Дисертації: "Thermal field simulation"

1

Terril, Nathaniel D. "Field Simulation for the Microwave Heating of Thin Ceramic Fibers." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/36863.

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Microwave processing of ceramics has seen a growth in research and development efforts throughout the past decade. One area of interest is the exploration of improved heating control through experiments and numerical modeling. Controlled heating may be used to counteract non-uniform heating and avoid destructive phenomena such as cracking and thermal runaway. Thermal runaway is a potential problem in materials with temperature dependent dielectric properties. As the material absorbs electromagnetic energy, the temperature increases as does its ability to absorb more energy. Controlled processing of the material may be achieved by manipulating the applied field. The purpose of this research is to model the interaction of the EM-field with a thin ceramic fiber to investigate possible mechanisms that may affect the heating process. The fiber undergoes microwave heating in a single-mode resonant applicator. Maxwell's equations for the fields within the cavity are solved using mode-matching techniques taking into account the field interaction of the fiber and an arbitrarily shaped coupling aperture. Effects of varying the aperture shape on the field distribution are explored. The coupled nature of the electromagnetic solution with the material's temperature-dependent properties, including an analysis of non-uniform heating, is also discussed.
Master of Science

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2

Yarimpabuc, Durmus. "Numerical Simulation Of Thermal Convection Under The Influence Of A Magnetic Field By Using Solenoidal Bases." Phd thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613393/index.pdf.

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The effect of an imposed magnetic field on the thermal convection between rigid plates heated from below under the influence of gravity is numerically simulated in a computational domain with periodic horizontal extent. The numerical technique is based on solenoidal basis functions satisfying the boundary conditions for both velocity and induced magnetic field. The expansion bases for the thermal field are also constructed to satisfy the boundary conditions. The governing partial differential equations are reduced to a system of ordinary differential equations governing the time evolution of the expansion coefficients under Galerkin projection onto the subspace spanned by the dual bases. In the process, the pressure term in the momentum equation is eliminated. The system validated in the linear regime is then used for some numerical experiments in the nonlinear regime.

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3

Huang, Zhida. "SIMULATION OF METAL GRAIN GROWTH IN LASER POWDER BED FUSION PROCESS USING PHASE FIELD THERMAL COUPLED MODEL." Case Western Reserve University School of Graduate Studies / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=case1554391043588225.

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4

Li, Jingran. "Integration of Physically-based and Data-driven Approaches for Thermal Field Prediction in Additive Manufacturing." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/79620.

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A quantitative understanding of thermal field evolution is vital for quality control in additive manufacturing (AM). Because of the unknown material parameters, high computational costs, and imperfect understanding of the underlying science, physically-based approaches alone are insufficient for component-scale thermal field prediction. Here, I present a new framework that integrates physically-based and data-driven approaches with quasi in situ thermal imaging to address this problem. The framework consists of (i) thermal modeling using 3D finite element analysis (FEA), (ii) surrogate modeling using functional Gaussian process, and (iii) Bayesian calibration using the thermal imaging data. Based on heat transfer laws, I first investigate the transient thermal behavior during AM using 3D FEA. A functional Gaussian process-based surrogate model is then constructed to reduce the computational costs from the high-fidelity, physically-based model. I finally employ a Bayesian calibration method, which incorporates the surrogate model and thermal measurements, to enable layer-to-layer thermal field prediction across the whole component. A case study on fused deposition modeling is conducted for components with 7 to 16 layers. The cross-validation results show that the proposed framework allows for accurate and fast thermal field prediction for components with different process settings and geometric designs.
Master of Science
This paper aims to achieve the layer to layer temperature monitoring and consequently predict the temperature distribution for any new freeform geometry. An engineering statistical synergistic model is proposed to integrate the pure statistical methods and finite element modeling (FEM), which is physically meaningful as well as accurate for temperature prediction. Besides, this proposed synergistic model contains geometry information, which can be applied to any freeform geometry. This paper serves to enable a holistic cyber physical systems-based approach for the additive manufacturing (AM) not only restricted in fused deposition modeling (FDM) process but also can be extended to powder-based process like laser engineered net shaping (LENS) and selective laser sintering (SLS). This paper as well as the scheduled future works will make it affordable for customized AM including customized geometries and materials, which will greatly accelerate the transition from rapid prototyping to rapid manufacturing. This article demonstrates a first evaluation of engineering statistical synergistic model in AM technology, which gives a perspective on future researches about online quality monitoring and control of AM based data fusion principles.

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5

Liu, Wei. "Electro-thermal simulations and measurements of silicon carbide power transistors." Doctoral thesis, Stockholm, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-86.

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6

Wirnsberger, Peter. "Computer simulation and theoretical prediction of thermally induced polarisation." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/282988.

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In this thesis, we study the phenomenon of thermally induced polarisation using a combination of theory and computer simulation. Molecules of sufficiently low symmetry exhibit thermo-molecular orientation when subjected to a temperature gradient, leading to considerable electrostatic fields in polar liquids. Here, we first use non-equilibrium molecular dynamics simulations to study this interesting effect numerically. To this end, we propose an integration algorithm to impose a constant heat flux in simulations and show that it greatly improves energy conservation compared to a previous algorithm. We next investigate the thermal polarisation of water and find that truncation of electrostatic interactions can lead to severe artefacts, such as the wrong sign of polarisation and an overestimation of the electric field. We further show that the quadrupole-moment contribution to the electric field is significant and responsible for an inversion of its sign. To facilitate the theoretical description of electrostatic interactions, we propose a new dipolar model fluid as a perturbation of a Stockmayer fluid. Using this modified Stockmayer model, we provide numerical evidence for the recently proposed phenomenon of thermally induced monopoles. We show that the electrostatic field generated by a pair of heated/cooled colloidal particles immersed in such a solvent can be trivially described by two Coulomb charges. Finally, we propose a mean-field theory to predict the thermo-polarisation effect exhibited by our model fluid theoretically, and demonstrate near quantitative agreement with simulation results.

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7

James, William Thomas. "Electro-thermal-mechanical modeling of GaN HFETs and MOSHFETs." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41212.

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High power Gallium Nitride (GaN) based field effect transistors are used in many high power applications from RADARs to communications. These devices dissipate a large amount of power and sustain high electric fields during operation. High power dissipation occurs in the form of heat generation through Joule heating which also results in localized hot spot formation that induces thermal stresses. In addition, because GaN is strongly piezoelectric, high electric fields result in large inverse piezoelectric stresses. Combined with residual stresses due to growth conditions, these effects are believed to lead to device degradation and reliability issues. This work focuses on studying these effects in detail through modeling of Heterostructure Field Effect Transistors (HFETs) and metal oxide semiconductor hetero-structure field effect transistor (MOSHFETs) under various operational conditions. The goal is to develop a thorough understanding of device operation in order to better predict device failure and eventually aid in device design through modeling. The first portion of this work covers the development of a continuum scale model which couples temperature and thermal stress to find peak temperatures and stresses in the device. The second portion of this work focuses on development of a micro-scale model which captures phonon-interactions at the device scale and can resolve local perturbations in phonon population due to electron-phonon interactions combined with ballistic transport. This portion also includes development of phonon relaxation times for GaN. The model provides a framework to understand the ballistic diffusive phonon transport near the hotspot in GaN transistors which leads to thermally related degradation in these devices.

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8

Shala, Enise, and Caroline Svanholm. "Thermodynamics of the Subsurface of Glaciers with Insights from Lomonosovfonna Ice Field at Svalbard." Thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-351658.

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Glaciers are important components of the Earth's environment and are mainly found in polar and high elevation areas. They are crucial for understanding the past, ongoing and upcoming environmental changes, relevant for fresh water supply, logistical and recreational purposes. Subsurface temperature of glaciers is an important parameter heavily influencing the fluxes of mass and energy. The project focuses on how the temperature changes inside glaciers and which factors contribute to the change. Thermal conduction is one of the key processes controlling the thermodynamics of glaciers. This defines how well heat is transferred inside glaciers and how well the temperature propagates. The process of heat conduction at Lomonosovfonna ice field, Svalbard, is described using numerical simulations constrained by measured initial and boundary conditions. Simulated subsurface temperature is in line with measurements before the onset of melt in summer. After that deviations increase as the used model does not consider the process of melt water refreezing. This makes the simulation only partially successful.
Glaciärer är viktiga komponenter i jordens omgivning och återfinns främst i polarområden och områden på hög höjd. De är viktiga för att förstå tidigare, pågående och kommande miljöförändringar, relevanta för färskvattenförsörjning, logistiska och återskapande ändamål. Temperaturen inom glaciärer är en viktig parameter som påverkar flödena av massa och energi. Projektet fokuserar på hur temperaturen förändras inom glaciärer och vilka faktorer som bidrar till förändringen. Värmeledning är en av nyckelprocesserna som kontrollerar termodynamiken hos glaciärer. Detta definierar hur väl värme förflyttas inom glaciärer och hur väl temperaturen sprider sig. Värmeledningsprocessen på isfältet Lomonosovfonna, Svalbard, beskrivs med hjälp av numeriska simuleringar begränsade av uppmätta initial- och gränsförhållanden. Simulering av temperaturen under ytan stämmer överens med mätningarna före smältningen på sommaren. Därefter ökar avvikelsen, eftersom modellen som använts inte tar hänsyn till processen av återfrysning av smältvatten. Detta gör att simuleringen endast är delvist lyckad.

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9

Pimenta, Paulo Vicente de Cassia Lima. "Thermomechanical simulation of continuous casting process using element based finite-volume method." Universidade Federal do CearÃ, 2014. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=13684.

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CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior
The continuous casting technique in the last four decades has been large used for to production of semi-finished steel. The heat transfer is major mechanism and it occurs in various steps during the continuous casting. The quality of steel is directly related to the way the heat transfer occur because the thermal variations produce mechanical loads as well as contact forces which are generated through the rollers and shake of the mold. Such factors may cause defects such as fractures or cracks in the final product if the resulting stresses and strains exceed critical values. The technique must be improved in order to reduce the appearance of defects and the production time. For this a good understanding of physical phenomena involved during the solidification process is critical. The focus of this work is to apply the EbFVM (Element based Finite-Volume Method) approach to study the effects of linear tensions unidirectionally coupled with the temperature applied to continuous casting of the steel 1013D (0,3% of carbon) In the simulations we adopted some simplifications such as the Plane Strain and isotropic material. We also neglected the body forces contact with the rollers the liquid pressure on the walls of the steel ingot (ferrostatic pressure) and the convective effect. However despite of the simplifications adopted this work provides quantitative informations on the linear tensions accumulation that point out to areas of possible of cracks formations
A tÃcnica de lingotamento contÃnuo nas Ãltimas quatro dÃcadas Ã cada vez mais utilizada na produÃÃo de aÃo semiacabado. A transferÃncia de calor Ã o principal mecanismo dominante e ocorre em todas as etapas do processo. A qualidade do aÃo no lingotamento estÃ diretamente relacionada Ã forma que ocorrem as trocas de calor pois as variaÃÃes tÃrmicas produzem carregamentos mecÃnicos assim como as forÃas de contato as quais sÃo geradas por intermÃdio dos rolos e da oscilaÃÃo do molde. Tais fatores podem causar defeitos como fraturas ou trincas no produto final caso as tensÃes e deformaÃÃes resultantes excedam valores crÃticos. O aprimoramento da tÃcnica tem a finalidade de evitar o surgimento de defeitos e reduzir o tempo de produÃÃo. Para isso Ã fundamental uma boa compreensÃo dos fenÃmenos fÃsicos envolvidos ao longo do processo de solidificaÃÃo. O foco deste trabalho Ã aplicar a abordagem do EbFVM (Element based Finite-Volume Method) no estudo dos efeitos das tensÃes lineares acopladas unidirecionalmente com a temperatura aplicado ao lingotamento contÃnuo do aÃo 1013D (0,3% de carbono) Nas simulaÃÃes adotou-se algumas simplificaÃÃes com o estado plano de tensÃes e isotropia do material. Descartando-se as forÃas de corpo o contato com os rolos a pressÃo do aÃo lÃquido nas paredes do lingote (pressÃo ferrostÃtica) e o efeito convectivo. Contudo apesar das simplificaÃÃes adotadas este trabalho traz informaÃÃes quantitativas quanto a formaÃÃo do acÃmulo das tensÃes lineares que apontam para regiÃes de possÃveis formaÃÃes de trincas

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10

Mehra, Bineet. "Design and optimisation of innovative electronic cooling heat sinks with enhanced thermal performances using numerical and experimental methods." Thesis, Ecole nationale supérieure Mines-Télécom Lille Douai, 2019. http://www.theses.fr/2019MTLD0005/document.

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Cette thèse de doctorat s’intéresse aux mécanismes d’amélioration des transferts dans des géométries de dissipateurs thermiques à plaques et ailettes. Une première partie est consacrée à l’étude d’une configuration académique à l’aide de simulations numériques visant à obtenir une amélioration du transfert de chaleur conjugué en modifiant uniquement par des découpes la forme géométrique des ailettes planes conductrices. Une analyse locale approfondie de l’écoulement et des champs thermiques a été effectuée avec notamment le principe de synergie locale, des champs de vitesse et de gradients thermiques, pour comprendre l’effet des modifications géométriques. Ce mémoire présente également le développement de dissipateurs aux performances thermo-aérauliques augmentées pour des applications de refroidissement de coffrets électronique embarqués. L’intensification des transferts thermiques est obtenue par la génération d’écoulements secondaires qui provoquent un brassage de fluide et réduisent la résistance thermique à la paroi en perturbant le développement de la couche limite thermique. Différentes configurations de dissipateurs avec deux types de générateurs d’écoulements secondaires, paires d’ailettes Delta et protrusions, ont été étudiées numériquement, en employant une modélisation de type « RANS ». Les performances thermo-aérauliques des géométries munies de générateurs de vorticité ont été comparées à celle d’un dissipateur thermique de référence « lisse ». Des prototypes ont également été fabriqués et testés sur un banc expérimental spécifiquement développé pour réaliser des mesures des performances globales en termes de puissance thermique et de pertes de charge. Les résultats expérimentaux et numériques ont été confrontés afin de qualifier les simulations réalisées. Par la suite, une étude d’optimisation employant l’analyse factorielle Taguchi a été utilisée afin d’optimiser les paramètres géométriques des dissipateurs retenus. Deux fonctions objectif ont été considérées : la maximisation du facteur de performance thermique à iso puissance de ventilation (PEC) et la réduction de la température moyenne de paroi du dissipateur par rapport au cas de référence. L’analyse des performances thermo-aérauliques globales des géométries étudiées a été complétée par une analyse qualitative locale des champs thermiques et d’écoulement notamment avec le principe de synergie
This doctoral thesis focuses on mechanisms of heat transfer enhancement in plate and fin heat sink geometries. First part of the thesis is dedicated to study an academic configuration using numerical simulations to achieve an improvement in conjugate heat transfer by modifying only the geometrical shape (through punching) of the conductive plane fins. An in-depth local analysis of the flow and thermal fields was carried out with the local synergy principle, velocity and thermal gradients, to understand the effect of geometric modifications. This thesis also presents the development of heat sinks with increased thermo-hydraulic performance for on-board electronic box cooling applications. The intensification of the heat transfer is obtained by the generation of secondary flows which cause an intensive mixing of fluid and reduces the thermal resistance to the wall by disrupting the development of the thermal boundary layer. Different heat sink geometries with two types of secondary flow generators : delta winglet pair and protrusions were numerically studied using RANS approach. The thermo-hydraulic performances of the geometries equipped with vortex generators were compared with that of a smooth reference heat sink. The prototypes were also manufactured and tested on an experimental bench specifically designed to perform global performance measurements in terms of thermal power and pressure drops. Experimental and numerical results were compared to qualify the simulations performed. Subsequently, an optimization study using Taguchi factorial analysis was used to optimize the geometrical parameters of the chosen dissipaters. Two objective functions were considered : maximization of either iso-pumping power performance criteria (PEC) or average wall temperature of the dissipaters compared to the reference case. The global thermo-hydraulic performance analysis of the studied geometries was completed by a qualitative analysis of local flow and thermal fields, in particular with the local field synergy principle

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11

Bakhtiari, Hossein. "Evaluation of Thermal Comfort and Night Ventilation in a Historic Office Building in Nordic Climate." Licentiate thesis, Högskolan i Gävle, Energisystem och byggnadsteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-33941.

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Envelopes with low thermal performance are common characteristics in European historic buildings resulting in insufficient thermal comfort and higher energy use compared to modern buildings. There are different types of applications for the European historic buildings such as historic churches, historic museums, historic theatres, etc. In historic buildings refurbished to offices, it is vital to improve thermal comfort for the staff. Improving thermal comfort should not increase, preferably reduce, energy use in the building. The overall aim in this research is to explore how to improve thermal comfort in historic buildings without increasing, preferably reducing, energy use with the application of non-intrusive methods. This is done in form of a case study in Sweden. Thermal comfort issues in the case study building are determined through a field study. The methods include field measurements with thermal comfort equipment, data logging on BMS, and evaluating the occupant’s perception of a summer and a winter period indoor environment using a standardized questionnaire. According to questionnaire and thermal comfort measurements results, it is revealed that the summer period has the most dissatisfied occupants, while winter thermal comfort is satisfactory – but not exceptionally good. Accordingly, natural heat sinks could be used in form of NV, as a non/intrusive method, in order to improve thermal comfort in the building. For the historic building equipped with mechanical ventilation, NV strategy has the potential to both improve thermal comfort and reduce the total electricity use for cooling (i.e. electricity use in the cooling machine + the electricity use in the ventilation unit’s fans). It could decrease the percentage of exceedance hours in offices by up to 33% and reduce the total electricity use for cooling by up to 40%. The optimal (maximum) NV rate (i.e. the potential of NV strategy) is dependent on the thermal mass capacity of the building, the available NV cooling potential (dependent on the ambient air temperature), COP value of the cooling machine, the SFP model of the fans (low SFP value for high NV rate is optimal), and the offices’ door scheme (open or closed doors).

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12

Евсеенко, Олег Николаевич. "Моделирование работы ШИМ-регулятора с предсказанием для управления температурой в помещении". Thesis, Політехперіодика, 2017. http://repository.kpi.kharkov.ua/handle/KhPI-Press/49262.

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Работа посвящена проблеме рационального использования тепловых ресурсов для отопления жилых и офисных зданий. В среде ANSYS Fluent построена тепловая модель помещения и разработан регулятор с предсказанием поведения объекта. Результаты моделирования показывают, что использование регулятора с предсказанием, учитывающего суточный график температуры за окном и поддержание минимально допустимой рабочей температуры воздуха в помещении ночью, в выходные и праздничные дни помогут сэкономить тепловой ресурс. Полученные результаты экспериментов дают основания для практического применения регулятора с предсказанием.
The study is devoted to the problem of rational use of thermal energy for heating residential and office buildings. The problems of the current heat supply systems are discussed. The major attention is paid to the process of room model creation and choosing the boundary conditions. The experiments with decreasing temperature level to minimum value and maintaining the set temperature are made. It is shown that using PWM modulator with prediction filter could save heat resources.

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13

Grozdek, Marino. "Load Shifting and Storage of Cooling Energy through Ice Bank or Ice Slurry Systems modelling and experimental analysis /." Doctoral thesis, Stockholm : Skolan för industriell teknik och management, Kungliga Tekniska högskolan, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11119.

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14

Morrison, Graeme A. "Thermally driven hydromagnetic dynamos." Thesis, University of Glasgow, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312706.

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15

Willschütz, Hans-Georg. "Thermomechanische Modellierung eines Reaktordruckbehälters in der Spätphase eines Kernschmelzunfalls." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2006. http://nbn-resolving.de/urn:nbn:de:swb:14-1138712734373-55289.

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Анотація:

Considering the late in-vessel phase of an unlikely core melt down scenario in a light water reactor (LWR) with the formation of a corium pool in the lower head of the reactor pressure vessel (RPV) the possible failure modes of the RPV and the time to failure have to be investigated to assess the possible loadings on the containment. In this work, an integral model was developed to describe the processes in the lower plenum of the RPV. Two principal model domains have to be distinguished: The tem-perature field within the melt and RPV is calculated with a thermodynamic model, while a mechanical model is used for the structural analysis of the vessel wall. In the introducing chapters a description is given of the considered accident scenario and the relevant analytical, experimental, and numerical investigations are discussed which were performed worldwide during the last three decades. Following, the occurring physical phenomena are analysed and the scaling differences are evaluated between the FOREVER-experiments and a prototypical scenario. The thermodynamic and the mechanical model can be coupled recursively to take into account the mutual influence. This approach not only allows to consider the temperature dependence of the material parameters and the thermally induced stress in the mechanical model, it also takes into account the response of the temperature field itself upon the changing vessel geometry. New approaches are applied in this work for the simulation of creep and damage. Using a creep data base, the application of single creep laws could be avoided which is especially advantageous if large temperature, stress, and strain ranges have to be covered. Based on experimental investigations, the creep data base has been developed for an RPV-steel and has been validated against creep tests with different scalings and geometries. It can be stated, that the coupled model is able to exactly describe and predict the vessel deformation in the scaled integral FOREVER-tests. There are uncertainties concerning the time to failure which are related to inexactly known material parameters and boundary conditions. The main results of this work can be summarised as follows: Due to the thermody-namic behaviour of the large melt pool with internal heat sources, the upper third of the lower RPV head is exposed to the highest thermo-mechanical loads. This region is called hot focus. Contrary to that, the pole part of the lower head has a higher strength and therefore relocates almost vertically downwards under the combined thermal, weight and internal pressure load of the RPV. On the one hand, it will be possible by external flooding to retain the corium within the RPV even at increased pressures and even in reactors with high power (as e.g. KONVOI). On the other hand, there is no chance for melt retention in the considered scenario if neither internal nor external flooding of the RPV can be achieved. Two patents have been derived from the gained insights. Both are related to passively working devices for accident mitigation: The first one is a support of the RPV lower head pole part. It reduces the maximum mechanical load in the highly stressed area of the hot focus. In this way, it can prevent failure or at least extend the time to failure of the vessel. The second device implements a passive accident mitigation measure by making use of the downward movement of the lower head. Through this, a valve or a flap can be opened to flood the reactor pit with water from a storage reservoir located at a higher position in the reactor building. With regard to future plant designs it can be stated - differing from former presumptions - that an In-Vessel-Retention (IVR) of a molten core is possible within the reactor pressure vessel even for reactors with higher power
Für das unwahrscheinliche Szenario eines Kernschmelzunfalls in einem Leichtwasserreaktor mit Bildung eines Schmelzesees in der Bodenkalotte des Reaktordruckbehälters (RDB) ist es notwendig, mögliche Versagensformen des RDB sowie Versagenszeiträume zu ermitteln, um die daraus resultierende mögliche Belastung des Sicherheitsbehälters bestimmen zu können. In dieser Arbeit wird ein integrales Modell entwickelt, das die Vorgänge im unteren Plenum beschreibt. Dabei sind zwei prinzipielle Modellbereiche zu unterscheiden: Das Temperaturfeld in der Schmelze und im RDB wird mit einem thermodynamischen Modell berechnet, während für die Strukturanalyse des RDB ein mechanisches Modell verwendet wird. Zunächst werden das betrachtete Unfallszenario dargestellt und die bisher in den letzten drei Dekaden weltweit durchgeführten wesentlichen analytischen, experimentellen und numerischen Untersuchungen diskutiert. Anschließend werden die auftretenden physikalischen Vorgänge analysiert. Gleichzeitig werden Skalierungsunterschiede zwischen den in dieser Arbeit betrachteten Experimenten der FOREVER-Reihe und einem prototypischen Szenario herausgearbeitet. Das thermodynamische und das mechanische Modell können rekursiv gekoppelt werden, wodurch die wechselseitige Beeinflussung berücksichtigt werden kann. Insbesondere werden damit neben der Temperaturabhängigkeit der Materialparameter und den thermisch induzierten Spannungen im mechanischen Modell auch die Rückwirkungen der Behälterverformung auf das Temperaturfeld selber erfasst. Für die Kriech- und Schädigungssimulation werden in dieser Arbeit neue Verfahren angewendet. Durch die Entwicklung und den Einsatz einer Kriechdatenbasis konnte die bei sehr unterschiedlichen Temperaturen, Spannungen und Dehnungen ungeeignete Verwendung einzelner Kriechgesetze umgangen werden. Aufbauend auf experimentellen Untersuchungen wurde eine Kriechdatenbasis für einen RDB-Stahl entwickelt und an Hand von Kriechversuchen verschiedener Geometrie und Dimension validiert. Als Ergebnis lässt sich festhalten, dass das gekoppelte Modell prinzipiell in der Lage ist, die Behälterdeformation im Falle der skalierten FOREVER-Experimente exakt zu beschreiben bzw. vorherzusagen. Unsicherheiten bezüglich der Versagenszeit resultieren aus nicht exakt bekannten Materialparametern und Randbedingungen. Die wesentlichen Ergebnisse dieser Arbeit lassen sich wie folgt zusammenfassen: Aufgrund des thermodynamischen Verhaltens eines großen Schmelzesees mit inneren Wärmequellen erfolgt die höchste thermomechanische Belastung des RDB im oberen Drittel der Bodenkalotte. Dieser Bereich wird als heißer Fokus bezeichnet. Der untere Bereich der Kalotte weist hingegen eine höhere Festigkeit auf und verlagert sich deswegen bei entsprechender Belastung des RDB im wesentlichen senkrecht nach unten. Bei einer externen Flutung besteht auch bei hohen Innendrücken für einen Reaktor großer Leistung (KONVOI) die Möglichkeit, die Schmelze im RDB zurückzuhalten. Ohne interne oder externe Flutung besteht für das betrachtete Szenario keine Aussicht für eine Schmelzerückhaltung im RDB. Aus den gewonnenen Erkenntnissen wurden zwei Patente abgeleitet. Dabei handelt es sich um passiv wirkende Einrichtungen zur Schadensbegrenzung: Die erste reduziert durch Abstützen des unteren Kalottenzentrums die Maximalspannungen im hochbeanspruchten Bereich des heißen Fokus und kann damit ein Versagen verhindern oder zumindest verzögern. Die zweite Einrichtung ermöglicht die passive Auslösung einer Flutung, indem die Abwärtsbewegung der Kalotte zur Steuerung genutzt wird. Hierdurch kann beispielsweise ein Ventil geöffnet werden, um Wasser aus im Gebäude höher angeordneten Reservoirs in die Reaktorgrube zu leiten. Abweichend von bisherigen Annahmen kann im Hinblick auf die Entwicklung zukünftiger Baulinien festgehalten werden, dass eine Kernschmelzerückhaltung im Reaktordruckbehälter auch für Reaktoren größerer Leistung möglich ist

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16

Vakil, Sachin Suresh. "Flow and Thermal Field Measurements in a Combustor Simulator Relevant to a Gas Turbine Aero-Engine." Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/36324.

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Анотація:

The highly competitive gas turbine industry has been motivated by consumer demands for higher power-to-weight ratios, increased thermal efficiencies, and reliability while maintaining affordability. In its continual quest, the industry must continually try to raise the turbine inlet temperature, which according to the well-known Brayton cycle is key to higher engine efficiencies. The desire for increased turbine inlet temperatures creates an extremely harsh environment for the combustor liner in addition to the components downstream of the combustor. Shear layers between the dilution jets and the mainstream, as well as combustor liner film-cooling interactions create a complex mean flow field within the combustor, which is not easy to model. A completely uniform temperature and velocity profile at the combustor exit is desirable from the standpoint of reducing the secondary flows in the turbine. However, this seldom occurs due to a lack of thorough mixing within the combustor. Poor mixing results in non-uniformities, such as hot streaks, and allow non-combusted fuel to exit the combustor.

This investigation developed a database documenting the thermal and flow characteristics within a combustor simulator representative of the flowfield within a gas turbine aero-engine. Three- and two-component laser Doppler velocimeter measurements were completed to quantify the flow and turbulence fields, while a thermocouple rake was used to quantify the thermal fields.

The measured results show very high turbulence levels due to the dilution flow injection. Directly downstream of the dilution jets, an increased thickness in the film-cooling was noted with a fairly non-homogeneous temperature field across the combustor width. A highly turbulent shear layer was found at the leading edge of the dilution jets. Measurements also showed that a relatively extensive recirculation region existed downstream of the dilution jets. Despite the lack of film-cooling injection at the trailing edge of the dilution hole, there existed coolant flow indicative of a horse-shoe vortex wrapping around the jet. As a result of the dilution jet interaction with the mainstream flow, kidney-shaped thermal fields and counter-rotating vortices developed. These vortices serve to enhance combustor mixing.
Master of Science

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17

Willschütz, Hans-Georg. "Thermomechanische Modellierung eines Reaktordruckbehälters in der Spätphase eines Kernschmelzunfalls." Doctoral thesis, Technische Universität Dresden, 2005. https://tud.qucosa.de/id/qucosa%3A24635.

Повний текст джерела

Анотація:

Considering the late in-vessel phase of an unlikely core melt down scenario in a light water reactor (LWR) with the formation of a corium pool in the lower head of the reactor pressure vessel (RPV) the possible failure modes of the RPV and the time to failure have to be investigated to assess the possible loadings on the containment. In this work, an integral model was developed to describe the processes in the lower plenum of the RPV. Two principal model domains have to be distinguished: The tem-perature field within the melt and RPV is calculated with a thermodynamic model, while a mechanical model is used for the structural analysis of the vessel wall. In the introducing chapters a description is given of the considered accident scenario and the relevant analytical, experimental, and numerical investigations are discussed which were performed worldwide during the last three decades. Following, the occurring physical phenomena are analysed and the scaling differences are evaluated between the FOREVER-experiments and a prototypical scenario. The thermodynamic and the mechanical model can be coupled recursively to take into account the mutual influence. This approach not only allows to consider the temperature dependence of the material parameters and the thermally induced stress in the mechanical model, it also takes into account the response of the temperature field itself upon the changing vessel geometry. New approaches are applied in this work for the simulation of creep and damage. Using a creep data base, the application of single creep laws could be avoided which is especially advantageous if large temperature, stress, and strain ranges have to be covered. Based on experimental investigations, the creep data base has been developed for an RPV-steel and has been validated against creep tests with different scalings and geometries. It can be stated, that the coupled model is able to exactly describe and predict the vessel deformation in the scaled integral FOREVER-tests. There are uncertainties concerning the time to failure which are related to inexactly known material parameters and boundary conditions. The main results of this work can be summarised as follows: Due to the thermody-namic behaviour of the large melt pool with internal heat sources, the upper third of the lower RPV head is exposed to the highest thermo-mechanical loads. This region is called hot focus. Contrary to that, the pole part of the lower head has a higher strength and therefore relocates almost vertically downwards under the combined thermal, weight and internal pressure load of the RPV. On the one hand, it will be possible by external flooding to retain the corium within the RPV even at increased pressures and even in reactors with high power (as e.g. KONVOI). On the other hand, there is no chance for melt retention in the considered scenario if neither internal nor external flooding of the RPV can be achieved. Two patents have been derived from the gained insights. Both are related to passively working devices for accident mitigation: The first one is a support of the RPV lower head pole part. It reduces the maximum mechanical load in the highly stressed area of the hot focus. In this way, it can prevent failure or at least extend the time to failure of the vessel. The second device implements a passive accident mitigation measure by making use of the downward movement of the lower head. Through this, a valve or a flap can be opened to flood the reactor pit with water from a storage reservoir located at a higher position in the reactor building. With regard to future plant designs it can be stated - differing from former presumptions - that an In-Vessel-Retention (IVR) of a molten core is possible within the reactor pressure vessel even for reactors with higher power.
Für das unwahrscheinliche Szenario eines Kernschmelzunfalls in einem Leichtwasserreaktor mit Bildung eines Schmelzesees in der Bodenkalotte des Reaktordruckbehälters (RDB) ist es notwendig, mögliche Versagensformen des RDB sowie Versagenszeiträume zu ermitteln, um die daraus resultierende mögliche Belastung des Sicherheitsbehälters bestimmen zu können. In dieser Arbeit wird ein integrales Modell entwickelt, das die Vorgänge im unteren Plenum beschreibt. Dabei sind zwei prinzipielle Modellbereiche zu unterscheiden: Das Temperaturfeld in der Schmelze und im RDB wird mit einem thermodynamischen Modell berechnet, während für die Strukturanalyse des RDB ein mechanisches Modell verwendet wird. Zunächst werden das betrachtete Unfallszenario dargestellt und die bisher in den letzten drei Dekaden weltweit durchgeführten wesentlichen analytischen, experimentellen und numerischen Untersuchungen diskutiert. Anschließend werden die auftretenden physikalischen Vorgänge analysiert. Gleichzeitig werden Skalierungsunterschiede zwischen den in dieser Arbeit betrachteten Experimenten der FOREVER-Reihe und einem prototypischen Szenario herausgearbeitet. Das thermodynamische und das mechanische Modell können rekursiv gekoppelt werden, wodurch die wechselseitige Beeinflussung berücksichtigt werden kann. Insbesondere werden damit neben der Temperaturabhängigkeit der Materialparameter und den thermisch induzierten Spannungen im mechanischen Modell auch die Rückwirkungen der Behälterverformung auf das Temperaturfeld selber erfasst. Für die Kriech- und Schädigungssimulation werden in dieser Arbeit neue Verfahren angewendet. Durch die Entwicklung und den Einsatz einer Kriechdatenbasis konnte die bei sehr unterschiedlichen Temperaturen, Spannungen und Dehnungen ungeeignete Verwendung einzelner Kriechgesetze umgangen werden. Aufbauend auf experimentellen Untersuchungen wurde eine Kriechdatenbasis für einen RDB-Stahl entwickelt und an Hand von Kriechversuchen verschiedener Geometrie und Dimension validiert. Als Ergebnis lässt sich festhalten, dass das gekoppelte Modell prinzipiell in der Lage ist, die Behälterdeformation im Falle der skalierten FOREVER-Experimente exakt zu beschreiben bzw. vorherzusagen. Unsicherheiten bezüglich der Versagenszeit resultieren aus nicht exakt bekannten Materialparametern und Randbedingungen. Die wesentlichen Ergebnisse dieser Arbeit lassen sich wie folgt zusammenfassen: Aufgrund des thermodynamischen Verhaltens eines großen Schmelzesees mit inneren Wärmequellen erfolgt die höchste thermomechanische Belastung des RDB im oberen Drittel der Bodenkalotte. Dieser Bereich wird als heißer Fokus bezeichnet. Der untere Bereich der Kalotte weist hingegen eine höhere Festigkeit auf und verlagert sich deswegen bei entsprechender Belastung des RDB im wesentlichen senkrecht nach unten. Bei einer externen Flutung besteht auch bei hohen Innendrücken für einen Reaktor großer Leistung (KONVOI) die Möglichkeit, die Schmelze im RDB zurückzuhalten. Ohne interne oder externe Flutung besteht für das betrachtete Szenario keine Aussicht für eine Schmelzerückhaltung im RDB. Aus den gewonnenen Erkenntnissen wurden zwei Patente abgeleitet. Dabei handelt es sich um passiv wirkende Einrichtungen zur Schadensbegrenzung: Die erste reduziert durch Abstützen des unteren Kalottenzentrums die Maximalspannungen im hochbeanspruchten Bereich des heißen Fokus und kann damit ein Versagen verhindern oder zumindest verzögern. Die zweite Einrichtung ermöglicht die passive Auslösung einer Flutung, indem die Abwärtsbewegung der Kalotte zur Steuerung genutzt wird. Hierdurch kann beispielsweise ein Ventil geöffnet werden, um Wasser aus im Gebäude höher angeordneten Reservoirs in die Reaktorgrube zu leiten. Abweichend von bisherigen Annahmen kann im Hinblick auf die Entwicklung zukünftiger Baulinien festgehalten werden, dass eine Kernschmelzerückhaltung im Reaktordruckbehälter auch für Reaktoren größerer Leistung möglich ist.

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18

Gur, Sourav, and George N. Frantziskonis. "Linking simulations and experiments for the multiscale tracking of thermally induced martensitic phase transformation in NiTi SMA." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/623018.

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Анотація:

Martensitic phase transformation in NiTi shape memory alloys (SMA) occurs over a hierarchy of spatial scales, as evidenced from observed multiscale patterns of the martensitic phase fraction, which depend on the material microstructure and on the size of the SMA specimen. This paper presents a methodology for the multiscale tracking of the thermally induced martensitic phase transformation process in NiTi SMA. Fine scale stochastic phase field simulations are coupled to macroscale experimental measurements through the compound wavelet matrix method (CWM). A novel process for obtaining CWM fine scale wavelet coefficients is used that enhances the effectiveness of the method in transferring uncertainties from fine to coarse scales, and also ensures the preservation of spatial correlations in the phase fraction pattern. Size effects, well-documented in the literature, play an important role in designing the multiscale tracking methodology. Molecular dynamics (MD) simulations are employed to verify the phase field simulations in terms of different statistical measures and to demonstrate size effects at the nanometer scale. The effects of thermally induced martensite phase fraction uncertainties on the constitutive response of NiTi SMA is demonstrated.

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19

Winter, Lukas. "Detailing radio frequency controlled hyperthermia and its application in ultrahigh field magnetic resonance." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2014. http://dx.doi.org/10.18452/17012.

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Анотація:

Die vorliegende Arbeit untersucht die grundsätzliche Machbarkeit, Radiofrequenzimpulse (RF) der Ultrahochfeld (UHF) Magnetresonanztomographie (MRT) (B0≥7.0T) für therapeutische Verfahren wie die RF Hyperthermie oder die lokalisierte Freigabe von Wirkstoffträgern und Markern zu nutzen. Im Rahmen der Arbeit wurde ein 8-Kanal Sened/Empfangsapplikator entwickelt, der bei einer Protonenfrequenz von 298MHz operiert. Mit diesem weltweit ersten System konnte in der Arbeit experimentell bewiesen werden, dass die entwickelte Hardware sowohl zielgerichtete lokalisierte RF Erwärmung als auch MR Bildgebung und MR Thermometrie (MRTh) realisiert. Mit den zusätzlichen Freiheitsgraden (Phase, Amplitude) eines mehrkanaligen Sendesystems konnte aufgezeigt werden, dass der Ort der thermischen Dosierung gezielt verändert bzw. festgelegt werden kann. In realitätsnahen Temperatursimulationen mit numerischen Modellen des Menschen, wird in der Arbeit aufgezeigt, dass mittels des entwickelten Hybridaufbaus eine kontrollierte und lokalisierte thermische Dosierung im Zentrum des menschlichen Kopfes erzeugt werden kann. Nach der erfolgreichen Durchführung dieser Machbarkeitsstudie wurden in theoretischen Überlegungen, numerischen Simulationen und in ersten grundlegenden experimentellen Versuchen die elektromagnetischen Gegebenheiten von MRT und lokal induzierter RF Hyperthermie für Frequenzen größer als 298MHz untersucht. In einem Frequenzbereich bis zu 1.44GHz konnte der Energiefokus mit Hilfe spezialisierter RF Antennenkonfigurationen entscheidend weiter verkleinert werden, sodass Temperaturkegeldurchmesser von wenigen Millimetern erreicht wurden. Gleichzeitig konnte gezeigt werden, dass die vorgestellten Konzepte ausreichende Signalstärke der zirkular polarisierten Spinanregungsfelder bei akzeptabler oberflächlicher Energieabsorption erzeugen, um eine potentielle Machbarkeit von in vivo MRT bei B0=33.8T oder in vivo Elektronenspinresonanz (ESR) im L-Band zu demonstrieren.
The presented work details the basic feasibility of using radiofrequency (RF) fields generated by ultrahigh field (UHF) magnetic resonance (MR) (B0≥7.0T) systems for therapeutic applications such as RF hyperthermia and targeted drug delivery. A truly hybrid 8-channel transmit/receive applicator operating at the 7.0T proton MR frequency of 298MHz has been developed. Experimental verification conducted in this work demonstrated that the hybrid applicator supports targeted RF heating, MR imaging and MR thermometry (MRTh). The approach offers extra degrees of freedom (RF phase, RF amplitude) that afford deliberate changes in the location and thermal dose of targeted RF induced heating. High spatial and temporal MR temperature mapping can be achieved due to intrinsic signal-to-noise ratio (SNR) gain of UHF MR together with the enhanced parallel imaging performance inherent to the multi-channel receive architecture used. Temperature simulations in human voxel models revealed that the proposed hybrid setup is capable to deposit a controlled and localized RF induced thermal dose in the center of the human brain. After demonstrating basic feasibility, theoretical considerations and proof-of-principle experiments were conducted for RF frequencies of up to 1.44GHz to explore electrodynamic constraints for MRI and targeted RF heating applications for a frequency range larger than 298MHz. For this frequency regime a significant reduction in the effective area of energy absorption was observed when using dedicated RF antenna arrays proposed and developed in this work. Based upon this initial experience it is safe to conclude that the presented concepts generate sufficient signal strength for the circular polarized spin excitation fields with acceptable specific absorption rate (SAR) on the surface, to render in vivo MRI at B0=33.8T or in vivo electron paramagnetic resonance (EPR) at L-Band feasible.

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20

Duine, Gert-Jan. "Caractérisation des vents de vallée en conditions stables à partir de la campagne de mesures KASCADE et de simulations WRF à méso-échelle." Thesis, Toulouse 3, 2015. http://www.theses.fr/2015TOU30258/document.

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Cette thèse est dédiée à la caractérisation des vents descendants de vallée en terrain complexe d'orographie modérée à moyenne latitude, dans le contexte de la réglementation des rejets atmosphériques de Cadarache. Cadarache est un des centres de recherche du "Commissariat à l'énergie atomique et aux énergies alternatives" (CEA), installé dans une petite vallée (CV) confluente à la vallée de la Durance (DV). Ces deux vallées se distinguent par leur taille, et sont le siège d'écoulements aux caractéristiques différentes en stratification stable. Un forçage synoptique faible associé à un ciel dégagé sont dans la région des conditions fréquentes qui favorisent la stabilité atmosphérique et consécutivement la mauvaise dispersion des polluants, faisant de cette situation un sujet d'intérêt majeur. La campagne de mesure KASCADE (KAtabatic winds and Stability over CAdarache for Dispersion of Effluents) constitue le volet expérimental de l'étude. Réalisée pendant l'hiver 2013 elle a couvert 3 mois d'observation continue et complétée de 23 périodes d'observation intensive (POI). L'analyse montre que les écoulements descendant les vallées de Cadarache (CDV) et de la Durance (DDV) dominent pendant toute la période d'étude. La stabilité s'installant dès le coucher du soleil, le courant CDV s'épaissit progressivement. Le profil de vent en forme de jet présente son maximum à environ 30 m où il atteint 2 à 3 m s-1. Il se maintient toute la nuit et disparaît avec l'inversion de stabilité. Comme la station météorologique du centre manque de capteur de vent dans la CV même, une méthode a été développée pour diagnostiquer le CDV en exploitant l'instrumentation actuelle. Ainsi, si la prévision de ce vent n'est pas à la portée du modèle méso-échelle WRF avec une résolution kilométrique, cette méthode le permet en combinant une descente d'échelle dynamique et statistique. Le vent DDV est identifié comme un vent qui suit l'axe de la vallée, fortement corrélé à la stabilité à l'échelle régionale car il n'apparaît que la nuit lorsque le forçage synoptique est faible. Ce vent n'arrive à Cadarache que 6 à 9 heures après le coucher du soleil avec une grande variabilité. D'un autre côté, il est à son maximum au lever du soleil avant que les processus convectifs ne démarrent, et présente un jet autour de 200 m avec des vitesses de 4 à 8 m s-1 et dont la hauteur est corrélée à la profondeur de la vallée. Dans les simulations avec WRF, malgré des défauts, la DV étant bien résolue avec une maille de 1 km, l'occurrence de ce vent est assez bien simulée. Par ailleurs l'examen de ses caractéristiques spatiales montre qu'il s'agit soit d'un écoulement de drainage, soit d'un écoulement canalisé forcé. Bien qu'on ne dispose pas de données suffisantes pour élucider le mécanisme dominant de déclenchement du vent DDV, les deux précédemment identifiés sont de bons candidats
Stable stratification can be one of the most penalizing condition concerning pollutants in the atmospheric boundary layer. Over complex terrain under these conditions, the relief may modify the flow. Therefore the knowledge of down-valley wind characteristics influencing the wind field at Cadarache and its close surroundings is crucial for safety regulation in the context of sanitary impact of the site. Cadarache is a CEA research centre and located in the Prealps of southeast France. It is embedded in a small valley, the Cadarache Valley (CV), which is one of the tributaries of the larger Durance Valley (DV). The two valleys are distinct in size and therefore react differently to stable conditions, and are investigated by means of observations (field experiment KASCADE : KAtabatic winds and Stability over CADarache for Dispersion of Effluents) and simulations (the Weather Research and Forecasting (WRF) model). To investigate the valley wind behaviour, the KASCADE campaign has been designed and conducted in the winter of 2013, covering a 3-month period and 23 intensive observation periods (IOP). It resulted in a well-documented campaign, from which the analysis shows that the Cadarache and Durance down-valley (CDV and DDV respectively) winds are both dominant flows during the period of investigation. The CDV wind is a thermally driven flow, with regular wind speeds up to 2 - 3 m s-1 up to 50 m agl. It persists throughout the night and disappears in the early morning with the stability. The current observational network of Cadarache lacks means of measurement for inside CDV wind. This work shows that it can be nowcasted from available meteorological tower observations. Due to the CV small scale, currently a wind forecast on kilometer resolution is out of reach, but the methodology developed here can be used to forecast the wind through a combination of dynamical and statistical downscaling. The DDV wind has been recognized as down-valley oriented, and strongly related to stability at a regional scale, as it exists only after sunset when synoptic forcing is very weak. DDV wind arrival at Cadarache is mostly observed 6 to 9 hours after sunset, but however dominantly present around sunrise, when convectively driven processes are not yet established. Jets are observed mostly at around 200 m agl with wind speeds between 4 and 8 m s-1. Despite some (general) deficiencies of the WRF model, the DDV wind is simulated close to reality thanks to the 1-km resolution allowing a correct representation of the Durance valley orography. The ensemble of 23 simulated IOPs allowed further to characterize the flow in a spatial sense and to recognize drainage and flow channelling as most important candidates for the flow mechanism

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21

Johnson, Janine B. "Fracture Failure of Solid Oxide Fuel Cells." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4847.

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Анотація:

Among all existing fuel cell technologies, the planar solid oxide fuel cell (SOFC) is the most promising one for high power density applications. A planar SOFC consists of two porous ceramic layers (the anode and cathode) through which flows the fuel and oxidant. These ceramic layers are bonded to a solid electrolyte layer to form a tri-layer structure called PEN (positive-electrolyte-negative) across which the electrochemical reactions take place to generate electricity. Because SOFCs operate at high temperatures, the cell components (e.g., PEN and seals) are subjected to harsh environments and severe thermomechanical residual stresses. It has been reported repeatedly that, under combined thermomechanical, electrical and chemical driving forces, catastrophic failure often occurs suddenly due to material fracture or loss of adhesion at the material interfaces. Unfortunately, there have been very few thermomechanical modeling techniques that can be used for assessing the reliability and durability of SOFCs. Therefore, modeling techniques and simulation tools applicable to SOFC will need to be developed. Such techniques and tools enable us to analyze new cell designs, evaluate the performance of new materials, virtually simulate new stack configurations, as well as to assess the reliability and durability of stacks in operation. This research focuses on developing computational techniques for modeling fracture failure in SOFCs. The objectives are to investigate the failure modes and failure mechanisms due to fracture, and to develop a finite element based computational method to analyze and simulate fracture and crack growth in SOFCs. By using the commercial finite element software, ANSYS, as the basic computational tool, a MatLab based program has been developed. This MatLab program takes the displacement solutions from ANSYS as input to compute fracture parameters. The individual stress intensity factors are obtained by using the volume integrals in conjunction with the interaction integral technique. The software code developed here is the first of its kind capable of calculating stress intensity factors for three-dimensional cracks of curved front experiencing both mechanical and non-uniform temperature loading conditions. These results provide new scientific and engineering knowledge on SOFC failure, and enable us to analyze the performance, operations, and life characteristics of SOFCs.

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22

Simon, Nataline. "Développement des méthodes actives de mesures distribuées de température par fibre optique pour la quantification des écoulements souterrains : apports et limites pour la caractérisation des échanges nappe/rivière." Thesis, Rennes 1, 2020. http://www.theses.fr/2020REN1B028.

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Les échanges entre les rivières et les nappes d’eau souterraine jouent un rôle essentiel dans le maintien des écosystèmes aquatiques. Or, leur caractérisation demeure difficile du fait de leur forte variabilité dans l’espace et dans le temps. Dans ce contexte, l’objectif de ce travail de thèse est de développer des méthodes actives de mesures distribuées de température pour quantifier la dynamique des interactions nappe/rivière. Après avoir établi une nouvelle approche pour évaluer la résolution spatiale des mesures de température, nous avons validé deux nouvelles méthodes d’interprétation permettant d’estimer de manière distribuée les flux d’eau et la conductivité thermique du milieu poreux. Les travaux, associant modélisations numériques et mesures expérimentales en laboratoire, montrent que les méthodes d’interprétation développées permettent d’estimer avec une excellente précision les écoulements et que la gamme de flux pouvant être investiguée est particulièrement large. Pour tester cette approche prometteuse, des expériences actives ont ensuite été réalisées sur le terrain dans deux environnements différents : d’abord dans un petit cours d’eau d’ordre 1 de tête de bassin versant, puis dans un fleuve s’écoulant le long d’une plaine alluviale. Ces applications ont démontré le fort potentiel des méthodes actives pour quantifier les écoulements à l’interface nappe/rivière et décrire leur variabilité spatiale et temporelle. La comparaison des résultats obtenus sur les deux sites a permis finalement de discuter la faisabilité, les apports mais aussi les limites de la méthode dans différents contextes hydrologiques
Groundwater/surface water interactions play a fundamental role in the functioning of aquatic ecosystems. However, their quantification is challenging because exchange processes vary both in time and space. Here, we propose an active distributed heat transport experiment in order to quantify the spatial and temporal variability of groundwater/surface water interactions. As a first step, we proposed a new approach to evaluate the spatial resolution of temperature measurements. Then, two interpretation methods of active-DTS experiments were developed and fully validated to estimate the distribution of porous media thermal conductivity and the groundwater fluxes in sediments. Based on numerical simulations and sandbox experiments, results demonstrated the potentiality of these methods for quantifying distributed groundwater fluxes with high accuracy. The large range of groundwater fluxes that can be investigated with the method makes specially promising the application of active experiments for many subsurface applications. Secondly, we conducted heat transport experiments within the streambed sediments of two different streams: in a first-order stream, then in a large flow-system located along an alluvial plain. These applications demonstrated the relevance of using active experiments to characterize the spatial complexity of stream exchanges. Finally, the comparison of results obtained for each experimental site allowed discussing the capabilities and limitations of using active-DTS field experiments to characterize groundwater/surface water interactions in different hydrological contexts

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23

Chen, Chia-Wen, and 陳洽文. "Thermal-Flow Field Simulation and Analysis of the Greenhouse." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/8r8tgg.

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Анотація:

碩士
國立臺灣科技大學
機械工程系
99
Due to the growing concerns on environmental quality and energy consumption of the greenhouse, this work intends to study the fluid field inside a closed greenhouse for mushroom plantation. With the aids of CFD code FLUENT, the flow simulation is firstly executed numerically and analyzed for identifying the drawbacks of the original greenhouse design. Several severe circulations and reversed flows are found near the intakes of cooling air. These phenomena result in velocity decrease and non-uniformity on the cooling air stream; thus the environmental quality is downgraded for the crops growing. Thereafter, two alternatives, changing the inlet location and adding extra exhausting outlets, are proposed for diminishing these reversed flows and circulations. These CFD results indicate that changing inlet location can eliminate the reversed flow and increase the air speed by 12%. Also, the cooling air speed is enhanced further from 0.04 m/sec to 0.24 m/sec at the center of greenhouse by optimizing the exhausting outlet number. Both modifications have significant influence in modifying the flow field feature for the corps growing. In summary, this study successfully enhances the air velocity and distribution inside greenhouse for improving mushroom plantation by using a systematic and rigorous CFD technique.

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24

Yang, Ching-Hsiang, and 楊景翔. "Thermal and fluid field simulation of G6 directional solidification furnace." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/39355s.

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Анотація:

碩士
國立交通大學
機械工程系所
106
The present study adopts company’s chamber model and experimental properties to simulate producing big size multi-silicon ingot process by directional solidification method. The first set of examined the impact of heat flux as heater boundary condition, when it adopted, TC2 temperature is closer to experiment log data. One interesting finding is side heater have huge temperature difference between its own top and bottom. The second one was to implement separated side heater in the furnace. Simulation result revealed that temperature gradient was improved around 5%; V/G value in center and near crucible was enhanced 29% and 57% and electric energy was saved 6% in the same time. Overall, these results indicate that heat flux as boundary condition can properly fit side heater and separated heater can improve temperature and conserve energy. Moreover, side heater position can be shifted downward and length can be extended for future work. Argon flow plays important role in both heating and growth process of production silicon. The conventional design for argon flow is yet sufficient. In this study, we installed a plate under graphite cover and find out optimized size and spacing of plate afterward design the outlet for sweeping accumulation then combined all cases. The result showed corner outlet with guiding plate had the lowest chemical deposit in low flow rate and conventional case outlet with plate had selected performance. Performance improved by corner outlet with plate in low flow rate and conventional case outlet with plate in high flow rate were 6% and 13%. However, corner outlet with plate could save 33% argon gas consumption in low flow. Transient simulation indicated the performance of guiding plate in heating process was much powerful than growth process which simulated in steady state.

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25

James and 許進旺. "The Numerical Simulation of a MOCVD Reactor’s Thermal/Flow Field." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/66140915034367020591.

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碩士
國立屏東科技大學
機械工程系
88
Abstract The purpose of this research is to analyze the horizontal MOCVD reactor for fabrication of GaAs deposited epitaxy by using the computational fluid dynamics methods. To use a commercial software(cosmos 2.0) to obtain reactor’s thermal and velocity distribution of the gas on the wafer surface such that the amount of GaAs deposited on the wafer can be calculated. The flow must be laminar and without any recirculation. The reactor will be cold wall type, with R.F heater, the carrier gas is helium (He) or nitrogen(N2) , and reacting gases are TMGa and AsH3.High tempture to cause the density to change. By Gr/Re2 numerical analysis, we can obtain the fluid running’s condition. By changing the fluid’s velocity and cold wall’s tempture to improve the fluid turbulence to make the deposited thin film with correct thickness and uniform thickness distribution (thickness variation must be controlled with 2%). In the future, I hope that the research can provide the imformation on the MOCVD reactor’s design.

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26

ZENG, WEI-WEN, and 曾偉文. "Numerical simulation and analysis of the thermal field in compartment fire." Thesis, 1991. http://ndltd.ncl.edu.tw/handle/bmxt42.

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27

Cheng, Chao-Jung, and 鄭朝榮. "Thermal Fluid Field Model Simulation for a Townhouse Fire in Yang-mei." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/40929436903744536588.

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Анотація:

碩士
元智大學
機械工程學系
98
During the past decades in Taiwan, there were many fire cases occurred in apartment buildings, and most of which were often illegally rebuilt with metal sheet. In recent years, despite the rapid economy development in Taiwan, there still standing a lot of this kind of houses in villages and towns. Due to lack of overall rebuild plan, the inner old electric wire and the improper use of electric devices, plus narrow street sidewalks parked with cars which prevented fire engine from entering, as well as dense population and residential environment, if the fire happened, it could often cause great casualties and property losses. This paper is using an attached townhouse fire in Yangmei township in 2008 for fire study. There are too much combustibles in the fire house, and because all house additions are reconstructed with metal sheets at third floors, the fire spread out rapidly without effective isolation. This study uses Fire Dynamics Simulator (FDS) software to analyze the physical phenomenon of the fire scene and to analyze the heat conduction, smoke flows, upper layer temperature, change of carbon monoxide (CO) concentrations, and by adjusting the parameters of the key factors to analyze the influence of different conditions in fire scene. The simulation result is expected to provide a reference for fire protection engineering of the residential buildings.

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28

Min-HsiungHung and 洪敏雄. "Study for Flow Field and Thermal Field of Thin Slab Mold by Physical Models and Numerical Simulation." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/21499513189321552424.

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Анотація:

碩士
國立成功大學
材料科學及工程學系碩博士班
101
In this study, a physical model and a mathematical model have been developed to analysis the flow field and thermal field in the funnel-type mold of thin slab continuous casting. In the physical model experiment, a 0.5 scale model is used to analysis the influences of flow field with three types of nozzle. In order to simulate the real situation of thin slab continuous casting, a cooling system is built around the water model to cool down the mold and grow the solidification shell in the water model. By using this cooling system, the change of flow characteristic with solidification shell can be observed. According to the experiment results, there are four swirls in the mold and the positions of the swirls change by using different nozzles. In the cooling experiment, the existence of solidification shell does not affect the formation of swirls in the mold. In the mathematical experiment, the commercial software ProCAST is used to simulate the process of physical model experiment. The simulate results of thermal field and flow field are compared with the results of physical model and then confirm this mathematical model is reliable. Finally, this mathematical model with the actual casting cooling conditions is employed to predict the actual flow field and the solidified layer thickness inside the mold.

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29

Zang, Zhong-Yuan, and 臧忠元. "The Simulation of Thermal Flow Field in LPCVD Chamber Using Parallel DSMC Method." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/73951074901214840920.

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Анотація:

碩士
國立交通大學
機械工程系
90
In this thesis, the parallelization is applied to DSMC method by utilizing chain partitioner. The computation is carried out on a PC cluster system consisting of nine processors. The preliminary results are compared with the Hsiao’s single-processor results [5], to demonstrate the advantage of parallelization. The computational domain is decomposed according to the same number of simulated particles in each processor. When a parallel program is executed on a distributed memory system, the speedup may not be proportional linearly to the number of processor. The computing load in each processor becomes lighter by increasing the processor number, whereas the communication load becomes heavier at the same time. Therefore the efficiency becomes worse with an increment of processor number. The parametric studies are based on the variations of particle number, computing domain size and time step, respectively. The better speedup and efficiency can be achieved when the particle number and computational domain increase. The performance does not depend on time step in present case because the variation of particle number is not severe.

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30

Lin, Chun-Hsien, and 林俊賢. "Field Testing and Numerical Simulation for The Precise Thermal Control of Large Laboratory." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/n87bx5.

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Анотація:

碩士
國立臺北科技大學
冷凍空調工程系所
93
This research simulates and analyzes the airflow in the experimental area of a national research center. According to the field measuring results of the air-conditioning system, boundary conditions of computational fluid dynamics (CFD), can be deduced, and the airflow simulation can then be simulated according to the actual conditions of the present space under various design cases. The air side performance is predicted to provide assists and evidence in air-conditioning engineering. The function of an air supplying system depends on the shapes and positions of the air outlets. Many researches show that in isothermal jet the throw is related to the mean surface velocity of the outlet, and the jet distance is related to the velocity, volume, the mean area of the outlet and the distribution of velocity. Therefore, the evaluation of air-conditioning space focuses on the parameters of the air supplying system. The goal of this research aims to ensure that the precision instruments in the research space air in an environment with constant temperature and humidity to avoid errors due to temperature fluctuations, and discuss the environmental temperature stability in a large space under the minimum temperature fluctuation. Via the numerical simulation and analysis and the concept of air-conditioning system design, a design solution is proposed that fits the requirements to improve the conditioning system. The basic concept is to use raised temperature air supply (lowered the temperature difference between the space and the supply air), appropriate outlets layouts and high air displacement rate (increasing the supply air flow rate) to take the sensible energy load away, make the air well mixed, and control the temperature fluctuation within ±0.5 ℃.

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31

Rei-YiChen and 陳睿翊. "Field experiment and simulation of the daylighting and thermal environment in naturally ventilated classrooms." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/2v7nk8.

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32

"Application of Phase Change Material in Buildings: Field Data vs. EnergyPlus SImulation." Master's thesis, 2010. http://hdl.handle.net/2286/R.I.8716.

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abstract: Phase Change Material (PCM) plays an important role as a thermal energy storage device by utilizing its high storage density and latent heat property. One of the potential applications for PCM is in buildings by incorporating them in the envelope for energy conservation. During the summer season, the benefits are a decrease in overall energy consumption by the air conditioning unit and a time shift in peak load during the day. Experimental work was carried out by Arizona Public Service (APS) in collaboration with Phase Change Energy Solutions (PCES) Inc. with a new class of organic-based PCM. This "BioPCM" has non-flammable properties and can be safely used in buildings. The experimental setup showed maximum energy savings of about 30%, a maximum peak load shift of ~ 60 min, and maximum cost savings of about 30%. Simulation was performed to validate the experimental results. EnergyPlus was chosen as it has the capability to simulate phase change material in the building envelope. The building material properties were chosen from the ASHRAE Handbook - Fundamentals and the HVAC system used was a window-mounted heat pump. The weather file used in the simulation was customized for the year 2008 from the National Renewable Energy Laboratory (NREL) website. All EnergyPlus inputs were ensured to match closely with the experimental parameters. The simulation results yielded comparable trends with the experimental energy consumption values, however time shifts were not observed. Several other parametric studies like varying PCM thermal conductivity, temperature range, location, insulation R-value and combination of different PCMs were analyzed and results are presented. It was found that a PCM with a melting point from 23 to 27 °C led to maximum energy savings and greater peak load time shift duration, and is more suitable than other PCM temperature ranges for light weight building construction in Phoenix.
Dissertation/Thesis
M.S. Mechanical Engineering 2010

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33

Kuo, Yong-Chih, and 郭勇志. "Field Experiment and Long-term Simulation on The Effect of Shading Factor on The Outdoor Thermal Environment." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/x52uc3.

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Анотація:

碩士
國立虎尾科技大學
休閒遊憩研究所
100
Global warming effects not only increase the energy consumption of indoors but also decrease the thermal comfort in outdoor environment. Shading is the import factors contribute to micro-climate due to the blocking sunlight mitigate the thermal uncomfortable due to of short-wave radiation. Furthermore, the shadows on the ground decrease surface temperature which reduces the long-wave radiation. However, the trees and artificial may cause different effect of thermal comfort which should be further discussed. Since Taiwan have hot and humid weather, its important to offer a guideline for the designer while deal with the microclimate, which help to release the heat island effect and enhance the thermal comfort.

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34

Hsiao, Chi-Hong, and 蕭啟宏. "The Simulation of Thermal Flow Field and Film Deposition in Vertical Rotating Substrate for LPCVD Using DSMC Method." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/00031111807177172417.

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Анотація:

碩士
國立交通大學
機械工程系
89
This thesis analyzes the flow and thermal field in a vertical LPCVD chamber with rotating susceptor by using DSMC method. It aims at the remodeling of boundary conditions to eliminate the shortcoming in Dei’s work [1], the extra design parameters, such as inlet tube diameter, gravity, and side-wall temperature and an application of parallel computation. For the different design parameters, the predicted results show that a higher average deposition rate and better uniformity can be achieved by shortening the distance between inlet and substrate. It leads to a better deposition rate but a poorer uniformity by increasing the operating pressure, inlet flow, substrate temperature and side wall temperature, respectively. Putting an annular baffle, whose width is equal to the one of outlet area in inlet area, results in a better uniformity but a poorer deposition rate. Rotating the susceptor will improve the uniformity without affecting the deposition rate. Increasing the percentage of reactant, Cu, can raise the deposition rate without affecting the uniformity. The gravity orientation has insignificant effect on the uniformity and deposition rate of LPCVD. The parallelization of DSMC is done in output process only. The saving times, 0.23 second and 0.97 second, are for 4-inch and 8-inch wafer computations, respectively.

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35

Lin, Angela A. "Two dimensional numerical simulation of a non-isothermal GaAs MESFET." Thesis, 1992. http://hdl.handle.net/1957/37014.

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The low thermal conductivity of gallium arsenide compared to silicon results in self-heating effects in GaAs MESFETs that limit the electrical performance of such devices for high power applications. To date, analytical thermal models of self heating in GaAs MESFETs are based on the assumption of a uniformly heated channel. This thesis presents a two dimensional analysis of the electrothermal effect of this device based on the two dimensional power density distribution in the channel under various bias conditions. The numerical simulation is performed using the finite difference technique. The results of the simulation of an isothermal MESFET without heat effects is compared with various one dimensional analytical models in the literature. Electro thermal effects into the two-dimensional isothermal MESFET model allowed close examination of the temperature profile within the MESFET. The large gradient in power distribution results in a localized heat source within the channel which increases the overall channel temperature, which shows that the assumption of a uniformly heated channel is erroneous, and may lead to an underestimation of the maximum channel temperature.
Graduation date: 1992

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36

Xu, Haomin. "Potential for non-thermal cost-effective chemical augmented waterflood for producing viscous oils." 2012. http://hdl.handle.net/2152/19695.

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Chemical enhanced oil recovery has regained its attention because of high oil price and the depletion of conventional oil reservoirs. This process is more complex than the primary and secondary recovery flooding and requires detailed engineering design for a successful field-scale application. An effective alkaline/co-solvent/polymer (ACP) formulation was developed and corefloods were performed for a cost efficient alternative to alkaline/surfactant/polymer floods by the research team at the department of Petroleum and Geosystems Engineering at The University of Texas at Austin. The alkali agent reacts with the acidic components of heavy oil (i.e. 170 cp in-situ viscosities) to form in-situ natural soap to significantly reduce the interfacial tension, which allows producing residual oil not contacted by waterflood or polymer flood alone. Polymer provides mobility control to drive chemical slug and oil bank. The cosolvent added to the chemical slug helps to improve the compatibility between in-situ soap and polymer and to reduce microemulsion viscosity. An impressive recovery of 70% of the waterflood residual oil saturation was achieved where the remaining oil saturation after the ACP flood was reduced to only 13.5%. The results were promising with very low chemical usage for injection. The UTCHEM chemical flooding reservoir simulator was used to model the coreflood experiments to obtain parameters for pilot scale simulations. Geological model was based on unconsolidated reservoir sand with multiple seven spot well patterns. However, facility capacity and field logistics, reservoir heterogeneity as well as mixing and dispersion effects might prevent coreflood design at laboratory from large scale implementation. Field-scale sensitivity studies were conducted to optimize the design under uncertainties. The influences of chemical mass, polymer pre-flush, well constraints, and well spacing on ultimate oil recovery were closely investigated. This research emphasized the importance of good mobility control on project economics. The in-situ soap generated from alkali-naphthenic acid reaction not only mobilizes residual oil to increase oil recovery, but also enhances water relative permeability and increases injectivity. It was also demonstrated that a closer well spacing significantly increases the oil recovery because of greater volumetric sweep efficiency. This thesis presents the simulation and modeling results of an ACP process for a viscous oil in high permeability sandstone reservoir at both coreflood and pilot scales.
text

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37

Chiang, Pei-yi, and 江姵儀. "Numerical simulation of flow, thermal and oxygen distributions for a Czochralski silicon growth with in a transverse magnetic field." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/26192033905626159946.

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Анотація:

碩士
國立中央大學
機械工程學系
102
A three-dimensional numerical simulation has been performed to understand the motion of the melt flow, thermal field and oxygen distributions during the Czochralski silicon single crystal growth process under the influence of a transverse magnetic field. With the application of a transverse magnetic, the velocity, temperature and oxygen concentration fields in the melt become three-dimensional and asymmetric. There were two different flow patterns on the plane parallel and crossing transverse magnetic field, separately. Therefore, the presence of a transverse magnetic field decreases the oxygen concentration level along the melt-crystal interface. The uniformity of oxygen concentration at the melt-crystal interface is also improved when the magnetic field is applied. However, the two flow motion will cause the different temperature distributions form distorted in the whole melt. It is hard to simulation and crystal growth. In this study, the numerical simulation has been performed to clear the mechanism of oxygen transportation, such as the distribution of oxygen concentration in the melt is related to the crystal rotation rate and crucible rate. The lower temperature at the crucible wall and the free surface velocity decrease as the crucible rotation rate decrease. When the crucible rotation rate reaches below 1 rpm, the oxygen concentration value along the melt-crystal interface decrease enlarges. The uniformity of oxygen concentration is better for higher crystal diameters. The crystal rotation rate has negligible influence on the oxygen concentration. But the radial distribution of oxygen uniformity is improved at higher crystal rotation rates. In the case of transverse field, the crucible rotation rate is a key parameter in the control of oxygen concentration in the crystal. The quantity of the oxygen transportation and silica concentration on the free surface can be increased by increasing the gas flow rate. Because the argon gas velocity affect the radial velocity and interfere the free surface flow motion. However, the crystal oxygen concentration was increased with an increase in the flow velocity of argon gas in the TMCZ. This thesis analysis silicon crystal growth process under magnetic Czochralski method, this trend is in consistence with the experimental one. The variation of the axial oxygen concentration with the growth length of the silicon crystal is related to the melt depth of the crucible, the flow structure inside the melt, the crucible temperature, and the argon flow speed along the free surface. In order to improve the axial non-uniform of oxygen concentration, the heater position and crucible rates are adjusted. The axial non-uniform of oxygen concentration can be improved approximately 24.7% and 6.6% by revising the crucible rates and modifying the heater position.

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38

Hsueh, Yu-Lin, and 薛玉麟. "Simulation and analysis of coupling flow field for thermal stage separation of two-stage rockets using moving grid with dynamic pressure." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/15072130602041763597.

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39

Sun, Yun-Chiang, and 孫運強. "Analysis of Thermal Flow Field in Vertical Rotating Injector Low Pressure Chemical Vapor Deposition Reactor Using the Directs Simulation Monte Carlo Method." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/47907890823565153955.

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Анотація:

碩士
國立交通大學
機械工程研究所
86
This thesis applies a numerical technique, DSMC, to simulate the thermal flow field in a vertical low-pressure Cu-CVD reactor. It is incorporated with a project supported by a manufacturer and the National Science council, ROC, under a contract, NSC87-2622-E-009-004. The main purpose is to provide the simulation data as a reference for designing the reacting chamber. According to the requirement of the manufacturer, the effects of rotating injector with fixed suscepter are investigated numerically in this thesis. The parametric studies are based on the changes in physical conditions, such as reactor pressure, temperature of substrate, inlet flow rate, angular velocity of rotating injector and carrier gas. The effect of distance between the injector and substrate is also studied. In the meantime, the influence of two different chemical reaction models on the surface deposition of substrate is considered as well. 　　The results show that a good deposition uniformity for the angular velocities within the domain of 10 to 20 rpm can be achieved. When the reactor pressure increases, the deposition rate increases but the uniformity becomes worse. Increasing the percentage of reactant in precursor can raise the deposition rate more effectively than increasing the reactor pressure. It can also obtain a better deposition uniformity. A higher deposition rate and a better deposition uniformity can be reached by shorting the distance between the injector and substrate. However, an enough distance should be reserved to let the robot arm be able to deliver the wafer into and out from the reacting chamber. When a carrier gas with lower molecular weight is used, a higher deposition rate but with a worse deposition uniformity is found. The high temperature of substrate results in a high temperature in the injector, therefore, the temperature of suscepter suggested not too high in order not to make the reactant deposition on the its aperture to block the transportation of carrier gas and reactants.

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40

Yu-LingHuang and 黃鈺綾. "Numerical Simulation of Thermal and Flow Fields inside Stirling Engines." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/33804644923143006778.

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41

"An efficient algorithm for calculating fluctuation field and simulating the thermal magnetic aftereffect." THE GEORGE WASHINGTON UNIVERSITY, 2009. http://pqdtopen.proquest.com/#viewpdf?dispub=3341358.

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42

Chen, Zhong-Dian, and 陳重典. "Experiment and Numerical Simulation on the Flow and Thermal Fields of LED Coolers." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/08132687141346201572.

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Анотація:

碩士
國立臺灣海洋大學
機械與機電工程學系
97
The LED industry emerges as environmental protection and energy conservation become a global issue. White-light LED receives more attention among various LED applications. As the crystalline technology progresses and the lighting efficiency increases, LED is expected to occupy a larger share in the lighting market. In essence, LED has the advantage of energy saving and long life compared to traditional lighting. However, high power density is the drawback since it will result in high working temperature. Good thermal management and design is critical in stabilizing the lighting output and extending the life period. This work investigates cooling ability of the LED coolers by both numerical analysis and experiments. Finite-volume method (FVM) is employed to construct the numerical model and the numerical results are compared with the experimental results to examine the validity of the numerical model. More numerical analyses are conducted for some complicated cases in order to understand in depth the factors which influence the LED working temperature. The results obtained in this study can be provided for the thermal engineers in the LED thermal design. The experimental results indicate that due to higher thermal conductivity, the 3-D graphite is used more suitably as the spreading plate than the copper or aluminum plates in the LED coolers (the spreading plate and fins). Various factors were found to have different impacts on the natural convection of the coolers. These factors are (from strong to weak impacts) conducting pads, insulating plates, and orientation of the fins. It was also found that as the fin height gets too long, heat transfer augmentation is not significant despite the increase in the total fin area. The heat transfer rate for three heat sinks of LED for forced convection is about 6 to 8 times for natural convection. The heat sink, model B, was found to outperform model C for both forced and natural convection due to good interconnection between flow channels. The numerical results indicate that the introduction of the “chimney” effect and some holes drilled on the spreading plate can increase the heat transfer rate.

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43

Wu, Chia-hao, and 吳家豪. "A Numerical Simulation and Analysis on Thermal Flow Fields in the Galvanized Pot." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/12134980144434996932.

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Анотація:

碩士
義守大學
機械與自動化工程學系碩士班
98
This paper aims to study the galvanized pot of the thermal flow field in the continuous 55% Al-Zn galvanized line pot and explore the influential components to the liquid in the pot as well as the relevant boundary condition. The results of the numerical simulation are able to indicate the range, which can produce the bottom dross of the dead zone in the flow field. These results can be employed to suggest how to reduce the bottom dross in the pot, extend its service life, and improve coating quality on the strip surface. In order to obtain the trend of the actual temperature distributions in the pot and testify the numerical results, the measurement of liquid temperature in the pot was conducted. The CFD technique was adopted to study on various parameter, explore the differences of inductors with different power, discuss the differences in the inner flow field caused by the bottom shapes, and compare the thermal flow field in different pot models. It has been found that most of the dead zones exist near the entrance to the pot of the strip. The results indicate that in terms of the dead zones distributions, the influence by the inductors was minor while the influence by the collocation of the components in the pot was obvious.

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44

Ning, Li-Yen, and 甯立言. "Field measurements and computer simulations of two built thermal environments of different large-area glass windows." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/10964572907348574578.

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碩士
國立臺灣科技大學
機械工程系
98
This research focuses on field measurement and computer simulation of two prototype houses having the same shape. Two houses use different properties of glass. One uses ordinary glass and the other one uses the heat-insulation solar power glass, a research product of NTUST, which combines functions of self-clean, heat-insulation and power generation. The house using the heat-insulation solar power glass can effectively reflect internal and external radiation of the house, and maintain stable indoor temperature. The house using regular glass window has more extreme hot and cold indoor temperature. This research uses building energy simulation program, DesignBuilder, to simulate the indoor environmental temperature. The simulation work replaces inputs of regular Typical Meteorological Year (TMY) data with inputs of local outside measurement data, and weather station data. This thesis focuses on comparing the field measurements of two prototype houses and the simulation results of two houses in different seasons. Differences between field measurements and simulation results are significant especially in the Fall, the Winter and the Spring, the possible causes are incorrect calculations of radiation heat transfer. The research proposes two compensation methods of radiation heat transfer. The first method uses the differences between solar radiation temperature and outdoor air temperature to modify the simulation results. The second method uses measurement inside ceiling glass temperature and simulation indoor temperature to estimate the radiation heat transfer effect and modify the simulation results. The research results show that the second method is more precise than the first method.

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45

Chang, Yu-Yuan, and 張育源. "Simulation and Analysis Technology of the Thermo-Flow Field inside a Moving Office." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/58ry67.

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碩士
國立臺北科技大學
車輛工程系所
96
Fluid flow and heat transfer phenomena in nowadays has been exist in nature and others field, while the numerical analysis of CFD (Computational Fluid Dynamics) can simulate these complex physical phenomena systematically. In recent years CFD has widely been used to analyze the airflow structure of vehicular cabin, which to step out the development of research time and resources saving, and accurate analysis of various thermo-flow field inside a vehicular cabin. This study will carry out the simulation and analysis of thermo-flow field for Ford E350 cabin that establish the influence of the thermal comfort of manikins which the internal configuration were already modified. Research methods used CFD software - FLUENT module for the thermo-flow of temperature, pressure and velocity distribution, and take into account the solar radiation, physiological heat of manikins and heat sources, in addition, the grid adaption technology will use to increase the accuracy of simulation results and quote from PMV and PPD index of ISO 7730 to estimate the thermal comfort of manikins. Simulation results show that by the change of internal configuration of vehicular cabin, the thermal comfort is not generally comfortable, because the vent location of inlet and outlet can not removed the heat effectively from the inside, in the future, we can apply an air flow management technique to improve the thermal comfort for its.

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46

CHU, PO-CHANG, and 朱柏昶. "Two-Dimensional and Three-Dimensional Simulation of Flow and Thermal Fields in Internal Combustion Engines." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/98999838633935526135.

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碩士
中華大學
機械工程學系碩士班
102
A high order differential algorithm has been carried to solve the unsteady compressible Navier-Stokes equations for a moving grid. The order of differencing is raised progressively from the walls toward the center of the cylinder, enabling oscillation free and accurate calculations on a very coarse grid. The numerical fluxes are integrated based on the dual-time stepping of the preconditioned matrix with a third-order Runge-Kutta scheme. The absolute pressure is enforced from the global mass conservation at the instantaneous grid. The predicted results of the absolute pressure, temperature, and velocity components of the fluid inside the cylinder at any instant during the start-up and the periodically stable periods are compared well with the results given in the literature. Further, a study on engine speed, compression ratio, and the shapes of cylinder head is present to reveal the nonequilibrium behavior of the flow. Finally, the solution is extended to three-dimensional for a square piston under the same operating condition of the two-dimensional one. This gives a quick check on the three-dimensional flow solver and a good examination of the corner flow on the boundary layer and also the heat transfer.

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47

TruongNguyen and 阮長. "Numerical Simulation of Thermal and Flow Fields in a Double-Acting Alpha-Type Stirling Engine." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/68438573855544272855.

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48

Yeh, Bea-Chun, and 葉碧純. "Three-Dimensional Global Simulation of Thermal and Flow Fields in Horizontal Zone Melting Crystal Growth System." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/01603419275286172676.

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Анотація:

碩士
國立臺灣大學
化學工程學研究所
92
The hot zone design is the most important task to decide the growth interface, the quality of the crystal and the growth rate. A computational model has been developed to simulate the three-dimensional global thermal and flow fields in horizontal zone melting crystal growth system. The method is so called “ two-level model”, which includes global model and local model. The global model includes the whole crystal growth system. We use the commercial Computational Fluid Dynamics software to combined convection/conduction/surface-to-surface radiation calculations. The melt convection and growth interface calculations in the local model are then made by the an efficient Finite volume method using multigrid acceleration within ampoule, feed, crystal, and melt, with the boundary conditions supplied by the global model simulations. The growth interface shape can be modified in the next global model simulation. The backwards and forwards calculations can be carried out until the thermal fields convergence. We also discuss the effects of gas flow on the global thermal fields and interface shape. Finally, we discuss some influences on the interface shape. To combine the two-level model can be efficient to analyze the global thermal fields and interface shape and it is helpful to design the hot zone in crystal growth system.

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49

Hsi-YaoYang and 楊錫堯. "Numerical Simulation of Three-Dimensional Thermal and Flow Fields in a Four-Cylinder Double-Acting Stirling Engine." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/kkk827.

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50

Chu, Chia-bao, and 朱家葆. "Numerical Simulations of Thermal-Fluid Fields and Fluid-Structure Interactions for an Alpha Type Stirling Engine." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/77203950858312114000.

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Анотація:

碩士
逢甲大學
航太與系統工程所
99
In this study, the numerical method is applied to solve the two-dimensional thermal-fluid field of an Alpha type Stirling engine. The effect of related parameters on the power output of the engine is investigated. The parameters include charge pressure, temperature of hot end, the size of the regenerative channel, phase lag, rotational speed, the porosity of the regenerator, working fluid, bore/stroke ratio and so on. For the case of thermal-fluid simulation, rotational speed is assumed to be constant. However, whenever the effect of fluid-structure interaction with rigid body motion on the performance of the engine take into account, this constrain is relaxed. The numerical results of these two simulations are in comparison with each other. The prototype of the engine is an Alpha type Stirling engine. The dynamic simulation and the adaptive grid generation are utilized in the numerical computations. It is assumed that the working fluids is compressible ideal-gas and the flow is transient and turbulent.

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