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Colomer, Rey Guillem. "Numerical methods for radiative heat transfer." Doctoral thesis, Universitat Politècnica de Catalunya, 2006. http://hdl.handle.net/10803/6691.
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L'objectiu principal d'aquesta tesi es l'estudi de la transferència d'energia per radiació. Per aquest motiu, s'ha estudiat la fenomenologia bàsica de la transferencia de calor per radiació. Tenint en compte el tipus d'equació que descriu aquesta transferència d'energia, aquesta tesi esta encarada als metodes numèrics que ens permetran incorporar la radiació en els nostres càlculs. Donat que aquest és el primer treball d'aquestes característiques en el grup de recerca CTTC ("Centre Tecnològic de Transferència de Calor"), està limitat a geometries senzilles, cartesianes i cilíndriques. En el capítol 1 s'exposa una breu introducció a la transferència d'energia per radiació, i una explicació de les equacions que la governen. Es tracta de l'equació del transport radiatiu, formulada en termes dels coeficients d'absorció i de dispersió, i l'equació de l'energia. També s'indica quan cal tenir en compte aquest fenòmen, i a més a més, es defineixen totes les magnituds i conceptes que s'han utilitzat en aquesta tesi. També es dóna una breu descripció d'algunes simplificacions que es poden fer a les equacions governants.
El mètode de les radiositats s'explica en el capítol 2. També s'hi descriu un procediment numèric que permet calcular els factors de vista en geometries amb simetria cilíndrica, i es presenten resultats obtinguts amb el mètode descrit. Tot i que aquest capítol està una mica deslligat de la resta de la tesi, l'algoritme ideat per tractar geometries tridimensionals amb un temps computacional molt proper al de geometries bidimensionals, sense un increment de memòria apreciable, dóna uns resultats prou bons com per formar part de la tesi.
El mètode de les ordenades discretes (DOM) es detalla en el capítol 3. L'aspecte més important d'aquest mètode es l'elecció del conjunt d'ordenades per integrar l'equació del transport radiatiu. S'enumeren quines propietats han d'acomplir aquests conjunts. S'hi explica amb detall la discretització de la equació del transport radiatiu, tant en coordenades cartesianes com en cilíndriques. Es presenten també alguns resultats ilustratius obtinguts amb aquest mètode.
En el moment en que es vol resoldre un problema real, cal tenir present que el coeficients d'absorció pot dependre bruscament de la longitud d'ona de la radiació. En aquesta tesi s'ha considerat aquesta dependència amb especial interés, en el capítol 4. Aquest interès ha motivat una recerca bibliogràfica sobre la modelització aquesta forta dependència espectral del coeficient d'absorció. Aquesta recerca s'ha dirigit també a l'estudi dels diferents models numèrics existents capaços d'abordar-la, i de resoldre la equació del transport radiatiu en aquestes condicions. Es descriuen diversos mètodes, i, d'aquests, se n'han implementat dos: el mètode de la suma ponderada de gasos grisos (WSGG), i el mètode de la suma de gasos grisos ponderada per línies espectrals (SLW). S'hi presenten també resultats ilustratius.
S'han realitzat multitud de proves en el codi numèric resultant de l'elaboració d'aquesta tesi. Tenint en compte els resultats obtinguts, es pot dir que els objectius proposats a l'inici de la tesi s'han acomplert. Com a demostració de la utilitat del codi resultant, aquest ha estat integrat en un codi de proposit general (DPC), resultat del treball de molts investigadors en els darrers anys.
Aquesta esmentada integració permet la resolució de problemes combinats de transferència de calor, analitzats en els capítols 5 i 6, on la radiació s'acobla amb la transferència de calor per convecció. La influència de la radiació en la transferència total de calor s'estudia en el capítol 5, publicat a la International Journal of Heat and Mass Transfer, volum 47 (núm. 2), pàg. 257-269, 2004. En el capítol 6, s'analitza l'efecte d'alguns paràmetres del mètode SLW en un problema combinat de transferència de calor. Aquest capítol s'ha enviat a la revista Journal of Quantitative Spectroscopy and Radiative Transfer, per què en consideri la publicació.
The main objective of the present thesis is to study the energy transfer by means of radiation. Therefore, the basic phenomenology of radiative heat transfer has been studied. However, considering the nature of the equation that describes such energy transfer, this work is focussed on the numerical methods which will allow us to take radiation into account, for both transparent and participating media. Being this the first effort within the CTTC ("Centre Tecnològic de Transferència de Calor") research group on this subject, it is limited to simple cartesian and cylindrical geometries.
For this purpose, chapter 1 contains an introduction to radiative energy transfer and the basic equations that govern radiative transfer are discussed. These are the radiative transfer equation, formulated in terms of the absorption and scattering coefficients, and the energy equation. It is also given a discussion on when this mode of energy transfer should be considered. In this chapter are also defined all of the magnitudes and concepts used throughout this work. It ends with a brief description of some approximate methods to take radiation into account.
The Radiosity Irradiosity Method is introduced in chapter 2. In this chapter it is also described a numerical method to calculate the view factors for axial symmetric geometries. The main results obtained in such geometries are also presented. Although a little disconnected from the rest of the present thesis, the algorithm used to handle "de facto"' three dimensional geometries with computation time just a little longer than two dimensional cases, with no additional memory consumption, is considered worthy enough to be included in this work.
In chapter 3, the Discrete Ordinates Method (DOM) is detailed. The fundamental aspect of this method is the choice of an ordinate set to integrate the radiative transfer equation. The characterization of such valuable ordinate sets is laid out properly. The discretization of the radiative transfer equation is explained in etail. The direct solution procedure is also outlined. Finally, illustrative results obtained with the DOM under several conditions are presented.
In the moment we wish to solve real problems, we face the fact that the absorption and scattering coefficients depend strongly on radiation wavelength. In the present thesis, special emphasis has been placed on studying the radiative properties of real gases in chapter 4. This interest resulted on a bibliographical research on how the wavenumber dependence of the absorption coefficient is modeled and estimated. Furthermore, this bibliographical research was focussed also on numerical models able to handle such wavenumber dependence. Several methods are discussed, and two of them, namely the Weighted Sum of Gray Gases (WSGG) and the Spectral Line Weighted sum of gray gases (SLW), have been implemented to perform non gray calculations. Some significant results are shown.
Plenty of tests have been performed to the numerical code that resulted from the elaboration of this thesis. According to the results obtained, the objectives proposed in this thesis have been satisfied. As a demonstration of the usefulness of the implemented code, it has been succesfully integrated to a general purpose computational fluid dynamics code (DPC), fruit of the effort of many researchers during many years.
Results of the above integration lead to the resolution of combined heat transfer problems, that are analyzed in chapters 5 and 6, where radiative heat transfer is coupled to convection heat transfer. The effect of radiation on the total heat transfer is studied in chapter 5, which has been published as International Journal of Heat and Mass Transfer, volume 47 (issue 2), pages 257--269, year 2004. In chapter 6, the impact of some parameters of the SLW model on a combined heat transfer problem is analyzed. This chapter has been submitted for publication at the Journal of Quantitative Spectroscopy and Radiative Transfer.
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Ramamoorthy, Babila. "Numerical simulation of radiative heat transfer." Birmingham, Ala. : University of Alabama at Birmingham, 2008. https://www.mhsl.uab.edu/dt/2009r/ramamoorthy.pdf.
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Hoggard, T. W. "Numerical methods in aero-engine heat transfer." Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376577.
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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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Wang, Xiaolin. "A numerical study of vorticity-enhanced heat transfer." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/54017.
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In this work, we have numerically studied the effect of the vorticity on the enhancement of heat transfer in a channel flow. In the first part of the work, we focus on the investigation of a channel flow with a vortex street as the incoming flow. We propose a model to simulate the fluid dynamics. We find that the flow exhibits different properties depending on the value of four dimensionless parameters. In particularly, we can classify the flows into two types, active and passive vibration, based on the sign of the incoming vortices. In the second part of the work, we discuss the heat transfer process due to the flows just described and investigate how the vorticity in the flow improves the efficiency of the heat transfer. The temperature shows different characteristics corresponding to the active and passive vibration cases. In active vibration cases, the vortex blob improves the heat transfer by disrupting the thermal boundary layer and preventing the decay of the wall temperature gradient throughout the channel, and by enhancing the forced convection to cool down the wall temperature. The heat transxfer performance is directly related to the strength of the vortex blobs and the background flow. In passive vibration cases, the corresponding heat transfer process is complicated and varies dramatically as the flow changes its properties. We also studied the effect of thermal parameters on heat transfer performance. Finally, we propose a more realistic optimization problem which is to minimize the maximum temperature of the solids with a given input energy. We find that the best heat transfer performance is obtained in the active vibration case with zero background flow.
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KC, Amar. "Numerical Simulations of Magnetohydrodynamic Flow and Heat Transfer." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1411495287.
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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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Spring, Sebastian [Verfasser]. "Numerical Prediction of Jet Impingement Heat Transfer / Sebastian Spring." München : Verlag Dr. Hut, 2011. http://d-nb.info/1011441330/34.
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Isiklar, Yasar Vehbi. "A numerical study of heat transfer behavior in welding." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1998. http://handle.dtic.mil/100.2/ADA350125.
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Thesis (M.S. in Mechanical Engineering) Naval Postgraduate School, June 1998."June 1998." Thesis advisor(s): Ashok Gopinath. Includes bibliographical references (p. 107-109). Also available online.
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Chacko, Salvio. "Numerical analysis of unsteady heat transfer for thermal management." Thesis, University of Warwick, 2012. http://wrap.warwick.ac.uk/54478/.
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In this study, thermal management of Lithium ion (Li-ion) battery pack used in electric vehicle (EV) is considered. Li-ion cells generate a significant amount of heat during normal operation. Previous study has clearly identified that temperature affects the efficiency, safety, reliability and lifespan of the Li-ion battery. Therefore, a battery thermal management system (BTMS) enabling effective temperature control is essential for safety and overall performance of the Li-ion battery. Two critical aspects are key to design of efficient BTMS: firstly being able to predict the heat generated from Li-ion cells, and secondly to predict how the generated heat is removed though the cooling plate of the BTMS. To predict the heat generated from the Li-ion cell, a time-dependent, thermal behavior of a Li-ion polymer cell has been modelled for electric vehicle drive cycles with a view to developing an effective battery thermal management system. The fully coupled, new three-dimensional transient electrothermal model has proposed and implemented based on a finite volume method. To support the numerical study, a high energy density Li-ion polymer pouch cell was tested in a climatic chamber for various electric load cycles consisting of a series of charge and discharge rates, and a good agreement was found between the model predictions and the experimental data. To predict the heat removed, a numerical study has been performed on a cooling plate of a indirect liquid cooled BTMS. The BTMS has a battery cooling plate with coolant flowing through rectangular serpentine channels. The temperature distribution as well as the pressure drop across the battery cooling plate were investigated. Particular emphasis was placed on the temperature uniformity on the cooling plate surface as the lifespan of a battery is severely affected by non-uniform temperature distribution. From the simulations, it is found that the aspect ratio and the curvature have a significant effect on the surface temperature uniformity, and that a compromise of the battery cooling plate design would be required between the temperature uniformity and the pressure drop penalty. Thermal management of batteries for high discharge applications, for instance, in hybrid electric vehicle, is more challenging and typically requires turbulent heat transfer. In turbulent heat transfer not only mean temperatures but also temperature fluctuations need to be predicted correctly. For this, a numerical turbulent heat transfer of a triple jet is considered. In this study, a large eddy simulation (LES) technique was applied to predict the unsteady heat transfer behavior of turbulent flow. It is found that LES predicted the correct amplitude of temperature fluctuations which was in good agreement with the available experimental data in terms of mean, RMS, skewness and kurtosis. RANS simulations with two turbulence models were also conducted along with LES. The RANS based turbulence models produced a very small amplitude of fluctuations, and failed to predict the correct magnitude of unsteady thermal fluctuations, highlighting its limitations in unsteady turbulent heat transfer simulations. Keywords: battery thermal management; lithium-ion polymer battery; electro thermal model; EV drive cycles; finite volume method, electric vehicle; BTMS; conjugate heat transfer; battery cooling plate; rectangular serpentine channel; laminar flow; triple jet; thermal striping; mixing; thermal fatigue; LES; RANS.
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Schroder, Andrew Urban. "Experimental and Numerical Study of Impingement Jet Heat Transfer." University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1305897623.
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Manson, Steven James. "Numerical analysis of two dimensional natural convection heat transfer following a contained explosion /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
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Ozerinc, Sezer. "Heat Transfer Enhancement With Nanofluids." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12611862/index.pdf.
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A nanofluid is the suspension of nanoparticles in a base fluid. Nanofluids are promising for heat transfer enhancement due to their high thermal conductivity. Presently, discrepancy exists in nanofluid thermal conductivity data in the literature, and enhancement mechanisms have not been fully understood yet. In the first part of this study, a literature review of nanofluid thermal conductivity is performed. Experimental studies are discussed through the effects of some parameters such as particle volume fraction, particle size, and temperature on conductivity. Enhancement mechanisms of conductivity are summarized, theoretical models are explained, model predictions are compared with experimental data, and discrepancies are indicated.
Nanofluid forced convection research is important for practical application of nanofluids. Recent experiments showed that nanofluid heat transfer enhancement exceeds the associated thermal conductivity enhancement, which might be explained by thermal dispersion, which occurs due to random motion of nanoparticles. In the second part of the study, to examine the validity of a thermal dispersion model, hydrodynamically developed, thermally developing laminar Al2O3/water nanofluid flow inside a circular tube under constant wall temperature and heat flux boundary conditions is analyzed by using finite difference method with Alternating Direction Implicit Scheme. Numerical results are compared with experimental and numerical data in the literature and good agreement is observed especially with experimental data, which indicates the validity of the thermal dispersion model for explaining nanofluid heat transfer. Additionally, a theoretical analysis is performed, which shows that usage of classical correlations for heat transfer analysis of nanofluids is not valid.
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Drakulic, Radenko. "Numerical modelling of flow and heat transfer in louvred fans." Thesis, University of Brighton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246008.
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Aylangan, Benan. "Numerical Analysis Of Natural Convective Heat Transfer Through Porous Medium." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/2/12607026/index.pdf.
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In this thesis, natural convective heat transfer through an impermeable and fluid saturated porous medium is investigated numerically. A FORTRAN based code is developed and used in order to present the outputs of the applied model and the assumptions.
The solutions of flow fields and temperature fields are presented within the medium. Moreover, Nusselt number variations for different values of Darcy, Prandtl, and Rayleigh numbers, and some other thermodynamic properties are investigated and presented. Comparisons with previous studies are also presented.
Finally, the transition from convection to conduction in the heat transfer regime inside the porous medium is examined and an equation for estimating the heat transfer inside the porous medium is presented.
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Hou, Xiaofei. "Numerical modeling of complex heat transfer phenomena in cooling applications." Doctoral thesis, Universitat Politècnica de Catalunya, 2015. http://hdl.handle.net/10803/309294.
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Multiphase and multicomponent flows are frequently encountered in the cooling applications due to combined heat transfer and phase change phenomena. Two-fluid and homogeneous mixture models are chosen to numerically study these flows in the cooling phenomena. Therefore this work is divided in two main parts. In the first part, a two-fluid model algorithm for free surface flows is presented. The two fluid model is usually used as a tool to simulate dispersed flow. With its extension, it may also be applied to large interface (separated) flow. In the second part, the homogeneous mixture model for the multicomponent flow is employed to solve evaporation problems. Finally the simulation is focused on the mixed transitional or turbulent flow with and without evaporation.
In detail, this thesis consists of six chapters. The first chapter is devoted to an introduction to the two-fluid and homogeneous mixture models employed in the multiphase/multicomponent flow. The multiphase classification is explained and the previous works on the two models are reviewed.
The second chapter is mainly focused on the application of the Fractional step method algorithm in the two-fluid model. In addition, the Conservative Level Set method(interface sharpening) is applied to overcome the weakness of the two-fluid model (numerical diffusion of the interface), which is often encountered in the simulations using this model. With the proposed algorithm, the two-fluid model suitable for the dispersed flow is extended to the separated flow.
The homogeneous mixture model is introduced in the third chapter. As an application of this model, different evaporation cases have been tested. A hydrodynamically fully developed laminar flow in a horizontal duct is firstly studied. It is used to verify the model in a laminar flow considering constant physical properties. Water falling films are often applied to enhance the heat transfer. Therefore the second case analyzes the natural convection in a cavity with liquid film (assuming variable physical properties), and validates the falling film model. Finally, a third case is focused
on mixed convective flow interacting with a water falling liquid film. The effects of heat flux on the evaporation rate and the flow structure are investigated employing numerical experiments.
In the fourth chapter, the laminarization phenomena of turbulent forced flow in a vertical pipe with constant heat flux is studied. These studies validate the prediction ability of large eddy simulation in this complex situation. Afterwards additional cases in a long vertical pipe (100 times diameters) are conducted and the results are compared with the existing experimental data. Throughout the whole pipe, the flow state follows a complicated process, which includes turbulent-laminar and laminar-turbulent transitions. This problem is of great significance in industrial applications for it may result in the enhancement or impairment of heat transfer.
Based on the previous verification of the model in turbulent and transitional flow, the simulation of the cooling in a uniformly heated vertical tube is conducted in the fifth chapter with an ascending flow of air and a falling film. This case also involves the transitional complex flow and boundary conditions of falling film with simultaneous heat/mass transfer. The variable factors affecting the evaporation and thermal efficiency have been analyzed.
In Appendix C, as an application in engineering of the work developed within the thesis, a series of flows in a complex geometry of a refrigerator chamber without or with fins are simulated to obtain their effects on the flow distribution and mixing feature.
In the last chapter, the main conclusions are summarized and the future works are listed.Debido a la transferencia de calor y de cambio de fase, fenomenología multifase y multicomponente se encuentra en las aplicaciones de refrigeración. Dependiendo de la estructura de interfaz multifase pueden clasificarse como flujo separado (flujo estratificado), de transición o mezclado flujo y flujo disperso. Dependiendo de los diferentes estados de flujo de dos fases, se deben aplicar diferentes modelos. La presente tesis se centra principalmente en flujo separado. Modelos de mezcla homogénea de dos fluidos se emplean para simular fenómenos de enfriamiento en multifase. Este trabajo se divide en dos partes principales. En la primera parte, un algoritmo de modelo de dos fluidos de la superficie libre se presenta. El modelo de dos fluidos se utiliza generalmente como una herramienta para simular flujo disperso. En la segunda parte, el modelo de mezcla homogénea para flujo multicomponente se emplea para resolver el problemas de evaporación. Finalmente se simulan flujos turbulentos con influencia de la fuerza de flotabilidad. El objetivo a largo plazo es acoplar los dos modelos, que podrían resolver todos los regímenes de flujo y tendrian aplicación en problemas industriales. La presente tesis se compone de seis capítulos. El primer capítulo está dedicado a una introducción a los modelos de mezcla homogénea de dos fluidos empleados en el flujo multifásico / multicomponente. La clasificación de múltiples fases se explica y se revisa la bibliografia existente. El segundo capítulo se centra principalmente en la aplicación del Fractional Step Method en bifasico. Con el algoritmo propuesto, el modelo de dos fluidos adecuado para el flujo disperso se extiende al flujo separado. El modelo para mezcla homogénea se introduce en el tercer capítulo con las mismas ecuaciones de masa, cantidad de movimiento, energía y concentración. Se aplica en casos de evaporación y condensación. El flujo laminar completamente desarrollado en un conducto horizontal se estudia en primer lugar considerando propiedades físicas constantes para verificar el modelo en un flujo laminar. La simulacion de convección natural en una cavidad con propiedades físicas variables y película de líquido se realiza numéricamente para validar el modelo de película descendente. Finalmente, el flujo de convección mixta se investiga en un film descendente. Los efectos de los diferentes parámetros en la evaporación y el flujo son investigados mediante experimentos numéricos. En el cuarto capítulo, la laminarización de flujo turbulento forzado en un tubo vertical con flujo de calor constante se estudia para validar la capacidad de predicción de los modelos LES en el flujo de convección mixta de transición turbulenta-laminar con fuerte fuerza de flotación. Se llevan a cabo estudios numericos y los resultados se comparan con los datos experimentales existentes. A lo largo de toda el conducto, el estado de flujo sigue un proceso complicado, que incluye turbulencia.
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Liewkongsataporn, Wichit. "A numerical study of pulse-combustor jet impingement heat transfer." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22651.
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Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2008.Committee Co-Chair: Ahrens, Fred; Committee Co-Chair: Patterson, Tim; Committee Member: Aidun, Cyrus; Committee Member: Empie, Jeff; Committee Member: Frederick, Jim.
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Mroue, Hassan. "Numerical and experimental investigation of a multi-pass heat-pipe-based heat exchanger." Thesis, Brunel University, 2018. http://bura.brunel.ac.uk/handle/2438/16131.
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Theoretical, numerical and experimental investigations have been successfully carried out to characterise the thermal performance of an air-to-water multi-pass heat exchanger equipped with thermosyphon technology. Air and water are the heat source and the heat sink on the evaporator and condenser, respectively. Evaporator and condenser are connected by six thermosyphons, through which thermal energy is transferred. The investigation was performed for two multi-pass configurations at various inlet conditions: a range of air inlet temperatures (100, 150, 200 and 250°C) and mass flow rates (0.05, 0.08, 0.11 and 0.14 kg/s). The water inlet conditions were kept constant (a temperature of 15°C and a mass flow rate of 0.08 kg/s). The theoretical model was built by applying the thermal resistance analogy with the aid of convection, boiling and condensation correlations found in the literature. It was found that the thermal resistances in the first pass act in parallel mode along the ones in the second pass. Similarly, in the case of three passes. Also, the external convective thermal resistance were found to be the major contributor to the overall thermal resistance in the entire heat exchanger. ANSYS Fluent was the numerical tool used to investigate the shell-side convective heat transfer for two multi-pass configurations. The CFD model has been experimentally validated. The two-phase change processes inside the thermosyphons were not modelled during the simulation. Instead, the thermosyphons were treated as solid rods with a constant thermal conductivity, which was calculated. The overall rate of heat transfer was obtained by both CFD and a theoretical model, and the results lay within 15% of the experimental data. The numerical predictions demonstrated that the K-ε Realizable turbulence model with scalable wall function is a reliable tool for predicting heat transfer and fluid flow in such types of heat exchangers. This investigation will add a great knowledge to the academia in terms of both experimentation and modelling in the area of multi-pass thermosyphons-based heat exchangers. Also, it provides the industries with a cost effect design tool for future modelling of similar heat exchanger systems.
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Park, Do Seo. "Experimental and numerical study of laminar forced convection heat transfer for a dimpled heat sink." Thesis, [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-1571.
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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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Injeti, Phaninder. "Numerical simulation of steady state and transient heat transfer in microchannels." [Tampa, Fla.] : University of South Florida, 2007. http://purl.fcla.edu/usf/dc/et/SFE0002157.
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Hernandez-Ontiveros, Cesar F. "Numerical analysis of heat transfer during jet impingement on curved surfaces." [Tampa, Fla.] : University of South Florida, 2007. http://purl.fcla.edu/usf/dc/et/SFE0002123.
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El-Hawat, Salem M. "Numerical modelling of flow and heat transfer for high-performance surfaces." Thesis, University of Brighton, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251804.
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Wijaya, Kusuma I. Gusti Bagus. "Numerical investigations of airflow and heat transfer in traditional Balinese buildings." Thesis, Brunel University, 1999. http://bura.brunel.ac.uk/handle/2438/5379.
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Traditional Balinese architecture is commonly related to culture and traditional reasoning. When subjected to several modem problems such as energy demand, pollution, and impact of urbanisation and tourism, traditional architecture becomes less attractive since the definitions behind traditional reasoning are not clear and can be interpreted in different ways. To understand this feature, the study of traditional Balinese architecture starts by using several key parameters such as wind engineering and heat transfer, as presented and used in several countries. The flow patterns around a cubic building have been studied by many researchers. The velocity profile at the model position and the local surface roughness are specific to each building model and cannot be estimated from general tests of a standard building shape, therefore specific velocity profiles and conditions are used in this particular study. The air flow around a cluster of traditional Balinese buildings is extremely complicated and difficult to determine by modelling an isolated building (via symmetric conditions) since the buildings are linked to each other. Full scale models of traditional buildings have been investigated by using CFD to predict the above aspects. Simulations using this method can be done more quickly and less expensively than with wind tunnel experiments, and are capable of delivering more detailed and comprehensive information about the flow structure. Two-dimensional models of traditional Balinese building arrangements are simulated by using a commercial code Fidap based on the finite element method to assess the effects of type of roof, fence and surface roughness. Three-dimensional models are simulated by using a commercial code CFX based on the finite volume method to verify some traditional definitions. A standard к-ε model is adopted because it needs less computational power and has achieved notable successes in calculating a wide variety of thin shear layer and recirculating flows without the need of adjustment of the model constants, but with the imposition of boundary conditions to reduce the over-prediction near windward edges. Adopting lower values of к and ε combined with multi-blocks is shown to reduce this over-estimation. For a cubic building, the results can be compared with several other turbulence models. It appears that traditional Balinese architecture has a strong and significant correlation with several engineering fields, therefore traditional communities can develop by considering the Tri Hita Karana concept in order to improve thermal comfort and reduce cooling loads, with corresponding energy savings.
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Mahdavi, Nejad Alireza. "Numerical Study of Heat and Mass Transfer Using Phase Change Materials." Digital WPI, 2018. https://digitalcommons.wpi.edu/etd-dissertations/500.
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Phase Change Materials (PCM) absorb and release heat at preset temperatures. Due to their relatively high values of latent heat, they are capable of storing and releasing large amounts of energy during phase change. When a PCM is in its solid phase, it will absorb heat as the external temperature rises. The temperature of the PCM will mirror the external temperature until the melting point of PCM is reached. At this stage, the PCM will begin to melt with almost no change in its temperature. PCM plays an opposite role when the external temperature drops. It releases the stored energy back while going through phase change from liquid phase to solid phase.
The present work is a numerical study towards fundamental understanding of the impact of using PCM on enhancement of heat and mass transfer in several scenarios. A numerical analysis has been carried out to determine the impact of presence of PCM on the insulating characteristics of paper board packaging. Two different cases of a layered PCM and uniformly dispersed PCM within the packaging wall are considered. The numerical results illustrate significant reduction in exchange of heat between the exterior and the interior of the packaging.
Specifically, the unique concept of utilizing PCM in drying of paper is proposed and a numerical investigation is performed to determine the corresponding transport characteristics. The results indicate that the PCM acts as a heat source and a heat sink alternatingly throughout the conventional paper drying process, enhancing the drying energy efficiency. This study also included presence of gas-fired infrared emitters in the drying process as well for which the spectral absorption coefficient of PCM was measured and incorporated into the theoretical model.
Finally, the impact of the presence of PCM in convective air-drying of moist paper is numerically investigated. The hot air ow is generated by an in-line jet nozzle. The air impinges on the exposed surface of the moist paper while the other side is considered to be perfectly insulated. The results provide the corresponding air flow field as well as air temperature distribution in between the nozzle exit and the surface of the moist paper. The results also reveal the enhancement of drying rates with PCM, fundamentally confirming the role of PCM on enhancing the energy efficiency of convective drying of moist paper.
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Pohl, Julien. "Turbine stator well heat transfer and design optimisation using numerical methods." Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/15939/.
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Engine components are commonly exposed to air temperatures exceeding the thermal material limit in order to increase the overall engine performance and to maximise the engine specific fuel consumption. To prevent the overheating of the materials and thus the reduction of the component life, an internal flow system must be designed to cool the critical engine parts and to protect them. As the coolant flow is bled from the compressor and not used for the combustion an important goal is to minimise the amount of coolant in order to optimise the overall engine performance. Predicting the metal temperatures is of paramount importance as they are a major factor in determining the component stresses and lives. In addition, as modern engines operate in ever harsher conditions due to efficiency requirements, the ability to predict thermo-mechanical displacements becomes very relevant: on the one hand, to prevent damage of components due to excessive rubbing, on the other hand, to understand how much air is flowing internally within the secondary air system for cooling and sealing purposes, not only in the design condition but throughout the engine life-span. In order to achieve this aero-engine manufacturers aim to use more and more accurate numerical techniques requiring multi-physics models, including thermo-mechanical finite elements and CFD models, which can be coupled in order to investigate small variations in temperatures and displacements. This thesis shows a practical application and extension of a numerical methodology for predicting conjugate heat transfer. Extensive use is made of FEA (solids) and CFD (fluid) modeling techniques to understand the thermo-mechanical behaviour of a turbine stator well cavity, due to the interaction of cooling air supply with the main annulus. Previous work based on the same rig showed diffculties in matching predictions to thermocouple measurements near the rim seal gap. In this investigation, further use is made of existing measurements of hot running seal clearances in the rig. The structural deflections are applied to the existing model to evaluate the impact in flow interactions and heat transfer. Furthermore, for one test case unsteady CFD simulations are conducted in order to take into account the flow unsteadiness in the heat transfer predictions near the rim. In addition to a baseline test case without net ingestion, a case simulating engine deterioration with net ingestion is validated against the available test data, also taking into account cold and hot running seal clearances. Furthermore an additional geometry with a stationary deflector plate is modelled and validated for the same flow cases. Experiments as well as numerical simulations have shown that due to the deflector plate the cooling flow is fed more directly into the disc boundary layer, allowing more effective use of less cooling air, leading to improved engine efficiency. Therefore, the deflector plate geometry is embedded in a CFD-based automated optimisation loop to further reduce the amount of cooling air. The optimisation strategy concentrates on a flexible design parameterisation of the cavity geometry with deflector plate and its implementation in an automatic 3D meshing system with respect of finally executing an automated design optimisation. Special consideration is given to the flexibility of the parameterisation method in order to reduce design variables to a minimum while also increasing the design space flexibility & generality. The parameterised geometry is optimised using a metamodel-assisted approach based on regressing Kriging in order to identify the optimum position and orientation of the deflector plate inside the cavity. The outcome of the optimisation is validated using the benchmarked FEA-CFD coupling methodology.
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Chang, Dongil. "Numerical simulations of turbulent flow and heat transfer in rod bundles." Thesis, University of Ottawa (Canada), 2006. http://hdl.handle.net/10393/29282.
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The unsteady Reynolds-averaged Navier-Stokes equations, supplemented by a Reynolds stress model, were solved with relatively high spatial and temporal resolutions to determine the time-averaged mean velocity and turbulent stresses in isothermal, single phase flows in a rectangular duct containing a single rod and in a 37-rod rod bundle. In addition, the time-averaged mean temperature, temperature fluctuation variance and turbulent heat fluxes were computed in the single-rod duct flow in which the rod was heated passively. The computed values were, in general, in fair agreement with available experimental results. The simulations also resolved the formation of coherent structures in the form of counter-rotating vortices with axes alternating on either side of rod-rod and rod-wall gaps. The contributions of these coherent structures on the turbulent and thermal fields and on cross-gap mixing were documented and found to be substantial. The action of coherent structures moderates the mean temperature rise in the gap region but creates substantial local variation of the instantaneous temperature fluctuations at relatively low frequencies. Reduction of the gap size below a critical value resulted in a decrease of the frequency of coherent fluctuations and the cross-channel mixing efficiency, contrary to predictions based on the extrapolation of available empirical correlations. In the case of the 37-rod bundle, the coherent velocity fluctuations were found to be strongly correlated in the entire computational domain.
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Faucher, Florent Patrice. "A Numerical Model of a Microwave Heated Fluidized Bed." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/36217.
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This proposes a model for a microwave heated fluidized
bed by ceramic pellets to highlight the possibility
to obtain a temperature gradient between the gas and
the pellets. After a review of the recent work on
microwave effects on chemical reactions, a short
description of fluidization is given for a better
understanding of the phenomena, followed by a
development of a model of the heat transfer
processes taking place in the fluidized bed. A
parameter study describes the trends that should be
expected despite the numerous restrictions and
assumptions. Also, a set of parameters is proposed
for optimal conditions that are close to the real
conditions often encountered in practice. Numerous
figures and tables are added, completing the main
argument advanced in the thesis: it is possible to
obtain a temperature difference between the gas
and the pellets of a chemical bed reactor heated by
microwaves by carefully choosing the following
parameters: pellet diameter, bed height, gas
velocity, pellet density and electric field.Master of Science
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Miró, Jané Arnau. "Flow and heat transfer of impinging synthetic jets." Doctoral thesis, Universitat Politècnica de Catalunya, 2019. http://hdl.handle.net/10803/667300.
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Synthetic jets are produced by the oscillatory movement of a membrane inside a cavity, causing fluid to enter and leave through a small orifice. This results in a net jet that is able to transfer kinetic energy and momentum to a fluid medium without the need of an external fluid source. This is why synthetic jets are interesting and will have key roles in a wide range of relevant applications such as active flow control, thermal cooling or fuel mixing. From the phenomenological point of view, synthetic jets are formed by elaborate flow patterns given their non-linear nature and, under certain conditions, unstable complex flows can be observed.
The present dissertation is focused on the investigation of the fluid flow and thermal performance of synthetic jets. Two different synthetic jet actuator geometries (i.e., slotted and circular) are studied. The jets in both configurations are confined by two parallel isothermal plates with an imposed temperature difference, and impinge into a heated plate located at a certain distance from the actuator orifice. The unsteady three-dimensional Navier-Stokes equations are solved for a range of Reynolds numbers using time-accurate numerical simulations. Moreover, a detailed model of the actuator that uses Arbitrary Lagrangian-Eulerian (ALE) formulation to account for the movement of the actuator membrane is developed. This model, based on the governing numbers of the flow, is used to conduct the numerical analyses.
The flows obtained in both configurations are noticeably different and three-dimensional for almost all the Reynolds numbers considered. The jet in the slotted configuration is formed by a pair of vortices that undergo turbulent transition and eventually coalesce into the jet. The external flow is dominated by two major recirculation structures that find their counterparts inside the actuator cavity. A new vortical structure, observed in confined slotted jets, appears as an interaction of the synthetic jet flow with the bottom wall and results in a change on the jet’s heat transfer mechanisms. On the other hand, the jet in the circular configuration presents three different flow regions that have been identified according to the literature: the main vortex ring, the trailing jet and the potential core. In this case, the external flow is dominated by the main vortex ring and the trailing jet, thus presenting a different morphology and heat transfer behavior than the slotted configuration. A detailed analysis of the vortex trajectories has shown that the advected vortices on the circular configuration reach the impingement before their slotted counterparts. Distributions of turbulent kinetic energy at the expulsion and vortex swirl and shear strength have revealed that the flow on the circular jet is mostly concentrated near the jet centerline, while it is more spread for the slotted configuration. For these reasons, at the same jet ejection velocity and actuator geometry, synthetic jet formation on the circular configuration can occur at higher frequencies than on the slotted configuration.
The analysis of the synthetic jet outlet temperature has shown that assuming a uniform profile is reasonable if the Reynolds number is high enough. Moreover, the outlet jet temperature is significantly higher than the cold plate temperature. The two configurations present different impinging behaviors due to the differences on the flow. Heat transfer analysis on the hot wall has revealed that the circular configuration reaches a higher heat transfer peak than the slotted configuration, however, heat transfer decays faster in the circular configuration when moving away from the jet centerline. Eventually, correlations for the heat transfer at the hot wall and the outlet temperature with the Reynolds number are proposed. They can be useful to include the cavity effects when using simplified models that do not account for actuator cavity.Els jets sintètics (SJ) són produïts pel moviment oscil·latori d'una membrana a l'interior d'una cavitat, cosa que fa que el líquid entri i surti per un petit orifici. Això es tradueix en un jet que és capaç de transferir energia cinètica i impuls a un medi fluid sense la necessitat d'una font externa. És per això que els SJ són interessants i tindran un paper clau en una àmplia gamma d'aplicacions rellevants, com ara el control actiu de flux, el refredament tèrmic o la barreja de combustible. Des del punt de vista fenomenològic, els SJ estan formats per patrons de flux elaborats per la seva naturalesa no lineal i, sota certes condicions, es poden observar fluxos complexos i inestables. Aquesta tesis està centrada en la investigació del flux de fluids i el rendiment tèrmic dels jets sintètics. S'estudien dues geometries diferents d’actuadors de SJ (és a dir, ranurats i circulars). Els jets en ambdues configuracions estan confinats per dues plaques isotèrmiques paral·leles amb una diferència de temperatura imposada i afecten a una placa escalfada situada a una certa distància de l'orifici de l'actuador. Les equacions tridimensionals inestables de Navier-Stokes es resolen per un nombre de Reynolds utilitzant simulacions numèriques precises en el temps. A més, es desenvolupa un model detallat de l'actuador que utilitza la formulació arbitrària lagrangiana-euleriana (ALE) per explicar el moviment de la membrana de l'actuador. Aquest model, basat en els números de govern del flux, s'utilitza per realitzar els anàlisis numèrics. Els fluxos obtinguts en ambdues configuracions són notablement diferents i tridimensionals per a gairebé tots els números de Reynolds considerats. El jet en la configuració ranurada està format per un parell de vòrtexs que experimenten una transició turbulenta que finalment formen el jet. El flux extern està dominat per dues recirculacions principals amb els seus homòlegs dins de la cavitat de l'actuador. Una nova estructura, observada en els jets ranurats confinats, apareix com una interacció del flux amb la paret inferior i provoca un canvi en els mecanismes de transferència de calor del jet. D'altra banda, el jet en la configuració circular presenta tres regions de flux diferents que s'han identificat segons la literatura: l'anell de vòrtex principal, el jet final i el nucli potencial. En aquest cas, el flux extern està dominat per l'anell de vòrtex principal i el jet de sortida, presentant així un comportament diferent de morfologia i transferència de calor que la configuració ranurada. Un anàlisi detallat de les trajectòries de vòrtex ha demostrat que els vòrtexs de la configuració circular arriben a la paret superior abans que els seus homòlegs ranurats. Les distribucions d'energia cinètica turbulenta a l'expulsió, entre altres, han revelat que el flux del jet circular es concentra majoritàriament a prop de la línia central del jet, mentre que és més estès per a la configuració ranurada. Per aquestes raons, a la mateixa velocitat d'ejecció del jet i geometria de l'actuador, la formació de SJ en la configuració circular pot produir-se a freqüències més altes que a la configuració ranurada. L'anàlisi de la temperatura de sortida dels SJ ha demostrat que assumir un perfil uniforme és raonable si el nombre de Reynolds és prou elevat. A més, la temperatura del jet de sortida és significativament superior a la temperatura de la placa freda. Les dues configuracions presenten diferents comportaments a causa de les diferències en el flux. L’anàlisi de la transferència de calor a la paret calenta ha revelat que la configuració circular arriba a un màxim de transferència de calor més gran que la configuració ranurada, però, la transferència de calor es desaccelera més ràpidament en la configuració circular quan s’allunya de la línia central. Finalment, es proposen correlacions per a la transferència de calor a la paret calenta i la temperatura de sortida amb el nombre de Reynolds. Poden ser útils per incloure els efectes de la cavitat quan s’utilitzen models simplificats que no tenen en compte la cavitat de l’actuador.
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Domeij, Bäckryd Rebecka. "Simulation of Heat Transfer on a Gas Sensor Component." Thesis, Linköping University, Department of Mathematics, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-131.
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Gas sensors are today used in many different application areas, and one growing future market is battery operated sensors. As many gas sensor components are heated, one major limit of the operation time is caused by the power dissipated as heat. AppliedSensor is a company that develops and produces gas sensor components, modules and solutions, among which battery operated gas sensors are one targeted market.
The aim of the diploma work has been to simulate the heat transfer on a hydrogen gas sensor component and its closest surroundings consisting of a carrier mounted on a printed circuit board. The component is heated in order to improve the performance of the gas sensing element.
Power dissipation occurs by all three modes of heat transfer; conduction from the component through bond wires and carrier to the printed circuit board as well as convection and radiation from all the surfaces. It is of interest to AppliedSensor to understand which factors influence the heat transfer. This knowledge will be used to improve different aspects of the gas sensor, such as the power consumption.
Modeling and simulation have been performed in FEMLAB, a tool for solving partial differential equations by the finite element method. The sensor system has been defined by the geometry and the material properties of the objects. The system of partial differential equations, consisting of the heat equation describing conduction and boundary conditions specifying convection and radiation, was solved and the solution was validated against experimental data.
The convection increases with the increase of hydrogen concentration. A great effort was made to finding a model for the convection. Two different approaches were taken, the first based on known theory from the area and the second on experimental data. When the first method was compared to experiments, it turned out that the theory was insufficient to describe this small system involving hydrogen, which was an unexpected but interesting result. The second method matched the experiments well. For the continuation of the project at the company, a better model of the convection would be a great improvement.
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Mon, Mi Sandar. "Numerical Investigation of Air-Side Heat Transfer and Pressure Drop in Circular Finned-Tube Heat Exchangers." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2009. http://nbn-resolving.de/urn:nbn:de:swb:105-26331.
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A three-dimensional numerical study is performed to investigate the heat transfer and pressure drop performance on the air-side of circular finned tube bundles in cross flow. New heat transfer and pressure drop correlations for the air-cooled heat exchangers have been developed with the Reynolds number ranging from 5000 to 70000. The heat transfer and pressure drop results agree well with several existing experimental correlations. In addition, the influence of the geometric parameters on the heat transfer and pressure drop are studied in detail and their results discussed. The numerical flow visualization results for the boundary layer developments, horseshoe vortex system, and local velocity and temperature distributions are presented.
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Oh, Sung Hyuk. "Experimental and numerical investigation of turbulent flow and heat (mass) transfer in a two-pass trapezoidal channel with turbulence promoters." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-3198.
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Boonpongmanee, Thaveesak. "NUMERICAL AND EXPERIMENTAL INVESTIGATION OF HEAT AND MASS TRANSFER IN ROTATING SYSTEMS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=case1112791338.
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Zhai, Qiang. "A NUMERICAL STUDY OF A HEAT EXCHANGER SYSTEM WITH A BYPASS VALVE." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1461252171.
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Rastan, Hamidreza. "Investigation of the heat transfer of enhanced additively manufactured minichannel heat exchangers." Thesis, KTH, Skolan för industriell teknik och management (ITM), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-264278.
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Mini-/microchannel components have received attention over the past few decades owing to their compactness and superior thermal performance. Microchannel heat sinks are typically manufactured through traditional manufacturing practices (milling and sawing, electrodischarge machining, and water jet cutting) by changing their components to work in microscale environments or microfabrication techniques (etching and lost wax molding), which have emerged from the semiconductor industry. An extrusion process is used to produce multiport minichannel-based heat exchangers (HXs). However, geometric manufacturing limitations can be considered as drawbacks for all of these techniques. For example, a complex out-of-plane geometry is extremely difficult to fabricate, if not impossible. Such imposed design constraints can be eliminated using additive manufacturing (AM), generally known as three-dimensional (3D) printing. AM is a new and growing technique that has received attention in recent years. The inherent design freedom that it provides to the designer can result in sophisticated geometries that are impossible to produce by traditional technologies and all for the redesign and optimization of existing models. The work presented in this thesis aims to investigate the thermal performance of enhanced minichannel HXs manufactured via metal 3D printing both numerically and experimentally. Rectangular winglet vortex generators (VGs) have been chosen as the thermal enhancement method embedded inside the flat tube. COMSOL Multiphysics, a commercial software package using a finite element method (FEM), has been used as a numerical tool. The influence of the geometric VG parameters on the heat transfer and flow friction characteristics was studied by solving a 3D conjugate heat transfer and laminar flow. The ranges of studied parameters utilized in simulation section were obtained from our previous interaction with various AM technologies including direct metal laser sintering (DMLS) and electron-beam melting (EBM). For the simulation setup, distilled water was chosen as the working fluid with temperaturedependent thermal properties. The minichannel HX was assumed to be made of AlSi10Mg with a hydraulic diameter of 2.86 mm. The minichannel was heated by a constant heat flux of 5 Wcm−2 , and the Reynolds number was varied from 230 to 950. A sensitivity analysis showed that the angle of attack, VG height, VG length, and longitudinal pitch have notable effects on the heat transfer and flow friction characteristics. In contrast, the VG thickness and the distance from the sidewalls do not have a significant influence on the HX performance over the studied range. On the basis of the simulation results, four different prototypes including a smooth channel as a reference were manufactured with AlSi10Mg via DMLS technology owing to the better surface roughness and greater design uniformity. A test rig was developed to test the prototypes. Owing to the experimental facility and working fluid (distilled water), the experiment was categorized as either a simultaneously developing flow or a hydrodynamically developed but thermally developing flow. The Reynolds number ranged from 175 to 1370, and the HX was tested with two different heat fluxes of 1.5 kWm−2 and 3 kWm−2 . The experimental results for the smooth channel were compared to widely accepted correlations in the literature. It was found that 79% of the experimental data were within a range of ±10% of the values from existing correlations developed for the thermal entry length. However, a formula developed for the simultaneously developing flow overpredicted the Nusselt number. Furthermore, the results for the enhanced channels showed that embedding VGs can considerably boost the thermal performance up to three times within the parameters of the printed parts. Finally, the thermal performance of the 3D-printed channel showed that AM is a promising solution for the development of minichannel HXs. The generation of 3D vortices caused by the presence of VGs ii can notably boost the thermal performance, thereby reducing the HX size for a given heat duty.
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Lee, Hoki. "Experimental and numerical study of evaporating flow heat transfer in micro-channel." Pullman, Wash. : Washington State University, 2008. http://www.dissertations.wsu.edu/Dissertations/Fall2008/h_lee_112408.pdf.
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Thesis (Ph. D.)--Washington State University, December 2008..Title from PDF title page (viewed on July 10, 2009). "School of Mechanical and Materials Engineering." Includes bibliographical references (p. 176-187).
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Kirez, Oguz. "A Numerical Forced Convection Heat Transfer Analysis Of Nanofluids Considering Performance Criteria." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12615167/index.pdf.
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A nanofluid is a new heat transfer fluid produced by mixing a base fluid and solid nano sized particles. This fluid has great potential in heat transfer applications, because of its increased thermal conductivity and even increased Nusselt number due to higher thermal conductivity, Brownian motion of nanoparticles, and other various effects on heat transfer phenomenon.
In this work, the first aim is to predict convective heat transfer of nanofluids. A numerical code is created and run to obtain results in a pipe with two different boundary conditions, constant wall temperature and constant wall heat flux. The results for laminar flow for thermally developing region in a pipe are obtained for Al2O3/water nanofluid with different volumetric fraction and particle sizes with local temperature dependent conductivity approach. Various effects that influence nanofluid heat transfer enhancement are investigated. As a result, a better heat transfer performance is obtained for all cases, compared to pure water. The important parameters that have impact on nanofluid heat transfer are particle diameter of the nanoparticles, nanoparticle volumetric fraction, Peclet number, and viscous dissipation.
Next, a heat transfer performance evaluation methodology is proposed considering increased pumping power of nanofluids. Two different criteria are selected for two boundary conditions at constant pumping power. These are heat transfer rate ratio of the nanofluid and the base fluid for constant wall temperature boundary condition and difference between wall temperature of the pipe at the exit and inlet mean temperature of the fluid ratio for constant wall heat flux case. Three important parameters that influence the heat transfer performance of nanofluids are extracted from a parametric study. Lastly, optimum particle size and volumetric fraction values are obtained depending on Graetz number, Nusselt number, heat transfer fluid temperature, and nanofluid type.
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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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Santoyo-Gutierrez, Edgar Rolando. "Transient numerical simulation of heat transfer processes during drilling of geothermal wells." Thesis, University of Salford, 1997. http://usir.salford.ac.uk/14689/.
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The transient thermal history of a well drilling system has been identified as one of the main problems that the geothermal well drilling industry needs to solve. In particular, the estimation of temperatures, in and around a geothermal well during drilling (circulation) and shut-in (thermal recovery) conditions, is required. To overcome this problem, a computer simulator (WELLTHER) has been developed which uses a direct solution method to solve the finite difference equations describing the transient heat transfer processes in a wellbore during drilling and shut-in operations in the presence of the lost circulation to the formation. The new computer simulator uses a numerical model to account for the transient convective heat transfer in the formation surrounding a well, due to lost circulation. This feature of the present simulator is important, since previous wellbore simulators consider the heat transfer process in the formation (rock) as a merely conductive problem. The WELLTHER simulator is capable of accounting for these losses at any point in the well and it has been applied to the study of several Mexican geothermal wells. The results show that the effect of lost circulation on the shut-in temperature profiles can be reproduced satisfactorily. Likewise, a parametric analysis, carried out using the simulator, indicates that a number of assumptions made in previous numerical models are invalid and that certain factors ignored in previous models have a significant effect on the dynamic wellbore temperature distribution. Finally, a coupling of the new simulator with another computer code (STATIC TEMP) can be used as a tool to infer more reliably the static formation temperatures in geothermal systems.
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Zhang, Hongbo. "Numerical simulation of electrohydrodynamic effect on single and two-phase heat transfer." Thesis, Nottingham Trent University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.409390.
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"Numerical methods for radiative heat transfer." Universitat Politècnica de Catalunya, 2006. http://www.tesisenxarxa.net/TDX-0516107-103916/.
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Sam, Yaw-Wing, and 沈耀榮. "Numerical Study of Microjet Impingement Heat Transfer." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/13267187380666237252.
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碩士國立成功大學
機械工程學系碩博士班
93
The investigation of the flow field and heat transfer characteristic of an axisymmetric, confined, incompressible microjet impinging on a flat surface with an uniform heat flux has been carried out numerically in this study. The numerical simulation of a steady, 2D cylindrical coordinate, turbulent flow heat transfer is adopted to test the accuracy of the physical model. The turbulent governing equations are solved by using the Control-Volume based finite-difference method with the power-law scheme, and the well-known turbulence model to describe the turbulent structure. The SIMPLE algorithm is used to solve the pressure-velocity coupling. The parameters studied include nozzle to impinging surface spacing (H/D=2、4)、Reynolds number (Re=210、419、524), and also heat flux (q" =50 、100 、150 ). The working medium is air. The local Nusselt number distributions along with the nondimensional temperature, heat transfer coefficient distributions and the velocity vector plots near the impingement surface are predicted and analyzed. According to the experimental studies of microjet impingement by Shen (2003) and Yen (2004), even the Reynolds numbers are low, the corresponding velocities are very fast. And also, in order to verify the results of Pence et al. (2003) that there was no obvious change in the surface temperature along the impingement surface using a turbulence model, therefore turbulent flow is adopted for this numerical calculation. From the velocity vector plots, it is found that there is a coherence structures of large vortex observed at the low impinging distance (H/D=2) and low Reynolds number (Re=210). Owing to the fact that instability waves in the shear layer do not have enough energies to roll up into the ring vortex for the microjet, the large vortex will disappear by increasing the impinging distance and the Reynolds number, the same flow structure characteristics as presented by the experiments of Shen (2003) and Yen (2004). The effects of Reynolds number on heat transfer and flow field are significant. The Nusselt number increases with increasing Reynolds number, and the local maxima is observed near r/R=1.2 rather than at the centerline, showing good agreement with Pence et al.(2003) and supporting the validity of the present study. Numerical predictions obtained from this study will provide physical insight into the MEMS system and the cooling of CPU.
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Kuo, Po-hsuan, and 郭伯軒. "Numerical Analysis of the Heat Transfer Characteristics of Micro Heat Pipes." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/10918793389012710404.
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碩士國立成功大學
機械工程學系碩博士班
95
Micro heat pipes can be used in an electronic chip to render its temperature distribution more uniform. In this thesis, based on the Young-Laplace equation and conservation laws for mass, momentum, and energy transport, we construct a one-dimensional thermofluid model for analyzing the steady-state flow and heat transfer characteristics of micro heat pipes consisting of V-shaped micro grooves. The model is then used to calculate the flow and evaporation/condensation of the working fluid in a micro heat pipe, and to calculate the critical heat input beyond which the heat pipe would dry out. It is found that the critical heat input can be increased by increasing the surface tension coefficient, thermal conductivity and density of the working fluid, but decreased if the viscosity of the working fluid increases. Moreover, the equivalent thermal conductivity of a micro heat pipe increases with the convection heat transfer coefficients on the liquid-substrate and liquid-vapor interfaces. We have also found that, for the case studied in this thesis, the critical heat input obtains a maximum when the apex angle of the grooves is around 33 degrees.
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Tsao, Yu-Nan, and 曹聿男. "Numerical laminar flow and heat transfer in microtubes." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/92135170532111896436.
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碩士國立中央大學
機械工程研究所
90
Abstract This study use the FIDAP software to simulate the laminar thermal-flow characteristics of the small tubes (where the diameter range: 0.502
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Yang, Chia-Hao, and 楊嘉豪. "Numerical Investigation into heat transfer of oil cooler." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/74227692284770113312.
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碩士國立屏東科技大學
車輛工程系所
100
This study aims to use CFD methods to explore the oil cooler heat transfer. Understanding oil cooler construction, and design the best heat transfer. Oil cooler most device on motor. The use of air makes oil cooler heat dissipation by riding and in internal pipeline is uses by oil through oil cooler, to discussion the heat dissipation of trend. This oil cooler have 15 row, using porous media and full module simulation results of speed and pressure to simplified model. Then uses simplified model, Then through Taguchi method design pipeline, such as height, and width, and angle, and temperature , uses two species evaluation to find the best value. The best value is at height 2.1mm, width 3mm, angle 13o, temperature 350K.
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Feng-HsiangLai and 賴逢祥. "Numerical Study of Convective Heat Transfer with Nanofluids." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/11151118451843878212.
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林世檳. "Numerical Analysis on Heat Transfer of Computer Heat Sinks with Various Geometries." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/71920473973695375623.
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碩士國立臺灣科技大學
機械工程系
92
Abstract In recent years, heat sinks apply extensively to various electronic equipment. Not only an indispensable apparatus but also a challenge that system engineering and design analysts have to deal with. This project is aimed at module of heat sink dedicated for computers, by using software-package of computational fluid dynamics “STAR-CD”, we process the numerical stimulation analysis between the flow field’s condition surrounded by heat sinks and behaviors of convective heat transfer. In order to testify the accuracy, we further relate experimental data to outcome derived from software-package. We discuss the difference among different software-package and its reasons, realize the impact that fluid’s flow status of fan causes on heat sink, research on form geometric resistance and thermal resistance ,and change its design to achieve better efficiency. With adequate ability to heat transfer analysis, Designing different geometric fins, given fixed parameters, plus the stable condition of flow field, we change vertical plate fin to heat sink with bevel, square, cylinder and tabulate fin and install real fans to objects. Observe the changes of temperature and speed for different geometric heat sinks and stimulate the flow field of real fans. Fully understand the characteristics of heat sink modules through different geometric fins and the trend of heat sink and clarify the efficiency brought by them. This research shows that flow ability is a significant factor for heat transfer. For the geometric fins used in this research, because there is less resistance to fluid flow for cylinder-pin fin, the enhancement of heat transfer is thus larger than that of other fins. Therefore, given heat sinks with same areas, cylinder-pin fin has better ability to transfer heat than other pin fins. This outcome demonstrates the influence of heat transfer.
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Lai, Feng-Hsiang, and 賴逢祥. "Numerical Study of Turbulent Heat Transfer Enhancement with Nanofluids." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/53876348513378958297.
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碩士國立成功大學
機械工程學系碩博士班
95
In this study, the problem of turbulent forced convection flow of nanofluids has been investigated numerically for two particular geometrical configurations, namely a uniformly heated tube and radial flow. Both water-Cu and water-Al2O3 nanofluids are discussed. The numerical simulations are undertaken for the parameters：the Reynolds number Re, the volume concentration , the constant heat flux and the particle diameter. The turbulent governing equations are solved with the Low Reynolds number turbulence model for tube flow and the Standard turbulence model for radial flow, respectively. The theoretical model developed for tube flow is validated by comparing the numerical predictions with available experimental data in the literature, and the numerical results show that the averaged Nusselt numbers are reasonably predicted with a maximum discrepancy within 10%. The present study indicates that in the tube flow, with the use of volume fraction 1% and 2% water/Cu nanofluids, the thermal enhancement can achieve 15%、30% compared with pure fluid. As for the radial flow, volume fraction 0.5% and 1% water/alumina nanofluids can result in 16%、40% thermal enhancement, respectively. The heat transfer coefficient increases with the increase of the particle concentration and Reynolds number. Besides, the inclusion of smaller particles into water can produce a more considerable augmentation of the heat transfer coefficient at the fixed particle volume concentration. Among the mixtures studied, the water/Cu nanofluid appears to offer a better heat transfer enhancement than water/Al2O3. On the other hand, the friction factor of the nanofluids is discussed, and it seems that no significant augmentation in pressure drop for the dilute nanofluid is found. Compared with the use of water, it will not cost more input power to make the dilute nanofluids flow.
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Lin, Wen-Long, and 林文龍. "Numerical Simulation on The Local Heat Transfer Enhancement of." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/25427045972526864156.
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碩士國立成功大學
航空太空工程學系
82
(nonstaggered grid)上解 Navier - Stokes 方程式，而在對流項使用 QUICK方法(Hayase et al.,1992)；並在靠近固體邊界，引用強健式低雷 諾數紊流模式(robust low - Reynolds number turbulence model) In this dissertation ，The local heat transfer enhancement of the force convection flow between a parallel duct through the use of local blowing slot at the heated wall has been numerically studied．The numerical program is written on a nonstaggered grid system．The Navier - Stokes equations are approximated via the finite volume method ，SIMPLE algorithm and the convective terms are treated by QUICK scheme of Hayase et al．In near wall region ，the robust low - Reynolds - number turbulence model is employed．
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Lin, Jae-Yuh, and 林傑毓. "A New Numerical Method for Transient Heat Transfer Problems." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/83234466129091307938.
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