Dissertations / Theses on the topic 'Modeling of heat flows'
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Yao, Guang-Fa. "Numerical modeling of condensing two-phase channel flows." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/17678.
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Pond, Ian. "Toward an Understanding of the Breakdown of Heat Transfer Modeling in Reciprocating Flows." ScholarWorks @ UVM, 2015. http://scholarworks.uvm.edu/graddis/477.
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Reynolds average Navier-Stokes (RANS) modeling has established itself as a critical design tool in many engineering applications, thanks to its superior computational efficiency. The drawbacks of RANS models are well known, but not necessarily well understood: poor prediction of transition, non-equilibrium flows, mixing and heat transfer, to name the ones relevant to our study. In the present study, we use a direct numerical simulation (DNS) of a reciprocating channel flow driven by an oscillating pressure gradient to test several low- and high-Reynolds' RANS models. Temperature is introduced as a passive scalar to study heat transfer modeling. Low-Reynolds' models manage to capture the overall physics of wall shear and heat flux well, yet with some phase discrepancies, whereas high-Reynolds' models fail. We have derived an integral method for wall shear and wall heat flux analysis, which reveals the contributing terms for both metrics. This method shows that the qualitative agreement appears more serendipitous than driven by the ability of the models to capture the correct physics. The integral method is shown to be more insightful in the benchmarking of RANS models than the typical comparisons of statistical quantities. This method enables the identification of the sources of discrepancies in energy budget equations. For instance, in the wall heat flux, one model is shown to have an out of phase dynamic behavior when compared to the benchmark results, demonstrating a significant issue in the physics predicted by this model. Our study demonstrates that the integral method applied to RANS modeling yields information not previously available that should guide the derivation of physically more accurate models.
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Preston, Alastair Thomas Colonius Timothy E. "Modeling heat and mass transfer in bubbly cavitating flows and shock waves in cavitating nozzles /." Diss., Pasadena, Calif. : California Institute of Technology, 2004. http://resolver.caltech.edu/CaltechETD:etd-12182003-150738.
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Vincent, Tyler Graham. "Total Temperature Probe Performance for Subsonic Flows using Mixed Fidelity Modeling." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/88867.
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An accurate measurement of total temperature in turbomachinery flows remains critical for component life models and cycle performance optimization. While many techniques exist to measure these flows, immersed thermocouple based probes remain highly desirable due to well established practices for probe design and implementation in typical industrial flow applications. However, as engine manufacturers continue to push towards higher maximum cycle temperatures and smaller flow passages, the continued use of these probes requires new probe designs considering both improved sensor durability and measurement accuracy. Increased maximum temperatures introduce many challenges for total temperature measurements using conventional immersed probes, including increased influences of conduction, convection, and radiation heat transfer between the sensor, fluid and the surroundings due to large thermal gradients present in real turbomachinery systems. While these effects have been previously investigated, the available design models are very limited to specific geometries and flow conditions. In this Dissertation, a more fundamental understanding of the flow behavior around typical vented shield style total temperature probes as a function of probe geometry and operating condition is gained using results from high-fidelity Computational Fluid Dynamics simulations with Conjugate Heat Transfer. A parametric study was conducted considering three non-dimensional probe geometric ratios (vent location to shield length (0.029-0.806), sensor diameter to shield inner diameter (0.252-0.672), and shield outer diameter to strut/mount thickness (0.245-0.759)) and three operating conditions (total temperature (70, 850, 2500°F) and pressure (1, 1, 10 atm), respectively) at a moderate Mach number of 0.4. Results were further quantified in the form of new empirical correlations necessary for rapid thermal performance evaluations of current and future probe designs. Additionally, a new mixed-fidelity or Reduced Order Modeling technique was developed which allows the coupling of high fidelity surface heat transfer data from CFD with a generalized form of the 1-D conducting solid equations for evaluating radiation and transient influences on sensor performance.
These new flow and heat transfer correlations together with the new Reduced Order Modeling technique developed here greatly enhance the capabilities of designers to evaluate performance of current and future probe designs, with higher accuracy and with significant reductions in computational resources.Doctor of Philosophy
An accurate measurement of total temperature in turbomachinery flows remains critical for component life models and cycle performance optimization. While many techniques exist to measure these flows, immersed thermocouple based probes remain highly desirable due to well established practices for probe design and implementation in typical industrial flow applications. However, as engine manufacturers continue to push towards higher maximum cycle temperatures and smaller flow passages, the continued use of these probes requires new probe designs considering both improved sensor durability and measurement accuracy. Increased maximum temperatures introduce many challenges for total temperature measurements using conventional immersed probes, including increased influences of conduction, convection, and radiation heat transfer between the sensor, fluid and the surroundings due to large thermal gradients present in real turbomachinery systems. While these effects have been thoroughly described and quantified in the past, the available design models are very limited to specific geometries and flow conditions. In this Dissertation, a more fundamental understanding of the flow behavior around typical vented shield style total temperature probes as a function of probe geometry and operating condition is gained using results from high-fidelity Computational Fluid Dynamics simulations with Conjugate Heat Transfer (CHT) capabilities. Results were further quantified in the form of new empirical correlations necessary for rapid thermal performance evaluations of current and future probe designs. Additionally, a new mixed-fidelity or Reduced Order Modeling (ROM) technique was developed which allows the coupling of high fidelity surface heat transfer data from CFD with a generalized form of the 1-D conducting solid equations for readily predicting the impact of radiation environment and transient errors on sensor performance.
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Liao, Meng. "Modeling of fluid flows and heat transfer with interface effects, from molecular interaction to porous media." Thesis, Paris Est, 2018. http://www.theses.fr/2018PESC1054/document.
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Les objectifs de la thèse sont d'étudier le transport de fluide et le transfert de chaleur dans les pores micro et nanométriques. Les expériences et les simulations ont révélé des preuves de l'augmentation du flux provoquée par la vitesse de glissement à la paroi solide. D'autre part, la résistance thermique finie à l'interface fluide-solide est responsable de la différence de température des deux phases. Ces deux phénomènes d'interface peuvent avoir un impact considérable sur la perméabilité et la diffusivité thermique des milieux poreux constitués de micro et nanopores. La contribution se concentre sur l'étude des trois problèmes suivants. Premièrement, nous examinons les effets de glissement des liquides confinés dans un canal de graphème en utilisant le formalisme de Green Kubo et la méthode de la dynamique moléculaire. On montre que lorsque la surface solide est soumise à une contrainte mécanique uniaxiale, la friction présente une anisotropie due à la modification de l'énergie potentielle et de la dynamique des molécules composant le fluide. Les formes moléculaires jouent également un rôle important sur les écarts de frottement entre les deux directions principales. Deuxièmement, nous étudions le régime des gaz raréfiés. Dans ce cas, la vitesse de glissement et le saut de température sont régis par les collisions entre les atomes de gaz et la paroi solide. Ces effets peuvent être déterminés à l’aide d’un modèle statistique qui peut être construit à partir des vitesses incidente et réfléchie des molécules de gaz. A cette fin, différentes méthodes basées sur des techniques d'apprentissage statistique ont été proposées. Enfin, la méthode des éléments finis est utilisée pour calculer la perméabilité et la diffusivité thermique des milieux poreux sous l'influence des effets d'interfaceThe objectives of the thesis are to study the fluid transport and heat transfer in micro and nano-scale pores. Both experiments and simulations revealed evidence of an enhancement of flow-rate, originated from slip velocity at the solid boundary. On the other hand, the finite thermal resistance at the fluid-solid interface is responsible for the temperature difference between the two phases. These two interface phenomena can have a considerable impact on the permeability and thermal diffusivity of porous media constituted of micro and nano-pores. This contribution focuses on studying the following three issues. First, we examine the slip effects of liquids confined in graphene channel using Green Kubo formalism and Molecular Dynamics method. It is shown that when the solid surface is subject to mechanical uniaxial strain, the friction exhibits anisotropy due to the modification of the potential energy and the dynamics of the fluid molecules. The molecular shapes also play an important factor on the friction discrepancies between two principal directions. The quantification of both effects is addressed. Second, we investigate the rarefied gas regime. In this case, the velocity slip and temperature jump are governed by the collisions between the gas and the solid boundary. Those effects can be determined via the study of scattering kernel and its construction from MD simulation data. To this end, different methods based on statistical learning techniques have been proposed including the nonparametric (NP) kernel and Gaussian mixture (GM) kernel. Finally, the finite element method is used to compute the permeability and the thermal diffusivity of porous media under the influence of the interface effects
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You, Lishan. "Computational Modeling of Laminar Swirl Flows and Heat Transfer in Circular Tubes with Twisted-Tape Inserts." University of Cincinnati / OhioLINK, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1029525889.
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Huzayyin, Omar A. "Computational Modeling of Convective Heat Transfer in Compact and Enhanced Heat Exchangers." University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1313754781.
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Khan, Waqar. "Modeling of Fluid Flow and Heat Transfer for Optimization of Pin-Fin Heat Sinks." Thesis, University of Waterloo, 2004. http://hdl.handle.net/10012/947.
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In this study, an entropy generation minimization procedure is employed to optimize the overall performance (thermal and hydrodynamic) of isolated fin geometries and pin-fin heat sinks. This allows the combined effects of thermal resistance and pressure drop to be assessed simultaneously as the heat sink interacts with the surrounding flow field. New general expressions for the entropy generation rate are developed using mass, energy, and entropy balances over an appropriate control volume. The formulation for the dimensionless entropy generation rate is obtained in terms of fin geometry, longitudinal and transverse pitches, pin-fin aspect ratio, thermal conductivity, arrangement of pin-fins, Reynolds and Prandtl numbers. It is shown that the entropy generation rate depends on two main performance parameters, i. e. , thermal resistance and the pressure drop, which in turn depend on the average heat transfer and friction coefficients. These coefficients can be taken from fluid flow and heat transfer models. An extensive literature survey reveals that no comprehensive analytical model for any one of them exists that can be used for a wide range of Reynolds number, Prandtl number, longitudinal and transverse pitches, and thermal conductivity. This study is one of the first attempts to develop analytical models for the fluid flow and heat transfer from single pins (circular and elliptical) with and without blockage as well as pin-fin arrays (in-line and staggered). These models can be used for the entire laminar flow range, longitudinal and transverse pitches, any material (from plastic composites to copper), and any fluid having Prandtl numbers (≥0. 71). In developing these models, it is assumed that the flow is steady, laminar, and fully developed. Furthermore, the heat sink is fully shrouded and the thermophysical properties are taken to be temperature independent. Using an energy balance over the same control volume, the average heat transfer coefficient for the heat sink is also developed, which is a function of the heat sink material, fluid properties, fin geometry, pin-fin arrangement, and longitudinal and transverse pitches. The hydrodynamic and thermal analyses of both in-line and staggered pin-fin heat sinks are performed using parametric variation of each design variable including pin diameter, pin height, approach velocity, number of pin-fins, and thermal conductivity of the material. The present analytical results for single pins (circular and elliptical) and pin-fin-arrays are in good agreement with the existing experimental/numerical data obtained by other investigators. It is shown that the present models of heat transfer and pressure drop can be applied for a wide range of Reynolds and Prandtl numbers, longitudinal and transverse pitches, aspect ratios, and thermal conductivity. Furthermore, selected numerical simulations for a single circular cylinder and in-line pin-fin heat sink are also carried out to validate the present analytical models. Results of present numerical simulations are also found to be in good agreement.
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Moglan, Raluca. "Modeling and numerical simulation of flow and heat phenomena in a telecommunication heat cabinet." Rouen, 2013. http://www.theses.fr/2013ROUES060.
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Nous proposons dans cette étude une nouvelle approche 3D pour la résolution des équations de Navier-Stokes incompressibles sous l’approximation de Boussinesq. La nouveauté du code développé est l’utilisation des méthodes d’ordre élevé pour l’intégration en temps (schéma de Runge-Kutta à l’ordre trois) et pour la discrétisation spatiale (schéma aux différences finies à l’ordre six). Une étude de l’ordre de la méthode numérique a été faite, suivie par une validation détaillée pour plusieurs cas de convection naturelle. Une méthode d’éléments finis été développée pour le même problème, codée avec FreeFem++, et validée pour les mêmes cas de convection naturelle. Nous avons considéré ensuite le cas d’une armoire de télécommunications, modélisée sous la forme d’un domaine rectangulaire, avec des objets (obstacles) intérieurs, représentés par une méthode de type frontière immergée. Cette méthode a été validée par rapport aux cas existants dans la littérature et par rapport aux résultats obtenus avec le code éléments finis (qui représente exactement les obstacles). Nous présentons des résultats pour plusieurs configurations, avec des obstacles chauffants placés différemment à l’intérieur de la cavité. Une comparaison avec les mesures expérimentales effectuées dans une armoire avec deux composantes dissipant de la chaleur est aussi effectuée. Le code de type éléments finis est finalement développé et testé pour simuler des matériaux à changement de phaseIn this thesis we present a new 3D approach for solving the incompressible Navier-Stokes equations under the Boussinesq approximation. The advantage of the developed numerical code is the use of high order methods for time integration (3rd order Runge-Kutta method) and spatial discretization (6th order finite difference schemes). A study of the order of the numerical method was made, followed by an extensive validation for several cases of natural convection. A finite element simulation code for the same problem was developed using FreeFem++, and was validated with respect to the same cases of natural convection. The case of a telecommunication cabinet was treated by modelling interior obstacles generating heat using an immersed boundary method. This method was validated with respect to the finite element simulation, and many other cases from the literature. We present the results for different 2D and 3D configurations, with obstacles differently placed inside the cavity. Results are also presented for the comparison with experimental measurements in a cabinet with two components dissipating heat. The finite element code is finally extended and tested to simulate phase change materials that could serve as passive cooling devices
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Momeni, Parham. "Modelling the Effect of Pulsation on Flow and Heat Transfer in Turbulent Separated and Reattaching Flows." Thesis, University of Manchester, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492875.
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The focus of this thesis is on the response of separated turbulent flows to imposed unsteadiness in the form of pulsation. There are substantial modelling challenges in imputing flows exhibiting even steady separation and reattachment. Furthermore, to minimise computing times - particularly important in unsteady flows, given the requirement to perform a large number of time steps - there is a desire to use relatively simple RANS models of turbulence. However, simple linear eddy-viscosity models are known to perform badly in separated flows, hi this study refinements are introduced to both a non-linear eddy-viscosity (Craft et al; 2005) scheme and a DSM model (lacovides and Raisee; 1999) and these are shown to perform quite successfully in predicting the steady state flow and heat transfer through a sudden pipe-expansion. The main aim of current study is to then asses the performance of these models in computing three types of forced unsteady separated flows.
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ZHANG, JIEHAI. "NUMERICAL SIMULATIONS OF STEADY LOW-REYNOLDS-NUMBER FLOWS AND ENHANCED HEAT TRANSFER IN WAVY PLATE-FIN PASSAGES." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1109015881.
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Al-sarraf, Hayder Hasan Jaafar. "Modeling Two Phase Flow Heat Exchangers for Next Generation Aircraft." Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright1503935509157319.
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Izgec, Bulent. "Transient fluid and heat flow modeling in coupled wellbore/reservoir systems." Thesis, [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2801.
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Rhodes, Matthew D. "Theoretical modeling of onset of ledinegg flow instability in a heated channel." Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/18898.
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Ho, Minh Tuan. "Kinetic modeling of the transient flows of the single gases and gaseous mixtures." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4741/document.
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Un gaz à l'intérieur d’un microsystème ou d’un milieu poreux est dans un état hors équilibre, car le libre parcours moyen des molécules est comparable à la dimension caractéristique du milieu. Ce même état degaz, appelé raréfié, se retrouve en haute altitude ou dans un équipement de vide à basse pression. Ces gaz raréfiés suivent des types d’écoulements qui peuvent être décrits par des modèles cinétiques dérivés de l'équation de Boltzmann. Dans ce travail nous présentons les principaux modèles et leurs mises en oeuvre numériquepour la simulation des écoulements de gaz raréfiés. Parmi les modèles utilisés nous présentons les deux modèles complets de l'équation de Boltzmann, le modèle de Shakhov(S-model) pour un gaz monoatomique et le modèle de McCormack pour un mélange de gaz toujours monoatomiques. La méthode des vitesses discrètes est utilisée pour la discrétisation numérique dans l'espace des vitesses moléculaires et le schéma de type TVD est mis en œuvre dans l'espace physique. L’aspect original de ce travail se situe sur les régimes transitoires et, en particuliersur les comportements non-stationnaires des transferts de chaleur et de masse. Cependant, pour certaines configurations nous considérons uniquement les conditions stationnaires des écoulements et un schéma implicite est développé afin de réduire le coût de calcul. En utilisant ces approches numériques, nous présentons les résultats pour plusieurs types d’écoulements non-stationnaires, de gaz raréfiés monoatomiqueset de mélanges binaires de gaz monoatomiquesA gas inside the microsystems or the porous media is in its non-equilibrium state, due to the fact that the molecular mean free path is comparable to the characteristic dimension of the media. The same state of a gas, called rarefied, is found at high altitude or in the vacuum equipment working at low pressure. All these types of flow can be described by the kinetic models derived from the Boltzmann equation. This thesis presents the development of the numerical tools for the modeling and simulations of the rarefied gas flows. The two models of the full Boltzmann equation, the Shakhov model (S-model) for the single gas and the McCormack model for the gas mixture, are considered. The discrete velocity method is used to the numerical discretization in the molecular velocity space and the TVD-like scheme is implemented in the physical space. The main aspect of this work is centered around the transient properties of the gas flows and, especially, on the transient heat and mass transfer behaviors. However, for some configurations only steady-state solutions are considered and the implicit scheme is developed to reduce the computational cost. Using the proposed numerical approach several types of the transient rarefied single gas flows as well as the binary mixture of the monoatomic gases are studied
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Khalifa, Hamdy Elhoussainy Mohammed. "Modeling coupled heat and moisture flow within a bare desert soil." Diss., The University of Arizona, 1992. http://hdl.handle.net/10150/185882.
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Revegetation of semi-desert rangeland is dependent on rainfall, weather, and soil factors affecting seed germination and seedling establishment. To aid in predicting seed zone temperature and moisture following rainfall, a weather driven one-dimensional computer model was developed to simulate the simultaneous flow of heat and water within a bare semi-desert soil. The Newton-Raphson method was used to solve the surface energy budget equation for surface temperature. The coupled soil heat and water flow equations were then solved numerically using the weighted average finite-difference method to calculate the subsurface temperature (T(s)) and water content (θᵥ) profiles. Weather data and soil thermal and hydraulic properties were the only required inputs to the model. The model was tested using two data sets collected in the Altar Valley of Arizona during the summer rainy season of 1988. Data set 1, collected from calendar day (CD) 198 to 205, was used to calibrate the model. Calibration tests revealed that the model markedly underestimated T(s) when measured values exceeded 37°C. Underestimation of T(s) was found to be related to overestimation of latent heat flux. Therefore, the modelled latent heat flux was reduced as a linear function of air temperature (Tₐᵢᵣ) when Tₐᵢᵣ > 30°C. Also, soil thermal conductivity values predicted by the de Vries model had to be reduced 80% in order to achieve acceptable agreement between measured and modelled T(s). Data set 2, from CD 191 to 195, was then used to validate the calibrated (modified) model. Results obtained with data set 2 indicated that the modified model accurately simulated T(s) at 0.01 m depth even when the measured T(s) at that depth exceeded 50°C. Simulated T(s) values for the soil profile were generally within ± 3°C of the measured values. Results also showed good agreement between modelled and measured net radiation flux densities. In addition, the modified model predicted surface layer (0-0.03 m) moisture content remained wet enough for seed germination, i.e. θᵥ > 0.09 m³ m⁻³, about 24 to 36 hours longer than indicated by measured (resistance block) θᵥ values.
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Spezia, Kyle. "Numerical Modeling of Fluid Flow and Heat Transfers in Porous Media." Thesis, University of Louisiana at Lafayette, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10003759.
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Field studies of Cordilleran metamorphic core complexes indicate that meteoric fluids permeated the upper crust down to the detachment shear zone and interacted with highly deformed and recrystallized (mylonitic) rocks. The presence of fluids in the brittle/ductile transition zone is recorded in the oxygen and hydrogen stable isotope compositions of the mylonites, and may play an important role in the thermomechanical evolution of the detachment shear zone. Geochemical data show that fluid flow in the brittle upper crust is primarily controlled by the large-scale fault-zone architecture.
We conduct finite element numerical modeling of groundwater flow in an idealized cross-section of a metamorphic core complex. The simulations investigate the effects of crust and fault permeability fields on groundwater flow. Results show that fluid migration to mid- to lower-crustal levels is fault-controlled and depends primarily on the permeability contrast between the fault zone and the crustal rocks. High fault/crust permeability ratios lead to channelized flow in the fault and shear zones, while lower ratios allow leakage of the fluids from the fault into the crust.
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Bard, Ari. "Modeling and Predicting Heat Transfer Coefficients for Flow Boiling in Microchannels." Case Western Reserve University School of Graduate Studies / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=case1619091352188123.
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Carapanayotis, Achilles E. "Modeling of fluid flow and heat transfer processes in an engine." Thesis, University of Ottawa (Canada), 1987. http://hdl.handle.net/10393/5228.
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Masters, Nathan Daniel. "Efficient Numerical Techniques for Multiscale Modeling of Thermally Driven Gas Flows with Application to Thermal Sensing Atomic Force Microscopy." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11574.
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The modeling of Micro- and NanoElectroMechanical Systems (MEMS and NEMS) requires new computational techniques that can deal efficiently with geometric complexity and scale dependent effects that may arise. Reduced feature sizes increase the coupling of physical phenomena and noncontinuum behavior, often requiring models based on molecular descriptions and/or first principles. Furthermore, noncontinuum effects are often localized to small regions of (relatively) large systemsprecluding the global application of microscale models due to computational expense. Multiscale modeling couples efficient continuum solvers with detailed microscale models to providing accurate and efficient models of complete systems.
This thesis presents the development of multiscale modeling techniques for nonequilibrium microscale gas phase phenomena, especially thermally driven microflows. Much of this focuses on improving the ability of the Information Preserving DSMC (IP-DSMC) to model thermally driven flows. The IP-DSMC is a recent technique that seeks to accelerate the solution of direct simulation Monte Carlo (DSMC) simulations by preserving and transporting certain macroscopic quantities within each simulation molecules. The primary contribution of this work is the development of the Octant Splitting IP-DSMC (OSIP-DSMC) which recovers previously unavailable information from the preserved quantities and the microscopic velocities. The OSIP-DSMC can efficiently simulate flow fields induced by nonequilibrium systems, including phenomena such as thermal transpiration. The OSIP-DSMC provides an efficient method to explore rarefied gas transport phenomena which may lead to a greater understanding of these phenomena and new concepts for how these may be utilized in practical engineering systems.
Multiscale modeling is demonstrated utilizing the OSIP-DSMC and a 2D BEM solver for the continuum (heat transfer) model coupled with a modified Alternating Schwarz coupling scheme. An interesting application for this modeling technique is Thermal Sensing Atomic Force Microscopy (TSAFM). TSAFM relies on gas phase heat transfer between heated cantilever probes and the scanned surface to determine the scan height, and thus the surface topography. Accurate models of the heat transfer phenomena are required to correctly interpret scan data. This thesis presents results demonstrating the effect of subcontinuum heat transfer on TSAFM operation and explores the mechanical effects of the Knudsen Force on the heated cantilevers.
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Storey, J. Kirk. "Modeling the transient response of a thermosyphon /." Diss., CLICK HERE for online access, 2003. http://contentdm.lib.byu.edu/ETD/image/etd304.pdf.
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Mayo, Nardone Pablo Sabino. "Modeling the Heat Flow Dynamics of a Houses Using Stochastic Differential Equations." Thesis, KTH, Skolan för industriell teknik och management (ITM), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-302557.
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This research aims to explore new ways of assessing energy performance within housing units. The mainobjective of this work is to propose a heat dynamics model based on monitoring data, to contribute towardsan energy-efficient transition in the building sector. An extensive study on the available mathematical and statistical tools is described in order to determine aholistic solution, found in grey-box models. This model approach offers the possibility of understandingmultivariate systems, which can be applied to a housing-unit heat flow dynamics. Through the iterative process of testing each possible model, this work determines the one with bestexplanatory power, defining the thermal characteristics of the studied housing unit. This method allows thedetection of underperforming dwellings among constructions with high energy-efficiency standards. This investigation reflects the feasibility of employing grey-box models to predict the dynamics of heatrelated systems. Moreover, it sets the basis for new ways of employing the monitoring data of dwellings.Denna forskning syftar till att utforska nya sätt att bedöma energiprestanda inom bostäder. Huvudsyftetmed detta arbete är att föreslå en värmedynamikmodell baserad på övervakningsdata för att bidra till enenergieffektiv övergång inom byggsektorn. En omfattande studie av tillgängliga matematiska och statistiska verktyg beskrivs för att bestämma enhelhetslösning, som finns i gråboxmodeller. Denna modellstrategi ger möjlighet att förstå multivariatasystem, som kan tillämpas på en hushålls värmedynamik. Genom den iterativa processen att testa varje möjlig modell bestämmer detta arbete den med bästförklarande kraft, och definierar de studerade husenhetens termiska egenskaper. Denna metod gör detmöjligt att upptäcka underpresterande bostäder bland anläggningar med hög energieffektivitetsstandard. Denna undersökning återspeglar möjligheten att använda gråboxmodeller för att förutsäga dynamiken ivärmerelaterade system. Dessutom lägger den grunden för nya sätt att använda övervakningsdata förbostäder.
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Montagna, Cimarelli Viktor Donna. "Stream Identification in Pinch Analysis : Fixed and Flexible flows." Thesis, Mittuniversitetet, Avdelningen för kemiteknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-34281.
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The purpose of this project is to find an identification tag that can be used in a future automated pinch analysis tool. It can be used to further analyse composite curves and pinch results by tracking the original streams that was converted. In real life situations, retrofitting a process industries streams, can decrease heat demands and costs. A pinch analysis and a heat exchange network is created with fixed and flexible flows to show a recommendation on how the system model can handle this type of situations. The models have been created by hand with support from pinch literature and the calculations validated with mathematical software such as matlab and other graphing tools. The literature study and pinch modelling resulted in a recommendation of tagging Hstart and Hend for each individual stream. By using a geographical tag in a coordinate system the analyst will be able to find the original streams in the pinch analysis and composite curves. The project also resulted in a heating exchange network created from the fixed and flexible data set. The enthalpy differences between the ideal pinch result and the fixed data set is smaller than one might expect because of enthalpy abundance in the specific intervals.
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Garcia-Hermosa, M. Isabel. "Morphodynamics of sand mounds in shallow flows." Thesis, University of Oxford, 2008. http://ora.ox.ac.uk/objects/uuid:c6ef38f8-d098-4ce5-b0f0-38e2ebe6caf5.
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Large-scale bed features are often encountered in coastal waters, and include sandbanks and spoil heaps. The morphodynamic development of such features involves complicated nonlinear interactions between the flow hydrodynamics, sediment transport, and bed profile. Numerical modelling of the morphodynamic evolution and migration of large-scale bed features is necessary in order to understand their long-term behaviour in response to changing environmental conditions. This thesis describes detailed measurements of the morphodynamics of sand mounds in unidirectional and oscillatory (tidal) flows, undertaken at the U.K. Coastal Research Facility (UKCRF). High quality data were collected, including water velocities, water levels and overhead images. The parameters tested are: three types of mound shape (circular and elliptical in plan shape, and Gaussian, cosine and triangular in cross-section); underlying fixed or mobile bed conditions; and initial crest height (submerged, surface-touching and surface-piercing). Peak flow velocities are about 0.5 m/s, the sand median grain size is 0.454 mm, and transport occurring mostly as bedload. When analysing the data, the bed contours are determined by digitising the shoreline at different water levels. From these plots, the volume, height, and centroid position of the mound are calculated. A large-scale fit method, based on a Gaussian function has been used to separate small-scale ripples from the large-scale bed structure during the evolution of an isolated sand mound or spoil heap. The bed profile after the ripples are removed is comparable to typical predictions by shallow-flow numerical solvers. The UKCRF experiments investigated the morphodynamic response of a bed mound to hydrodynamic forcing: shape changes, migration rates, volume decay and sediment transport rates. The measured migration rate and decay of a submerged sand mound in the UKCRF are found to be in satisfactory agreement with results from various theoretical models, such as the analytical solution derived by De Vriend. Numerical predictions of mound evolution by a commercial code, PISCES, are also presented for a fully submerged sand mound; the bed evolution is reasonably similar to that observed in the UKCRF. The data provided as a result of the research reported in this thesis provide insight into the behaviour of sand mounds in steady and unsteady flows at laboratory scale, and should also be useful for benchmark (validation) purposes to numerical modellers of large-scale morphodynamics.
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Atharifar, Hosein. "Material flow and heat transfer modeling, monitoring, and optimization of friction stir welding." Ann Arbor, Mich. : ProQuest, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3305958.
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Thesis (Ph.D. in Mechanical Engineering)--S.M.U.Title from PDF title page (viewed Mar. 16, 2009). Source: Dissertation Abstracts International, Volume: 69-03, Section: B, page: 1895. Adviser: Radovan Kovacevic. Includes bibliographical references.
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Fransen, Rémy. "LES based aerothermal modeling of turbine blade cooling systems." Phd thesis, Toulouse, INPT, 2013. http://oatao.univ-toulouse.fr/10012/1/fransen.pdf.
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This PhD dissertation, conducted as part of a CIFRE research project between TURBOMECA and CERFACS in partnership with the VKI, deals with improving performance of axial turbines from helicopter engines. One of the most critical design points of such engines is the control of the high pressure turbine blade lifetime which face the high temperatures from the combustor. Today, industrial numerical aerothermal predictions of the flows around the blade (in the vein and in its cooling system) are performed with the Reynolds Averaged Navier-Stokes (RANS). Thanks to the increasing computational power, Large Eddy Simulation (LES) becomes affordable to offer further flow predictions. Therefore, this thesis focuses on the capabilities of the LES to estimate the flow in turbine blade internal cooling channels. To simplify this analysis where several physical phenomenon are present, the problem is described in three parts with increasing complexity. The first part addresses simplified typical geometries of cooling channel (U-bend and ribbed channel) in a static configuration. Considering the flow regime, a wall-resolved approach using a hybrid unstructured mesh is proposed in view of the application on an industrial case. The second part extends the study of the ribbed channel in rotation using an inertial reference frame. LES provides mean and unsteady results in good agreement with the available experimental data and previous works, for the flow dynamic and the heat transfer. Finally, the third part presents the application of the method to an industrial case with conjugate heat transfer between a complex cooling channel and the blade. This last section is not present in the public manuscrit for confidential reasons. Results of the use of the wall-resolved approach in rotation in an inertial frame of reference are compared to RANS predictions and show the potential of the method with high local differences.
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Banete, Olimpia. "TOWARDS MODELING HEAT TRANSFER USING A LATTICE BOLTZMANN METHOD FOR POROUS MEDIA." Thesis, Laurentian University of Sudbury, 2014. https://zone.biblio.laurentian.ca/dspace/handle/10219/2200.
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I present in this thesis a fluid flow and heat transfer model for porous media using the lattice Boltzmann method (LBM). A computer simulation of this process has been developed and it is written using MATLAB software. The simulation code is based on a two dimensional model, D2Q9. Three physical experiments were designed to prove the simulation model through comparision with numerical results. In the experiments, physical properties of the air flow and the porous media were used as input for the computer model. The study results are not conclusive but show that the LBM model may become a reliable tool for the simulation of natural convection heat transfer in porous media.
Simulations leading to improved understanding of the processes of air flow and heat transfer in porous media may be important into improving the efficiency of methods of air heating or cooling by passing air through fragmented rock.
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Xu, Wenyue. "Towards numerical modeling of two-phase flow in seafloor hydrothermal systems." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/26014.
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Preetham, Preetham. "Modeling the Response of Premixed Flames to Flow Disturbances." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19817.
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Modeling the Response of Premixed Flames to Flow Disturbances
Preetham
178 pages
Directed by Dr. Tim Lieuwen
Low emissions combustion systems for land based gas turbines rely on a premixed or partially premixed combustion process. These systems are exceptionally prone to combustion instabilities which are destructive to hardware and adversely affect performance and emissions. The success of dynamics prediction codes is critically dependent on the heat release model which couples the flame dynamics to the system acoustics. So the principal objective of the current research work is to predict the heat release response of premixed flames and to isolate the key non-dimensional parameters which characterize its linear and nonlinear dynamics.
Explicit analytical solutions of the G- equation are derived in the linear and weakly nonlinear regime using the Small Perturbation Method (SPM). For the fully nonlinear case, the flame-flow interaction effects are captured by developing an unsteady, compressible, coupled Euler-G-equation solver with a Ghost Fluid Method (GFM) module for applying the jump conditions across the flame.
The flame s nonlinear response is shown to exhibit two qualitatively different behaviors. Depending on the operating conditions and the disturbance field characteristics, it is shown that a combustor may exhibit supercritical bifurcations leading to a single stable limit cycle amplitude or exhibit sub-critical bifurcations wherein multiple stable solutions for the instability amplitude are possible. In addition, this study presents the first analytical model which captures the effects of unsteady flame stretch on the heat release response and thus extends the applicability of current models to high frequency instabilities, such as occurring during screech. It is shown that unsteady stretch effects, negligible at low frequencies (100 s of Hz) become significant at screeching frequencies (1000 s of Hz). Furthermore, the analysis also yields insight into the significant spatial dependence of the mean and perturbation velocity field induced by the coupling between the flame and the flow field. In order to meaningfully compare the heat release response across different flame configurations, this study has identified that the reference velocity (for defining the transfer function) should be based on the effective normal velocity perturbing the flame and the Strouhal number should be based on the effective residence time of the flame wrinkles.
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Varela, Ballesta Sylvana Verónica. "Computational and experimental modeling of fluid flow and heat transfer processes in complex geometries." Doctoral thesis, Universitat Rovira i Virgili, 2012. http://hdl.handle.net/10803/80717.
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El objetivo principal de este trabajo es el estudio numérico (caffa3d.MB) y experimental (PIV) de los campos de velocidad y de temperatura en dominios complejos como los encontrados en las computadoras u otros sistemas electrónicos refrigerados que contengan circuitos impresos (PCB, Printed Circuit Board). La refrigeración es uno de los principales desafíos que estos dispositivos se deben tratar. La disipación del calor de los dispositivos de circuitos electrónicos se ha convertido en una cuestión importante a tener en cuenta durante su diseño. Los PCB son circuitos electrónicos que generan calor por efecto Joule y necesitan ser enfriados. Son cada vez más pequeños y por lo tanto los problemas del calentamiento disminuyen su eficiencia y vida útil. El estudio de la velocidad y los campos de temperatura está estrechamente relacionada con el análisis de la evolución espacial y temporal de las estructuras de flujo que se encuentran en las cavidades cerradas que contiene PCB y con el entendimiento de la influencia de la geometría, la velocidad de entrada de fluido y temperatura de la placa en el proceso de enfriamiento del PCB.The main objective of this work is the numerical (caffa3d.MB) and experimental (PIV) study of the velocity and temperature fields in complex domains like those encountered in computers or other electronic refrigerated systems with printed circuit board (PCB). Cooling is one of the main challenges these devices have to deal with. Heat removal from the electronic circuit devices has become an important issue to take into account during their design. PCB's are electronic circuits that generate heat by Joule effect and need to be cooled down. They are becoming smaller and therefore some warming problems appear that lowers their efficiency and lifespan. The study of the velocity and temperature fields is closely connected with the analysis of the spatial and temporal evolution of the flow structures found in PCB enclosed cavities and with the understanding of the influence of the geometry, the inlet fluid velocity and plate temperature in the cooling process of the PCB.
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Dongaonkar, Amruta J. "Numerical Modeling and Analysis of Fluid Flow and Heat Transfer in Circular Tubes Fitted with Different Helical Twisted Core-Fins." University of Cincinnati / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1377866455.
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Ben, Nasr Ouissem. "Numerical simulations of supersonic turbulent wall-bounded flows." Phd thesis, INSA de Rouen, 2012. http://tel.archives-ouvertes.fr/tel-01059805.
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This work deals with spatially-evolving supersonic turbulent boundary layers over adiabatic and cold walls at M∞ = 2 and up to Re0 ≈ 2600 using 3 different SGS models. The numerical methodology is based on high-order split-centered scheme to discretize the convective fluxes of the Navier-Stokes equations . For the adiabatic case, it is demonstrated that all SGS models require a comparable minimum grid-refinement in order to capture accurately the near-wall-turbulence. Overall, the models exhibit correct behavior when predictiong the dynamic properties, but show different performances for the temperature distribution in the near-wall region. For the isothermal case, it is found that the compressibility effects are not enhanced due to the wall cooling. As expected, the total temperature fluctuations are not negligible in the near-wall region. The study shows that the anti-correlation linking both velocity and temperature fields, derived from the Morkovin's hypothesis, is not satisfied.
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Vondál, Jiří. "Computational Modeling of Turbulent Swirling Diffusion Flames." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2012. http://www.nusl.cz/ntk/nusl-234149.
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Schopnost predikovat tepelné toky do stěn v oblasti spalování, konstrukce pecí a procesního průmyslu je velmi důležitá pro návrh těchto zařízení. Je to často klíčový požadavek pro pevnostní výpočty. Cílem této práce je proto získat kvalitní naměřená data na experimentálním zařízení a využít je pro validaci standardně využívaných modelů počítačového modelování turbulentního vířivého difúzního spalování zemního plynu. Experimentální měření bylo provedeno na vodou chlazené spalovací komoře průmyslových parametrů. Byly provedeny měření se pro dva výkony hořáku – 745 kW a 1120 kW. Z měření byla vyhodnocena data a odvozeno nastavení okrajových podmínek pro počítačovou simulaci. Některé okrajové podmínky bylo nutné získat prostřednictvím dalšího měření, nebo separátní počítačové simulace tak jako například pro emisivitu, a nebo teplotu stěny. Práce zahrnuje několik vlastnoručně vytvořených počítačových programů pro zpracování dat. Velmi dobrých výsledků bylo dosaženo při predikci tepelných toků pro nižší výkon hořáku, kde odchylky od naměřených hodnot nepřesáhly 0.2 % pro celkové odvedené teplo a 16 % pro lokální tepelný tok stěnou komory. Vyšší tepelný výkon však přinesl snížení přesnosti těchto predikcí z důvodů chybně určené turbulence. Proto se v závěru práce zaměřuje na predikce vířivého proudění za vířičem a identifikuje několik problematických míst v použitých modelech využívaných i v komerčních aplikacích.
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Keshmiri, Amir. "Thermal-hydraulic analysis of gas-cooled reactor core flows." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/thermalhydraulic-analysis-of-gascooled-reactor-core-flows(29335acf-a397-4b8c-8217-fd2ee0d26967).html.
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In this thesis a numerical study has been undertaken to investigate turbulent flow and heat transfer in a number of flow problems, representing the gas-cooled reactor core flows. The first part of the research consisted of a meticulous assessment of various advanced RANS models of fluid turbulence against experimental and numerical data for buoyancy-modified mixed convection flows, such flows being representative of low-flow-rate flows in the cores of nuclear reactors, both presently-operating Advanced Gas-cooled Reactors (AGRs) and proposed ‘Generation IV’ designs. For this part of the project, an in-house code (‘CONVERT’), a commercial CFD package (‘STAR-CD’) and an industrial code (‘Code_Saturne’) were used to generate results. Wide variations in turbulence model performance were identified. Comparison with the DNS data showed that the Launder-Sharma model best captures the phenomenon of heat transfer impairment that occurs in the ascending flow case; v^2-f formulations also performed well. The k-omega-SST model was found to be in the poorest agreement with the data. Cross-code comparison was also carried out and satisfactory agreement was found between the results.The research described above concerned flow in smooth passages; a second distinct contribution made in this thesis concerned the thermal-hydraulic performance of rib-roughened surfaces, these being representative of the fuel elements employed in the UK fleet of AGRs. All computations in this part of the study were undertaken using STAR-CD. This part of the research took four continuous and four discrete design factors into consideration including the effects of rib profile, rib height-to-channel height ratio, rib width-to-height ratio, rib pitch-to-height ratio, and Reynolds number. For each design factor, the optimum configuration was identified using the ‘efficiency index’. Through comparison with experimental data, the performance of different RANS turbulence models was also assessed. Of the four models, the v^2-f was found to be in the best agreement with the experimental data as, to a somewhat lesser degree were the results of the k-omega-SST model. The k-epsilon and Suga models, however, performed poorly. Structured and unstructured meshes were also compared, where some discrepancies were found, especially in the heat transfer results. The final stage of the study involved a simulation of a simplified 3-dimensional representation of an AGR fuel element using a 30 degree sector configuration. The v^2-f model was employed and comparison was made against the results of a 2D rib-roughened channel in order to assess the validity and relevance of the precursor 2D simulations of rib-roughened channels. It was shown that although a 2D approach is extremely useful and economical for ‘parametric studies’, it does not provide an accurate representation of a 3D fuel element configuration, especially for the velocity and pressure coefficient distributions, where large discrepancies were found between the results of the 2D channel and azimuthal planes of the 3D configuration.
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Rocha, José Renê de Sousa. "Modeling and numerical simulation of fluid flow and heat transfer of a steel continuous casting tundish." reponame:Repositório Institucional da UFC, 2017. http://www.repositorio.ufc.br/handle/riufc/24518.
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ROCHA, J. R. S. Modeling and numerical simulation of fluid flow and heat transfer of a steel continuous casting tundish. 2017. 91 f. Dissertação (Mestrado em Ciência de Materiais)-Centro de Tecnologia, Universidade Federal do Ceará, Fortaleza, 2017.Submitted by Hohana Sanders (hohanasanders@hotmail.com) on 2017-07-25T11:20:37Z No. of bitstreams: 1 2017_dis_jrsrocha.pdf: 3666906 bytes, checksum: 42780d960166d0354f84586d96a51b44 (MD5)
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Currently, the continuous casting process is the most used technique to produce steel. Being an inherently component of the caster machine, the tundish has been designed to be not only an intermediate vessel between the ladle and the mold, but also a device to remove inclusions and a metallurgical reactor. Therefore, the tundish has an important role in the continuous casting process. The physical model for heat transfer and fluid flow into the tundish is very complex, thus analytical solutions are not available. Physical studies might present many difficulties for analyzing the process. Hence, Computational Fluid Dynamics (CFD) emerges as an attractive alternative. CFD is based on numerical approaches that are used to solve several classes of engineering problems. The main goal of the present study is to analyze the fluid flow and temperature fields into an actual tundish configuration that is used in continuous casting processes of a local steelmaker company. Based on the performed simulations, some modifications in the geometry of the tundish are proposed in order to improve the steel quality; these modifications make use of weirs and dams. For solving the governing equations arising from the physical model, the Ansys CFX software, which is based on the Element-based Finite-Volume Method (EbFVM) were used. Simulations were performed using water and steel as working fluids for a turbulent flow in a 3D tundish. The results were presented in terms of velocity and temperature fields and Residence Time Distribution (RTD) curves, which evaluated them qualitatively and quantitatively.
O processo de lingotamento contínuo é o processo mais utilizado na produção de aço atualmente. Sendo um importante componente da máquina de lingotamento, o distribuidor tem sido projetado para atuar não apenas como um reservatório entre a panela e o molde, mas também como um dispositivo para remoção de inclusões e servir como um reator metalúrgico. Logo, o distribuidor assume um papel de relevância no processo de lingotamento contínuo. O modelo físico que rege a transferência de calor e escoamento dentro do distribuidor apresenta grande complexidade, tornando a sua solução analítica indisponível. Estudos físicos podem apresentar várias dificuldades para a análise do processo. Portanto, a Dinâmica dos Fluidos Computacional (CFD) surge com uma alternativa viável. CFD é baseada em aproximações numéricas as quais são utilizadas para a solução de várias classes de problemas de engenharia. O principal objetivo do presente trabalho é analisar os campos de escoamento e temperatura no interior de um distribuidor o qual é utilizado nos processos de lingotamento contínuo de uma companhia siderúrgica local. Com base nas simulações realizadas, modificações na geometria do distribuidor são propostas com o intuito de aumentar a qualidade do aço. Essas modificações são feitas através do uso de diques e barragens. Para a solução das equações de conservação originadas do modelo físico, o programa Ansys CFX, o qual utiliza o Método dos Volumes Finitos baseado em Elementos (EbFVM), foi utilizado. As simulações foram feitas utilizando-se aço e água como fluidos de trabalho para um escoamento turbulento em um distribuidor tridimensional. Os resultados foram apresentados em termos de campos de velocidade e temperatura e curvas de Distribuição de Tempo de Residência (RTD) as quais serviram para analisá-los qualitativa e quantitativamente.
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Su, Yung-Chieh. "Selection of Prediction Methods for Thermophysical Properties for Process Modeling and Product Design of Biodiesel Manufacturing." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/32675.
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To optimize biodiesel manufacturing, many reported studies have built simulation models to quantify the relationship between operating conditions and process performance. For mass and energy balance simulations, it is essential to know the four fundamental thermophysical properties of the feed oil: liquid density (Ï L), vapor pressure (Pvap), liquid heat capacity (CpL), and heat of vaporization (Î Hvap). Additionally, to characterize the fuel qualities, it is critical to develop quantitative correlations to predict three biodiesel properties, namely, viscosity, cetane number, and flash point. Also, to ensure the operability of biodiesel in cold weather, one needs to quantitatively predict three low-temperature flow properties: cloud point (CP), pour point (PP), and cold filter plugging point (CFPP). This article presents the results from a comprehensive evaluation of the methods for predicting these four essential feed oil properties and six key biodiesel fuel properties. We compare the predictions to reported experimental data and recommend the appropriate prediction methods for each property based on accuracy, consistency, and generality. Of particular significance are (1) our presentation of simple and accurate methods for predicting the six key fuel properties based on the number of carbon atoms and the number of double bonds or the composition of total unsaturated fatty acid methyl esters (FAMEs) and (2) our posting of the Excel spreadsheets for implementing all of the evaluated accurate prediction methods on our group website (www.design.che.vt.edu) for the reader to download without charge.Master of Science
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Зіменко, Сергій Вікторович. "Моделювання теплових втрат через огороджувальні конструкції складної форми." Master's thesis, Київ, 2018. https://ela.kpi.ua/handle/123456789/24683.
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Обсяг магістерської роботи 113 – аркушів, кількість рисунків – 51, таблиць – 48, додатків – 2.
Мета магістерської дисертації – оцінка теплозахисних властивостей огороджувальних конструкцій житлових будівель з урахуванням теплопровідних включень.
Під час виконання магістерської дисертації було розглянуто наявні програмні та приладові інструменти, методики оцінки на прикладі об’єкту житлового фонду, підходи до зниження рівня теплопередачі огороджувальних конструкцій, економічний ефект від впровадження енергоефективних проектів з врахуванням результатів моделювання та його вплив на загальний енергетичний баланс будівлі. На основі розділу аналізу програмного забезпечення складено передумови та визначено потребу у впровадженні стартап проекту, для якого визначено потенційну стратегію виходу на ринок.
Результати даної дисертації активно впроваджувалися у практичний процес енергетичного обстеження та можуть бути використані у сферах інжинірингу та проектування.The volume master's thesis equals 113 pages, quantity of figures – 51, tables – 48, applications – 2. The purpose of the master's dissertation is the assessment of the heat-protective properties of the enclosing structures of residential buildings of non-standard constructions. During the implementation of the master's thesis, existing software and instrumental tools, valuation techniques on an example of a housing stock, approaches to reducing the level of heat transfer of fencing structures, the economic effect of implementing energy efficient projects taking into account the results of modeling and their impact on the overall energy balance of the building were considered. Based on the software analysis section, the preconditions have been created and the need for implementation of the project startup has been determined, for which a potential market entry strategy has been identified. The results of this dissertation have been actively implemented in the practical process of energy survey and can be used in the fields of engineering and design.
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lamnaouer, mouna. "NUMERICAL MODELING OF THE SHOCK TUBE FLOW FIELDS BEFORE ANDDURING IGNITION DELAY TIME EXPERIMENTS AT PRACTICAL CONDITIONS." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4095.
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An axi-symmetric shock-tube model has been developed to simulate the shock-wave propagation and reflection in both non-reactive and reactive flows. Simulations were performed for the full shock-tube geometry of the high-pressure shock tube facility at Texas A&M University. Computations were carried out in the CFD solver FLUENT based on the finite volume approach and the AUSM+ flux differencing scheme. Adaptive mesh refinement (AMR) algorithm was applied to the time-dependent flow fields to accurately capture and resolve the shock and contact discontinuities as well as the very fine scales associated with the viscous and reactive effects. A conjugate heat transfer model has been incorporated which enhanced the credibility of the simulations. The multi-dimensional, time-dependent numerical simulations resolved all of the relevant scales, ranging from the size of the system to the reaction zone scale. The robustness of the numerical model and the accuracy of the simulations were assessed through validation with the analytical ideal shock-tube theory and experimental data. The numerical method is first applied to the problem of axi-symmetric inviscid flow then viscous effects are incorporated through viscous modeling. The non-idealities in the shock tube have been investigated and quantified, notably the non-ideal transient behavior in the shock tube nozzle section, heat transfer effects from the hot gas to the shock tube side walls, the reflected shock/boundary layer interactions or what is known as bifurcation, and the contact surface/bifurcation interaction resulting into driver gas contamination. The non-reactive model is shown to be capable of accurately simulating the shock and expansion wave propagations and reflections as well as the flow non-uniformities behind the reflected shock wave. Both the inviscid and the viscous non-reactive models provided a baseline for the combustion model iii which involves elementary chemical reactions and requires the coupling of the chemistry with the flow fields adding to the complexity of the problem and thereby requiring tremendous computational resources. Combustion modeling focuses on the ignition process behind the reflected shock wave in undiluted and diluted Hydrogen test gas mixtures. Accurate representation of the Shock  tube reactive flow fields is more likely to be achieved by the means of the LES model in conjunction with the EDC model. The shock-tube CFD model developed herein provides valuable information to the interpretation of the shock-tube experimental data and to the understanding of the impact the facility-dependent non-idealities can have on the ignition delay time measurements.Ph.D.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Mechanical Engineering PhD
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Nigon, Benoit [Verfasser], Christophe [Gutachter] Pascal, and Andreas [Gutachter] Englert. "Fracture flow and heat transport modeling using natural joint surfaces / Benoit Nigon ; Gutachter: Christophe Pascal, Andreas Englert ; Fakultät für Geowissenschaften." Bochum : Ruhr-Universität Bochum, 2019. http://d-nb.info/1175205028/34.
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Farough, Aida. "A Parameterized Approach to Partitioning Between Focused and Diffuse Heat Output and Modeling Hydrothermal Recharge at The East Pacific Rise 9°50´N." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/78062.
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Ever since the discovery of seafloor hydrothermal systems at mid ocean ridges, scientists have been trying to understand the complex dynamic processes by which thermal energy is transported advectively by chemically reactive aqueous fluids from Earth's interior to the surface. Hydrothermal systems are generally assumed to consist of a heat source and a fluid circulation system. Understanding the interconnected physical, chemical, biological, and geological processes at oceanic spreading centers is important because these processes affect the global energy and biogeochemical budgets of the Earth system.
Despite two decades of focused study of hydrothermal systems, several key questions remain concerning the behavior and evolution of hydrothermal vent systems. Among these are: (a) the partitioning of heat transport between focused and diffuse flow, and (b) the spatial extent and distribution of hydrothermal recharge. These are the main topics of investigation in this thesis.
To address these issues, I first use a single-pass modeling approach using a variety of observational data in a simple parametric scale analysis of a hydrothermal vent field to determine fundamental parameters associated with the circulation and magmatic heat transfer for a number of seafloor hydrothermal systems for which the constraining data are available. To investigate the partitioning of heat flux between focused high temperature and diffuse flow I extend the one-limb single pass model to incorporate two single-pass limbs to represent deep and shallow circulation pathways. As a result, I find that 90% of the heat output is from high temperature fluid circulating in the deep limb even though much of the heat loss appears at the seafloor as low-temperature diffuse flow.
Next, I use the parametric description of hydrothermal circulation to investigate hydrothermal recharge at the East Pacific Rise 9°50′ N hydrothermal site. Using a 1-D model of recharge through an area of 10⁵ m² elucidated by microseismicity in the oceanic crust I find that anhydrite precipitation is likely to result in rapid sealing of pore space in the recharge zone. This would lead to rapid decay of hydrothermal venting, which is contrary to observations. Then I consider two-dimensional numerical models of hydrothermal circulation in a porous box heated from below. The preliminary results of these models suggests that the anhydrite precipitation zone will be more diffuse, but additional work is needed to test whether anhydrite precipitation will seal the pore space.Master of Science
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Chen, Tao Verfasser], Christoph [Akademischer Betreuer] [Clauser, Olaf [Akademischer Betreuer] Kolditz, and Gabriele [Akademischer Betreuer] Marquart. "Upscaling permeability for fractured porous rocks and modeling anisotropic flow and heat transport / Tao Chen ; Christoph Clauser, Olaf Kolditz, Gabriele Marquart." Aachen : Universitätsbibliothek der RWTH Aachen, 2017. http://d-nb.info/1180733703/34.
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Chen, Tao [Verfasser], Christoph [Akademischer Betreuer] Clauser, Olaf [Akademischer Betreuer] Kolditz, and Gabriele [Akademischer Betreuer] Marquart. "Upscaling permeability for fractured porous rocks and modeling anisotropic flow and heat transport / Tao Chen ; Christoph Clauser, Olaf Kolditz, Gabriele Marquart." Aachen : Universitätsbibliothek der RWTH Aachen, 2017. http://d-nb.info/1180733703/34.
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Venkata, Padma Priya. "Computational modeling of heat and mass transfer in planar SOFC effects of volatile species/oxidant mass flow rate and electrochemical reaction rate /." Cincinnati, Ohio : University of Cincinnati, 2008. http://www.ohiolink.edu/etd/view.cgi?acc%5Fnum=ucin1205169104.
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Thesis (M.S.)--University of Cincinnati, 2008.Committee/Advisors: Raj M Manglik PhD (Advisor), Milind A Jog PhD (Committee Member), Anastasios P Angelopoulos PhD (Committee Member) Title from electronic thesis title page (viewed April 23, 2008). Includes abstract. Keywords: SOFC, Solid oxide fuel cells, ASR, interconnect, CFD, heat and mass transfer, electrochemistry. Includes bibliographical references.
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VENKATA, PADMA PRIYA. "Computational Modeling of Heat and Mass Transfer in Planar SOFC: Effects of Volatile Species/Oxidant Mass Flow Rate and Electrochemical Reaction Rate." University of Cincinnati / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1205169104.
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Hu, Chih-Chieh. "Mechanistic modeling of evaporating thin liquid film instability on a bwr fuel rod with parallel and cross vapor flow." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28148.
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Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009.Committee Chair: Abdel-Khalik, Said; Committee Member: Ammar, Mostafa H.; Committee Member: Ghiaasiaan, S. Mostafa; Committee Member: Hertel, Nolan E.; Committee Member: Liu, Yingjie.
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Hill, David. "Numerical modeling of flow and heat transfer in friction stir welding a thesis presented to the faculty of the Graduate School, Tennessee Technological University /." Click to access online, 2009. http://proquest.umi.com/pqdweb?index=0&did=2000384991&SrchMode=1&sid=4&Fmt=6&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1277841643&clientId=28564.
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Chatziefstratiou, Efthalia. "SIMULATION OF TREE STEM INJURY, AIR FLOW AND HEAT DISPERSION IN FORESTS FOR PREDICTION OF FIRE EFFECTS." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1420644169.
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Druet, Pierre-Etienne. "Analysis of a coupled system of partial differential equations modeling the interaction between melt flow, global heat transfer and applied magnetic fields in crystal growth." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät II, 2009. http://dx.doi.org/10.18452/15893.
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Hauptthema der Dissertation ist die Analysis eines nichtlinearen, gekoppelten Systems partieller Differentialgleichungen (PDG), das in der Modellierung der Kristallzüchtung aus der Schmelze mit Magnetfeldern vorkommt. Die zu beschreibenden Phenomäne sind einerseits der im elektromagnetisch geheizten Schmelzofen erfolgende Wärmetransport (Wärmeleitung, -konvektion und -strahlung), und andererseits die Bewegung der Halbleiterschmelze unter dem Einfluss der thermischen Konvektion und der angewendeten elektromagnetischen Kräfte. Das Modell besteht aus den Navier-Stokeschen Gleichungen für eine inkompressible Newtonsche Flüssigkeit, aus der Wärmeleitungsgleichung und aus der elektrotechnischen Näherung des Maxwellschen Systems. Wir erörtern die schwache Formulierung dieses PDG Systems, und wir stellen ein Anfang-Randwertproblem auf, das die Komplexität der Anwendung widerspiegelt. Die Hauptfrage unserer Untersuchung ist die Wohlgestelltheit dieses Problems, sowohl im stationären als auch im zeitabhängigen Fall. Wir zeigen die Existenz schwacher Lösungen in geometrischen Situationen, in welchen unstetige Materialeigenschaften und nichtglatte Trennfläche auftreten dürfen, und für allgemeine Daten. In der Lösung zum zeitabhängigen Problem tritt ein Defektmaß auf, das ausser der Flüssigkeit im Rand der elektrisch leitenden Materialien konzentriert bleibt. Da eine globale Abschätzung der im Strahlungshohlraum ausgestrahlten Wärme auch fehlt, rührt ein Teil dieses Defektmaßes von der nichtlokalen Strahlung her. Die Eindeutigkeit der schwachen Lösung erhalten wir nur unter verstärkten Annahmen: die Kleinheit der gegebenen elektrischen Leistung im stationären Fall, und die Regularität der Lösung im zeitabhängigen Fall. Regularitätseigenschaften wie die Beschränktheit der Temperatur werden, wenn auch nur in vereinfachten Situationen, hergeleitet: glatte Materialtrennfläche und Temperaturunabhängige Koeffiziente im Fall einer stationären Analysis, und entkoppeltes, zeitharmonisches Maxwell für das transiente Problem.The present PhD thesis is devoted to the analysis of a coupled system of nonlinear partial differential equations (PDE), that arises in the modeling of crystal growth from the melt in magnetic fields. The phenomena described by the model are mainly the heat-transfer processes (by conduction, convection and radiation) taking place in a high-temperatures furnace heated electromagnetically, and the motion of a semiconducting melted material subject to buoyancy and applied electromagnetic forces. The model consists of the Navier-Stokes equations for a newtonian incompressible liquid, coupled to the heat equation and the low-frequency approximation of Maxwell''s equations. We propose a mathematical setting for this PDE system, we derive its weak formulation, and we formulate an (initial) boundary value problem that in the mean reflects the complexity of the real-life application. The well-posedness of this (initial) boundary value problem is the mainmatter of the investigation. We prove the existence of weak solutions allowing for general geometrical situations (discontinuous coefficients, nonsmooth material interfaces) and data, the most important requirement being only that the injected electrical power remains finite. For the time-dependent problem, a defect measure appears in the solution, which apart from the fluid remains concentrated in the boundary of the electrical conductors. In the absence of a global estimate on the radiation emitted in the cavity, a part of the defect measure is due to the nonlocal radiation effects. The uniqueness of the weak solution is obtained only under reinforced assumptions: smallness of the input power in the stationary case, and regularity of the solution in the time-dependent case. Regularity properties, such as the boundedness of temperature are also derived, but only in simplified settings: smooth interfaces and temperature-independent coefficients in the case of a stationary analysis, and, additionally for the transient problem, decoupled time-harmonic Maxwell.
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Nop, Raksmy. "Experimental investigation and modeling of the transient flow boiling crisis of water at moderate pressure and high subcooling." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPAST046.
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Lors d’une insertion accidentelle de réactivité dans un réacteur nucléaire expérimental, la puissance du cœur peut augmenter de manière exponentielle, avec un temps caractéristique allant de quelques millisecondes à quelques centaines de millisecondes. À cause des effets neutroniques et thermohydrauliques, le système peut atteindre les conditions de crise d’ébullition à même d’engendrer une réaction explosive. Bien que la crise d’ébullition ait été largement étudiée en conditions de chauffage stationnaires, ce n’est pas le cas pour les transitoires notamment de type excursions de puissance. Le but de ce travail est donc de comprendre et de prédire la crise d'ébullition sous l’effet d’un chauffage transitoire rapide de l'eau sous fortes sous-saturations à pression modérée. Des campagnes expérimentales ont été réalisées pour étudier la crise d’ébullition dans de telles conditions au moyen de vidéos et de thermographie IR hautement résolues en temps et en espace. L’analyse de ces données a permis de déterminer la dépendance du flux critique en transitoire rapide en fonction des différents paramètres d’intérêt (temps caractéristique d’excursion de puissance, vitesse d’écoulement, sous-saturation, pression, largeur du canal, longueur de chauffe). De plus, une analyse approfondie de ces données a permis de mettre en évidence les mécanismes sous-jacents à la crise d’ébullition dans ces conditions. En convection forcée et avec de fortes sous-saturations, les bulles générées en paroi présentent un comportement pulsant. Ce phénomène assure un transfert de chaleur efficace depuis la paroi vers le fluide environnant. Le déclenchement de la crise d’ébullition se produit lorsqu’une fine couche de fluide adjacente à la paroi atteint les conditions de saturation. Un modèle développé à partir de ces observations met en évidence deux paramètres adimensionnés utiles pour décrire la nature transitoire du processus ainsi que pour identifier le mode de refroidissement dominant. Grâce à la connaissance du flux critique en régime permanent, le modèle permet d’estimer de manière conservative le flux critique en fonction de la période d’excursion de puissance et du sous-refroidissement. Ce modèle est maintenant prêt à être implémenté dans des codes de simulation pour l’étude des transitoires accidentelsIn case of a reactivity insertion accident in an experimental nuclear reactor, heat generation in the core can grow exponentially in time, with a power escalation period ranging from a few to a few hundreds of milliseconds. Due to neutronic and thermohydraulic effects, boiling crisis may arise, possibly leading to an explosive reaction. If the boiling Crisis has been widely investigated in steady-state conditions, this has not been the case for transient heat inputs. The aim of the present work is to understand and to predict the transient flow boiling crisis in the conditions of moderate pressure and high subcooling. To this end, an experimental campaign has been realized making use of space and time highly resolved videos and IR thermography covering a wide range of experimental parameters. The analysis of the massive amount of data produced by these experiments gives a better insight on the dependency of the transient Critical Heat Flux to the different parameters of interest (power escalation period, flow velocity, subcooling, pressure, channel width, heating length). Moreover, their fine analysis enables to highlight the underlying mechanisms. For conditions of forced flow and high subcooling, the bubbles generated at the wall present a pulsating behavior. This specific process leads to an efficient heat transfer from the wall to the neighboring fluid. Boiling crisis is stated to occur when a thin layer of liquid contacting the wall reaches the saturation temperature. Starting from these observations, a model is developed which brings to light two non-dimensional parameters useful to describe the transient nature of the process and the dominant cooling processes. With the knowledge of the steady-state CHF, the model permits to conservatively estimate the value of the Critical Heat Flux for any power escalation period and subcooling. This model is now ready for implementation into simulation codes to investigate nuclear accidental transients
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Kestel, Matthias. "Numerical modeling of moving carbonaceous particle conversion in hot environments." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2016. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-204732.
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The design and optimization of entrained flow gasifiers is conducted more and more via computational fluid dynamics (CFD). A detailed resolution of single coal particles within such simulations is nowadays not possible due to computational limitations. Therefore the coal particle conversion is often represented by simple 0-D models. For an optimization of such 0-D models a precise understanding of the physical processes at the boundary layer and within the particle is necessary.
In real gasifiers the particles experience Reynolds numbers up to 10000. However in the literature the conversion of coal particles is mainly regarded under quiescent conditions. Therefore an analysis of the conversion of single particles is needed. Thereto the computational fluid dynamics can be used.
For the detailed analysis of single reacting particles under flow conditions a CFD model is presented. Practice-oriented parameters as well as features of the CFD model result from CFD simulations of a Siemens 200MWentrained flow gasifier. The CFD model is validated against an analytical model as well as two experimental data-sets taken from the literature. In all cases good agreement between the CFD and the analytics/experiments is shown.
The numerical model is used to study single moving solid particles under combustion conditions. The analyzed parameters are namely the Reynolds number, the ambient temperature, the particle size, the operating pressure, the particle shape, the coal type and the composition of the gas. It is shown that for a wide range of the analyzed parameter range no complete flame exists around moving particles. This is in contrast to observations made by other authors for particles in quiescent atmospheres. For high operating pressures, low Reynolds numbers, large particle diameters and high ambient temperatures a flame exists in the wake of the particle. The impact of such a flame on the conversion of the particle is low. For high steam concentrations in the gas a flame appears, which interacts with the particle and influences its conversion.
Furthermore the impact of the Stefan-flow on the boundary layer of the particle is studied. It is demonstrated that the Stefan-flow can reduce the drag coefficient and the Nusselt number for several orders of magnitude. On basis of the CFD results two new correlations are presented for the drag coefficient and the Nusselt number. The comparison between the correlations and the CFD shows a significant improvement of the new correlations in comparison to archived correlations.
The CFD-model is further used to study moving single porous particles under gasifying conditions. Therefore a 2-D axis-symmetric system of non-touching tori as well as a complex 3-D geometry based on the an inverted settlement of monodisperse spheres is utilized. With these geometries the influence of the Reynolds number, the ambient temperature, the porosity, the intrinsic surface and the size of the radiating surface is analyzed. The studies show, that the influence of the flow on the particle conversion is moderate. In particular the impact of the flow on the intrinsic transport and conversion processes is mainly negligible. The size of the radiating surface has a similar impact on the conversion as the flow in the regarded parameter range.
On basis of the CFD calculations two 0-D models for the combustion and gasification of moving particles are presented. These models can reproduce the results predicted by the CFD sufficiently for a wide parameter range.