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1
Rudkiewicz, Martin. "Analyse de la stabilité d'un échangeur générateur de vapeur à plaques". Electronic Thesis or Diss., Université de Toulouse (2023-....), 2024. http://www.theses.fr/2024TLSEP016.
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Dans un contexte de réduction des Gaz à Effet de Serre, une attention croissante est portée sur les sources de production d'énergie électrique décarbonée. Pour répondre à cette demande des projets de réacteurs nucléaires de petite taille, les Small Modular Reactor sont en phase de développement, à l’instar du projet NUWARD et de son réacteur à eau pressurisé de 170MWe. Cette technologie se distingue par sa modularité et le design très compact de ses générateurs de vapeur (GV) en comparaison des GV usuels. Le fluide secondaire est, en outre, vaporisé en une unique passe dans des canaux de taille millimétrique. Ces GV sont susceptibles d'être le siège d'instabilités thermohydrauliques diphasiques statiques (Ledinegg) ou dynamiques (onde de densité, ...). Ces instabilités modifient les niveaux de températures, débits et pressions, capables d’impacter l'efficacité, la durée de vie, voire l'intégrité des GV. Elles justifient ainsi une bonne compréhension et modélisation des conditions d’apparition de ces instabilités. Cette thèse analyse l'instabilité de Ledinegg dans les conditions de fonctionnement des GV compacts à plaques. Un modèle simplifié d'évaporation en convection forcée en domaine confiné est proposé et exploré. Considérant que les interfaces sont dominées par la capillarité et localisées par les gradients longitudinaux de température, ce modèle décrit le couplage thermique se produisant dans le cas d’un front de vaporisation, plan, d'épaisseur infinitésimale, séparant un domaine liquide d'un domaine vapeur. Les champs de température sont résolus à l'aide de la méthode des modes de Graetz généralisés, spécifiquement adaptée au modèle d'évaporation choisi. La décomposition en modes de Graetz généralisés résout semi-analytiquement des problèmes tridimensionnels de convection-diffusion permettant d'analyser finement les échanges convectifs conjugués. Dans le premier chapitre cette approche est utilisée pour étudier les transferts thermiques dans les boucles monophasiques en circulation naturelle. Une analyse numérique a permis d'établir une nouvelle loi d’échelle universelle reliant les nombres de Grashof et Reynolds, confirmée par une analyse asymptotique des couches limites pariétales. Cette loi a été confrontée avec succès aux corrélations empiriques existantes et à des jeux de données expérimentales. L'étude a mis en évidence le pilotage des transferts thermiques par la nature des conditions aux limites, les couches limites et le rapport des conductivités thermiques fluide/solide. Dans le second chapitre, la méthode des modes de Graetz généralisés est étendue à la résolution des champs de température avec un front d’évaporation permettant de déterminer le positionnement de celui-ci. Cette méthode est ensuite appliquée à un mono-canal chauffé uniformément et un échangeur co-courant. L’étude de la vaporisation dans un micro-canal à flux imposé a permis d’établir une loi linéaire entre position du front et nombre de Péclet. Les résultats numériques sont cohérents avec l’analyse analytique du bilan d’énergie et les données expérimentales de la littérature, à des débits et puissances de chauffe modérés. La loi d'évolution du front d'évaporation associée à un modèle de pertes de charge ont mené aux les contours des zones instables pour un micro-canal chauffé isolé et/ou en réseau ont été tracés et caractérisés. Dans le cas de l'échangeur co-courant, la majorité des études de stabilité considère des canaux à flux thermique imposé et thermiquement isolés. Or les transferts conjugués dans un échangeur s’écartent a priori, par nature, des échanges à flux imposé. Le modèle d’évaporation confiné prédit ainsi une relation logarithmique entre position du front et Péclet d'entrée. Les dépendances de cette relation aux propriétés du fluide et de la paroi, des débits du circuit primaire ont été étudiées et permis d’établir des critères de stabilité pour un échangeur seul et/ou en réseau, représentatifs des GV considérésIn the context of greenhouse gases reduction, an increasing attention is dedicated to carbon–free power plants solutions. To answer to this growing demand, tiny nuclear reactors or Small Modular Reactors (SMR), are being developed such as the 170Mwe Pressurized Water Reactor within the NUWARD project. This technology is downscaled, modular, with a very compact Steam Generators (SG) design in comparison to current recirculating SG. Moreover, the secondary fluid is vaporized through one unique passage in millimetric channels. However, such devices potentially include static (Ledinegg) and dynamic (density wave oscillations, …) two-phase flow instabilities. These instabilities can alter the SG’s efficiency, lifetime, and even integrity from modifying the temperature, mass flow and pressure levels. Consequently, it justifies a more precise analysis and understanding of the instability’s mechanism. In this PhD, a thorough study of the Ledinegg instability and the flow maldistribution phenomenon is carried out in the compact plates SG’s operating conditions. In a capillary dominated regime we consider a localized, infinitesimally thin interfacial front plunged into a forced longitudinal temperature gradient whereby vaporization arises leading to successive liquid-gas phases distribution within the channel. Whereas the liquid and vapor velocity profiles are provided by the Poiseuille’s law, the temperature fields in the solid and the fluid are obtained using the generalized Graetz modes method, specifically adapted to the considered vaporization model. The generalized Graetz modes decomposition permits a semi-analytical solution of the 3D convection-diffusion problems provided that the velocity field, domain’s section and Peclet’s number are longitudinally invariant along the flow direction. In the first chapter, this methodology is used to analyse heat transfers in single-phase natural convection circulation loop. A new universal scaling law for the relation between the Grashof and the Reynolds numbers is obtained, this is confirmed by an asymptotic analysis and direct numerical simulations and is successfully compared with experimental data sets. This analysis has highlighted the influence of boundary conditions, boundary layers, and fluid to solid thermal conductivity ratio in the heat transfer control. In the second chapter, the generalized Graetz modes method is extended to solve the temperature fields as well as the two-phase interface position within the vaporization model. This methodology is applied to two configurations: a uniformly heated single channel and a co-current heat exchanger. The vaporization’s numerical computation with imposed heat flux in a microchannel depicts the proportionality between the front’s position and the liquid Peclet’s number. The results are consistent with the theoretical energy balance analysis as well as with experimental data obtained in the literature for moderated mass flows and heating powers. Using the resulting interface’s position law into a pressure drops model, the boundaries of the stability areas in a single heated microchannel and many parallel channels have been computed and analysed. In the case of the co-current heat exchanger, the state-of-the-art remains spotty because most of stability studies deals with imposed heat flux and thermally insulated channels, not relevant for conjugated heat transfers in a heat exchanger which deviate from such simplified assumptions. Our confined vaporization model predicts a logarithmic dependence between the two-phase interface’s position and the secondary inlet Peclet’s number. The influence of the fluid properties, primary mass flow and the wall thermal conductivity on this law has been studied and allowed to specify the stability criteria for a single heat exchanger and a network composed of parallel heat exchangers, closer to the compact plates’ SG
2
Jin, Ze. "Conjugated heat transfer in crossflow boiling". Thesis, University of Ottawa (Canada), 1989. http://hdl.handle.net/10393/5803.
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Macbeth, Tyler James. "Conjugate Heat Transfer and Average Versus Variable Heat Transfer Coefficients". BYU ScholarsArchive, 2016. https://scholarsarchive.byu.edu/etd/5801.
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An average heat transfer coefficient, h_bar, is often used to solve heat transfer problems. It should be understood that this is an approximation and may provide inaccurate results, especially when the temperature field is of interest. The proper method to solve heat transfer problems is with a conjugate approach. However, there seems to be a lack of clear explanations of conjugate heat transfer in literature. The objective of this work is to provide a clear explanation of conjugate heat transfer and to determine the discrepancy in the temperature field when the interface boundary condition is approximated using h_bar compared to a local, or variable, heat transfer coefficient, h(x). Simple one-dimensional problems are presented and solved analytically using both h(x) and h_bar. Due to the one-dimensional assumption, h(x) appears in the governing equation for which the common methods to solve the differential equations with an average coefficient are no longer valid. Two methods, the integral equation and generalized Bessel methods are presented to handle the variable coefficient. The generalized Bessel method has previously only been used with homogeneous governing equations. This work extends the use of the generalized Bessel method to non-homogeneous problems by developing a relation for the Wronskian of the general solution to the generalized Bessel equation. The solution methods are applied to three problems: an external flow past a flat plate, a conjugate interface between two solids and a conjugate interface between a fluid and a solid. The main parameter that is varied is a combination of the Biot number and a geometric aspect ratio, A_1^2 = Bi*L^2/d_1^2. The Biot number is assumed small since the problems are one-dimensional and thus variation in A_1^2 is mostly due to a change in the aspect ratio. A large A_1^2 represents a long and thin solid whereas a small A_1^2 represents a short and thick solid. It is found that a larger A_1^2 leads to less problem conjugation. This means that use of h_bar has a lesser effect on the temperature field for a long and thin solid. Also, use of ¯ over h(x) tends to generally under predict the solid temperature. In addition is was found that A_2^2, the A^2 value for the second subdomain, tends to have more effect on the shape of the temperature profile of solid 1 and A_1^2 has a greater effect on the magnitude of the difference in temperature profiles between the use of h(x) and h_bar. In general increasing the A^2 values reduced conjugation.
4
Maffulli, Roberto. "Conjugate heat transfer in high pressure turbines". Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:6044f198-77ae-43e2-99af-cea4960e9407.
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In the present thesis the link between aerodynamics and heat transfer in high pressure turbines is investigated through steady numerical calculations. The investigations include the effect of wall temperature on the Heat Transfer coefficient (HTC), aiming to understand whether the conventional assumption of HTC being invariant with the thermal boundary condition does hold in a typical compressible flow, where the aerodynamic and thermal fields are strongly coupled. A novel non-linear three point method is proposed to scale wall heat transfer accounting for the dependence of HTC on wall temperature and local flow history. The effect of wall boundary condition on external aerodynamics and heat transfer calls for the need of Conjugate Heat Transfer (CHT) methods as design tools. For this reason CHT capabilities have been developed and integrated in Rolls-Royce Hydra CFD solver. The implemented CHT solver is fully-coupled, allowing for simultaneous solution of the solid and fluid domains. The implemented CHT coupling has been shown to be numerically stable with a good convergence rate for all cases tested. The implemented code has been successfully validated against both experimental, analytical and numerical data. Conjugate analysis of a double-wall trailing edge cooling design has been performed under matched external Biot conditions. Aim of the investigation has been to quantify the effect of CHT on the cooling discharge characteristics and external aerodynamics in a cooling configuration where coolant and external flow are separated by a lower thermal resistance than in a traditional internal cooling configuration. Detailed CHT results for this case are presented and discussed.
5
Gardner, David Alan. "Numerical analysis of conjugate heat transfer from heat exchange surfaces". Thesis, University of Leeds, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329229.
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Salazar, Santiago. "Conjugate heat transfer on a gas turbine blade". Master's thesis, University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4546.
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Clearances between gas turbine casings and rotating blades is of quite importance on turbo machines since a significant loss of efficiency can occur if the clearances are not predicted accordingly. The radial thermal growths of the blade may be over or under predicted if poor assumptions are made on calculating the metal temperatures of the surfaces exposed to the fluid. The external surface of the blade is exposed to hot gas temperatures and it is internally cooled with air coming from the compressor. This cold air enters the radial channels at the root of the blade and then exists at the tip. To obtain close to realistic metal temperatures on the blade, the Conjugate Heat Transfer (CHT) approach would be utilized in this research. The radial thermal growth of the blade would be then compared to the initial guess. This work focuses on the interaction between the external boundary conditions obtained from the commercial Computational Fluid Dynamics software package CFX, the internal boundary conditions along the channels from a 1D flow solver proprietary to Siemens Energy, and the 3D metal temperatures and deformation of the blade predicted using the commercial Solid Mechanics software package ANSYS. An iterative technique to solve CHT problems is demonstrated and discussed. The results of this work help to highlight the importance of CHT in predicting metal temperatures and the implications it has in other aspect of the gas turbine design such as the tip clearances.ID: 029049805; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (M.S.M.S.E.)--University of Central Florida, 2010.; Includes bibliographical references (p. 44-46).
M.S.M.S.E.
Masters
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
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Subramaniam, Vignaesh. "Topology Optimization of Conjugated Heat Transfer Devices : Experimental and Numerical investigation". Thesis, Ecole nationale supérieure Mines-Télécom Lille Douai, 2018. http://www.theses.fr/2018MTLD0013/document.
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Concevoir des dispositifs thermiques plus compacts, nécessitant moins de masse de matière, produisant moins de pertes de charge et présentant un rendement thermique accru représente un enjeu clé pour des performances améliorées à un coût moindre. La présente thèse étudie le potentiel et la validité de l’optimisation topologique en tant qu’outil CFD viable permettant de générer des designs thermiques optimaux par rapport aux approches conventionnelles telles que l’optimisation de forme et paramétrique. La première partie de la thèse présente une étude expérimentale de structures bi matériaux arborescentes optimales obtenues par optimisation topologique. Le problème mathématique d’optimisation topologique est formulé et implémenté dans OpenFOAM®. Il est appliqué au problème d’optimisation de la conduction thermique dans une configuration de type volume-vers-point. Des mesures thermiques expérimentales sont effectuées sur les structures optimisées, en utilisant la thermographie infrarouge afin de quantifier leurs performances de transfert de chaleur et ainsi validé les performances des structures optimales déterminées par le code d’optimisation topologique développé. La deuxième partie de la thèse présente une technique bi-objectif innovante d’optimisation topologique des systèmes de transferts de chaleur conjugués (CHT, Conjugate Heat Transfer) en régimes d’écoulement laminaires. Pour cela, le problème est développé mathématiquement et implémenté dans le solveur OpenFOAM® basé sur une méthode directe par volumes finis. La fonction objectif est formulée par la pondération linéaire de deux fonctions objectifs, l’une pour la réduction de la perte de charge et l’autre pour l’augmentation du transfert de chaleur. Ceci représente une cible très difficile du point de vue numérique en raison de la concurrence entre les deux objectifs (minimisation de la perte de charge et maximisation de la puissance thermique récupérable). Des designs non intuitifs, mais optimaux au sens de Pareto, ont été obtenus, analysés, discutés et justifiés à l’aide de diverses méthodes d’analyses numériques globale et locale. De plus, une configuration identique à une optimisation par une méthode Lattice Boltzmann issue de la bibliographie a été optimisée en utilisant le solveur OpenFOAM® développé. L’objectif, en complément de la comparaison des solutions optimales, est également d’initier un cas de référence pour les futures études dans ce domaine de recherche et d’innovation de façon à pouvoir pleinement comparer les solutions optimales obtenues par différences méthodes et différents solveurs. Enfin, les différents points expérimentaux et numériques mis en lumière et illustrés dans cette thèse démontrent l’importance de la méthodologie et potentiel très important de l’optimisation topologique pour la conception de systèmes thermiques industriels plus performantsDesigning thermal devices that are more compact with less mass, less frictional losses and increased thermal efficiency is a key requirement for enhanced performances at a lower cost. The present PhD thesis investigates the potential and validity of topology optimization numerical method as a viable CFD tool to generate optimal thermal designs as compared to conventional approaches like shape and parametric optimization. The first part of the thesis presents an experimental investigation of topology optimized tree-like structures made of two materials. The topolgy optimization mathematical problem is formulated and implemented in OpenFOAM®. It is applied to the topolgy optimization problem of volume-to-point heat removal. Experimental thermal measurements are carried out, on the optimal structures, using infrared thermography in order to quantify their heat transfer performances and thus validate the performances of the optimal structures determined by the developed topology optimization code. The second part of the thesis presents an innovative bi-objective optimization technique for topology optimization of Conjugate Heat Transfer (CHT) systems under laminar flow regimes. For that purpose, an inequality constrained bi-objective topology optimization problem is developed mathematically and implemented inside the Finite Volume based OpenFOAM® solver. The objective function is formulated by linear combination of two objective functions for pressure drop reduction and heat transfer enhancement which is numerically a very challenging task due to a competition between the two objectives (minimization of pressure drop and maximization of recoverable thermal power). Non-intuitive Pareto-optimal designs were obtained, analyzed, discussed and justified with the help of various global and local numerical analysis methods. Additionally, a recent Lattice Boltzmann topology optimization problem form the literature was solved using the developed OpenFOAM® solver. The objective, in addition to the comparison of the optimal solutions, is also to initiate a case of reference for future studies in this field of research and innovation so as to be able to fully compare the optimal solutions obtained by different and different methods. solvers. Finally, the various experimental and numerical findings highlighted and illustrated in this PhD thesis, demonstrate the importance of the methodology and immense potential behind topology optimization method for designing efficient industrial thermal systems
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Webster, Robert Samuel. "A numerical study of the conjugate conduction-convection heat transfer problem". Diss., Mississippi State : Mississippi State University, 2001. http://library.msstate.edu/etd/show.asp?etd=etd-04102001-144805.
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Mathie, Richard. "Unsteady and conjugate heat transfer in convective-conductive systems". Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/10951.
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Unsteady (time-varying) heat transfer is an important transport phenomenon that is found in many engineering and industrial applications. In such systems, generic spatiotemporal variations in the flow give rise to variations in the heat flux for a given fluid-solid temperature difference, which can be interpreted as spatiotemporal fluctuations of the instantaneous heat transfer coefficient. These variations can lead to unsteady and conjugate heat transfer, in which the exchanged heat flux arises from an interaction between the bulk fluid temperature and the temperature in the solid. Further, the non-linear coupling between the fluctuating temperature differences and the heat transfer coefficients can lead to an effect we refer to as augmentation, which quantitatively describes the ability of a particular arrangement to have a different time-mean heat flux from the product between the mean heat transfer coefficient and the mean temperature difference across the fluid. In this thesis we investigate unsteady conductive-convective heat transfer, and the resulting augmentative and conjugate effects. The overriding purpose is to propose a simple framework for the description of the effect of unsteadiness on the overall heat exchange performance, leading to the improved understanding and prediction of related processes. An analytical model is developed that describes the thermal interaction between the solid and the fluid domains with the use of a time-varying heat transfer coefficient, and assuming 1-D conductive heat transfer in the solid. It is found that the degree of augmentation can be defined in terms of key independent problem variables, including: a time-averaged Biot number, a dimensionless solid thickness (normalised by an unsteady thermal diffusion length), a heat transfer coefficient fluctuation intensity (amplitude normalised by the mean), and a heat capacity ratio between the fluid and solid domains. The model is used to produce regime maps that describe the range of conditions in which augmentation effects are exhibited. Such maps can be used in the design of improved heat exchangers or thermal insulation, for example through the novel selection of materials that can exploit these augmentation effects. Cases are considered for which the bulk fluid temperature is fixed, and for which the bulk fluid temperature is allowed to respond to the solid, both in thermally developing and fully developed flows. Generally the augmentation effect is found to be negative, reflecting a reduction in the heat exchange capability. However, regions of positive augmentation are uncovered in thermally developing convective flows, which has important implications for heat exchanger design. The approach is used to model two different thermodynamic cycles; gas springs and two-phase thermodynamic oscillator engines. Firstly, for the gas spring it is found that at low Peclet numbers the addition of an insulating layer exacerbates the thermal losses in the spring as it shifts the system away from the isothermal ideal operation. Conversely at high Peclet numbers thicker insulating layers reduces the loss as it shifts the system towards the adiabatic ideal. It is also found that there is an intermediate thickness of material thickness which maximises the loss in the gas spring, by up to 20 % of the nominal maximum loss for an isothermal cylinder lining. Secondly the heat transfer and resulting shuttle loss in the vapour space of a two-phase thermofluidic oscillator was studied. This model was compared to experimental data from a working test bed and resulted in a substantial improvement in the calculation of the cycle efficiency of the engine. Detailed flow measurements were also conducted on a fluid film flowing down a heated incline, to investigate the effects of unsteady heat transfer in these flows. These wavy interfacial flows exhibit large and periodic fluctuations in heat transfer and the frequency and amplitude of the waves was controlled by a specially constructed flow preparation arrangement. To enable the temperature and heat flux measurements the heated incline consisted of a thin titanium foil. A novel measurement technique was developed (here, for the first time) to measure the film interface height (film thickness), film temperature and instantaneous heat flux through the heated surface. This was achieved with a combination of spatiotemporally resolved Laser Induced Florescence (LIF) measurements and Infra-red (IR) thermography. In the case of steady flow conditions (without forced waves) the formation of Marangoni driven rivulet structures are observed on the film surface. In the case of unsteady flow the formation of waves on the film surface result in visible mixing of the rivulet structures. The mixing and the unsteady motion of the waves give rise to a periodic fluctuation in the heat transfer coefficient, with fluctuation intensities of up to 35 % being recorded. The model predictions of the augmentation ratio for these problems are also compared to direct measurements from each case. Good agreement is observed with the experimental results for the global heat transfer trends. In both cases the augmentation ratio is negative, reflecting a reduction in time-averaged heat transfer. Finally, a backwards-facing step flow is also studied, for which a low magnitude of augmentation was observed (< 1 %), considerably lower than the augmentation measured in the thin film flows which were up to 10 %.
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Gupta, Jatin. "Application Of Conjugate Heat Transfer (Cht) Methodology For Computation Of Heat Transfer On A Turbine Blade". The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1230064860.
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Kose, Serhat. "Theoretical Investigation Of Conjugate Condensation Heat Transfer Inside Vertical Tubes". Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612396/index.pdf.
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Based on the well-known theoretical studies related to the film condensation inside vertical tubes, a known temperature distribution is prescribed as boundary condition at the inner surface of the tube wall. But, in reality, there is a thermal interaction between the condensate fluid and conduction through the wall where the temperature variation along the inner surface of the tube wall is unknown and this unknown temperature profile should be determined by taking account of this interaction. In other words, the heat conduction equation for the tube wall and the energy equation for the condensate fluid flow should be coupled and solved simultaneously. Therefore, this type of problem is named &ldquoconjugate condensation heat transfer problem&rdquo
. Subject to the conjugate condensation heat transfer problem in the industrial applications, there are two different fluid flows separated by a tube where the vapor flowing inside the tube condensates whereas the other one is heated and it flows externally in the counter current direction in the annular passages. Because of its fundamental and practical importance, in this doctoral thesis, the studies are focused on the analytical and numerical investigation of conjugate heat transfer due to the steam condensation inside vertical tubes which is cooled externally by a fluid flowing in the counter current direction. The unknown wall temperatures of the condenser tube, condensate liquid layer inside the tube and the turbulent coolant flow outside the tube are coupled. A computer code, named ZEC, containing condensation conjugate heat transfer model is developed in FORTRAN 90 Language. This code and the models it contains are assessed against the various experimental databases. The predictions of the code ZEC are found to reasonably agree with the experimental results over a wide range of conditions. Therefore, this developed code, ZEC, may be used for the preliminary design of in-tube condensers and for the performance evaluation of such condensers in operation.
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Cha'o-Kuang, C. "The conjugated convection-conduction analysis of heat transfer in a vertical fin". Thesis, University of Liverpool, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377119.
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Sjölinder, Emil. "Spray and Wall Film Modeling with Conjugate Heat Transfer in OpenFOAM". Thesis, Linköpings universitet, Mekanisk värmeteori och strömningslära, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-84487.
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This master thesis was provided by Scania AB. The objective of this thesis was to modify an application in the free Computational Fluid Dynamics software OpenFOAM to be able to handle spray and wall film modeling of a Urea Water Solution together with Conjugate Heat Transfer. The basic purpose is to widen the knowledge of the vaporization process of a Urea Water Solution in the exhaust gas after treatment system for a diesel engine by using OpenFOAM. First, urea has been modeled as a very viscous liquid at low temperature to mimic the solidication process of urea. Second, the development of the new application has been done. At last, test simulations of a simple test case are performed with the new application. The results are then compared with simplied hand calculations to verify a correct behavior of certain exposed source terms. The new application is working properly for the test case but to ensure the reliability, the results need to be compared with another Computational Fluid Dynamics software or more preferable, real experiments. For more advanced geometries, the continued development presented last in this thesis is highly recommended to follow.
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Gari, Abdullatif Abdulhadi. "Analysis of conjugate heat transfer in tube-in-block heat exchangers for some engineering applications". [Tampa, Fla] : University of South Florida, 2006. http://purl.fcla.edu/usf/dc/et/SFE0001716.
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Knapke, Robert. "High-Order Unsteady Heat Transfer with the Harmonic Balance Method". University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1427962937.
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Uapipatanakul, Sakchai. "Development of computational methods for conjugate heat transfer analysis in complex industrial applications". Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/development-of-computational-methods-for-conjugate-heat-transfer-analysis-in-complex-industrial-applications(3910eec7-601d-4da1-8c08-854404bbba3a).html.
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Conjugate heat transfer is a crucial issue in a number of turbulent engineering fluidflow applications, particularly in nuclear engineering and heat exchanger equipment. Temperature fluctuations in the near-wall turbulent fluid lead to similar fluctuationsin the temperature of the solid wall, and these fluctuations in the solid cause thermalstress in the material which may lead to fatigue and finally damage. In the present study, the Reynolds Average Navier-Stokes (RANS) modelling approachhas been adopted, with four equation k−ε−θ2−εθ eddy viscosity based modelsemployed to account for the turbulence in the fluid region. Transport equations forthe mean temperature, temperature variance, θ2, and its dissipation rate, εθ, have beensimultaneously solved across the solid region, with suitable matching conditions forthe thermal fields at the fluid/solid interface. The study has started by examining the case of fully developed channel flow withheat transfer through a thick wall, for which Tiselj et al. [2001b] provide DNS dataat a range of thermal activity ratios (essentially a ratio of the fluid and solid thermalmaterial properties). Initial simulations were performed with the existing Hanjali´cet al. [1996] four-equation model, extended across the solid region as described above. However, this model was found not to produce the correct sensitivity to thermal activityratio of the near wall θ2 values in the fluid, or the decay rate of θ2 across the solid wall. Therefore, a number of model refinements are proposed in order to improve predictionsin both fluid and solid regions over a range of thermal activity ratios. These refinementsare based on elements from a three-equation non-linear EVM designed to bring aboutbetter profiles of the variables k, ε, θ2 and εθ near the wall , and their inclusion is shownto produce a good matching with the DNS data of Tiselj et al. [2001b].Thereafter, a further, more complex test case has been investigated, namely an opposedwall jet flow, in which a hot wall jet flows vertically downward into an ascendingcold flow. As in the channel flow case, the thermal field is also solved across the solidwalls. The modified model results are compared with results from the Hanjali´c modeland LES and experimental data of Addad et al. [2004] and He et al. [2002] respectively. In this test case, the modified model presents generally good agreement with the LESand experimental data in the dynamic flow field, particularly the penetration point ofthe jet flow. In the thermal field, the modified model also shows improvements in the θ2predictions, particularly in the decay of the θ2 across the wall, which is consistent withthe behaviour found in the simple channel flow case. Although the modified model hasshown significant improvements in the conjugate heat transfer predictions, in some instancesit was difficult to obtain fully-converged steady state numerical results. Thusthe particular investigation with the inlet jet location shows non-convergence numericalresults in this steady state assumption. Thus, unsteady flow calculations have beenperformed for this case. These show large scale unsteadiness in the jet penetration area. In the dynamic field, the total rms values of the modelled and mean fluctuations showgood agreement with the LES data. In the thermal field calculation, a range of the flowconditions and solid material properties have been considered, and the predicted conjugateheat transfer predicted performance is broadly in line with the behaviour shownin the channel flow.
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Koren, Chai. "Modeling conjugate heat transfer phenomena for multi-physics simulations of combustion applications". Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLC001/document.
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Dans un souci d’optimisation des fours industriels et de réduction des émissions de gaz à effet de serre,l’oxy-combustion est considérée comme l’une des solutions d’avenir. Les conditions existantes dans les chambres d’oxycombustion créent une interaction forte entre les différents phénomènes : Combustion,turbulence et transferts de chaleur. Pour mieux dimensionner les configurations futures il est nécessaire de pouvoir étudier la physique qui y règne, et ce pour un coût et un temps de retour raisonnables. De tels études nécessitent l’emploi d’outils de simulation de haute fidélité,et afin de modéliser les interactions inter-phénomènes à un coût acceptable le couplage de codes est utilisé. C’est avec cet objectif que les travaux présentés dans ce manuscrit se concentrent sur la mise au point d’une méthodologie de couplage entre codes d’écoulements réactifs et de transfert de chaleur dans les parois pour la réalisation de simulations de haute-fidélité massivement parallèles prédictives des chambres futuresOxycombustion is seen as one mean to attain the wished goals in terms of efficiency optimisation and Greenhouse Effect Gases emissions reduction for industrial furnaces. The extreme operating conditions, high pressure and temperature, lead to a strong interaction between the different phenomena which take place inside the combustion chambe r: Combustion, turbulence and heat transfer. To better design these futur oxyfuel processes, a mean to study the related physics with a reasonable computational cost and return time. Such studies require the use of high-fidelity numerical resolution tools, and in order to model the multi-physics interaction in a cost efficient way, code coupling. The operating conditions being extreme : High pressure and temperature, a strong interaction exists between the different phenomena occuring inside the chamber. To better understand the physics inside oxycombustion chambers,a multiphysics high-fidelity simulation methodology is developped
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Goktolga, Mustafa Ugur. "Simulation Of Conjugate Heat Transfer Problems Using Least Squares Finite Element Method". Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614787/index.pdf.
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In this thesis study, a least-squares finite element method (LSFEM) based conjugate heat transfer solver was developed. In the mentioned solver, fluid flow and heat transfer computations were performed separately. This means that the calculated velocity values in the flow calculation part were exported to the heat transfer part to be used in the convective part of the energy equation. Incompressible Navier-Stokes equations were used in the flow simulations. In conjugate heat transfer computations, it is required to calculate the heat transfer in both flow field and solid region. In this study, conjugate behavior was accomplished in a fully coupled manner, i.e., energy equation for fluid and solid regions was solved simultaneously and no boundary conditions were defined on the fluid-solid interface. To assure that the developed solver works properly, lid driven cavity flow, backward facing step flow and thermally driven cavity flow problems were simulated in three dimensions and the findings compared well with the available data from the literature. Couette flow and thermally driven cavity flow with conjugate heat transfer in two dimensions were modeled to further validate the solver. Finally, a microchannel conjugate heat transfer problem was simulated. In the flow solution part of the microchannel problem, conservation of mass was not achieved. This problem was expected since the LSFEM has problems related to mass conservation especially in high aspect ratio channels. In order to overcome the mentioned problem, weight of continuity equation was increased by multiplying it with a constant. Weighting worked for the microchannel problem and the mass conservation issue was resolved. Obtained results for microchannel heat transfer problem were in good agreement in general with the previous experimental and numerical works.
In the first computations with the solverquadrilateral and triangular elements for two dimensional problems, hexagonal and tetrahedron elements for three dimensional problems were tried. However, since only the quadrilateral and hexagonal elements gave satisfactory results, they were used in all the above mentioned simulations.
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Weaver, Michael A. "Nonlinear multiple-discipline analysis of conjugate heat transfer and fluid-structure interaction". Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/12461.
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Wang, Hong Zhi 1971. "3D conjugate heat transfer simulation of aircraft hot-air anti-icing systems". Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=83942.
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When an aircraft flies through clouds under icy conditions, supercooled water droplets at temperatures below the freezing point may impact on its surfaces and result in ice accretion. The design of efficient devices to protect aircraft against in-flight icing continues to be a challenging task in the aerospace industry. Advanced numerical tools to simulate complex conjugate heat transfer phenomena associated with hot-air anti-icing are needed. In this work, a 3D conjugate heat transfer procedure based on a loose-coupling method has been developed to solve the following four domains: the external airflow, the water film, conduction in the solid, and the internal airflow. The domains are solved sequentially and iteratively, with an exchange of thermal conditions at common interfaces until equilibrium of the entire system is achieved. A verification test case shows the capability of the approach in simulating a variety of anti-icing and de-icing cases: fully evaporative, running wet, or iced. The approach is validated against a 2D dry air experimental test case, because of the dearth of appropriate open literature 3D test data.
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Sosnowski, Pawel. "Numerical investigation of evaporation and condensation of thin films in conjugated heat transfer systems". Doctoral thesis, Università degli studi di Trieste, 2013. http://hdl.handle.net/10077/8662.
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2011/2012Evaporation and condensation of thin liquid films on solid surfaces are common elements of industrial processes. In many cases they have a significant impact on the physics of the studied case. At the same time, experimental studies can prove to be troublesome, mostly because of the amount of possible setups, complex geometries of interest, numerous materials being used and cost. For that reason it is reasonable to study this phenomena using numerical methods. Having the advantage in speed and cost of performance, computational studies become a valuable tool. For evaporation and condensation process, one has to deal with buoyancy driven fluid flows, conjugated heat transfer between gaseous and solid phases, film thickness modeling, vapor phase behavior, and phase transition of the thin fluid film into vapor phase. The strong conjunction and mutual interaction of mentioned effects is the main focus of presented work. The gas phase behavior is being calculated using incompressible Navier-Stokes equations under Boussinesq approximation. The solutions of the partial differential equations are obtained with numerical methods using Eulerian finite volume discretization (Kundu and Cohen [2002]). Time advancement is being treated with second order implicit discretization. For cases with high Reynolds number, large eddy simulation (LES) techniques are used. Due to the complexity of the geometries of interest a dynamic computation of the Smagorinsky constant is preferred, applying the lagrangian dynamic model proposed by Meneveau et al. [1996]. The liquid film present on the surface of the solids is modeled following Petronio[2010]. Since the film is thin, it is assumed that it can be represented only by its thickness. This also leads to assumption that the heat transfer through the film is instantaneous. The vapor is represented by concentration of this phase in the volume of gas. The concentration is transported by convection and diffusion. The phenomena of evaporation and condensation of the thin films are driven by the presence of concentration gradients next to the surfaces. Phase transition of vapor to fluid, or other way around, acts on the energy balance, id. est latent heat is released into the gas when condensation occurs or the solid is cooled during evaporation. The heat transport is modeled in both solid and fluid domains. The case is split into separate regions with different material properties. These regions are solved one by one in a serial way using numerical techniques consistent with domain decomposition methods described by Quarteroni and Valli [1999]. The energy transport among the regions is performed by applying a heat coupling boundary conditions. The main focus of this work is to provide a reliable model for simulation system with complex physics involving fluid motion, heat transport in multi region domains (fluid-solid), vapor transport, thin film evolution and evaporation and condensation effects on energy balance. Proposed model is validated on simple geometries and later applied to problem of evaporation in vertical channel flow. The reference to the channel case is work of Laaroussi et at. [2009]. Presented study aims in providing comprehensive insights into physical effects that appear when the solid wall is being directly modeled and when latent heat transformations are taken into account. The final test is performed on a vertical channel with forced turbulent flow, directly modeled solid walls and evaporation or condensation happening on the boundary. Having the model working within such complex frame allows for its future usage in elaborate industrial applications.
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Xue, Qingluan. "Development of conjugate heat transfer capability to an unstructured flow solver - U²NCLE". Master's thesis, Mississippi State : Mississippi State University, 2005. http://sun.library.msstate.edu/ETD-db/ETD-browse/browse.
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El-Jummah, Abubakar Mohammed. "Impingement and impingement/effusion cooling of gas turbine components : conjugate heat transfer predictions". Thesis, University of Leeds, 2014. http://etheses.whiterose.ac.uk/9025/.
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Conjugate heat transfer (CHT) and computational fluid dynamics (CFD) were combined in this work using ICEM meshing and ANSYS Fluent software. Block-structured grids with hexahedral elements were used to investigates the key features of impingement cooling of gas turbine metal surfaces, with applications to combustor wall, nozzle and turbine blade cooling. Only flat wall cooling was investigated and not any influence of surface curvature. Combustor wall and turbine blade flank cooling both approximate to a flat wall as the hole diameter and pitch are all small in relation to the combustor or blade curvature. Also the experimental data base on impingement cooling predominantly uses a flat wall. The aim was to validate the computations against experimental data from hot metal wall research facilities and then to use the validated computational methodology to predict improved cooling geometries. Experimental investigations that used hot wall rigs at 770 K cross-flow temperature and 293 K coolant were modelled to predict the overall cooling effectiveness for impingement cooling. The impingement cooling of the metal surface with an equivalent heat flux was modelled, at a hot gas value equals to 100 kW/m2 and is an input relevant to real gas turbine combustor applications of 250 kW/m2K heat transfer coefficient (HTC). Much of the experimental data base with metal walls used electrically heated metal wall experiments with relatively low wall temperatures. These were also modelled using a constant hot gas side temperature and the thermal gradient through the thickness and between impingement and effusion holes were predicted. The work was confined to the internal wall heat transfer and did not investigate the combined film effusion cooling that is often used in combination with impingement cooling. However, the interaction of internal wall effusion cooling with impingement cooling was investigated, so that the whole internal wall cooling could be predicted. The heat transfer in a metal wall with a square array of 90o holes is a subcomponent of impingement and effusion cooling and was part of this study, which was used to evaluate the impact of the CFD turbulence models. The standard k - ɛ turbulence model with standard wall function (WF) for y+ values in the range 30 - 45 showed better agreement with the measured data, where all the flow features were predicted correctly. Also enhanced wall treatment approaches (EWT) were used for y+ values from 1 - 5, but there was no significant improvement in the predictions compared with the standard wall function approach. All the turbulence models available in Fluent were investigated for an array of holes in a metal wall, which involves only a computation of one hole that is classic short hole or pipe entry length heat transfer. Many of the models could not predict the flow separation and reattachment within a hole L/D of ~1 and as this was fundamental to both effusion and impingement heat transfer, indicating that these models were all poor at the predictions of impingement and impingement/effusions cooling. The experimental data base in impingement heat transfer has results that would not normally be expected and the CHT computations enabled the reason for the experimental trends to be explained. This includes the reduction in heat transfer along the impingement gap influenced by cross-flow, which would be expected to increase the heat transfer. The relatively low effect of turbulence enhancing obstacles in the impingement gap was also predicted. The influence of the number of impingement holes, which leads to methodology to choose a particular hole size has been predicted based on thermal gradients in the metal wall, this helps the designer in choosing optimum number of holes. For impingement cooling with single sided coolant exit from the cross-flow duct, it was shown that the deflection of the cross-flow onto the impingement jet wall surface was a major reason for the deterioration in the impingement target surface heat transfer along the gap. The very limited experimental database for heat transfer to the impingement jet wall surface was well predicted, thus showing that both wall surfaces were important in the overall impingement heat transfer. The design configurations investigated were the hole length, pitch, gap, height and depth to diameter ratios L/D, X/D, Z/D, H/D and E/D respectively. The range of L/D investigated was 0.78 - 4.85, by varying the hole diameter for a fixed metal wall thickness (length) of 6.35 mm. This heat transfer was dominated by thermal and aerodynamic entry length effects including the heat transfer on the hole approach surface. The X/D range investigated was 1.86 - 21.02 by varying D at constant X and also by varying X at constant D, which varies the number of holes per surface area, n. The range of Z/D investigated was from 0.76 - 7.65 at varied and also at a constant Z. The main coolant flow parameter varied was the mass flux G, which is equals to G*/P (kg/sm2bar) in this Ph. D thesis. The requirements for each G with a fixed hole geometry, is a new CHT computation, which is time consuming compared with fairly rapid experimental determinations of the effect of G. The literature survey showed that there were no available detailed flow dynamics investigations of multi-hole impingement cooling. The key experimental measurement that indicates the correctness of the aerodynamic predictions was the pressure loss, which was as a result of the air feed to the impingement gap or effusion hole discharge. The results showed, for the range of geometries, reasonable agreement with the experimental measurements. For heat transfer the experimental measurements were all surface averaged, either for the whole wall or for each row of holes. The predictions were shown to give excellent agreement with surface average heat transfer, which also gave the surface distribution of the heat transfer. It was shown that the surface distribution of heat transfer was directly related to the surface distribution of the turbulence kinetic energy. The experimental influence of turbulence enhancing obstacles in the impingement gap was well predicted. The experimental data base was for one obstacle per impingement hole using two flow configurations: flow parallel to the obstacles, so that the action was to increase the surface area for heat transfer at low blockage increase and flow across the obstacles, so that the action was to increase turbulence and surface area, but at the expense of higher pressure loss. Two obstacles shapes were investigated experimentally, simple continuous ribs and slotted ribs which gave rectangular pin fins relative to the cross-flow, with both turbulence generation and surface area increased. The predictions agreed with the experiments that showed the main effect of the obstacles, for which the deterioration of heat transfer with distance was reduced, but to only have a relatively small (~ 20%) increase in the surface averaged heat transfer. The validated computational procedures were used to investigate other obstacle geometries for the same impingement configuration: surface dimples, round pin-fins and inclined ribs in a zig-zag of ‘W’ format. The zig-zag design predicted an improvement in overall heat transfer compared with the other designs. Impingement/effusion internal wall heat transfer was modelled with one effusion hole per impingement hole and a fixed 8 mm gap. It was shown that the key interaction effect was to remove any cross-flow from the gap, provided all the impingement air flow went through the effusion holes. This geometry is then only viable for low coolant mass flow rates and thus the modelling was confined to low G. This limitation of coolant flow was because effusion cooling improves if the hole velocity is low relative to the cross-flow, which occurs at low mass flow rates.
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CINTOLESI, CARLO. "Large-eddy simulations of conjugate heat transfer with evaporation-condensation and thermal radiation". Doctoral thesis, Università degli Studi di Trieste, 2016. http://hdl.handle.net/11368/2908064.
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Heat transfer in fluids and between a fluid and a surrounding solid body is often encountered in practical applications. The numerical investigations of such phenomena is of great interest for a number of practical applications, both on industrial and environmental side. Among the others we mention optimization of home appliances (oven, dishwasher, refrigerators), building design (ventilation and heating systems), electronic equipment design (solar collectors, device cooling systems), environmental flow analysis (atmospheric thermal stratification, evaporation from lakes and channels, solar thermal radiation).
Despite the wide range of application, the correct numerical simulation of such systems poses big challenges. First, the physics governing wet-surface evaporation/condensation processes and thermal radiation is extremely complex; thus, a mathematical model is derived only under simplification hypotheses. Second, the transient nature of surface heat transfer along with the complex geometry and anisotropic turbulence flow, requires a careful numerical resolution technique of the fluid flow equations. Third, particular attention has to be payed when the different heat transfer modes are coupled, because of their mutual strong interaction.
The present work focuses on numerical investigation of the heat transfer mechanisms in fluid dynamics systems, considering different physical processes. Specifically, this topic is declined in three different studies: (i) turbulent buoyant flow in a confined cavity with conjugate heat transfer; (ii) thin film evaporation and condensation process from a vertical plate inside an enclosure; (iii) radiative heat transfer in systems with participating media. All these points are tackled. A complete numerical solver is presented and employed.
In all cases we use large-eddy simulation, carried out in conjunction with a dynamic Lagrangian subgrid-scale turbulent model. Also, the thermal interaction between fluid and solid media is considered by means of conjugate heat transfer; the problem with evaporation and condensation over solid surfaces is studied taking advantage of the thin film assumption; a radiative heat transfer model is integrated in the numerical solver.
The heat exchange, through fluid and solid interface, is due to conduction, water change of phase and surface thermal radiation. The temperature alteration of conductive solids, can substantially change the system thermodynamic equilibrium and can eventually lead to significant variations on the overall fluid dynamics.
An in-house solver, developed within the open-source software package OpenFOAM, is used for the numerical studies and, later, extended to include the effects of thermal radiation and surface radiative heat exchange.
The influence of various solid boundary materials on natural convection in closed cavity is investigated, pointing out the different effects induced on the fluid motion by thermal conductors and insulators (this part of the research has been published in Physics of Fluid). The study has shown that thermal conductive boundaries strongly influence the fluid flow; the use of simplify boundary condition (such as the adiabatic condition) instead of conjugate heat transfer, leads to unrealistic results.
Successively, the cooling effects of water evaporation from a plate are studied, changing the plate materials, and the different behaviour of each substance is analysed. This study has shown that water change of phase completely rules the interface heat exchange and that material heat capacity governs the cooling process of wet bodies.
Finally, the physics of thermal radiation is reviewed, the mathematical derivation of the spherical harmonic approximation model is reported and its accuracy studied, the numerical implementation carefully documented and validated.
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Zitzmann, Tobias. "Adaptive modelling of dynamic conjugate heat transfer and air movement using computational fluid dynamics". Thesis, De Montfort University, 2007. http://hdl.handle.net/2086/4287.
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Ojeda, Steven Matthew. "A cut-cell method for adaptive high-order discretizations of conjugate heat transfer problems". Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/90783.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 143-151).
Heat transfer between a conductive solid and an adjacent convective fluid is prevalent in many aerospace systems. The ability to achieve accurate predictions of the coupled heat interaction is critical in advancing thermodynamic designs. Despite their growing use, coupled fluid-solid analyses known as conjugate heat transfer (CHT) are hindered by the lack of automation and robustness. The mesh generation process is still highly dependent on user experience and resources, requiring time-consuming involvement in the analysis cycle. This thesis presents work toward developing a robust PDE solution framework for CHT simulations that autonomously provides reliable output predictions. More specifically, the framework is comprised of the following components: a simplex cut-cell technique that generates multi-regioned meshes decoupled from the design geometry, a high-order discontinuous Galerkin (DG) discretization, and an anisotropic output-based adaptation method that autonomously adapts the mesh to minimize the error in an output of interest. An existing cut-cell technique is first extended to generate fully-embedded meshes with multiple sub-domains. Then, a coupled framework that combines separate disciplines is developed, while ensuring compatibility between the cut-cell and mesh adaptation algorithms. Next, the framework is applied to high-order discretizations of the heat, Navier-Stokes, and Reynolds-Averaged Navier-Stokes (RANS) equations to analyze the heat flux interaction. Through a series of numerical studies, high-order accurate outputs solved on autonomously controlled cut-cell meshes are demonstrated. Finally, the conjugate solutions are analyzed to gain physical insight to the coupled interaction.
by Steven Matthew Ojeda.
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Olakoyejo, O. T. (Olabode Thomas). "Geometric optimisation of conjugate heat transfer in cooling channels with different cross-sectional shapes". Thesis, University of Pretoria, 2012. http://hdl.handle.net/2263/25484.
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In modern heat transfer, shape and geometric optimisation are new considerations in the evaluation of thermal performance. In this research, we employed constructal theory and design to present three-dimensional theoretical and numerical solutions of conjugate forced convection heat transfer in heat generating devices with cooling channels of different cross-sectional shapes. In recent times, geometric configurations of cooling channel have been found to play an important role in thermal performance. Therefore, an efficient ways of optimally designing these cooling channels shapes is required. Experimentation has been extensively used in the past to understand the behaviour of heat removals from devices. In this research, the shapes of the cooling channels and the configurations of heat-generating devices were analytically and numerically studied to minimise thermal resistance and thus illustrate cooling performance under various design conditions. The cooling channels of five different cross-sectional shapes were studied: Circular, square, rectangular, isosceles right triangular and equilateral triangular. They were uniformly packed and arranged to form larger constructs. The theoretical analysis is presented and developed using the intersection of asymptotes method. This proves the existence of an optimal geometry of parallel channels of different cross-sectional shapes that penetrate and cool a volume with uniformly distributed internal heat generation and heat flux, thus minimising the global thermal resistance. A three-dimensional finite volume-based numerical model was used to analyse the heat transfer characteristics of the cross-sectional shapes of various cooling channels. The numerical computational fluid dynamics (CFD) package recently provided a more cost-effective and less time-consuming means of achieving the same objective. However, in order to achieve optimal design solutions using CFD, the thermal designers have to be well experienced and carry out a number of trial-and-error simulations. Unfortunately, this can not always guarantee an accurate optimal design solution. In this thesis a mathematical optimisation algorithm (a leapfrog optimisation program and DYNAMIC-Q algorithm) coupled with numerical CFD was employed and incorporated into the finite volume solver, –FLUENT, and grid (geometry and mesh) generation package, – GAMBIT to search and identify the optimal design variables at which the system would perform optimally for greater efficiency and better accuracy. The algorithm was also specifically designed to handle constraint problems where the objective and constraint functions were expensive to evaluate. The automated process was applied to different design cases of cooling channels shapes. These cooling channels were embedded in a highly conductive solid and the peak temperature was minimised. The trend and performance of all the cooling channel shapes cases studied were compared analytically and numerically. It was concluded that an optimal design can be achieved with a combination of CFD and mathematical optimisation. Furthermore, a geometric optimisation of cooling channels in the forced convection of a vascularised material (with a localised self-cooling property subjected to a heat flux) was also considered. A square configuration was studied with different porosities. Analytical and numerical solutions were provided. This gradient-based optimisation algorithm coupled with CFD was used to determine numerically the optimal geometry that gave the lowest thermal resistance. This optimiser adequately handled the numerical objective function obtained from numerical simulations of the fluid flow and heat transfer. The numerical results obtained were in good agreement with results obtained in the approximate solutions based on scale analyses at optimal geometry dimensions. The approximate dimensionless global thermal resistance predicted the trend obtained in the numerical results. This shows that there were unique optimal design variables (geometries) for a given applied dimensionless pressure number for fixed porosity. The results also showed that the material property had a significant influence on the performance of the cooling channel. Therefore, when designing the cooling structure of vascularised material, the internal and external geometries of the structure, material properties and pump power requirements would be very important parameters to be considered in achieving efficient and optimal designs for the best performance. Finally, this research investigated a three-dimensional geometric optimisation of conjugate cooling channels in forced convection with an internal heat generation within the solid for an array of cooling channels. Three different flow orientations based on constructal theory were studied numerically- firstly, an array of channels with parallel flow; secondly, an array of channels in which flow of every second row was in a counter direction and finally, an array of channels in which the flow direction in every channel was opposite to that of previous channel. The geometric configurations and flow orientations were optimised in such a way that the peak temperature was minimised subject to the constraint of fixed global volume of solid material. The optimisation algorithm coupled with CFD was also used to determine numerically the optimal geometry that gave the lowest thermal resistance. The use of the optimisation algorithm coupled with the computational fluid dynamics package; render the numerical results more robust with respect to the selection of optimal structure geometries, internal configurations of the flow channels and dimensionless pressure difference.Thesis (PhD(Eng))--University of Pretoria, 2012.
Mechanical and Aeronautical Engineering
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Xue, Qingluan. "Development of adaptive mesh refinement scheme and conjugate heat transfer model for engine simulations". [Ames, Iowa : Iowa State University], 2009.
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Greenland, Marc Robert. "Analysis of Conjugate Heat Transfer and Pressure Drop in Microchannels for Different Aspects Ratios". Diss., University of Pretoria, 2016. http://hdl.handle.net/2263/56077.
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In this study the heat transfer and hydrodynamic parameters were experimentally investigated for a single microchannel housed in a stainless steel solid base material for different aspect ratios in the laminar regime with water as the working fluid. The stainless steel base material had a low thermal conductivity (15.1 W / mK) which magnified the conjugative effects in order to better understand the heat transfer. Rectangular microchannels with a height and width of 0.64 mm x 0.41 mm for Test Section 1, 0.5 mm x 0.5 mm for Test Section 2 and 0.43 mm x 0.58 mm for Test Section 3 were considered. The overall width of the solid substrate was 1.5 mm and the length was 50 mm for all of the test sections. The aspect ratio of the channel and the solid substrate was kept equal. A constant heat flux of 10 W / cm2 was applied to the bottom outer wall of the test section. A sudden contraction inlet and a sudden expansion outlet manifold contained pressure ports, to measure the pressure drop across the test sections, and thermocouples measured the mean inlet and outlet fluid temperatures. Thermocouples were used to measure the outer top and side wall temperatures at four equally spaced positions along the axial direction. The amount of axial heat conduction was below 0.6 % for all of the test sections and therefore warranted the use of a two-dimensional conduction model to determine the heat transfer parameters at the fluid to solid interface based on the outer measured wall temperatures. The local Nusselt number decreased, along the axial direction but increased towards the exit for all of the test sections. The average Nusselt number increased with the flow rate and the critical Reynolds number for fully turbulent flow Test Section 1 was 1950, for Test Section 2 was 2250 and for Test Section 3 was 1650. The average Nusselt number was directly related to the perimeter of the microchannels two side walls and the bottom wall (not the top wall), and thus decreased as the aspect ratio of the channel increased. The experimentally determined Nusselt numbers were larger for all three test sections when compared to common acceptable correlations. The friction factor decreased with the flow rate and was smaller in magnitude when compared to conventional theories. The diabatic friction factor magnitudes were smaller than the adiabatic friction factors. The friction factor decreased as the aspect ratio decreased, where the aspect ratio was calculated by taking the maximum of the microchannels width or height, divided by the minimum of the two. The possibility of a relationship could exist between the Colburn j-factor and the friction factor when considering the results for Test Section 1 and Test Section 2 but the results for Test Section 3 were significantly different.Dissertation (MEng)--University of Pretoria, 2016.
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Mechanical and Aeronautical Engineering
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Brack, Stefan [Verfasser]. "Time-resolved Transient Convective and Conjugate Heat Transfer Experiments Using IR Thermography / Stefan Brack". München : Verlag Dr. Hut, 2020. http://d-nb.info/1219476323/34.
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Pettersson, Marcus. "Cooling Potential of Methane in Rocket Nozzle Cooling Channels : A Conjugate Heat Transfer Analysis". Thesis, KTH, Skolan för industriell teknik och management (ITM), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-264355.
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The use of hydrocarbons as fuel in rocket propulsion has been of great interest to the aerospace industry in recent years. Specifically, natural gas with a high content of methane has taken the interest of several actors, among them Sweden-based GKN Aerospace who in collaboration with KTH Royal Institute of Technology have started the MERiT project. In this project, the potential of methane as a fuel is explored through conjugate heat transfer analysis of a cooling channel geometry on a test rig. The goal is partly to find what the cooling potential of the methane is, and partly to determine the risks of thermal cracking occurring in the cooling channel. This report aims to provide a CFD analysis of the behavior of a test rig developed in earlier stages of the project. The analysis is to be used to provide design points that real experiments can be based upon. Studied behaviors include limitations regarding overheating, choke in the cooling channel and efficiency of the rig. In addition to this, the fluid temperature is studied in order to provide an estimate of which design points provide the highest potential risk of thermal cracking. In experiments, this potential risk is to be evaluated and explored in order to judge the viability of methane as a fuel. From this thesis a database of design points has been built regarding two potential channel geometries with different alloy materials. The post process and gathering of data are designed in such a way that specific behaviors can be monitored depending on a specific input. Inputs include mass flow, heat flux, inlet temperature and outlet pressure of the test rig. These were parametrized such that 243 specific design points could be examined for each channel geometry. Concluding this thesis, it was found that 131 of the cases examined for the first channel geometry were within the realm of being useful, and that a few cases fall within the realm of being at risk for coking. The risk for choke in the cooling channel is apparent at high mass flows and low pressures. The efficiency is heavily tied to heat flux and inlet temperature but shifts to be more dependent on Reynold’s number when cases with unintended behavior are filtered out.Användningen av kolväten som bränsle i syfte att driva rymdfarkoster har intresserat flyg- och rymdindustrin under de senaste åren. Naturgas med ett högt innehåll av metan har fångat intresset av flera aktörer, däribland Sverige-baserade GKN Aerospace som i ett samarbete med KTH Kungliga Tekniska Högskolan har startat projektet MERiT. Projektet avser att utforska metans potential som bränsle genom en kombinerad värmeöverföringsanalys för en kylkanal i en raketmotordysa. Målet är delvis att fastställa vilken kylningspotential metan har samt att undersöka när koksning uppstår i kylkanalen. Den här rapporten ämnar kartlägga arbetet med en CFD-modell med avsikten att fastställa beteendet för en testrigg som utvecklats i tidigare delar av projektet. Analysen skall användas som en databas för att generera designpunkter som kan användas i verkliga experiment. De beteenden som studeras inkluderar begränsningar på grund av överhettning, chokning på grund av överljudshastigheter och hur effektivt gasen absorberar värmen som flödar in i riggen. Utöver detta studeras gasens temperatur i ett försök att kartlägga fall som har högst risk för koksning. Denna risk skall utvärderas och utforskas genom verkliga experiment för att bedöma hur pålitligt metan är som bränsle. Från denna studie har databaser av designpunkter genererats för två kanalgeometrier innehållande två olika legeringsstål. Efterbehandlingen och insamlingen av data från databaserna är upplagda på ett sådant sätt att specifika beteenden kan studeras beroende på en specifik input. Dessa inputs inkluderar massflöde, värmeväxling, inloppstemperatur och utloppstryck för testriggen. För att utveckla processen sattes dessa upp i parametrar som genererade 243 unika designpunkter för varje kanalgeometri. Sammanfattningsvis var 131 av designpunkterna för den första kanalen användbara, samt att vissa av dessa hamnar inom vad som kan konstateras ett temperaturområde som riskerar koksning. Risken för chokning i kylkanalen är tydlig vid höga massflöden och låga utloppstryck. Den övergripande effekten av riggen fanns vara starkt knuten till värmeväxling och inloppstemperatur, men går över till att vara mer beroende av Reynoldstalet när oönskade fall sorteras bort.
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Dobbertean, Mark Michael. "Steady and Transient Heat Transfer for Jet Impingement on Patterned Surfaces". Scholar Commons, 2011. http://scholarcommons.usf.edu/etd/3076.
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Free liquid-jet impingement is well researched due to its high heat transfer ability and ease of implementation. This study considers both the steady state and transient heating of a patterned plate under slot-free-liquid jet impingement. The primary working fluid was water (H2O) and the plate material considered was silicon. Calculations were done for Reynolds number (Re) ranging from 500 to 1000 and indentation depths from 0.000125 to 0.0005 m for three different surface configurations. The effect of using different plate materials and R-134a as the working fluid were explored for the rectangular step case. The distributions of the local and average heat-transfer coefficient and the local and average Nusselt number were calculated for each case. A numerical model based in the FIDAP computer code was created to solve the conjugate heat transfer problem. The model used was developed for Cartesian coordinates for both steady state and transient conditions.
Results show that the addition of surface geometry alters the fluid flow and heat transfer values. The highest heat-transfer coefficients occur at points where the fluid flow interacts with the surface geometry. The lowest heat-transfer coefficients are found in the indentations between the changes in geometry. The jet velocity has a large impact on the heat transfer values for all cases, with increasing jet velocity showing increased local heat-transfer coefficients and Nusselt number. It is observed that increasing the indentation depth for the rectangular and sinusoidal surfaces leads to a decrease in local heat transfer whereas for triangular patterns, a higher depth results in higher heat-transfer coefficient. The transient analysis showed that changing surface geometry had little effect on the time required to reach steady state. The selection of plate material has an impact on both the final maximum temperatures and the time required to reach steady state, with both traits being tied to the thermal diffusivity (α) of the material.
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Li, Lifeng. "Numerical study of surface heat transfer enhancement in an impinging solar receiver". Thesis, Uppsala universitet, Fasta tillståndets fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-237365.
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During the impinging heat transfer, a jet of working fluid, either gas or liquid, will besprayed onto the heat transfer surface. Due to the high turbulence of the fluid, the heat transfer coefficient between the wall and the fluid will be largely enhanced. Previously, an impinging type solar receiver with a cylindrical cavity absorber was designed for solar dish system. However, non-uniform temperature distribution in the circumferential direction was found on absorber surface from the numerical model, which will greatly limit receiver's working temperature and finally affect receiver's efficiency. One of the possible alternatives to solve the problem is through modifying the roughness of the target wall surface. This thesis work aims to evaluate the possibility and is focusing on the study of heat transfer characteristics. The simulation results will be used for future experimental impinging solar receiver optimization work. Computational Fluid Dynamics (CFD) is used to model the conjugate heat transfer phenomenon of atypical air impinging system. The simulation is divided into two parts. The first simulation was conducted with one rib arranged on the target surface where heat transfer coefficient is relatively low to demonstrate the effects of rib shape (triangular,rectangular, and semi-circular) and rib height (2.5mm, 1.5mm, and 0.5mm). The circular rib with 1.5mm height is proved to be most effective among all to acquirerelatively uniform temperature distribution. In the second part, the amount of ribs is taken into consideration in order to reach more uniform surface heat flux. The target wall thickness is also varied to assess its influence.
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Takamuku, Kohei. "Analysis of Flow and Heat Transfer in the U.S. EPR Heavy Reflector". Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/36306.
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The U.S. Evolutionary Power Reactor (EPR) is a new, large-scale pressurized water reactor made by AREVA NP Inc. Surrounding the core of this reactor is a steel wall structure sitting inside called the heavy reflector. The purpose of the heavy reflector is to reduce the neutron flux escaping the core and thus increase the efficiency of the reactor while reducing the damage to the structures surrounding the core as well. The heavy reflector is heated due to absorption of the gamma radiation, and this heat is removed by the water flowing through 832 cooling channels drilled through the heavy reflector.
In this project, the temperature distribution in the heavy reflector was investigated to ascertain that the maximum temperature does not exceed the allowable temperature of 350 ºC, with the intent of modifying the flow distribution in the cooling channels to alleviate any hot spots. The analysis was conducted in two steps. First, the flow distribution in the cooling channels was calculated to test for any maldistribution. The temperature distribution in the heavy reflector was then calculated by simulating the conjugate heat transfer with this flow distribution as the coolant input.
The turbulent nature of the flow through the cooling channels made the calculation of the flow distribution computationally expensive. In order to resolve this problem, a simplification method using the â equivalent flow resistanceâ was developed. The method was validated by conducting a few case studies. Using the simplified model, the flow distribution was calculated and was found to be fairly uniform.
The conjugate heat transfer calculation was conducted. The same simplification method used in the flow distribution analysis could not be applied to this calculation; therefore, the computational cost of this model was reduced by lowering the grid density in the fluid region. The results showed that the maximum temperature in the heavy reflector is 347.7 ºC, which is below the maximum allowable temperature of 350 ºC. Additional studies were conducted to test the sensitivity of the maximum temperature with change in the flow distribution in the cooling channels. Through multiple calculations, the maximum temperature did not drop more than 3 ºC; therefore, it was concluded that the flow distribution in the cooling channels does not have significant effect on the maximum temperature in the heavy reflector.Master of Science
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Martinez, Luis Iñaki. "Investigation of CFD conjugate heat transfer simulation methods for engine components at SCANIA CV AB". Thesis, Linköpings universitet, Mekanisk värmeteori och strömningslära, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-138758.
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The main objective of this Master Thesis project is the development of a new methodology to perform Computational Fluid Dynamics (CFD) conjugate heat transfer simulations for internal combustion engines, at the Fluid and Combustion Simulations Department (NMGD) at Scania CV AB, Södertalje, Sweden. This new method allows to overcome the drawbacks identified in the former methodology, providing the ability to use the more advanced polyhedral mesh type to generate good quality grids in complex geometries like water cooling jackets, and integrating all the different components of the engine cylinder in one unique multi-material mesh. In the method developed, these advantages can be used while optimizing the process to perform the simulations, and obtaining improved accuracy in the temperature field of engine components surrounding the water cooling jacket when compared to the experimental data from Scania CV AB tests rigs. The present work exposes the limitations encountered within the former methodology and presents a theoretical background to explain the physics involved, describing the computational tools and procedures to solve these complex fluid and thermal problems in a practical and cost-effective way, by the use of CFD.A mesh sensitivity analysis performed during this study reveals that a mesh with low y+ values, close to 1 in the water cooling jacket, is needed to obtain an accurate temperature distribution along the cylinder head, as well as to accurately identify boiling regions in the coolant domain. Another advantage of the proposed methodology is that it provides new capabilities like the implementation of thermal contact resistance in periodical contact regions of the engine components, improving the accuracy of the results in terms of temperature profiles of parts like valves, seats and guides. The results from this project are satisfactory, providing a reliable new methodology for multi-material thermal simulations, improving the efficiency of the work to be performed in the NMGD department, with a better use of the available engineering and computational resources, simplifying all the stages of multi-material projects, from the geometry preparation and meshing, to the post-processing tasks.
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Abdoli, Abas. "Optimization of Cooling Protocols for Hearts Destined for Transplantation". FIU Digital Commons, 2014. http://digitalcommons.fiu.edu/etd/1579.
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Design and analysis of conceptually different cooling systems for the human heart preservation are numerically investigated. A heart cooling container with required connections was designed for a normal size human heart. A three-dimensional, high resolution human heart geometric model obtained from CT-angio data was used for simulations. Nine different cooling designs are introduced in this research. The first cooling design (Case 1) used a cooling gelatin only outside of the heart. In the second cooling design (Case 2), the internal parts of the heart were cooled via pumping a cooling liquid inside both the heart’s pulmonary and systemic circulation systems. An unsteady conjugate heat transfer analysis is performed to simulate the temperature field variations within the heart during the cooling process. Case 3 simulated the currently used cooling method in which the coolant is stagnant. Case 4 was a combination of Case 1 and Case 2. A linear thermoelasticity analysis was performed to assess the stresses applied on the heart during the cooling process.
In Cases 5 through 9, the coolant solution was used for both internal and external cooling. For external circulation in Case 5 and Case 6, two inlets and two outlets were designed on the walls of the cooling container. Case 5 used laminar flows for coolant circulations inside and outside of the heart. Effects of turbulent flow on cooling of the heart were studied in Case 6. In Case 7, an additional inlet was designed on the cooling container wall to create a jet impinging the hot region of the heart’s wall. Unsteady periodic inlet velocities were applied in Case 8 and Case 9. The average temperature of the heart in Case 5 was +5.0oC after 1500 s of cooling.
Multi-objective constrained optimization was performed for Case 5. Inlet velocities for two internal and one external coolant circulations were the three design variables for optimization. Minimizing the average temperature of the heart, wall shear stress and total volumetric flow rates were the three objectives. The only constraint was to keep von Mises stress below the ultimate tensile stress of the heart’s tissue.
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Krishnamurthy, Nagendra. "A Study of Heat and Mass Transfer in Porous Sorbent Particles". Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/64412.
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This dissertation presents a detailed account of the study undertaken on the subject of heat and mass transfer phenomena in porous media. The current work specifically targets the general reaction-diffusion systems arising in separation processes using porous sorbent particles. These particles are comprised of pore channels spanning length scales over almost three orders of magnitude while involving a variety of physical processes such as mass diffusion, heat transfer and surface adsorption-desorption. A novel methodology is proposed in this work that combines models that account for the multi-scale and multi-physics phenomena involved. Pore-resolving DNS calculations using an immersed boundary method (IBM) framework are used to simulate the macro-scale physics while the phenomena at smaller scales are modeled using a sub-pore modeling technique.
The IBM scheme developed as part of this work is applicable to complex geometries on curvilinear grids, while also being very efficient, consuming less than 1% of the total simulation time per time-step. A new method of implementing the conjugate heat transfer (CHT) boundary condition is proposed which is a direct extension of the method used for other boundary conditions and does not involve any complex interpolations like previous CHT implementations using IBM. Detailed code verification and validation studies are carried out to demonstrate the accuracy of the developed method.
The developed IBM scheme is used in conjunction with a stochastic reconstruction procedure based on simulated annealing. The developed framework is tested in a two-dimensional channel with two types of porous sections - one created using a random assembly of square blocks and another using the stochastic reconstruction procedure. Numerous simulations are performed to demonstrate the capability of the developed framework. The computed pressure drops across the porous section are compared with predictions from the Darcy-Forchheimer equation for media composed of different structure sizes. The developed methodology is also applied to CO2 diffusion studies in porous spherical particles of varying porosities.
For the pore channels that are unresolved by the IBM framework, a sub-pore modeling methodology developed as part of this work which solves a one-dimensional unsteady diffusion equation in a hierarchy of scales represented by a fractal-type geometry. The model includes surface adsorption-desorption, and heat generation and absorption. It is established that the current framework is useful and necessary for reaction-diffusion problems in which the adsorption time scales are very small (diffusion-limited) or comparable to the diffusion time scales. Lastly, parametric studies are conducted for a set of diffusion-limited problems to showcase the powerful capability of the developed methodology.Ph. D.
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Gorgulu, Ilhan. "Numerical Simulation Of Turbine Internal Cooling And Conjugate Heat Transfer Problems With Rans-based Turbulance Models". Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12615000/index.pdf.
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The present study considers the numerical simulation of the different flow characteristics involved in the conjugate heat transfer analysis of an internally cooled gas turbine blade. Conjugate simulations require full coupling of convective heat transfer in fluid regions to the heat diffusion in solid regions. Therefore, accurate prediction of heat transfer quantities on both external and internal surfaces has the uppermost importance and highly connected with the performance of the employed turbulence models. The complex flow on both surfaces of the internally cooled turbine blades is caused from the boundary layer laminar-to-turbulence transition, shock wave interaction with boundary layer, high streamline curvature and sequential flow separation. In order to discover the performances of different turbulence models on these flow types, analyses have been conducted on five different experimental studies each concerned with different flow and heat transfer characteristics. Each experimental study has been examined with four different turbulence models available in the commercial software (ANSYS FLUENT13.0) to decide most suitable RANS-based turbulence model. The Realizable k-&epsilonmodel, Shear Stress Transport k-&omega
model, Reynolds Stress Model and V2-f model, which became increasingly popular during the last few years, have been used at the numerical simulations. According to conducted analyses, despite a few unreasonable predictions, in the majority of the numerical simulations, V2-f model outperforms other first-order turbulence models (Realizable k-&epsilon
and Shear Stress Transport k-&omega
) in terms of accuracy and Reynolds Stress Model in terms of convergence.
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Wu, Zhao. "Direct simulation of a low momentum round jet in channel cross-flow with conjugate heat transfer". Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/direct-simulation-of-a-low-momentum-round-jet-in-channel-crossflow-with-conjugate-heat-transfer(53cd2317-917c-44ba-aa70-f4c796fbd6b3).html.
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Results of direct numerical simulations (DNS) of a jet in channel crossflow with conjugate heat transfer are presented. The hot laminar jet issues from a circular exit into the cold channel crossflow with a low jet-to- crossflow velocity ratio of 1/6. The steel channel wall has a finite thickness and its outer side is cooled under Robin type thermal boundary conditions for a realistic external environment, leading to a conjugate heat transfer system. The governing equations are solved by Incompact3d, an open-source code combining the high-order compact scheme and Poisson spectral solver. An internal recycling approach is used to generate the fully turbulent channel ow profile as the inflow conditions. The database is uploaded online for open access (http://dx.doi.org/10.17632/7nx4prgjzz.3). In the fluid domain, four main ow structures are identified: 1) a large recirculation immediately downstream of the jet-exit; 2) a contour-rotating vortex pair originated from the stretching and reorientation of the injection-ow vorticity; 3) a horseshoe vortex generated as a result of the stretching of the vorticity at the jet-exit windward side; and 4) shear layer vortices coming from the lifted and shed crossflow boundary layer vorticity. Proper orthogonal decomposition and dynamic mode decomposition are then used to study the energy and spectrum information of structures. The results show the horseshoe vortex is related to low-frequency modes, while the shear layer vortices are connected to the high-frequency ones. In the conjugate heat transfer problem, the above coherent structures lead to a complex convective and turbulent wall heat transfer pattern around the orifice. Finally, this study evaluates the capabilities of several turbulence models in predicting this type of ow and shows how the DNS database would help test, validate and improve the turbulence models.
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Jauré, Stéphan. "Conjugate heat transfer coupling relying on large eddy simulation with complex geometries in massively parallel environments". Phd thesis, Toulouse, INPT, 2012. http://oatao.univ-toulouse.fr/18534/1/Jaure_Stephan.pdf.
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Progress in scientific computing has led to major advances in simulation and understanding of the different physical phenomena that exist in industrial gas turbines. However' most of these advances have focused on solving one problem at a time. Indeed' the combustion problem is solved independently from the thermal or radiation problems' etc... In reality all these problems interact: one speaks of coupled problems. Thus performing coupled computations can improve the quality of simulations and provide gas turbines engineers with new design tools. Recently' solutions have been developed to handle multiple physics simultaneously using generic solvers. However' due to their genericity these solutions reveal to be ineffective on expensive problems such as Large Eddy Simulation (LES). Another solution is to perform code coupling: specialized codes are connected together' one for each problem and they exchange data periodically. In this thesis a conjugate heat transfer problem is considered. A fluid domain solved by a combustion LES solver is coupled with a solid domain in which the conduction problem is solved. Implementing this coupled problem raises multiple issues which are addressed in this thesis. Firstly' the specific problem of coupling an LES solver to a conduction solver is considered: the impact of the inter-solver exchange frequency on convergence' possible temporal aliasing' and stability of the coupled system is studied. Then interpolation and geometrical issues are addressed: a conservative interpolation method is developed and compared to other methods. These methods are then applied to an industrial configuration' highlighting the problems and solutions specific to complex geometry. Finally' high performance computing (HPC) is considered: an efficient method to perform data exchange and interpolation between parallel codes is developed. This work has been applied to an aeronautical combustion chamber configuration.
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Xu, Haoxin. "Numerical Study on the Thermal Performance of a Novel Impinging Type Solar Receiver for Solar Dish-Brayton System". Thesis, KTH, Kraft- och värmeteknologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-137091.
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An impinging type solar receiver has been designed for potential applications in a future Brayton Solar Dish System. The EuroDish system is employed as the collector, and an externally fired micro gas turbine (EFMGT) has been chosen as the power conversion unit. In order to reduce the risks caused by the quartz glass window, which is widely used in traditional air receiver designs, a cylinder cavity absorber without a quartz window has been adopted. Additionally, an impinging design has been chosen as the heat exchange system due to its high heat transfer coefficient compared to other single-phase heat exchange mechanisms. This thesis work introduces the design of an solar air receiver without a glass window, which features jet impingement to maximize the heat transfer rate. A detailed study of the thermal performance of the designed solar receiver has been conducted using numerical tools from the ANSYS FLUENT package. Concerning receiver performance, an overall thermal efficiency of 72.9% is attained and an output air temperature of 1100 K can be achieved, according to the numerical results. The total thermal power output is 38.05 kW, enough to satisfy the input requirements of the targeted micro gas turbine. A preliminary design layout is presented and potential optimization approaches for future enhancement of the receiver are proposed, regarding local thermal stress and pressure loss reduction. This thesis project also introduces a ray-thermal coupled numerical design method, which combines ray tracing techniques (using FRED®), with thermal performance analysis (using ANSYS Workbench).
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Zhang, Zexuan. "Simulation of Combustion and Thermal-flow Inside a Petroleum Coke Rotary Calcining Kiln". ScholarWorks@UNO, 2007. http://scholarworks.uno.edu/td/1073.
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Calcined coke is the best material for making carbon anodes for smelting of alumina to aluminum. Calcining is an energy intensive industry and a significant amount of heat is wasted in the calcining process. Efficiently managing this energy resource is tied to the profit margin and survivability of a calcining plant. 3-D computational models are developed using FLUENT to simulate the calcining process inside the long slender kiln. Simplified models are employed to simulate the moving petocke bed with a uniform distribution of moisture evaporation, devolatilization, and coke fines entrainment rate with a conjugate radiation-convection-conduction calculation. The results show the 3-D behavior of the flow, the reaction inside the kiln, heat transfer and the effect of the tertiary air on coke bed heat transfer. The ultimate goals are to reduce energy consumption, recover waste-heat, increase thermal efficiency, and increase the product yield.
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Oh, Tae Kyung. "Strongly-Coupled Conjugate Heat Transfer Investigation of Internal Cooling of Turbine Blades using the Immersed Boundary Method". Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/90894.
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The present thesis focuses on evaluating a conjugate heat transfer (CHT) simulation in a ribbed cooling passage with a fully developed flow assumption using LES with the immersed boundary method (IBM-LES-CHT). The IBM with the LES model (IBM-LES) and the IBM with CHT boundary condition (IBM-CHT) frameworks are validated prior to the main simulations by simulating purely convective heat transfer (iso-flux) in the ribbed duct, and a developing laminar boundary layer flow over a two-dimensional flat plate with heat conduction, respectively. For the main conjugate simulations, a ribbed duct geometry with a blockage ratio of 0.3 is simulated at a bulk Reynolds number of 10,000 with a conjugate boundary condition applied to the rib surface. The nominal Biot number is kept at 1, which is similar to the comparative experiment. As a means to overcome a large time scale disparity between the fluid and the solid regions, the use of a high artificial solid thermal diffusivity is compared to the physical diffusivity. It is shown that while the diffusivity impacts the instantaneous fluctuations in temperature, heat transfer and Nusselt numbers, it has an insignificantly small effect on the mean Nusselt number. The comparison between the IBM-LES-CHT and iso-flux simulations shows that the iso-flux case predicts higher local Nusselt numbers at the back face of the rib. Furthermore, the local Nusselt number augmentation ratio (EF) predicted by IBM-LES-CHT is compared to the body fitted grid (BFG) simulation, experiment and another LES conjugate simulation. Even though there is a mismatch between IBM-LES-CHT prediction and other studies at the front face of the rib, the area-averaged EF compares reasonably well in other regions between IBM-LES-CHT prediction and the comparative studies.Master of Science
The present thesis focuses on the computational study of the conjugate heat transfer (CHT) investigation on the turbine internal ribbed cooling channel. Plenty of prior research on turbine internal cooling channel have been conducted by considering only the convective heat transfer at the wall, which assumes an iso-flux (constant heat flux) boundary condition at the surface. However, applying an iso-flux condition on the surface is far from the realistic heat transfer mechanism occurring in internal cooling systems. In this work, a conjugate heat transfer analysis of the cooling channel, which considers both the conduction within the solid wall and the convection at the ribbed inner wall surface, is conducted for more realistic heat transfer coefficient prediction at the inner ribbed wall. For the simulation, the computational mesh is generated by the immersed boundary method (IBM), which can ease the mesh generation by simply immersing the CAD geometry into the background volume grid. The IBM is combined with the conjugate boundary condition to simulate the internal ribbed cooling channel. The conjugate simulation is compared with the experimental data and another computational study for the validation. Even though there are some discrepancy between the IBM simulation and other comparative studies, overall results are in good agreement. From the thermal prediction comparison between the iso-flux case and the conjugate case v using the IBM, it is found that the heat transfer predicted by the conjugate case is different from the iso-flux case by more than 40 percent at the rib back face. The present study shows the potential of the IBM framework with the conjugate boundary condition for more complicated geometry, such as full turbine blade model with external and internal cooling system.
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York, William David. "A robust conjugate heat transfer methodology with novel turbulence modeling applied to internally-cooled gas turbine airfoils". Connect to this title online, 2006. http://etd.lib.clemson.edu/documents/1175185039/.
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Findlay, Jonathon Peter. "3-D conjugate heat transfer analysis of a cooled transonic turbine blade using non-reflecting boundary conditions". Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=82486.
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Increasing the combustor exit temperature in gas turbines is an effective means to increase engine power. While occasional metallurgical advances allow gradual temperature increases, improving the internal/external cooling of the blades is the only way to permit significant temperature gains. In this work, a methodology for aerodynamic and conjugate heat transfer computational analysis of cooled turbine blades is developed. Flow solutions are obtained using an implicit, three-dimensional, finite-element Reynolds-Averaged Navier-Stokes flow solver. Efficient non-reflecting boundary conditions are derived and implemented to reduce the size of the solution domain and accelerate convergence. These are shown to be essential for the accurate capturing of shock waves and wakes. The methodology is demonstrated on the convection-cooled NASA-C3X turbine vane, by coupling heat conduction in the solid vane with heat transfer from the internal cooling flow and the external hot-gas flow. Both aerodynamic and heat transfer results are compared against experimental data.
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Bedi, Nishit. "Conjugate Heat Transfer Analysis in Multi Microchannel Heat Sink". Thesis, 2018. http://localhost:8080/iit/handle/2074/7575.
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Rajesh, Kumar V. "Conjugate Heat Transfer in Diverging Microchannels". Thesis, 2015. http://ethesis.nitrkl.ac.in/7410/1/2015_Conjugate_KUMAR.pdf.
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A numerical study has been carried out to determine the effects of axial wall conduction during single-phase steady laminar flow of fluid through rectangular diverging (across the length of the channel) cross-sectional microchannel involving conjugate heat transfer. A constant heat flux boundary condition has been applied on the bottom surface of the substrate on which the microchannel is carved, while all other surfaces of the substrate are subjected to adiabatic condition to simulate insulation. The simulations have been carried out by varying wall thickness to channel height ratio (dsf ~1-24), solid substrate conductivity to working fluid conductivity ratio (ksf ~0.17-703) and Reynolds number (Re~100-1000). For the purpose of comparison simulations for uniform cross-sectional area across the microchannel length has also been carried out. Four different geometrical dimensions, eleven substrate materials and three Reynolds numbers have been considered in this study, which would cover the common scope of uses experienced in micro fluids/microscale heat transfer areas and would provide a wide parametric variation for a generalized visualization of the outcome of this study. The results demonstrate that the conductivity ratio is the pivotal parameter in affecting the extent of axial wall conduction. Very low and very high values of ksf would result in decrease of Nussle number. Such a sensation also exists for uniform square and circular cross-sections.
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Biswal, Rasmikanti. "Conjugate Heat Transfer Analysis in Cryogenic Microchannel Heat Exchanger". Thesis, 2015. http://ethesis.nitrkl.ac.in/7401/1/2015_Conjugate_Biswal.pdf.
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Printed circuit heat exchanger (PCHE) is a highly integrated plate type compact heat exchanger and most important as well as a most critical component in the cryogenic application. Compact heat exchangers are characterized by area density (? = AHT / V) i.e. heat transfer area per unit volume of the heat exchanger. The area density of compact heat exchanger is =700m2/m3 where the area density of printed circuit heat exchanger is = 25000m2/m3. Printed circuit heat exchangers are highly compact compared to conventional heat exchangers. The hydraulic diameter is less than 1mm. Printed Circuit Heat Exchanger manufacturing process is followed by chemical etching and chemical bonding. Microchannel for fluid flow are constructed by chemical etching of the metal plates according to different configuration then plates are stacked alternately and assembled by diffusion bonding. Due to its compact size, high efficiency, large heat transfer area PCHE (microchannel heat exchanger) are used in cryogenic refrigeration and liquefaction systems. A counter flow rectangular microchannel (40 mm × 1.6 mm × 1.2 mm) printed circuit heat exchanger is designed and simulated using commercial ANSYS FLUENT. The performance is investigated numerically with helium at cryogenic temperature. The performance is affected by axial conduction at low Reynolds number (Re = 100). Because of length and viscous nature, the fluid flow through the channel is laminar and thermally fully developed. The Nussle number (Nu), flux, dimensionless fluid temperature and wall temperature, effectiveness are determined for different Reynolds number Reynolds number (Re = 100) with varying material i.e. wall to fluid thermal conductivity ratio (ksf = 141.58 - 5061.5). Axial conduction (?) is calculated by using Kroeger’s equation. Effectiveness is calculated to investigate the thermal performance of the microchannel heat exchanger.
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Marini, Remo. "A finite element conjugate heat transfer method". Thesis, 2002. http://spectrum.library.concordia.ca/2034/1/MQ77980.pdf.
Texto completoResumen
The need to accurately predict heat transfer in aircraft anti-icing systems or in turbomachinery cooling passages is a current topic of Computational Fluid Dynamics (CFD). In both applications, the flow structure is highly complex and three-dimensional. The traditional use of correlations might be useful in describing the average heat transfer behavior, but not the localized effects. Accurate heat transfer predictions are required to design efficient complex cooling or heating schemes and only a full 3D Navier-Stokes code, coupled with a solid conduction code, is the sole alternative. Conjugate Heat Transfer (CHT) is the commonly used term to identify such coupling of convection and conduction across one or several fluid-solid interfaces. The CHT approach proposed in this thesis solves both the fluid and solid thermal fields simultaneously, in a fully-implicit manner using the infrastructure of a 3D Navier-Stokes flow solver, FENSAP. The algorithm supports 3D structured, unstructured, and hybrid meshes, with mismatched node connectivity and with non-uniform grid densities between fluid and solid domains at CHT interfaces. The heat transfer validation is assessed for both laminar and turbulent flows against relevant open literature data. The CHT validation is assessed with three cases: a blunt flat plate flow, a fully-developed pipe flow, and the complex piccolo tube system flow in a 3D nacelle lip. The results show that the proposed method can be used as a reliable and cost-effective tool for the analysis and design of thermal anti-icing devices, and can easily be extended to cooled gas turbine components, such as: blades, vanes, shrouds, and disks.
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Gupta, Amit. "Conjugate Heat Transfer in a Converging Microchannel". Thesis, 2015. http://ethesis.nitrkl.ac.in/7402/1/2015_Conjugate_Gupta.pdf.
Texto completoResumen
A numerical simulation is performed to comprehend the effects of axial back conduction in the solid substrate in a conjugate heat transfer having steady and laminar flow. A heat flux with constant magnitude is applied at the lower end of the substrate and the remaining surfaces were insulated. Working fluid used is water having slug velocity profile at the inlet of the channel. The thermal conductivity ratio (ksf) has been varied in a wide range of 0.33 to 702, thickness of the substrate has been changed for varying thickness ratio (dsf) of 1 to 4, keeping the width of substrate unchanged to quantify its effect on the axial back conduction and simultaneously, the Reynolds number is varied from 100 to 500. Simulations have been carried out with converging microchannel along with the straight microchannel with the dimension of inlet and outlet of the converging microchannel and the result is compared with converging microchannel and a systematic study was done to comprehend the effect of axial back conduction by varying all the parameters as mentioned above.