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).

Submitted by Jorge Silva (jorgelmsilva@ufrrj.br) on 2017-10-17T16:30:00Z No. of bitstreams: 1 2016 - Maur?cio de Carvalho.pdf: 8945176 bytes, checksum: 4b68e7d4395ffbaee8b4d17639d8a28e (MD5) / Made available in DSpace on 2017-10-17T16:30:00Z (GMT). No. of bitstreams: 1 2016 - Maur?cio de Carvalho.pdf: 8945176 bytes, checksum: 4b68e7d4395ffbaee8b4d17639d8a28e (MD5) Previous issue date: 2016-04-12 / CAPES / In this work we consider the injection of water with dissolved ions into a linear horizontal porous rock cylinder with constant porosity and absolute permeability initially containing oil and water in several proportions. The water is assumed to have low salinity concentration, where some ions are dissolved. We disregard that there is in the rocks some possible minerals that can dissolve or precipitate in water phase. There are two chemical fluid components as well as two immiscible phases: water and oil, (w, o). The dissolved ions are: positive divalent ions: calcium ions, Ca2+ and magnesium ions, Mg2+; negative divalent ions: sulphate ions, SO42?; positive monovalent ions: sodium ions, Na+; negative monovalent ions: cloride ions, Cl?. The cations are modeled to be involved in fast ion exchange process with a surface negative X? which can absorb the positive ions, Ca2+, Mg2+ and Na+. We use simple mixing rules and we disregard any heat of precipitation/dissolution of substance reactions or ion desorption. Moreover we disregard any volume contraction efects resulting from mixing and reactions in any phase. We are going to solve in this work, the Riemann problem and we are going to discuss some features about the studied model. / Neste trabalho consideramos a inje??o de ?gua com ?ons dissolvidos em um meio po-roso linear horizontal cil?ndrico com porosidade e permeabilidade absoluta constantes, inicialmente, contendo ?leo e ?gua em v?rias propor??es. A ?gua ? assumida ter baixa concentra??o de sais, onde alguns ?ons est?o dissolvidos. Desconsideramos a exist?ncia de alguns poss?veis minerais na rocha que possam dissolver ou precipitar na fase da ?gua. Existem dois componentes qu?micos fluidos assim como duas imisc?veis fases: ?gua e ?leo,(w, o). Os ?ons dissolvidos s?o: ?ons divalentes positivos: ?ons c?lcio, Ca2+ e ?ons magn?sio, Mg2+; ?ons negativos divalentes: ?ons sulfato, SO42?; ?ons positivos monovalentes: ?ons s?dio, Na+; ?ons negativos monovalentes: ?ons cloro, Cl?. Os c?tions est?o envolvidos em um processo r?pido de troca de ?ons com a superf?cie do meio poroso carregada eletronega-tivamente X?, onde o meio absorver? os ?ons positivos Ca2+, Mg2+ e Na+. Usando regras simples de misturas e desconsiderando qualquer calor de precipita??o ou dissolu??o de rea??es de subst?ncias ou dessor??o de ?ons. Al?m disso, desconsideramos quaisquer efeitos de contra??o de volume resultante das misturas e rea??es em qualquer fase. Resolveremos neste trabalho, o Problema de Riemann e discutiremos algumas caracter?sticas do modelo estudado.

La lubrification eX-Poro-HydroDynamique (XPHD) est un mécanisme de lubrification d’inspiration biomimétique. Il s’agit principalement d’un écoulement dans un milieu poreux, dont la phase solide représentée par des fibres, induit des forces élastiques de compression considérées comme négligeables par rapport aux forces hydrodynamiques générées à l’intérieur du milieu poreux. L’idée essentielle de la lubrification XPHD consiste en remplacement du matériau antifriction et du film de fluide mince, traditionnellement utilisé dans les solutions classiques, par une couche poreuse imbibée d’un fluide qui fournit plus grande capacité de charge. Ce type de lubrification représente une solution technologique totalement nouvelle (en rupture avec la solution classique) qui peut permettre de remplacer les lubrifiants pétroliers, de créer des systèmes tribologiques autolubrifiants et donc plus écologiques et moins coûteux. Ce travail de recherche est donc focalisé sur l’évolution des performances de la lubrification XPHD dans le cadre d’un mouvement tangentiel, adapté à l’étude de butées pour faible et moyenne vitesses de rotation. Dans ce contexte scientifique, une étude approfondie d’un matériau poreux présélectionné (mousse en polyuréthane) fut réalisée avec le but de déterminer les caractéristiques physiques et les paramètres cruciaux pour la lubrification XPHD: la porosité et la perméabilité du matériau poreux. Les modèles théorique et numérique de lubrification XPHD proposés se basent sur l’équation de Darcy-Brinkman et les hypothèses de la lubrification classique, ainsi que l’écoulement à l’intérieur du milieu poreux sont prédit avec une nouvelle forme de l’équation de Reynolds. Le banc d’essais spécialement développé permet d’étudier expérimentalement le mécanisme de lubrification XPHD pour des différents types de dislocateur en combinaison avec des liquides newtoniens et nonnewtoniens. Une description détaillée du banc d’essais et de tous les dispositifs expérimentaux utilisés ainsi que la comparaison des résultats de modélisation et des résultats expérimentaux sont présentés. / The eX-Poro-HydroDynamic (XPHD) lubrication is a new biomimetic inspired lubrication mechanism. It consists of self-sustained fluid films generated within highly compressible porous layers imbibed with liquids, whose solid phase represented by fibers, induces compressive elastic forces considered negligible compared to the hydrodynamic forces generated inside the porous medium. The essential idea of XPHD lubrication is to replace the antifriction material and the thin fluid film, traditionally used for classical sliding motion, with a porous layer imbibed with a fluid that provides a greater load capacity. This type of lubrication represents a completely new technological solution (in rupture with the classical one) that can replace petroleum lubricants, create self-lubricating and therefore more ecological and less expensive tribological systems. This research work is focused on the evolution of XPHD lubrication performances in the context of a tangential movement, adapted to the study of thrust bearing for low and medium rotation speeds. In this scientific context, a thorough study of a preselected porous material (polyurethane foam) was carried out with the aim of determining the physical characteristics and the crucial parameters for XPHD lubrication: the porosity and the permeability of the porous material. The theoretical and numerical models of the XPHD lubrication proposed are based on the Darcy-Brinkman equation and the classical lubrication hypothesis, as well as the flow within the porous media is predicted with a new form of the Reynolds equation. The specially developed test rig is used to investigate experimentally the mechanism of the XPHD lubrication for different types of thrust bearing in combination with Newtonian and non-Newtonian liquids. A detailed description of the test rig and all used experimental devices, as well the comparison between the experimental and numerical results are presented.

This work is devoted to the numerical analysis of saturated porous media, taking into account the damage phenomenon on the solid skeleton. The porous media is taken into poroelastic framework, in full-saturated condition, based on the Biot\'s Theory. A scalar damage model is assumed for this analysis. An implicit Boundary Element Method (BEM) formulation, based on time-independent fundamental solutions, is developed and implemented to couple the fluid flow and the elasto-damage problems. The integration over boundary elements is evaluated by using a numerical Gauss procedure. A semi-analytical scheme for the case of triangular domain cells is followed to carry out the relevant domain integrals. The non-linear system is solved by a Newton-Raphson procedure. Numerical examples are presented, in order to validate the implemented formulation and to illustrate its efficiency. / Este trabalho trata da análise numérica de meios porosos saturados, considerando danificação na matriz sólida. O meio poroso é admitido em regime poroelástico, em condição saturada, com base na teoria de Biot. Um modelo de dano escalar é empregado nesta análise. Uma formulação implícita do Método dos Elementos de Contorno (MEC), baseada em soluções fundamentais independentes do tempo, é desenvolvida e implementada de forma a acoplar os problemas de difusão de fluido e de elasto-dano. A integração sobre os elementos de contorno é feita através da quadratura de Gauss. Um esquema semi-analítico é aplicado sobre células triangulares para avaliar as integrais de domínio do problema. A solução do sistema não linear é obtida através de um procedimento do tipo Newton-Raphson. Apresentam-se exemplos numéricos a fim de validar a formulação implementada e demonstrar sua eficiência.

Pour augmenter le taux de récupération du pétrole, une des solutions chimiques utilisées consiste à injecter des mousses dans les milieux poreux. En effet, les mousses permettent sous certaines conditions de diminuer la mobilité et ainsi d’améliorer le balayage du réservoir. Cependant, les mécanismes contrôlant la mobilité des mousses ne sont pas bien compris. Nous proposons une approche microfluidique permettant une observation directe de l’écoulement des bulles dans un micromodèle de milieux poreux. Nous observons que l’écoulement n’est pas homogène dans le milieu poreux: il se fait uniquement dans quelques chemins. Le nombre de chemins préférentiels dépend de la qualité de la mousse et du nombre capillaire. Si nous simplifions le milieu poreux à une boucle, nous montrons que la formation des chemins préférentiels dépend de la taille de la boucle. En effet, les bulles sont bloquées dans la boucle uniquement quand la taille de la boucle est de l’ordre de grandeur de la taille des bulles. / Crude oil is already usually trapped into heterogeneous porous media. In order to increase the recovery efficiency, one of the chemical solutions consists in injecting foams in porous media to expel oil from the rock. Foam is indeed able in some cases to greatly decrease the mobility, leading to a better sweeping of the reservoir. However, the mechanisms controlling the foam mobility are not well known. We propose a microfluidic approach allowing a direct observation of the flow of bubbles in a model of porous media. We observe that the flow is not homogeneous in the porous medium: it is concentrated in some paths. The number of these preferential paths depends of the foam quality and the capillary number. If we simplify the geometry of the porous medium to a loop, we prove that the formation of preferential paths depends of the size of the loop. Indeed we can only immobilize the bubbles if the size of the loop is around the size of the bubbles.

La pollution d’aquifères par des hydrocarbures est très persistante et difficile à traiter, devenant un enjeu majeur pour l’environnement en raison de l’effet négatif sur la santé humaine. La génération de mousse in situ combinée au lavage de sols est une technique de dépollution innovante, permettant un meilleur contrôle de la mobilité des fluides dans des formations hétérogènes. Le but de cette méthode est de bloquer l’écoulement dans les couches à forte perméabilité pour améliorer l’efficacité de balayage des strates peu perméables.Le mémoire se divise en deux parties principales décrivant une étude expérimentale et une étude numérique.Une sélection préalable de tensioactifs respectueux de l’environnement à été réalisée sur la base de leur moussabilité. Le sucrose laurate (émulsifiant alimentaire) a été retenu et comparé avec un tensioactif dit classique. Des tests sur colonnes 1-D ont permis d’étudier l’influence de la perméabilité, du type de tensioactif et de la qualité de la mousse sur le facteur de résistance à la mobilité du gaz. Les résultats, interprétés à l’aide de la pression capillaire, révèlent deux régimes d’écoulement, correspondants aux deux textures de mousse : « weak » et « strong ». Des expériences sur pilotes 2-D hétérogènes ont permis de visualiser les différentes phases du processus de remédiation et de comparer l’efficacité de balayage avec et sans une région bloquée par de la mousse.La partie modélisation comprend une simulation numérique des tests sur colonne 1-D en utilisant le code UTCHEM et une étude de sensibilité des paramètres les plus importants du modèle, ainsi qu’une modélisation des tests de traçage sur pilote 2-D avec le code MODFLOW. / Aquifer pollution with hydrocarbons is very persistent and difficult to treat, becoming a major issue for the environment because of the negative effect on human health. In situ foam generation combined with soil washing is an innovative remediation technology that allows a better fluid mobility control in heterogeneous formations. The purpose of this method is to block the flow through the high permeability layers in order to improve the sweep efficiency of low permeability strata.The thesis is divided into two main parts describing an experimental study and a numerical study.A preliminary selection of environmentally-friendly surfactants was carried out on the basis of their foamability. Sucrose laurate (emulsifier from food industry) was selected and compared with a conventional surfactant. 1-D column tests were performed to study the influence of permeability, surfactant type and foam quality on the resistance factor. The results, interpreted using the capillary pressure, show two flow regimes, corresponding to the two foam textures: "weak" and "strong". Experiments on 2-D heterogeneous pilot allowed visualizing the different steps of the remediation process and comparing the sweep efficiency with and without a region blocked by foam.The numerical part includes modeling 1-D column tests using UTCHEM, a sensitivity study of the most important parameters of the model, and a simulation of tracer tests on 2-D pilot using MODFLOW.

This thesis is motivated by problems studied as part of the Diavik Waste Rock Pile Project. Located at the Diavik Diamond Mine in the Northwest Territories, with academic support from the University of Waterloo, the University of Alberta, and the University of British Columbia, this project focuses on constructing mine waste rock piles and studying their physical and chemical properties and the transport processes within them. One of the main reasons for this investigation is to determine the effect of environmental factors on acid mine drainage (AMD) due to sulfide oxidation and the potential environmental impact of AMD. This research is concerned with modeling pressure driven flow through waste rock piles. Unfortunately, because of the irregular shape of the piles, very little data for fluid flow about such an obstacle exists, and the numerical techniques available to work with this domain are limited. Since this restricts the study of the mathematics behind the flow, this thesis focuses on a cylindrical domain, since flow past a solid cylinder has been subjected to many years of study. The cylindrical domain also facilitates the implementation of a pseudo-spectral method. This thesis examines a pressure driven flow through a cylinder of variable permeability subject to turbulent forcing. An equation for the steady flow of an incompressible fluid through a variable permeability porous medium is derived based on Darcy's law, and a pseudo-spectral model is designed to solve the problem. An unsteady time-dependent model for a slightly compressible fluid is then presented, and the unsteady flow through a constant permeability cylinder is examined. The steady results are compared with a finite element model on a trapezoidal domain, which provides a better depiction of a waste rock pile cross section.

The thermal properties of hydrate bearing sediments remain poorly studied, in part due to measurement difficulties inside the hydrate stability envelope. In particular, there is a dearth of experimental data on hydrate-bearing sediments, and most available measurements and models correspond to bulk gas hydrates. However, hydrates in nature largely occur in porous media, e.g. sand, silt and clay. The purpose of this research is to determine the thermal properties of hydrate-bearing sediments under laboratory conditions, for a wide range of soils from coarse-grained sand to fine-grained silica flour and kaolinite. The thermal conductivity is measured before and after hydrate formation, at effective confining stress in the range from 0.03 MPa to 1 MPa. Results show the complex interplay between soil grain size, effective confinement and the amount of the pore space filled with hydrate on the thermal conductivity of hydrate-bearing sediments.

Thermo-mechanical failure of components in planar-type solid oxide fuel cells (SOFCs) is a major obstacle on the path to bringing this technology to commercial viability. The probability of material degradation and failure in SOFCs depends strongly on the local temperature gradients at the interfaces of different materials. Therefore, it is of paramount importance to accurately predict and manage the temperature fields within the stack, especially near the interfaces. In this work we consider three effects in detail. First, we analyze radiative heat transfer effects within the semi-transparent solid electrolyte and compared them to thermal conduction. We also, present the modeling approach for calculation of surface-to-surface exchange within the flow channels and from the stack to the environment. The simplifying assumptions are identified and their carefully justified range of applicability to the problem at hand is established. This allows thermal radiation effects to be properly included in overall thermal modeling efforts with the minimum computational expense requirement. Second, we developed a series of reduced-order models for the transient heating and cooling of a cell, leading to a framework for optimization of these processes. The optimal design is one that minimizes heating time while maintaining thermal gradients below an allowable threshold. To this end, we formulated reduced order models (validated by rigorous CFD simulations) that yield simple algebraic design rules for predicting maximum thermal gradients and heating time requirements. Several governing dimensionless parameters and time scales were identified that shed light on the essential physics of the process. Finally, an analysis was performed to assess the degree of local thermal non-equilibrium (LTNE) within porous SOFC electrodes, and through a simple scaling analysis we discovered the parameter that gives an estimate of the magnitude of LTNE effects. We conclude that because of efficient heat transfer between the solid and gas in the microscale pores of the electrodes, the temperature difference between gas and solid is often negligible. However, if local variations in current density are significant, the LTNE effects may become significant and should be considered.

Diffusive mass transport within porous SOFC components is explored using two modeling approaches that can better inform the SOFC electrode design process. These approaches include performance metrics for electrode cross-sectional design and a fractal approach for modeling mass transport within the pore structure of the electrode reaction zone. The performance metrics presented are based on existing analytical models for transport within SOFC electrodes. These metrics include a correction factor for button-cell partial pressure predictions and two forms of dimensionless reactant depletion current density. The performance impacts of multi-dimensional transport phenomena are addressed through the development of design maps that capture the trade-offs inherent in the reduction of mass transport losses within SOFC electrode cross-sections. As a complement to these bulk electrode models, a fractal model is presented for modeling diffusion within the electrochemically active region of an SOFC electrode. The porous electrode is separated into bulk and reaction zone regions, with the bulk electrode modeled in one-dimension based on the dusty-gas formalism. The reaction zone is modeled in detail with a two-dimensional finite element model using a regular Koch pore cross-section as a fractal template for the pore structure. Drawing on concepts from the analysis of porous catalysts, this model leads to a straightforward means of assessing the performance impacts of reaction zone microstructure. Together, the modeling approaches presented provide key insights into the impacts of bulk and microstructural geometry on the performance of porous SOFC components.