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Orientador: Marcelo Moreira Ganzarolli / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-07-22T20:18:14Z (GMT). No. of bitstreams: 1 Avelar_AnaCristina_M.pdf: 5757345 bytes, checksum: ab66436b252ec7b8b48d4756dd9e7f42 (MD5) Previous issue date: 1997 / Resumo: Os constantes avanços tecnológicos em eletrônica e informática tem tornado os sistemas eletrônicos cada vez mais compactos, aumentando-se a quantidade de calor a ser removida dos componentes e placas de circuito impresso. Por este motivo, atualmente são exigidos sistemas de dissipação de calor altamente eficientes. Este estudo analisa teórica e experimentalmente a transferência de calor em canais verticais formados por placas de circuito impresso dispostas paralelamente, resfriadas por convecção natural e propõe uma modelagem, baseada em relações existentes na literatura, que busca prever a distribuição de temperaturas em pontos significativos nos canais e placas em função da potência dissipada e da distância entre as placas. Este estudo visa também analisar os efeitos do aquecimento não-uniforme das placas que formam o canal. Na simulação teórica, devido à pequena espessura da placa o gradiente de temperatura ao longo da espessura da mesma foi desprezado e resolveu-se numericamente a equação de transferência de calor em coordenadas cartesianas bidimensionais e em regime permanente. Equacionou-se balanços de energia para os componentes e para o ar no canal e o problema foi resolvido numericamente através de um programa computacional. As placas de circuito impresso utilizadas nos testes experimentais, concebidas exclusivamente para fins de estudos térmicos, possuem uma base de epóxi com 25 resistores discretamente distribuídos sobre sua superfície de 200x164mm. Realizou-se testes com aquecimento uniforme e não-uniforme, variando-se a potência por componentes nas placas. Variou-se também as potências por placas e as distâncias entre as mesmas. Testou-se as potências de 2, 4,6 e 8 W e as distâncias entre placas de 12,24, e 48mm. Verificou-se boa concordância entre os resultados numéricos e experimentais, principalmente para a menor distância entre placas, 12 mm, onde a diferença entre os resultados teóricos e experimentais foi muito pequena / Abstract: The constant technological advances in electronics and computations have made the electronic system increasingly more compact, thus increasing the amount of heat to be removed ITomthe components and printed circuit boards. For this reason, highly efficient system of heat removal are presently required. This study analyses both theoretically and experimentallyheat transfer in an array of vertical parallel printed circuit boards, cooled off by natural convection and proposes a modeling, based on correlation found in literature which tries to predict temperature distribution in significant places in the channels and boards as regards dissipated power and distance among boards. This study also aims at analyzing nonuniform heating effets of the channel made boards. In the theoritical simulation, due to the board' s small thickness, the temperature gradient across the board has been neglected, and the equation of heat transfer in two-dimensional Cartesian was numericallysolved, and on a steady state. Energy balances for the componentes were formulated, and the problem was numerically solved by a computer programo The printed circuit boards used in the experimental tests, manufactured speciallyfor heat trasnfer studies have an epoxy basis with 25 resistors discretely distributed on 200 x 164 mm. Uniform and non-uniform heating tests were performed, thus a variation of power and distance among them had a variation. The 2, 4, 6 and 8 W power and distance among 12, 24 and 48 mm boards were tested. Good agreements between numerical and experimentalresults were observed, mainlyfor the smaller distance among boards, 12 mm, the differencesbetween the theoretical and experimentalresults were small / Mestrado / Termica e Fluidos / Mestre em Engenharia Mecânica

The aim of this research dissertation is at studying natural and mixed convections of fluid flows, and to develop and validate numerical schemes for interface tracking in order to treat incompressible and immiscible fluid flows, later. In a first step, an original numerical method, based on Finite Volume discretizations, is developed for modeling low Mach number flows with large temperature gaps. Three physical applications on air flowing through vertical heated parallel plates were investigated. We showed that the optimum spacing corresponding to the peak heat flux transferred from an array of isothermal parallel plates cooled by mixed convection is smaller than those for natural or forced convections when the pressure drop at the outlet keeps constant. We also proved that mixed convection flows resulting from an imposed flow rate may exhibit unexpected physical solutions; alternative model based on prescribed total pressure at inlet and fixed pressure at outlet sections gives more realistic results. For channels heated by heat flux on one wall only, surface radiation tends to suppress the onset of recirculations at the outlet and to unify the walls temperature. In a second step, the mathematical model coupling the incompressible Navier-Stokes equations and the Level-Set method for interface tracking is derived. Improvements in fluid volume conservation by using high order discretization (ENO-WENO) schemes for the transport equation and variants of the signed distance equation are discussed

Le but de ce mémoire de recherche est d'étudier les convections naturelle et mixte d'écoulements fluides, et de développer et valider des méthodes numériques pour le suivi d'interfaces afin de traiter plus tard des écoulements incompressibles de fluides immiscibles. Dans une première étape, une méthode numérique originale, basée sur des discrétisations Volumes Finis, est développée pour modéliser les écoulements à faible nombre de Mach et grands écarts de température. Trois applications physiques, portant sur l'écoulement d'air à travers des plaques verticales parallèles chauffées, sont étudiées. Nous avons montré que l'espacement optimal, correspondant au pic de flux de chaleur transféré d'un réseau de plaques parallèles isothermes refroidies par convection mixte, est plus faible que ceux obtenus en convections naturelle ou forcée lorsque la chute de pression à la sortie est constante. Nous avons également prouvé que les écoulements de convection mixte à débit imposé peuvent présenter des solutions physiques inattendues ; un modèle alternatif basé sur une pression totale imposée à l'entrée et une pression fixée à la sortie donne de meilleurs résultats. Pour des canaux soumis un flux de chaleur sur une paroi seule, le rayonnement de surface tend à supprimer l'apparition des recirculations à la sortie et à uniformiser les températures des parois. Dans une seconde étape, le modèle mathématique couplant les équations de Navier-Stokes incompressibles et la méthode Level-Set pour le suivi d'interfaces est développé. Des améliorations de la conservation du volume fluide par l'utilisation de schémas de discrétisation d'ordres élevés (ENO-WENO) pour l'équation de transport et des variantes de l'équation de la distance signée sont discutées / The aim of this research dissertation is at studying natural and mixed convections of fluid flows, and to develop and validate numerical schemes for interface tracking in order to treat incompressible and immiscible fluid flows, later. In a first step, an original numerical method, based on Finite Volume discretizations, is developed for modeling low Mach number flows with large temperature gaps. Three physical applications on air flowing through vertical heated parallel plates were investigated. We showed that the optimum spacing corresponding to the peak heat flux transferred from an array of isothermal parallel plates cooled by mixed convection is smaller than those for natural or forced convections when the pressure drop at the outlet keeps constant. We also proved that mixed convection flows resulting from an imposed flow rate may exhibit unexpected physical solutions; alternative model based on prescribed total pressure at inlet and fixed pressure at outlet sections gives more realistic results. For channels heated by heat flux on one wall only, surface radiation tends to suppress the onset of recirculations at the outlet and to unify the walls temperature. In a second step, the mathematical model coupling the incompressible Navier-Stokes equations and the Level-Set method for interface tracking is derived. Improvements in fluid volume conservation by using high order discretization (ENO-WENO) schemes for the transport equation and variants of the signed distance equation are discussed