Le séchage des boues d'épuration est un problème environnemental actuel, qui n'est pas suffisamment décrit dans la littérature. Par conséquent, ce travail représente une étude numérique des transferts de chaleur et de masse lors du séchage solaire des boues d’épuration. Cette boue est assimilée à un milieu poreux et exposée à un écoulement laminaire de convection forcée à l'intérieur d'un canal horizontal. Les transferts dans le canal et le milieu poreux sont décrits respectivement par les équations classiques de la convection forcée et par le modèle de Darcy-Brinkman-Forchheimer. Une méthode implicite aux différences finies est utilisée pour discrétiser le système d'équations différentielles régissant les transferts. Les systèmes algébriques obtenus sont résolus en utilisant les algorithmes de Gauss, Thomas et Gauss-Seidel. Afin de déterminer la vitesse de séchage, nous associons à ces équations un modèle de cinétique de séchage. Ce modèle est basé sur le concept de la courbe caractéristique. Nous avons particulièrement étudié les effets des conditions climatiques et des conditions relatives à la boue sur les évolutions spatio-temporelles des nombres caractéristiques des transferts ainsi que sur la cinétique de séchage. Le travail est complété par des simulations en utilisant des données météorologiques réelles de la région de Tataouine au sud de la Tunisie. Ces données ont subi un traitement statistique à l’aide de la méthode de Liu et Jordan afin de déterminer la journée type de chaque mois. L’étude de rentabilité du séchoir a montré que la période estivale est la période optimale pour le séchage. / The drying of sewage sludge is a current environmental problem, not sufficiently described in the literature. Hence, the aim of this work is a numerical study of heat and mass transfers during solar drying of residual sludge. This sludge is assimilated to a porous medium and exposed to a forced convection laminar flow within a horizontal channel. The transfers in the channel and the porous medium are respectively described by the classic equations of forced convection and the Darcy-Brinkman-Forchheimer model. The implicit finite difference method is used to discretize the governing differential equation system. The algebraic systems obtained are solved using the Gauss, Thomas and Gauss-Seidel algorithms. To determine the drying rate, we associate a drying kinetics model. This model is based on the concept of the characteristic curve. We particularly studied the effects of climatic conditions (temperature, velocity and relative humidity of the ambient air as well as the solar radiation intensity) and the conditions relating to the sludge on the spatio-temporal evolutions of the transfers characteristic numbers as well as on drying kinetics. This work is completed by simulations using meteorological data from the Tataouine region in southern Tunisia. These data were statistically processed using the Liu and Jordan method to determine the typical day of each month. The rentability study of the dryer show that the summer period is the optimum period for drying.

Este trabalho tem como propósito investigar através do método Design Construtal a influência do espaçamento (S0) entre cilindros de seção transversal elíptica na maximização da densidade de transferência de calor em um escoamento externo sob efeito de convecção forçada. A razão de aspecto (r) entre os eixos vertical e horizontal dos cilindros elípticos também é um parâmetro avaliado. O estudo proposto é assumido bidimensional, incompressível, laminar e permanente. O regime de escoamento é dirigido por uma diferença de pressão ΔP, que se mantém através do domínio e é governada pelo número de Bejan (Be). Foram avaliados escoamentos com quatro diferentes números de Bejan, Be = 102, 103, 5.103, 104. O fluido que escoa através do domínio possui as propriedades termofisicas definidas pelo número de Prandtl, Pr = 0,72. O método Design Construtal, associado à busca exaustiva, foi empregado para determinar as restrições, graus de liberdade e o objetivo na avaliação geométrica do sistema A solução numérica das equações de conservação de massa, quantidade de movimento e energia foram resolvidas baseadas no método de volumes finitos, através do código comercial de dinâmica dos fluidos computacional FLUENT®. As geometrias e malha do domínio computacional foram desenvolvidas no pacote GAMBIT®. Como resultados, obteve-se que os casos ótimos apresentaram resultados consideravelmente melhores do que as demais configurações, onde se obteve ganhos de desempenho na densidade de transferência de calor de 50% a 97% em relação às configurações de menor desempenho estudadas. Além disso, foi possível verificar que o sistema adapta sua geometria ótima para cada condição de escoamento, a fim de proporcionar a melhor arquitetura de fluxo para atender ao objetivo térmico de maximizar a transferência de calor em um menor espaço físico, atendendo os princípios da Teoria Construtal. / This work investigates, through the Construtal Design method, the influence of the spacing (S0) between cylinders with elliptic cross in the maximization of the heat transfer density in an external flow with forced convection. The aspect ratio (r) between the vertical and horizontal axes of the elliptical cylinders is also evaluated. The proposed study is assumed twodimensional, incompressible, laminar and permanent. The flow regime is directed by a pressure difference ΔP, which is governed by the Bejan number (Be). The flows were evaluated for different values of the Bejan number, Be = 102, 103, 5.103, 104. The fluid flowing through the domain has its thermophysical properties defined by Prandtl number, Pr = 0.72. The Construtal Design method, associated with the exhaustive search, was used to determine the restrictions, degrees of freedom and objective in the geometric evaluation of the system. The numerical solution of the mass conservation, momentum and energy equations is solved based on the finite volume method, using the commercial fluid dynamics software FLUENT ®. The geometries and mesh of the computational domain were developed in the GAMBIT® package. The results show that the optimal cases performs considerably better than the other configurations, with an increase in the heat transfer density of 50% to 97% in comparison to the performance of lower level cases studied. In addition, it was possible to verify that the system adapts its optimal geometry to every flow condition in order to provide a better flow architecture that meets the thermal objective of maximizing a heat transfer in a smaller physical space in agreement with the principles of the Constructal Theory.

Resumo: O objetivo deste trabalho é a análise numérica e experimental de escoamento viscoso, incompressível, permanente, com transferência de calor, em um canal estreito contendo um arranjo de obstáculos retangulares. A análise experimental envolveu determinação de coeficiente de transferência de calor médio bem como o número de Nusselt médio e medidas de temperatura em esteira térmica para comparação com os resultados obtidos por simulação numérica. Para a análise numérica usamos o programa comercial de mecânica dos fluidos e transferência de calor computacional ICEPAK®. Verificamos que quanto mais adentro o obstáculo estiver no arranjo maior é a transferência de calor por convecção forçada. Determinamos coeficientes de transferência de calor médio e número de Nusselt médio (com incerteza entre 6 e 15%) e verificamos que o efeito da posição diminui à medida que a velocidade aumenta. Concluímos também que ambos os modelos de turbulência utilizados, k-ε padrão e k-ε RNG, foram incapazes de predizer o efeito da posição apropriadamente. Entretanto, o modelo k-ε RNG apresentou melhor comportamento, pois o seu uso resultou em soluções com valores de temperatura intermediários aos experimentais / Abstract: The purpose of this work is the study of the numerical and experimental viscous incompressible steady flow with heat transfer into a narrow channel containing a rectangular array of obstacles. The experimental approach involves determining the coefficient of heat transfer and temperature measurements in thermal wake for comparison with the results obtained in numerical simulations. For the numerical analysis we use the commercial program of fluid mechanics and heat transfer computational ICEPAK™. We confirmed that in the last lines of the array the biggest is the heat transfer by forced convection. We determined the average heat transfer coefficients (with uncertainty between 6 and 15%) and found that the effect of the position decreases as flow speed increases. We use in the simulations the k-ε turbulence model and the k-ε RNG turbulence model. We conclude that both turbulence models used were unable to predict the effect of the position properly. However, the k-ε RNG model showed better behavior. The numerical temperatures with this model were consistent to the experimental temperature / Orientador: João Batista Campos Silva / Coorientador: Amarildo Tabone Paschoalini / Coorientador: Marcio Antonio Bazani / Banca: Ricardo Alan Verdú Ramos / Banca: Marcio Higa / Mestre

Dans cette thèse, on présente une étude numérique de la convection forcée turbulente dans un dissipateur thermique muni d'une chicane transversale dans le by-pass. Le premier modèle est composé d’ailettes planes et le second consiste à ajouter des ailettes broches entre les ailettes planes. Les équations gouvernantes basées sur le modèle de turbulences k- SSt sont discrétisées et résolues par la méthode des volumes finis et l'algorithme SIMPLE. Les résultats dynamiques sont présentés en en termes de champs de vitesse, des profils de vitesse axiales dans des sections choisies ainsi que la perte de charge. L'étude thermique est présentée en terme de champs de température et de distribution du nombre de Nusselt. Un rapport entre les performances thermique et dynamique est présenté pour évaluer les différents dissipateurs thermiques. / In this thesis, we present an numerical study of turbulent forced convection in a heat sink provided with a transverse baffle in the bypass. The first model is composed of plates fins and the second consists of adding pin fins between the plates fins. The governing equations, based on the k- SSt turbulence model, are disscredized and solved by the finite volume method and the SIMPLE algorithm. Dynamic results are presented in terms of velocity fields, profiles of the axial velocities in selected sections and pressure drop. The thermal study is presented in terms of temperature fields and the distribution of Nusselt number. A ratio between the thermal and dynamic performances is presented to evaluate the different heat sinks.

La simulation numérique d'écoulements turbulents dans les systèmes de refroi- dissement de joints de pompes hydrauliques demande à considérer des domaines de calcul très étendus et des temps d'intégration très longs. La modélisation hybride RANS/LES zo- nale pourrait permettre de reproduire, dans un temps de calcul acceptable industriellement, l'ensemble des phénomènes thermiques et dynamiques en présence. L'approche consiste à faire interagir une simulation des grandes échelles (LES), représentant finement les phé- nomènes instationnaires de la turbulence dans certaines régions critiques de l'écoulement, avec l'approche statistique (RANS), moins coûteuse numériquement et dont la mise en oeuvre dans le reste du domaine permet de rendre compte des variations globales imposées à l'écoulement (injection d'eau froide dans de l'eau chaude, rotation de l'arbre et de la roue, etc...). Dans cette optique, une étude détaillée des modélisations adaptées aux écoulements en rotation est réalisée, suivant les deux approches RANS et LES. De nombreux modèles de turbulence sont comparés sur un cas test de canal en rotation. Le couplage zonal aux faces de bord par la méthode des structures turbulentes synthétiques (SEM) est étudié et une méthode innovante de couplage volumique par force de rappel (Forçage Linéaire Ani- sotrope) sur une zone de recouvrement RANS/LES est proposée. Ces deux méthodes sont étendues pour la première fois à la thermique. Les simulations hybrides RANS/LES zonales présentées, sur des cas test de canal fixe, en rotation ou en convection forcée, montrent la faisabilité de telles modélisations pour des applications industrielles.

The main task of the ventilation system in a building is to maintain the air quality and (together with the heating or cooling system) the thermal climate at an acceptable level within the building. This means that a sufficient amount of ventilation air at the appropriate temperature and quality must be supplied to satisfy thermal comfort and air quality demands and that this air is distributed to the parts of the building where people reside. Air movements caused by buoyancy forces can determine the distribution of ventilation air within buildings. The purpose of this thesis is to advance the state of knowledge of buoyancydriven air movements within buildings and to determine their importance both for ventilation air distribution and the maintenance of thermal comfort and air quality in buildings. The work is focused on studying thermally-driven air movements through large openings, both horizontal and vertical (i.e. doorways). The properties of a special type of thermally-driven currents, so called gravity currents, have also been explored. Large vertical openings like doorways are important for air exchange between rooms within a building. Air movements through doorways separating rooms with different air temperatures are often bidirectional and the buoyancy-driven flow rates are often greater than those caused by the mechanical ventilation system alone. Bidirectional flows through doorways can effectively spread contaminants, for example, from a kitchen or a hospital rooms, yet the results of this study indicate that the conversion of a thermally-driven bidirectional flow to a unidirectional flow via an increase of the mechanically forced flow rate requires forced flows that are more than three times greater than the thermally-driven flows. Experiments conducted in this project indicate that the resistance to buoyancy-driven flows in horizontal openings is significantly greater than that in vertical openings. Model tests have shown, however, that this problem may be mitigated if a simple model of a staircase located in the centre of the room (being ventilated) is linked to the horizontal ventilation opening. Gravity currents in rooms occur in connection with so called displacement ventilation as cool gravity currents propagate along the floor that are driven by the density difference of the ventilation air and the ambient, warmer air within the room. As these gravity currents easily pass obstacles and to a certain extent are self-controlling, they can effectively distribute the cool air within rooms in a building. Likewise, warm gravity currents occur when warmer air introduced in a room rises and spreads along the ceiling plane. One application where warm gravity currents may be used to advantage is when converting buildings from electric heating to district hot water heating thus, avoiding the introduction of an expensive hydronic heating system. This report includes a full-scale laboratory study of the basic properties of thermally-driven warm air gravity currents in a residential building and examines the possibilities of using the resulting air movements for the distribution of ventilation air as well as heat. Results from laboratory tests show that this conversion method may prove effective if certain conditions on the layout of the building are fulfilled. / QC 20100705

This thesis investigates the refrigerant (R-134a) flow in three minichannels having different geometries experimentally. During the last 40 years heat transfer in small scales has been a very attractive research area. Improvements in heat transfer in the refrigeration applications by means of usage of micro/minichannels provide significant developments in this area. Also it is known that experimental studies are very important to constitute a database which is beneficial for new developments and research. During the two-phase flow experiments conducted in the minichannels, low mass flow rates and constant wall temperature approach, which are the conditions in the evaporators of the refrigerator applications were applied because one of the purposes of this study is to determine the most ideal minichannel among the tested minichannels for usage in the evaporator section of the refrigerators. Two-phase flow experiments were made with refrigerant R134a in the three minichannels having hydraulic diameters of 1.69, 3.85 and 1.69 mm respectively. As distinct from the others, the third minichannel has a rough inner surface. Comparison of the experimental results of the three minichannels was made in terms of forced convection heat transfer coefficients and pressure drop at constant quality and mass flux values. As a result of the experiments, the most ideal minichannel among the tested minichannels was determined for the evaporator applications in the refrigerators.

Este trabalho tem como propósito investigar através do método Design Construtal a influência do espaçamento (S0) entre cilindros de seção transversal elíptica na maximização da densidade de transferência de calor em um escoamento externo sob efeito de convecção forçada. A razão de aspecto (r) entre os eixos vertical e horizontal dos cilindros elípticos também é um parâmetro avaliado. O estudo proposto é assumido bidimensional, incompressível, laminar e permanente. O regime de escoamento é dirigido por uma diferença de pressão ΔP, que se mantém através do domínio e é governada pelo número de Bejan (Be). Foram avaliados escoamentos com quatro diferentes números de Bejan, Be = 102, 103, 5.103, 104. O fluido que escoa através do domínio possui as propriedades termofisicas definidas pelo número de Prandtl, Pr = 0,72. O método Design Construtal, associado à busca exaustiva, foi empregado para determinar as restrições, graus de liberdade e o objetivo na avaliação geométrica do sistema A solução numérica das equações de conservação de massa, quantidade de movimento e energia foram resolvidas baseadas no método de volumes finitos, através do código comercial de dinâmica dos fluidos computacional FLUENT®. As geometrias e malha do domínio computacional foram desenvolvidas no pacote GAMBIT®. Como resultados, obteve-se que os casos ótimos apresentaram resultados consideravelmente melhores do que as demais configurações, onde se obteve ganhos de desempenho na densidade de transferência de calor de 50% a 97% em relação às configurações de menor desempenho estudadas. Além disso, foi possível verificar que o sistema adapta sua geometria ótima para cada condição de escoamento, a fim de proporcionar a melhor arquitetura de fluxo para atender ao objetivo térmico de maximizar a transferência de calor em um menor espaço físico, atendendo os princípios da Teoria Construtal. / This work investigates, through the Construtal Design method, the influence of the spacing (S0) between cylinders with elliptic cross in the maximization of the heat transfer density in an external flow with forced convection. The aspect ratio (r) between the vertical and horizontal axes of the elliptical cylinders is also evaluated. The proposed study is assumed twodimensional, incompressible, laminar and permanent. The flow regime is directed by a pressure difference ΔP, which is governed by the Bejan number (Be). The flows were evaluated for different values of the Bejan number, Be = 102, 103, 5.103, 104. The fluid flowing through the domain has its thermophysical properties defined by Prandtl number, Pr = 0.72. The Construtal Design method, associated with the exhaustive search, was used to determine the restrictions, degrees of freedom and objective in the geometric evaluation of the system. The numerical solution of the mass conservation, momentum and energy equations is solved based on the finite volume method, using the commercial fluid dynamics software FLUENT ®. The geometries and mesh of the computational domain were developed in the GAMBIT® package. The results show that the optimal cases performs considerably better than the other configurations, with an increase in the heat transfer density of 50% to 97% in comparison to the performance of lower level cases studied. In addition, it was possible to verify that the system adapts its optimal geometry to every flow condition in order to provide a better flow architecture that meets the thermal objective of maximizing a heat transfer in a smaller physical space in agreement with the principles of the Constructal Theory.

Made available in DSpace on 2015-05-08T14:59:45Z (GMT). No. of bitstreams: 1 Arquivototal.pdf: 1419023 bytes, checksum: 1bf50c9a366f8d01e4a2a3efdb0a5526 (MD5) Previous issue date: 2012-09-28 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In this study the forced convection in the laminar flow in simultaneous developing is studied by applying the Generalized Integral Transform Technique to provide a hybrid analytical solution for the fields of velocity, pressure and temperature in circular ducts. The Continuity, Navier-Stokes, Poisson and Energy equations are formulated using primitive variables,knowing that the Poisson Equation was obtained from some mathematical manipulation made on the Navier-Stokes equations. The integral transformation is done in the Momentum equation in x, Poisson and energy equations, and the resulting equations are solved using the IMSL, DBVPFD subroutines and recovering the original potential for each profile studied. In this way it is possible to find a solution to the system by means of an expansion in terms of convenient eigenfunctions, to circular ducts, the eigenfunctions will be Bessel functions. In the following, some results from a practical point of view will be calculated and exhibited graphically such as: The Nusselt number, the f Re value, the study of the convergence profile of the velocity field, the mean velocity, the temperature, the mean temperature, pressure and the mean pressure in the middle of the duct will be analyzed. The results will be compared with the ones found in the literature to validate and adjust the model. / No presente trabalho a convecção forçada interna no escoamento laminar em desenvolvimento simultâneo é estudada aplicando a Técnica da Transformada Integral Generalizada para produzir um solução híbrida para os campos de velocidade, pressão e temperatura em dutos circulres. As equações da Continuidade, de Navier-Stokes, de Possion e da Energia são formuladas utilizando variáveis primitivas, sabendo-se que a equação de Poisson foi obtida a partir de algumas manipulações matemáticas feitas na equação de Navier-Stokes. A transformação integral é aplicada nas equações da quantidade de movimento na direção x, de Poisson e na equação da energia, e as equações resultantes são resolvidas com a subrotina numérica do IMSL, DBVPFD recuperando o potencial original para cada perfil em estudo. Assim é possível encontrar uma solução para o sistema de equações em termos de um expansão de autofunções, que para dutos circulares, as autofunções serão funções de Bessel. Em seguida resultados de interesse prático são calculados e exibidos graficamente como: número de Nusselt e f Re e estudos da convergência dos perfis de velocidade,velocidade média, temperatura, temperatura média, pressãoo e pressão média no centro do duto são analisados. Os resultados são comparados com os dados disponíveis na literatura para validação e ajustes do modelo.

Made available in DSpace on 2015-05-08T14:59:45Z (GMT). No. of bitstreams: 1 Arquivototal.pdf: 1415567 bytes, checksum: 7b043cdad595239d38d4437820f24dd0 (MD5) Previous issue date: 2012-09-28 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In the present study, forced convection flow in two-dimensional laminar simultaneous development pipeline with rectangular geometry, is analyzed analytically using the Navier-Stokes, Poisson and Energy in its primitive form. These equations are solved by the Generalized Integral Transform Technique, which is characteristic hybrid-numeric. The development work is composed primarily by restructuring the problem, so that, it can be solved by using the subroutine Fortran, IMSL Library, DBVPFD. Then, the results obtained are considered of practical interest, such as the velocity field, the temperature profile, the behavior of the average temperature, the Nusselt number and the friction factor, with the goal of providing a better parameter for construction equipment. These parameters are assessed both longitudinally and horizontally. Finally, the results are validated through convergence charts in order to comparisons with literature articles. / No presente estudo, a convecção forçada no escoamento bidimensional em desenvolvimento simultâneo laminar em dutos com geometria retangular, é analisada analiticamente através das equações de Navier-Stokes, Poisson e da Energia em sua forma primitiva. Estas equações são resolvidas pela Técnica da Transformada Integral Generalizada, que tem característica hibrida-numérica. O desenvolvimento do trabalho é composto primeiramente pela reestruturação do problema, afim de que, possa ser resolvido pelo Fortran por meio da subrotina, da biblioteca IMSL, DBVPFD. Em seguida, são obtidos os resultados considerados de interesse práticos, como o campo de velocidade, o perfil da temperatura, o comportamento da temperatura média, o numero de Nusselt e o fator de atrito, com o objetivo de proporcionar parâmetros para melhor dimensionamento de equipamentos. Esses parâmetros são avaliados tanto longitudinalmente quanto horizontalmente. Por fim, os resultados são validados através de tabelas de convergência e comparações com artigos da literatura especializada.