This work can be viewed in three separate sections, each of which build off of the prior. The first part of this study examined the flow in a 1/16th scale calandria test section based on a typical CANDU moderator layout. The experiments utilized forced flow supplied to the vessel and electrical heated rods to mimic the heat flow from calandria tubes. The size of the vessel, flow rates, and power levels were used to scale the experiments such that the provided representative temperature fields. The temperature field inside the vessel was measured and shown to compare well with CFD predictions over a wide range of inlet conditions and power levels. Additionally, this work addressed the scaling distortions in the experiment which occurred due to physical limitations when performing experiments at 1/16 scale (e.g., a smaller number of heater rods with a larger diameter were used in the experiment because at 1/16-scale direct fabrication of 390 fuel channel simulators is not feasible). The work proposed the H factor addition to the Ar. This additional scaling criteria was shown to better maintain the flow regimes expected CANDU moderators by taking into account distortions introduced by surface heating instead of volumetric heating in addition to the reduction in total number of tubes. While this work involved forced convective flows at the inlet of the vessel, in some regions of the calandria buoyancy induced forces were sufficiently high such that these phenomena altered the direction and magnitude of the flows as compared to purely forced convective behavior. Hence further work, discussed below, was initiated to better understand and measure these local phenomena where buoyancy forces are of similar magnitude as those of forced convection. Such local conditions we have terms mixed convection regime for the purposes of this thesis. The second part of this work further examined the mixed convection between a subset of the CANDU calandria tubes, namely how does a lower tube effect the mixed convection heat transfer of the upper tube in an inline arrangement. To isolate and measure the phenomena with sufficient detail, a small number of tubes was studied and advanced diagnostics such as Particle Image Velocimetry (PIV) and Laser Induced Fluorescence (LIF) were employed. This study combined fluid velocity, temperature and wall temperature measurements with CFD simulations to develop a mechanistic model and understanding of the effect of natural convection plumes from lower elevations on the natural circulation phenomena on an upper cylinder. Superposition of the natural convection phenomena combined with pseudo forced convection effects from the lower elevation cylinder’s plume was used to model the mixed convection phenomena. This model was shown to perform well, with nearly all data being predicted to with +-20% for experiments performed in this work, and experiments in literature. A major finding from the preceding discussion is the importance of the lower elevation plume velocity on the local phenomena on the upper cylinder. The third section further expanded upon the prior two by replacing the lower cylinder with a diffuser nozzle which could provide a forced convective component with accurately defined velocities. Such measurements allow for accurate definition of the local Ri number and allowed full access for instrumentation to observe the velocity fields. The major contribution of this work was a flow regime map that defined the phenomena around a heated cylinder under mixed convection conditions. Additionally, the establishment of a database of fluid temperature and velocity measurements for a wide range of Ri was also developed and used to further validate CFD predictions. / Thesis / Doctor of Philosophy (PhD)

<p>In gas quenching, metal parts are rapidly cooled from hightemperatures, and the convection heat transfer coefficientdistributions are of importance for the hardness and thedistortion (the shape nonuniformities) of the quenched parts.Thermochromic liquid crystals (TLC) and a thin foil techniques,were investi- gated and used for studies of a circular cylinderin axial flows, affected and not affected by upstream owmodifying inserts. Quadratic prisms in cross ows were alsostudied, a single prism, two prisms arranged in-line, and forfour prisms arranged in a square pattern. In this study,particle image velocime- try (PIV) was used for visualizationof the flow, giving physical insight to the convection heattransfer data. Further, relations of the type<i>Nu</i>=<i>CRe</i><i>e</i>were established. The TLC and thin foil techniques werealso used to indicate the dimensions of separated flowregions.</p><p><b>Descriptors:</b>Fluid mechanics, wind-tunnel, turbulence,gas quenching, con- vection heat transfer, thermochromic liquidcrystals, calibration, temperature measurement errors, thinfoils, particle image velocimetry, cylinder in axial flow, flowmodifying inserts, quadratic prisms in cross flow</p>

No description available.

De nombreux procédés industriels utilisent ou génèrent des sources chaudes : fours, traitement de surface, soudage…Les dégagements de chaleur s’accompagnent généralement d’une dispersion de polluants dans l’atelier. Ainsi, la caractérisation des panaches de convection naturelle des sources thermiques est nécessaire au dimensionnement des installations de ventilation (hotte ou ventilation générale par déplacement d’air) pour l’assainissement des ambiances de travail. L’I.N.R.S a mis au point une méthode expérimentale pour caractériser en vraie grandeur le panache de sources thermiques de géométrie simple. Un banc d’essais a été réalisé et instrumenté à cet effet. Il est constitué d’une cellule aéraulique dont les dimensions sont 4,2 m x 4,8 m x 5,6 m équipé d’une centrale de traitement d’air et d’un système de ventilation permettant un déplacement vertical des flux d’air. La cellule est équipée d’un robot de déplacement tridimensionnel permettant le positionnement de sondes de température et de vitesses en tout point du volume. Les expérimentations menées étudient l’influence de la géométrie de la source sur les lois de développement de panache à partir de mesures de champs de température et de vitesse. Pour une même puissance thermique convectée, la géométrie des sources sera variée pour identifier son affluence sur le développement du panache. Une source cylindrique composée de cinq éléments d’aires identiques (4 cylindres identiques superposés et un disque supérieur) régulés indépendamment en température permettra de mener des études paramétriques sur des sources tridimensionnelles. De manière similaire une source rectangulaire modulable sera utilisée. / Many industrial processes use or generate hot sources: furnaces, surface treatment, welding... the releases of heat are generally accompanied by a dispersion of pollutants in the workshop. Thus, the characterization of the plumes of natural convection of the thermal sources is necessary to the dimensioning of the installations of ventilation (exhaust system localised or general ventilation by air volume displacement) for the cleansing of environments of work. I.N.R.S developed an experimental method to characterize in real-scale the plume of thermal sources of simple geometry. A test bench was realised and instrumented for this purpose. It consists of an aeraulic cell whose dimensions are 4,2 m x 4,8 m x 5,6 m equipped with a power station of treatment of air and with a system of ventilation allowing a vertical displacement of flows of air. The cell is equipped with a robot of three-dimensional displacement allowing the positioning of speed and temperature sensors in any point of volume. The carried out experiments study the influence of the geometry of the source on the laws of development of plume starting from measurements of fields of temperature and speed. For the same convective thermal power, the geometry of the sources will be varied to identify its multitude on the development of the plume. A cylindrical source made up of five elements of identical surfaces (4 superimposed identical cylinders and a higher disc) controlled independently in temperature will make it possible to undertake parametric studies on three-dimensional sources. In a similar way a flexible rectangular source will be used.

Thesis presented in fulfilment of the requirements for the degree of Doctor of Philosophy at the University of the Witwatersrand, Johannesburg, 2017. / This thesis investigates in detail the structure of models of turbulent convec tion with phenomenological closures for the eddy-viscosity. It explores the merits of replacing the canonical Mixing Length Theory of stellar convection with more realistic models of fluid turbulence that take into account the full spectrum of eddy sizes. The author provides a detailed exposition of the fun damental assumptions and the modus operandi of various approaches to the treatment of convective energy-transfer in stars. He focuses in particular on spectral descriptions of the convective process. The structure of several clo sure models developed by various authors are investigated, and he identifies and elucidates those aspects of these closures that lead to an improved descrip tion of convective turbulence in the stellar interior. The author also develops an implementation within the public-domain code, called Modules for Experi ments in Stellar Astrophysics, of two of these models and reports and discusses the results of his numerical experiments. / XL2018

Cette étude concerne la physique des écoulements convectifs résultant d’une instabilité d’évaporation de fluides binaires. Ce problème a de nombreuses applications, l’enrobage par centrifugation, le dépôt de films, les caloducs, etc, pour lesquels le changement de phase et la convection jouent un rôle prépondérant dans la conception et la qualité des procédés. Le système physique étudié est un mélange liquide sous sa propre vapeur, confiné par deux plaques conductrices de chaleur et des bords latéraux isolants. Les plaques sont utilisées pour appliquer un gradient thermique. Aucun gradient de concentration n’est imposé au système. Ces gradients sont induits par les différentes vitesses d’évaporation des composés. Dans ce système, il est important de comprendre comment la dynamique des fluides et les transferts de masse et de chaleur entrent en compétition pour la formation de structures. Le principal objectif de ce travail est d’identifier les conditions pour que le système évolue d’un état conductif vers un état de convection lorsque le gradient vertical de température dépasse une certaine valeur critique.Dans le système, la convection s’installe par trois mécanismes distincts : évaporation, gradients de densité et gradients de tension interfaciale. Trois forces convectives s’opposent aux effets de diffusion qui tendent à garder le système en état conductif. Le seuil d’apparition de la convection dépend de quelques variables, comme les dimensions du contenant, les propriétés thermophysiques des phases liquide et vapeur, la fraction massique, et les caractéristiques de perturbations. L’effet de chacune de ces variables sur le seuil est étudié en présence ou non de gravité.Pour représenter la physique, un modèle mathématique non linéaire complet est développé, basé sur les conservations de quantité de mouvement, d’énergie et de masse dans chaque phase avec les conditions aux limites appropriées. Le fluide binaire est composé de deux alcools légers comme l’éthanol et le sec-butanol. Dans les équations du modèle, la masse volumique ainsi que la tension interfaciale sont fonctions à le fois de la température et de la concentration. Pour la recherche du seuil de transition, les équations sont linéarisées autour d’un état de base connu. Dans notre cas, il s’agit de l’état conductif. Le système d’équations linéaires résultant est résolu par une méthode de collocation spectrale Chebyshev.Nous obtenons quatre résultats principaux. Premièrement, dans un système multi-composants sans gravitation, une instabilité n’apparaît que lorsque le système est chauffé du côté de la phase vapeur contrairement à un système mono-composant. Cela implique que, si on souhaite éviter les instabilités, il vaut mieux un apport de chaleur par la phase liquide en cas de processus d’évaporation en couches minces ou en micro-gravité.Deuxièmement, en présence de gravité, un système multi-composants peut devenir instable quelle que soit la direction du chauffage. Si la convection thermique est négligeable, alors nous montrons que le chauffage par la phase vapeur est la configuration la plus instable. Sinon, les deux modes de chauffage sont à même de produire une instabilité. Ce résultat implique que le gradient thermique appliqué doit être inférieur à une valeur seuil pour éviter les instabilités quelle que soit la direction du chauffage.Troisièmement, lorsque l’instabilité apparaît en absence de gravité, des structures n’apparaitront pas dans le cas de fluide pur mais apparaitront dans le cas d’un fluide multi-composants. De même, des structures apparaitront en présence de gravité en fonction du facteur d’aspect du confinement. Les facteurs d’aspect peuvent être choisis pour éviter des structures multi-cellulaires même en cas d’apparition d’instabilités durant l’évaporation.Enfin, des structures oscillantes ne sont pas prédites de façon générale malgré les effets opposés des convections solutale et thermique dans le problème d’évaporation. / This study focuses on understanding the physics of the convective flow resulting from evaporative instability in binary mixtures. This problem has wide applications in spin coating, film deposition, heat pipes, etc. where phase change and convection play a very important role in the design process and also final quality of the product. The physical system of interest consists of a liquid mixture underlying its own vapor sandwiched between two conducting plates with insulated sidewalls in a closed container. The conducting plates are used to apply a vertical temperature gradient while there is no applied concentration gradient in the system. Concentration gradients are induced by the different evaporation rate of the components. In this system it is important to understand how the fluid dynamics and the heat and mass transfer interact competitively to form patterns. The main goal of this work is to identify the conditions for the system going from the conductive no-flow state to a convection state when the applied vertical temperature gradient exceeds a certain value called the critical value.In the system convection arises due to three distinct phenomena; evaporation, density gradients, and interfacial tension gradients. These convective forces are opposed by the diffusion effects that try to keep the system in the conductive no-flow state. The onset point depends upon several variables such as the dimensions of the container, thermo-physical properties of both liquid and vapor phases, mass fraction, and the characteristic of the disturbance given to the system. The effects of each of these variables on the onset point are investigated both in the presence and in the absence of gravity. To represent the physics a complete non-linear mathematical model is developed including momentum, energy, and mass balances in both phases with appropriate boundary conditions. The binary mixture is assumed to be made up of two low weight alcohols such as ethanol and sec-butanol. In the modeling equations the density and the interfacial tension are taken to be function of both temperature and concentration. To identify the onset point the non-linear equations are linearized around a known base state. In this case the base state is the conductive no-flow state. The resulting set of linear equations is solved using a spectral Chebyshev collocation method. Four major results arise from this work. First, in a multi-component system in the absence of gravity, an instability arises only when the system is heated from the vapor side as opposed to evaporation in a single-component. The implication is that evaporative processes in thin layers or in micro-gravity are best conducted with heat from the liquid side if instabilities are to be avoided.Second, in the presence of gravity, a multi-component system may become unstable no matter the direction of heating. If thermal buoyancy is negligible then it is shown in this study that heating from the vapor side is the unstable arrangement. Otherwise either heating style can produce an instability. This result means that the applied temperature difference must be kept below a threshold in order to avoid flow instabilities no matter the heating direction.Third, whenever instability occurs in the absence of gravity, patterns will not result in the case of a pure component but may result in the case of multi-components. Likewise, patterns will result when gravity is taken into account provided the aspect ratio of the container lies in a suitable range. As a result, aspect ratios can be chosen to avoid multi-cellular patterns even if convective flow instabilities arise during evaporation.Lastly, oscillations are not ordinarily predicted despite opposing effects of solutaland thermal convection in the evaporation problem.

Le travail de la thèse est consacré à une étude analytique et numérique de l'instabilité thermique dans une cavité poreuse horizontale saturée par un fluide non-newtonien. Un champ magnétique externe, uniforme et constant est appliqué parallèlement à la gravité. Dans cette étude, nous avons envisagé deux types de conditions aux frontières aux parois actives de la cavité, les conditions aux frontières thermiques de type Neumann et de type Dirichlet. De plus, un modèle rhéologique de type loi en puissance a été utilisé pour modéliser le comportement non-newtonien du fluide. Nous avons résolu les équations non linéaires complètes en utilisant deux codes de calcul numériques, l'un est basé sur la méthode des différences finies et l'autre sur la méthode des volumes finis. Par ailleurs, une solution analytique, basée sur l’approximation de l'écoulement parallèle, a été développée dans le cas de cavités minces (A>>1) soumises à un flux de chaleur constant. Nous avons utilisé l'analyse de stabilité linéaire pour prédire l'apparition des mouvements convectifs. Les résultats obtenus ont montré que la présence du champ magnétique modifie les résultats des travaux antérieurs concernant les fluides newtoniens et non newtoniens de type loi de puissance. Par ailleurs, pour des champs magnétiques très élevés, il a été montré que la dissipation d'énergie par effet Joule domine la dissipation d'énergie par contrainte de cisaillement et confère au fluide un caractère non visqueux / The work of the thesis is devoted to an analytical and numerical study of thermal instability in a horizontal porous cavity saturated by a non-Newtonian fluid. An external magnetic field, uniform and constant is applied parallel to the gravity. In this study, we considered two types of boundary conditions at the active walls of the cavity, the thermal boundary conditions of Neumann type and Dirichlet type. In addition, a rheological model of the power law type was used to model the non-Newtonian behavior of the fluid. We solved the complete nonlinear equations using two numerical codes, one based on the finite difference method and the other on the finite volume method. In addition, an analytical solution, based on the parallel flow approximation, has been developed in the case of thin cavities (A >> 1) subjected to a constant heat flow. We used linear stability analysis to predict the onset of convective motion. The results obtained showed that the presence of the magnetic field modifies the results of previous work concerning Newtonian and non-Newtonian fluids of the power law type. Moreover, we also show that in the limit of very strong magnetic field, the dissipation of energy by Joule effect dominates the dissipation of energy by shear stress and gives to the liquid an inviscid character

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Song Hao = 湍流熱對流中的熱傳導測量 / 宋浩. / Thesis submitted in: December 2004. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 65-70). / Text in English; abstracts in English and Chinese. / Song Hao = Tuan liu re dui liu zhong de re zhuan dao ce liang / Song Hao. / Abstract (in English) --- p.i / Abstract (in Chinese) --- p.ii / Acknowledgements --- p.iii / Table of Contents --- p.iv / List of Figures --- p.vi / List of Tables --- p.ix / Chapters / Chapter 1. --- Introduction --- p.1 / Chapter 2. --- Experimental Setup and Methods --- p.7 / Chapter 2.1 --- The rough boundary cell / Chapter 2.1.1 --- Convection Cell --- p.7 / Chapter 2.1.2 --- Temperature Probes --- p.9 / Chapter 2.1.3 --- Working Fluids --- p.10 / Chapter 2.1.4 --- Temperature-stabilized Box --- p.12 / Chapter 2.2 --- Rectangular and Square Cell --- p.13 / Chapter 2.3 --- The Big Cell --- p.13 / Chapter 2.4 --- The Thermal Measurements --- p.16 / Chapter 3. --- Nusselt Number Measurement in the Rough Boundary Cell --- p.19 / Chapter 3.1 --- Nu correction --- p.19 / Chapter 3.2 --- Non-Boussinesq Effect --- p.25 / Chapter 3.3 --- Experimental Results --- p.28 / Chapter 3.3.1 --- Water --- p.28 / Chapter 3.3.2 --- 1-Pentonal --- p.29 / Chapter 3.3.3 --- Dipropylene Glycol --- p.30 / Chapter 3.3.4 --- Triethylene Glycol --- p.32 / Chapter 3.4 --- Discussion on the Results --- p.34 / Chapter 3.4.1 --- Nusselt number --- p.34 / Chapter 3.4.2 --- Comparison with the smooth cell --- p.35 / Chapter 3.4.3 --- Normalized Nusselt number enhancement --- p.37 / Chapter 3.4.4 --- Nu~Pr-Relation --- p.40 / Chapter 3.4.5 --- Effects of Roughness Size --- p.43 / Chapter 3.4.6 --- Temperature Fluctuation Measurement --- p.44 / Chapter 4. --- Geometry Dependence of Nusselt Number and Temperature Fluctuation --- p.47 / Chapter 4.1 --- Nusselt Number Measurement --- p.48 / Chapter 4.2 --- Temperature Fluctuation's Dependence on Geometry --- p.50 / Chapter 5. --- Nusselt Number in the Big Cell --- p.53 / Chapter 5.1 --- The Big Cell --- p.53 / Chapter 5.2 --- Correction for Big Cell --- p.57 / Chapter 5.3 --- Results and Discussion --- p.61 / Chapter 6. --- Conclusions --- p.63 / References --- p.65

Xu, Xiaoqi. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 91-92). / Abstracts in English and Chinese. / Xu, Xiaoqi. / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Experimental measurements --- p.10 / Chapter 3 --- Review of earlier work --- p.13 / Chapter 3.1 --- Moments of {xP fT) --- p.13 / Chapter 3.2 --- Earlier results of Xr --- p.18 / Chapter 4 --- Probability Density Functions --- p.24 / Chapter 5 --- Scaling behavior of the moments --- p.43 / Chapter 5.1 --- Longest time scale in the problem --- p.43 / Chapter 5.2 --- The maximum order of the moment that can be calculated from a given set of data --- p.47 / Chapter 5.3 --- Moments of the surrogate XT --- p.50 / Chapter 5.4 --- The surrogate XT using water measurements and helium measurements --- p.59 / Chapter 5.4.1 --- PDFs comparison --- p.59 / Chapter 5.4.2 --- Scaling behavior of moments --- p.61 / Chapter 5.5 --- Investigation --- p.64 / Chapter 5.5.1 --- Helium measurements and water measurements --- p.64 / Chapter 5.5.2 --- Xr and Xfr using water measurements --- p.69 / Chapter 5.6 --- Conclusion --- p.73 / Chapter 6 --- Conditional statistics of temperature fluctuations --- p.74 / Chapter 6.1 --- Estimating the maximum order of moment --- p.74 / Chapter 6.2 --- Conditional temperature structure functions using Xfr and Xr --- p.78 / Chapter 6.3 --- Conditional temperature structure functions using x/r and XT at various r in the temperature derivatives --- p.83 / Chapter 7 --- Conclusion --- p.89 / Bibliography --- p.91