Simulations are becoming increasingly popular in science and engineering. One type of simulation is Computation Fluid Dynamics (CFD) that is used when closed forms solutions are impractical. The field of Verification & Validation emerged from the need to assess simulation accuracy as they often contain approximations and calibrations. Validation involves the comparison of experimental data with simulation outputs and is the focus of this work. Errors in simulation predictions may be assessed in this way. Validation requires highly-detailed data and description to accompany these data, and uncertainties are very important. The purpose of this work is to provide highly complete validation data to assess the accuracy of CFD simulations. This aim is fundamentally different from the typical discovery experiments common in research. The measurement of these physics was not necessarily original but performed with modern, high fidelity methods. Data were tabulated through an online database for direct use in Reynolds-Averaged Navier Stokes simulations. Detailed instrumentation and documentation were used to make the data more useful for validation. This work fills the validation data gap for steady and transient mixed convection. The physics in this study included mixed convection on a vertical flat plate. Mixed convection is a condition where both forced and natural convection influence fluid momentum and heat transfer phenomena. Flow was forced over a vertical flat plate in a facility built for validation experiments. Thermal and velocity data were acquired for steady and transient flow conditions. The steady case included both buoyancy-aided and buoyancy-opposed mixed convection while the transient case was for buoyancy-opposed flow. The transient was a ramp-down flow transient, and results were ensemble-averaged for improved statistics. Uncertainty quantification was performed on all results with bias and random sources. An independent method of measuring heat flux was devised to assess the accuracy of commercial heat flux sensors used in the heated wall. It measured the convective heat flux by the temperature gradient in air very near the plate surface. Its accuracy was assessed by error estimations and uncertainty quantification.

O presente trabalho apresenta um estudo numérico do escoamento laminar em cavidade quadrada aletada sob o efeito de convecção mista. O escoamento proposto é assumido bidimensional, laminar e permanente. Objetiva-se através do “Constructal Design” a obtenção de geometria ótima da aleta de forma a maximizar a transferência de calor entre o fluido que escoa no interior da cavidade e a aleta aquecida cuja base está localizada no centro da base da cavidade. Para isto é fixada a relação das dimensões externas da cavidade (H/L) = 1 e variada a relação entre altura e comprimento da aleta (H1/L1) para otimização da troca térmica. A área da aleta apresenta 5% da área total da cavidade e este valor é mantido fixo. O fluido que escoa no inteiror da cavidade possui as propriedades termofísicas do ar para Pr = 0,7. A variação das forças de empuxo no escoamento é realizada através do uso de diferentes números de Rayleigh no intervalo Ra= 10³ a 106. As diferentes magnitudes das forças inerciais serão aplicadas ao escoamento através da variação do número de Reynolds variando entre ReL = 10 e 1000. Para solução numérica das equações de conservação de massa, quantidade de movimento e energia é utilizado o método de volumes finitos (VFM), programa comercial Fluent®, sendo o acoplamento entre velocidade e pressão realizado através do algoritmo SIMPLEC e a discretização espacial pelo método upwind de primeira ordem. Os resultados apresentam um acréscimo significativo na transferência de calor entre a aleta e o fluido a medida que o número de Rayleigh aumenta. Considerando o caso de maior influência do mecanismo de transferência de calor por convecção mista houve um aumento de 779% em comparação com o mesmo caso considerando apenas convecção forçada, o que comprova a importância da convecção natural na maximização da transferência de calor entre cavidade e fluido para os casos analisados. / The present work shows a numerical study of laminar flow inside C-shaped lid-driven square cavity under mixed convection effect. The flow is assumed to be two-dimensional, laminar and permanent. The main objective of this work is by means of Constructal Design to maximize the heat transfer between the fluid and the heated central fin intruded in the bottom of the cavity. The aspect ratio of the cavity is fixed and the fin aspect ratio (H1/L1) varies from 0.1 to 10 ranges in order to maximize heat transfer. The ratio area between fin and cavity (H/L) = 1 is kept fixed at 5%. The thermophysical properties of fluid the air are set at Pr = 0,71. To vary the magnitude of buoyancy forces the Rayleigh number is ranged between Ra=10³ and 106.The inertial forces of flow are ranged by the use of different Reynolds numbers between ReL=10 and 1000. In order to solve the proposed problem, the commercial software Fluent® based on finite volume method was used to solve mass, momentum and energy equations, making the pressure-velocity couple using SIMPLEC method and the spatial discretization using first order upwind scheme. The results showed a significant increase of heat transfer between fin and fluid as consequence of Rayleigh number increase. Considering the mixed convection most influenced case, an increase of 779% was sense in comparison with the same case with forced convection mechanism only, which makes evident the importance of natural convection in the maximization of heat transfer inside cavity in the analized cases.

O presente trabalho apresenta um estudo numérico do escoamento laminar em cavidade quadrada aletada sob o efeito de convecção mista. O escoamento proposto é assumido bidimensional, laminar e permanente. Objetiva-se através do “Constructal Design” a obtenção de geometria ótima da aleta de forma a maximizar a transferência de calor entre o fluido que escoa no interior da cavidade e a aleta aquecida cuja base está localizada no centro da base da cavidade. Para isto é fixada a relação das dimensões externas da cavidade (H/L) = 1 e variada a relação entre altura e comprimento da aleta (H1/L1) para otimização da troca térmica. A área da aleta apresenta 5% da área total da cavidade e este valor é mantido fixo. O fluido que escoa no inteiror da cavidade possui as propriedades termofísicas do ar para Pr = 0,7. A variação das forças de empuxo no escoamento é realizada através do uso de diferentes números de Rayleigh no intervalo Ra= 10³ a 106. As diferentes magnitudes das forças inerciais serão aplicadas ao escoamento através da variação do número de Reynolds variando entre ReL = 10 e 1000. Para solução numérica das equações de conservação de massa, quantidade de movimento e energia é utilizado o método de volumes finitos (VFM), programa comercial Fluent®, sendo o acoplamento entre velocidade e pressão realizado através do algoritmo SIMPLEC e a discretização espacial pelo método upwind de primeira ordem. Os resultados apresentam um acréscimo significativo na transferência de calor entre a aleta e o fluido a medida que o número de Rayleigh aumenta. Considerando o caso de maior influência do mecanismo de transferência de calor por convecção mista houve um aumento de 779% em comparação com o mesmo caso considerando apenas convecção forçada, o que comprova a importância da convecção natural na maximização da transferência de calor entre cavidade e fluido para os casos analisados. / The present work shows a numerical study of laminar flow inside C-shaped lid-driven square cavity under mixed convection effect. The flow is assumed to be two-dimensional, laminar and permanent. The main objective of this work is by means of Constructal Design to maximize the heat transfer between the fluid and the heated central fin intruded in the bottom of the cavity. The aspect ratio of the cavity is fixed and the fin aspect ratio (H1/L1) varies from 0.1 to 10 ranges in order to maximize heat transfer. The ratio area between fin and cavity (H/L) = 1 is kept fixed at 5%. The thermophysical properties of fluid the air are set at Pr = 0,71. To vary the magnitude of buoyancy forces the Rayleigh number is ranged between Ra=10³ and 106.The inertial forces of flow are ranged by the use of different Reynolds numbers between ReL=10 and 1000. In order to solve the proposed problem, the commercial software Fluent® based on finite volume method was used to solve mass, momentum and energy equations, making the pressure-velocity couple using SIMPLEC method and the spatial discretization using first order upwind scheme. The results showed a significant increase of heat transfer between fin and fluid as consequence of Rayleigh number increase. Considering the mixed convection most influenced case, an increase of 779% was sense in comparison with the same case with forced convection mechanism only, which makes evident the importance of natural convection in the maximization of heat transfer inside cavity in the analized cases.

Made available in DSpace on 2014-06-11T19:24:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2004Bitstream added on 2014-06-13T20:47:18Z : No. of bitstreams: 1 oliveira_sr_me_bauru.pdf: 4056726 bytes, checksum: da2b55b91a9531fddc60a2ca6a750172 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / É desenvolvido um modelo matemático para estudar o comportamento da estratificação térmica de líquido em um tanque armazenador com meio poroso. O tanque considerado é de geometria retangular com relação comprimento-altura igual a 1. O modelo utiliza a formulação transiente de vorticidade e função corrente para predizer o desenvolvimento dos campos de função corrente e temperaturas durante um processo de carregamento. Foi fixado um número de Reynolds igual a 200 para o escoamento de entrada e uma faixa do número de Richardson de 0,001 a 10. Outros parâmetros considerados incluem o número de Biot (perda de calor pelas paredes do tanque), o número de Darcy (permeabilidade do meio poroso), a posição e a espessura do meio poroso. Os resultados mostram a influência desses parâmetros físicos que devem ser considerados para um bom projeto de tanques armazenadores com estratificação térmica. / A mathematical model is developed to study the behaviour of thermal stratification of liquid in a typical storage tank with porous medium. The tank considered has rectangular geometry with lenght-to-height ratio equal of 1. The model employs a transient stream function-vorticity formulation to predict the development of stream function and temperature fields in a charging process. The Reynolds number of the inlet flow is fixed at 200 and a range of the Richardson number from 0,001 to 10. Other parameters considered include the Biot number (heat loss from tank walls), the Darcy number (permeability of the porous medium), the position and the thickness of the porous medium. The results show the influence of these physic parameters that should be considered for a good design of storage tanks with thermal stratification.

Orientador: Alcides Padilha / Resumo: É desenvolvido um modelo matemático para estudar o comportamento da estratificação térmica de líquido em um tanque armazenador com meio poroso. O tanque considerado é de geometria retangular com relação comprimento-altura igual a 1. O modelo utiliza a formulação transiente de vorticidade e função corrente para predizer o desenvolvimento dos campos de função corrente e temperaturas durante um processo de carregamento. Foi fixado um número de Reynolds igual a 200 para o escoamento de entrada e uma faixa do número de Richardson de 0,001 a 10. Outros parâmetros considerados incluem o número de Biot (perda de calor pelas paredes do tanque), o número de Darcy (permeabilidade do meio poroso), a posição e a espessura do meio poroso. Os resultados mostram a influência desses parâmetros físicos que devem ser considerados para um bom projeto de tanques armazenadores com estratificação térmica. / Abstract: A mathematical model is developed to study the behaviour of thermal stratification of liquid in a typical storage tank with porous medium. The tank considered has rectangular geometry with lenght-to-height ratio equal of 1. The model employs a transient stream function-vorticity formulation to predict the development of stream function and temperature fields in a charging process. The Reynolds number of the inlet flow is fixed at 200 and a range of the Richardson number from 0,001 to 10. Other parameters considered include the Biot number (heat loss from tank walls), the Darcy number (permeability of the porous medium), the position and the thickness of the porous medium. The results show the influence of these physic parameters that should be considered for a good design of storage tanks with thermal stratification. / Mestre

O presente trabalho apresenta um estudo numérico do escoamento laminar em cavidade quadrada aletada sob o efeito de convecção mista. O escoamento proposto é assumido bidimensional, laminar e permanente. Objetiva-se através do “Constructal Design” a obtenção de geometria ótima da aleta de forma a maximizar a transferência de calor entre o fluido que escoa no interior da cavidade e a aleta aquecida cuja base está localizada no centro da base da cavidade. Para isto é fixada a relação das dimensões externas da cavidade (H/L) = 1 e variada a relação entre altura e comprimento da aleta (H1/L1) para otimização da troca térmica. A área da aleta apresenta 5% da área total da cavidade e este valor é mantido fixo. O fluido que escoa no inteiror da cavidade possui as propriedades termofísicas do ar para Pr = 0,7. A variação das forças de empuxo no escoamento é realizada através do uso de diferentes números de Rayleigh no intervalo Ra= 10³ a 106. As diferentes magnitudes das forças inerciais serão aplicadas ao escoamento através da variação do número de Reynolds variando entre ReL = 10 e 1000. Para solução numérica das equações de conservação de massa, quantidade de movimento e energia é utilizado o método de volumes finitos (VFM), programa comercial Fluent®, sendo o acoplamento entre velocidade e pressão realizado através do algoritmo SIMPLEC e a discretização espacial pelo método upwind de primeira ordem. Os resultados apresentam um acréscimo significativo na transferência de calor entre a aleta e o fluido a medida que o número de Rayleigh aumenta. Considerando o caso de maior influência do mecanismo de transferência de calor por convecção mista houve um aumento de 779% em comparação com o mesmo caso considerando apenas convecção forçada, o que comprova a importância da convecção natural na maximização da transferência de calor entre cavidade e fluido para os casos analisados. / The present work shows a numerical study of laminar flow inside C-shaped lid-driven square cavity under mixed convection effect. The flow is assumed to be two-dimensional, laminar and permanent. The main objective of this work is by means of Constructal Design to maximize the heat transfer between the fluid and the heated central fin intruded in the bottom of the cavity. The aspect ratio of the cavity is fixed and the fin aspect ratio (H1/L1) varies from 0.1 to 10 ranges in order to maximize heat transfer. The ratio area between fin and cavity (H/L) = 1 is kept fixed at 5%. The thermophysical properties of fluid the air are set at Pr = 0,71. To vary the magnitude of buoyancy forces the Rayleigh number is ranged between Ra=10³ and 106.The inertial forces of flow are ranged by the use of different Reynolds numbers between ReL=10 and 1000. In order to solve the proposed problem, the commercial software Fluent® based on finite volume method was used to solve mass, momentum and energy equations, making the pressure-velocity couple using SIMPLEC method and the spatial discretization using first order upwind scheme. The results showed a significant increase of heat transfer between fin and fluid as consequence of Rayleigh number increase. Considering the mixed convection most influenced case, an increase of 779% was sense in comparison with the same case with forced convection mechanism only, which makes evident the importance of natural convection in the maximization of heat transfer inside cavity in the analized cases.

Afin de répondre à des problématiques bâtimentaires et des enjeux de sécurité incendie, cette thèse aborde l’écoulement de convection mixte à travers un orifice horizontal reliant deux compartiments. L’objectif est d’améliorer la connaissance et la modélisation de l’échange de gaz de masse volumique variable à travers l’orifice. Une étude expérimentale à échelle réduite couplée à une approche théorique est proposée. L'étude est d'abord focalisée sur l’influence du rapport géométrique L/D de l’orifice sur la variation de débit échangé pour un régime de convection naturelle. Les mesures non intrusives de ces débits, par suivit de l'interface entre deux liquides non miscibles lors d'une première approche densimétrique, ainsi que par Stéréo PIV en sortie d'orifice dans une approche thermique, permettent de décrire le processus d'échange bidirectionnel et de conforter les corrélations existantes.Des expériences en régime de convection mixte visent ensuite à caractériser l’influence d’une ventilation mécanique (en soufflage et en extraction) sur les débits échangés. La confrontation des corrélations existantes avec les points expérimentaux montre des écarts importants. Une modification de la corrélation de Cooper 89 est proposée et permet d'en accroître la précision. En parallèle, une approche théorique issue des équations de Navier Stokes simplifiées et sous l’approximation de Boussinesq permet de discuter la construction des corrélations existantes. L'ajustement de coefficients de pertes de charge à partir des points expérimentaux permet de proposer un modèle plus performant que ceux disponibles dans la littérature. / To answer to building issues and fire safety challenges, this thesis deals with the mixed convection flow through a horizontal orifice linking two compartments. The aim is to improve the understanding and modeling of the exchange of variable density gas through the opening. A small scale experimental study and a theoretical approach are proposed.The study is first focussed on the impact of the geometrical ratio L/D of the opening on the exchanged flow rate variation for free convection regime. Non-intrusive measurements of these flow rates, via the tracking of the interface between two non miscible liquids in an isothermal approach, and thanks to the SPIV in a thermal approach, permit to describe the bidirectional exchange process and to consolidate existing correlations.Experiments in mixed convection regime aim to study the impact of mechanical ventilation (in blowing and extracting mode) on the exchanged flow rates. The comparison between existing correlations and experimental data shows large differences. A change making the coorelation of Cooper 89 more accurate is proposed. A theoretical approach from the simplified Navier Stokes equations and with the Boussinesq approximation permits to discuss the construction of existing correlations. From this theory, a model more accurate than those available in the literature is proposed thanks to an adjustment of discharge coefficients from experimental data.

No description available.

Ce travail concerne une étude expérimentale du comportement hygrothermique de matériaux bio-sourcés sous la forme de briques de terre comprimée (BTC) et de briques de terre stabilisée (BTS). Nous avons déterminé les propriétés thermo-physiques et les isothermes de sorption de ces matériaux et évalué l'influence de l'ajout de stabilisants chimiques (ciment et chaux), sur leurs conductivités thermiques et leurs capacités hygroscopiques. Cette étude est complétée par une modélisation et une simulation numérique des transferts de chaleur et de masse dans une cavité ventilée dont l'une des parois verticales est composée de BTC. Les transferts hygrothermiques dans la paroi, assimilée à un milieux poreux, et dans la cavité ventilée sont décrits respectivement par le modèle de Luikov et les équations classiques de la convection mixte. Ces équations de transferts sont résolues par une méthode implicite aux différences finie, la méthode itérative de Gauss-Seidel et l'algorithme de Thomas. Nous avons analysé l'influence de la température, de l'humidité relative et de la vitesse de l'air ambiant, la densité du flux de chaleur appliqué sur la face externe de la paroi ainsi que la nature du matériau bio-sourcé sur les transferts hygrothermiques dans cette paroi et l'écoulement d'air dans la cavité. Les résultats montrent que la stabilisation chimique augmente la conductivité thermique de la BTC et réduit sa capacité de sorption. L'accroissement de la densité du flux de chaleur appliqué sur la face externe de la paroi de BTC provoque une augmentation des transferts de chaleur par mode latent et sensible entre la face interne de cette paroi et l'air qui s'écoule dans la cavité. / This work concerns an experimental study of the hygrothermal behavior of compressed earth bricks (CEB) and stabilized earth bricks (SEB). We determined its thermo-physical properties and sorption isotherms and evaluated the impact of the chemical stabilizers (cement and lime) addition on their thermal conductivities and hygroscopic capacities. This study is complemented by a modeling and numerical simulations of heat and mass transfers in a ventilated cavity one of its vertical walls is composed of CEB. The heat an mass transfers in this wall, assimilated to a porous medium, and in the ventilated cavity are respectively described by the Luikov model and the mixed convection equations. The transfer equations are solved using an implicit finite difference method, the Gauss–Seidel method and the Thomas algorithm. We have analyzed the effects on the heat and mass transfers within this wall and in the cavity of the temperature and relative humidity air, the inlet air velocity in the cavity and the heat flux density applied on the external face of the vertical wall composed of CEB. These results show that chemical stabilization increase the thermal conductivity of CEB and leads to a reduction in moisture sorption capacity. The increase of the heat flux density applied to the external face of the wall composed of CEB leads to an augmentation of the latent and sensible heat transfers between the inner face of this wall and the air flowing in the cavity.

No description available.