules adsorbantes. Une caractérisation complète de cette nouvelle membrane était alors nécessaire, plus précisément l'impact de la matrice mixte sur l'élimination des toxines urémiques de divers groupes devait être évalué, ainsi que la propension du matériau membranaire à se colmater. Les études des phénomènes de colmatage sont classiquement menées à l'échelle macroscopique (faisceau de fibres creuses) sans analyse à l'échelle d'une fibre isolée. Le but premier de la présente thèse a alors été de proposer un dispositif permettant une étude du colmatage membranaire induit par la protéine à l'échelle microscopique. Un dispositif microfluidique transparent dans lequel la membrane polymère est insérée a été élaboré et mis en œuvre pour la filtration des protéines modèles : l'albumine de sérum bovin (BSA) et l'a-lactalbumine. Grâce au couplage avec la microscopie de fluorescence, différents modes d'adsorption des protéines sur la surface de la membrane ont été observés et liés aux variations des conditions hydrodynamiques à l'intérieur de la puce. Il a été constaté, sous certaines conditions, une différence dans l'accumulation de protéines entre l'entrée, le centre et la sortie du canal tandis que dans d'autres conditions cet effet s'annule. En outre, un phénomène inattendu, l'agrégation de l'a-lactalbumine, a été observé au cours de la filtration. La localisation dans le canal et la forme des agrégats dépendent également des conditions hydrodynamiques et de la pression transmembranaire appliquée. Dans le but d'optimiser la conception de la membrane vis à vis de son aptitude à éliminer des molécules de taille moyenne de la circulation sanguine, un modèle mathématique a été proposé. L'objectif du modèle était, en prenant en compte la présence de particules adsorbantes à l'intérieur de la membrane double couche, de rendre compte de la combinaison des trois mécanismes d'élimination du soluté : la convection, la diffusion et l'adsorption. Le modèle permet de prédire l'influence de divers paramètres tels que la diffusivité de la molécule, l'épaisseur de la membrane, la présence de la convection, la charge en particules adsorbantes, sur l'intensification des flux à travers la membrane. Le modèle semble être un outil utile pouvant être appliqué à l'optimisation de membranes pour l'élimination des toxines. / Despite a long history of development, the hemodialysis procedure (artificial kidney) still possesses some limitations, such as loss of the initial properties of the membrane due to fouling and poor removal of the middle sized uremic toxins. The present study is part of an European project named BioArt the aim of which was to overcome these limitations. In that objective, one of the partners of BioArt project reported on the development of the novel promising concept of double layer membrane with embedded adsorptive particles. A thorough characterization of the new membrane was then necessary, more precisely the extent to which mixed matrix layer can improve the removal of the uremic toxins from various groups needed to be evaluated, as well as the propensity of the membrane material to become fouled. The studies of the fouling phenomena are conventionally performed at the macro scale (bundle of hollow fibers) without insights of what is happening at the scale of an isolated fiber. Therefore, the primary aim of the present Thesis was to transfer the research of the protein-induced membrane fouling from the macro to the micro scale. A novel transparent microfluidics device with the polymeric membrane inside has been developed and applied for the filtration of model proteins: bovine serum albumin (BSA) and a-lactalbumin. Thanks to the coupling of the microchip with the fluorescent microscopy, different patterns of protein deposition on the membrane surface were observed and related to the variations in the hydrodynamic conditions inside the microchip. It was found that at certain conditions one may observe the difference in protein accumulation in the inlet, the middle, and the outlet of the channel while at other conditions this effect vanishes. Additionally, the unexpected phenomena of a-lactalbumin aggregation was observed over the course of filtration. The location and shape of the aggregates were also dependent on the hydrodynamic conditions and the applied transmembrane pressure. Aiming to address the problem of membrane design optimization for the enhancement of the middle molecules elimination from the bloodstream, a mathematical model, which accounts for the presence of adsorptive particles inside the complex double-layer membrane, has been proposed. The objective of the model was to understand the interplay of three solute removal mechanisms: convection, diffusion, and adsorption. The model allows predicting the influence of various parameters such as molecule diffusivity, membrane thickness, the presence of convection, content of adsorptive particles on the flux intensification across the membrane. The developed model seems to be a useful tool, which may be applied to design optimized membranes for the removal of toxins.

Ce travail est une investigation expérimentale de l’hydrodynamique, du transfert massique et du mélange induit par un panache de bulles dans des milieux de différentes viscosités. Dans l’industrie on est souvent confronté à des problèmes de transfert et de mélange d’une phase liquide et d’une phase gazeuse afin de provoquer des réactions chimiques ou biochimiques. La plupart du temps on utilise des colonnes à bulles, simple à mettre en œuvre, pour ce type de procédé. Mais il existe d’autres situations adaptées aux très grands volumes comme par exemple les bassins d’aération de traitement des eaux ou les méthaniseurs. Dans ce cas de figure, la répartition des injecteurs de gaz doit être adaptée aux dimensions du bassin et contribuer au mélange du liquide. Ceci est autant plus vrai pour le bioréacteur de méthanisation où l’état du liquide change en continu pendant la fermentation. Cependant, il y a un manque d'informations concernant l'hydrodynamique induit par l'injection de gaz en milieu visqueux. Afin de mieux comprendre l'écoulement, le transfert massique et finalement le mélange dans ces situations, il a été décidé d’étudier le cas d'un panache de bulles, généré par un seul injecteur dans des liquides de différentes viscosités. Pour cela des expériences ont été effectuées dans deux types de colonne à bulles avec injection centrale. Un grand nombre de méthodes métrologiques tel que la PIV, l’ombroscopie, différents capteurs etc. ont été utilisés. Une attention particulière a été donnée aux fluctuations à différentes échelles induit par le mouvement oscillatoire du panache de bulles. / This work is an experimental investigation on hydrodynamics, mass transfer and mixing induced by a bubble plume. In chemical engineering, people are often confronted to mixing problems of liquid and gas to create chemical or biochemical reactions. Most of the time, bubble column of big height compared to its diameter are used for such kind or processes.But there are also situations using large scale reactors like tanks for methanization or wastewater treatment. In such configurations, spargers must be adapted to reactor dimensions and fluid properties. This particularly important for methanization reactors since fluid properties are changing continuously during the fermentation. In order to understand hydrodynamics, mass transfer and mixing it is easier to study one single bubble swarm, or so called bubble plume, first.Different experiments were figured out in two different columns types. First one is a pseudo two dimensional column (6cm * 35 cm * 130cm ) allowing the application of optical metrological methods. Hence, the gas phase was studied via shadowgraphy and the liquid phase via PIV. Plus, light intensity measurements after dye injection were done. Besides, pressure sensors and oxygen probes were used.In this way, one could study the oscillating behavior, the corresponding characteristic frequency, mass transfer and mixing time scales. In order to analyze fluid properties, a copolymer called Breox was used. Plus, two different spargers generating different bubble shapes and sizes were applied to estimate their impact. Additional experiments in a cylindrical bubble column were performed at the HDZR in Germany. The same fluids and the same spargers were used to compare results from both geometries. Due to the difficulty to apply optical methods, a Wire-Mesh system recently developed at the HZDR was used to follow the bubble plume movement. Finally, first CFD simulations showing encouraging results are presented at the end of the manuscript.

Este trabalho propõe um modelo de transferência de calor e massa para prever a formação de gelo em um container preenchido com legumes congelados. O problema físico é modelado como um meio poroso composto pelo próprio produto e o ar em seu entorno. O regime de convecção natural é assumido dentro do container, o qual promove o transporte de massa. Como uma primeira validação, o modelo é simulado considerando diferentes temperaturas de ar externo, causadas por flutuações da vizinhança. Resultados para quatro ciclos de temperaturas foram comparados, variando separadamente a temperatura média do ar, amplitude e frequência de oscilação. De modo geral, é observado que a temperatura do produto se comporta assim como era esperado e este resultado é diretamente associado à formação de gelo dentro do container. A formação de gelo cresce com uma maior amplitude de oscilação, porém decresce com um aumento na frequência e na temperatura média. Os parâmetros do modelo foram obtidos para dois diferentes produtos: fatias de cenouras congeladas e vagens congeladas, ambos em meio ao ar. As definições de parâmetros são oriundas de revisão bibliográfica, medições experimentais e simulações numéricas. Os parâmetros encontrados para a caracterização desses meios porosos foram similares para ambos os produtos, mesmo eles possuindo diferentes geometrias. A validação experimental foi feita para as fatias de cenoura considerando dois ciclos de temperatura O modelo numérico é capaz de prever o campo de velocidades do ar, as temperaturas do produto e a formação de gelo local. Os resultados foram validados em relação a um grupo independente de resultados numéricos, tal comparação apresentou uma boa concordância. A circulação de ar encontrada é, de fato, devido à convecção natural. O comportamento da temperatura dos produtos simulados concorda com os valores medidos e os valores de temperaturas diferem por menos de 12%. Com respeito à formação de gelo, o modelo é capaz de prevê-la corretamente nas regiões mais suscetíveis a este fenômeno. Porém, a quantidade de gelo formado prevista pelo modelo (1,56 g/semana) é menor do que a experimental (4,67 g/semana), apesar de serem de mesma ordem de magnitude. O efeito de cada parâmetro no modelo é estudado visando detectar maneiras de aprimorar o modelo. Foi encontrado que os parâmetros mais importantes para a formação de gelo total são a difusividade de massa efetiva e o coeficiente de transferência de calor convectivo dentro do container. Ajustando estes parâmetros duas vezes foi possível encontrar resultados melhores com respeito à formação de gelo (3,09 g/semana). / A model of heat and mass transfer is proposed in order to predict frost formation into a closed container filled with frozen vegetables. The physical problem is modeled as a macroporous media composed by the product itself and the surrounding air. Natural convection air flow is assumed into the container, who promotes water mass transport. As a first validation, the model is simulated for several exterior air temperatures, under environmental fluctuations (boundary conditions). Results of four temperature cycles were compared, varying average air temperature, amplitude and frequency of oscillation, one by one. As a general result, it is observed that the product temperature behavior is as expected, and it is directly associated with frost formation into the container. Frost formation increases with large amplitude of oscillation, but decreases with higher frequencies and higher mean temperatures. Model parameters were obtained for two assembling: frozen slices of carrots and air, and frozen extra thin green beans and air. Parameter definition and evaluation combines literature review, measurements and numerical simulation. In general, parameters which characterize these porous media were similar for both products, even though they display different geometries. The experimental validation is performed for carrot slices with two temperature cycles The numerical model is able to predict air velocity field, air and product temperatures, and local frost formation. Results are validated in respect to a set of independent experimental results that shown a good agreement. Air flow circulation is as expected due to natural convection. Product temperature simulated behavior agrees with measurements, and temperature values differ by less than 12%. Respect to frost formation predictions, the model predicts correctly the most susceptible regions to frost formation. However, the quantity of frost formed predicted by the model (1.56 g/ week)is lower than the experimental one (4.67g/week), despite being of the same order of magnitude. The effect of each parameter in the model is study in order to detect how to improve the model. The most important parameters affecting total frost formation are effective mass diffusivity and convective heat coefficient into the storage container. Adjusting these parameters to twice, better results in terms of frost formation could be obtained (3.09 g/ week).

Abstract In the sugar platform of biorefining, the complex polymeric structure of lignocellulose biomass is degraded into sugars, which are utilized by microbial cells in the further processing steps. The reaction steps in both biomass degradation and microbial fermentation processes involve multiphase reactions in which mass transfer and reaction kinetics often play a key role. The aim of this thesis is to characterize the effect of these conditions on enzymatic hydrolysis of cellulose and utilization of sugars by aerobic microbes. These types of liquid-solid (cellulose hydrolysis) and liquid-gas (microbial cultivation) systems are typically very demanding on the reactors that are used in the process. By the fed-batch process utilized in this work, sufficient mixing in enzymatic hydrolysis of cellulose is achieved even with high final substrate concentration. One of the main outcomes of this work is the kinetic model that concentrates on the kinetics of fed-batch process by discretizing the substrate into subpopulations. By using this approach, the model parameters were identified in an adequate manner, and the poorly identified parameters could be sorted out. Parameter identifiability has been an issue in previous models for enzymatic hydrolysis of cellulose. Based on the experiments and modelling studies, it can be concluded that the enzymes remain intact for time scales relevant for the hydrolysis process. Thus, the decrease in the hydrolysis rate found in many literature studies is probably mostly due to substrate-enzyme interactions rather than denaturation of the enzyme. In aerobic cell cultivations, the mixing and mass transfer conditions are often more critical for the process performance. In this work, we studied the performance and suitability of alternative reactor types to be used in aerobic cell cultivations and obtained some promising results. In addition, the thesis presents a modelling approach to study the effect of process conditions on metabolism and growth rate of Pichia pastoris yeast. The model combines a kinetic model for yeast growth and a model for the mixing and mass transfer conditions in stirred tank reactor. / Tiivistelmä Biojalostuksen sokerialustassa lignoselluloosapohjaisen biomassan monimutkaista polymeerirakennetta muokataan ja sieltä vapautetaan monomeerisia sokereita, joita voidaan edelleen hyödyntää jatkojalostuksessa. Monet jatkojalostusprosessit käyttävät mikrobeja, joiden aineenvaihdunnassa sokereita voidaan jalostaa arvokkaammiksi tuotteiksi ns. fermentointiprosesseissa. Tämän väitöstyön tarkoitus on tutkia reaktio- ja aineensiirtokinetiikan vaikutusta selluloosan entsymaattiseen hydrolyysiin ja aerobisiin mikrobifermentointeihin. Näistä ensimmäinen on neste-kiintoainesysteemi ja jälkimmäinen neste-kaasusysteemi, ja tällaiset prosessit asettavat tyypillisesti merkittäviä vaatimuksia niissä käytettäville reaktoreille. Tässä työssä hyödynnettiin kiinteän raaka-aineen vähittäistä syöttöä (ns. fed-batch prosessi) selluloosan hydrolyysissä, jolloin sekoitus voidaan pitää riittävänä suurillakin kiintoainemäärillä. Työn merkittävin tuotos on kineettinen malli, jossa hyödynnetään fed-batch prosessia ja koedataa osittamalla mallinnusyhtälöt raaka-aineen syöttöajan perusteella. Tällä tavalla mallin parametrit saatiin identifioitua kohtuullisella tarkkuudella sekä eriteltyä huonosti identifioituneet parametrit. Mallin parametrien identifiointi on ollut ongelmallista monissa vastaavan tyyppisissä malleissa aiemmin. Kokeiden ja mallinnustulosten perusteella voidaan sanoa, että hydrolyysissä käytettävät entsyymit pysyvät aktiivisina prosessin aikana, ja usein todettu hydrolyysin hidastuminen johtuu ennemmin kiinteän kuidun ja entsyymien vuorovaikutuksen muutoksista kuin entsyymin denaturoitumisesta. Aerobisiin mikrobikasvatuksiin liittyen tässä työssä tutkittiin vaihtoehtoisten reaktorityyppien hyödyntämistä, joista saatiin myös lupaavia tuloksia. Lisäksi työssä kehitettiin mallinnustyökaluja, joilla voidaan tutkia prosessiolosuhteiden vaikutusta Pichia pastoris –hiivan metaboliaan ja kasvunopeuteen. Mallissa yhdistetään hiivan kasvun kineettinen malli sekä reaktoriolosuhteiden mallinnus.