Dissertations / Theses on the topic 'Solidification systems'
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Verma, Sudeep. "Computational study of phase change and melt turbulence using PANS modelling in solidification systems." Thesis, IIT Delhi, 2019. http://eprint.iitd.ac.in:80//handle/2074/8054.
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Mehrle, Yvonne E. "Solidification and contraction of confectionery systems in rapid cooling processing." lizenzfrei, 2007. http://e-collection.ethbib.ethz.ch/view/eth:30497.
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Alcantara-Ortega, Elena. "Alkali-activated clinoptilolite, properties and use in solidification/stabilisation systems." Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.397147.
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Meco, Halim. "Solidification at the High and Low Rate Extreme." Washington, D.C. : Oak Ridge, Tenn. : United States. Dept. of Energy. Office of Science ; distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2004. http://www.osti.gov/servlets/purl/835376-9UiMWH/webviewable/.
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Aboutalebi, M. Reza. "Modelling of turbulent transport phenomena and solidification in continuous casting systems." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=41514.
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A numerical modelling study has been undertaken to analyze transport phenomena in various steel casters. During the course of this work, a general three-dimensional parabolic heat flow model was developed for casters of arbitrarily shaped mould using a body-fitted coordinate transformation technique. The heat flow model was specifically applied to a beam blank caster as well as to an industrial slab caster of regular rectangular cross section, so as to analyze solidification within casters.Furthermore, a fully coupled turbulent flow and solidification model was developed to describe the turbulent transport processes in the upper part of a steel slab caster as well as to evaluate the process variables affecting the casting. Solidification modelling was carried out using a fixed grid enthalpy method while the mushy zone was modelled based on a Darcy-porosity approach. A modified low-Reynolds number version of the $ kappa$-$ epsilon$ model of turbulence was employed to calculate eddy viscosity within the liquid and mushy regions. A control volume based on finite difference method was used to solve the transport equations, wherein a SIMPLER algorithm was adopted to resolve the velocity-pressure coupling in the momentum equations. In order to verify the turbulent flow model, a water modelling study was performed for fluid flow in the mould region of a slab caster. Reasonable agreement was obtained between the mathematical model's predictions, and water modelling experiments.
Macrosegregation of carbon in a steel billet caster was also modelled based on a continuum formulation, in which the conservation equations are derived in terms of mixture dependent variables. The effect of turbulence on the transport of solute in the liquid and mushy regions was taken into account using the $ kappa$-$ epsilon$ model adopted in this work.
Various parametric studies have been preformed on different casting systems, and their effects on temperature distributions and velocity fields within the strand, solidification profiles, and trajectories of inclusions were predicted. Typical predicted results of the models have been compared against the experimental measurements on operating casters reported in the literature and relatively good agreement was obtained.
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Ahmad, Nasir. "Numerical simulation of transport processes in multicomponent systems related to solidification problems /." [S.l.] : [s.n.], 1995. http://library.epfl.ch/theses/?nr=1349.
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Shuleshova, Olga. "Equilibrium and metastable solidification in Ti-Al-Nb and Al-Ni systems." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-38636.
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The presented work reports on the solidification studies in two alloy systems: the niobium bearing γ-TiAl, relevant for the automotive and aero-engine applications, and aluminium rich Raney-Ni, precursor alloys for catalyses used in the chemical industry. The time-resolved observations of equilibrium liquid-solid phase transformations, as well as non-equilibrium solidification from the undercooled melt, are performed by combination of in situ structural studies using high-energy X-rays at a synchrotron source and the electromagnetic levitation technique. Containerless processing assured the contamination-free environment leading to high undercooling levels even at moderate cooling rates.
For the critical part of the Ti-Al-Nb phase diagram an equilibrium involving the liquid phase is deduced from the phase transformations gathered on heating periods of levitation experiment. New experimental data on the partial liquidus and solidus surfaces are delivered as well as the information on the nature of the reactions along the univariant lines. These data provide a valuable contribution to the reassessment of the thermodynamic description. The primary phase selection as function of undercooling is studied in ternary Ti-Al-Nb alloys. The metastable formation of the cubic β phase within the primary solidification region of the hexagonal α phase is observed with increasing melt undercooling. Furthermore, the microstructure evolution of the β solidifying Ti-46Al-8Nb alloy discloses the transition to the thermal growth mode for ∆T>200−250 K, accompanied by complete solute trapping. Supplemented with the data on the solidification velocity determined as function of melt undercooling, this results are discussed within the local non-equilibrium model of the free dendrite growth.
The in situ observations of the non-equilibrium solidification of the binary Al-Ni system give insight into multiple phase transformation sequence. The achieved undercooling levels up to 320 K for the aluminium alloys containing 18–31.5 at.% Ni did not alter the primary phase selection. However, during further cooling of L+Al3Ni2 semisolid samples the peritectic formation of a metastable decagonal quasicrystalline phase is observed providing a critical undercooling below the peritectic temperature of Al3Ni phase is reached. On further cooling the metastable phase subsequently transforms into the equilibrium Al3Ni. A similar solidification pathways are expected for the Raney-Ni alloys produced by gas atomisation, where the associated high cooling rates allowed to retain the metastable phase at room temperature.
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Iyengar, S. R. "Application of two novel magnesia-based binders in stabilisation/solidification treatment systems." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604975.
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Portland cements (PC) and blended PCs are the most commonly used binders in stabilisation/solidification (S/S) applications. However, such systems have found limited suitability with organic contaminants. Moreover, the high alkalinity associated with PC militates against the soil microbes and hence, hinders the natural attenuation of the organics. Furthermore, the production of PC is not only an extremely resource and energy intensive process but also has significant negative environmental impacts. Thus, with the aim of tackling the above issues, this research has been focused on firstly developing and applying a low-pH binder system for facilitating microbial activity in parallel to the S/S of heavy metals, and additionally on investigating the application of less environmentally damaging cement in S/S. These were addressed employing two novel binders; viz. low pH magnesia phosphate cements (MPCs) and reactive magnesia (MgO) cements respectively. This study was successful in formulating MPC mixes which not only developed low-pH ranges favourable to soil microbes but were also more effective in immobilising heavy metals than PC-based binders in an individual contamination scenario. Furthermore, the heavy metal stabilisation performance of the MPC mixes suffered negligible impact in the presence of organic contaminant.
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Juarez-Hernandez, Arturo. "Growth temperature measurements and solidification microstructure selection in Al-Ni and Al-lanthanide systems." Thesis, University of Sheffield, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301607.
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Berry, Joel. "Liquid-solid systems out of equilibrium: phase-field crystal studies of solidification, melting, and plasticity." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=106330.
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Dynamic processes in nonequilibrium liquid-solid systems are studied over mesoscopic time scales and atomistic length scales using phase-field crystal (PFC) models. Various freezing and melting transitions are examined in two and three dimensions, and microscopic phenomena responsible for solid-phase plasticity are investigated. A primary focus is on the issue of describing atomistic dynamics over time scales that are generally inaccessible to conventional approaches. Glass forming dynamics in supercooled liquids near a glass transition are studied numerically, and the central features of the transition, including a number of behaviors previously undemonstrated within PFC / classical density functional theory simulations, are successfully reproduced. A connection between the liquid dynamic correlation length and transition fragility is identified, and a physically motivated time scaling applied to the simulation data is shown to generate qualitative agreement with basic glass transition phenomenology across 12 orders of magnitude in time. The competing processes of amorphous precursor nucleation and crystallization in diffusion-dominated spinodal and non-spinodal simple liquids are also examined. Melting and premelting transitions in defected body-centered cubic solids are studied numerically, and a localized melting theory based on defect elastic energies is formulated. Basic features of the dynamic phase separation patterns that develop in growing heteroepitaxially strained alloy films are also outlined based on numerical simulations of a binary PFC model. Finally, dislocation dynamics are examined in strained periodic systems. The central features of dislocation glide, climb, and annihilation are shown to naturally emerge within PFC models, and the dynamics of individual dislocations are found to reduce to a simple generalized equation of motion.Des procédés dynamiques dans des systèmes liquide-solide non-équilibrés sont étudiés au cours d'échelles de temps mésoscopiques et d'échelles de longueur atomistiques en utilisant des modèles « phase-field crystal » (PFC). Diverses transitions de congélation et de fusion sont examinées en deux et trois dimensions, et les phénomènes microscopiques responsables de la plasticité des phases solides sont étudiées. Un accent est mis sur la problématique des dynamiques atomistiques au cours d'échelles de temps qui sont généralement inaccessibles aux approches conventionnelles. Les dynamiques de formation vitreuse dans les liquides metastables surfondus près d'une transition vitreuse sont étudiés numériquement, et les caractéristiques centrales de la transition, y compris un certain nombre de comportements qui n'ont pas été démontrées précédemment par les modèles PFC / simulations de la théorie classique densité fonctionnelle, sont reproduites avec succès. Un lien entre la longueur de corrélation dynamique liquide et la fragilité est identifié, et il est démontré par une normalisation de temps physiquement motivé, appliquée aux données de simulation, qu'il y a une correspondance qualitative avec des bases phénomènes de transition vitreuse sur 12 ordres de grandeurs de temps. Les procédés concurrentiels de la nucléation de précurseurs amorphes et de la cristallisation dominées par la diffusion dans les liquides simples spinodaux et non-spinodaux sont aussi examinés. Les transitions de fusion et pré-fusion dans des solides cubiques centrés ayant des défauts sont étudiés numériquement, et une théorie de fusion localisée basée sur les énergies élastiques des défauts est formulée. Des caractéristiques de base des motifs de la séparation de phase dynamique qui se développent pendant la croissance des films tendus heteroepitaxiellement sont également etudiés en utilisant des simulations numériques d'un modèle binaire PFC. Enfin, les dynamiques des dislocations sont examinées dans les systèmes périodiques tendus, ainsi il est démontré que les caractéristiques fondamentales des procédés de glisse, d'escalade, et d'annihilation émergent naturellement des modèles PFC.
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Benítez, Iglesias Raúl. "Phase-field study of transient stages and fluctuations in solidification." Doctoral thesis, Universitat Politècnica de Catalunya, 2005. http://hdl.handle.net/10803/6583.
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L'estudi de la formació de microstructures en processos de solidificació té importants aplicacions científiques i tecnològiques. L'aparició d'aquestes estructures determina les propietats elèctriques i mecàniques del material solidificat, i té per tant un important interès tecnològic. La majoria d'aquestes estructures tenen el seu origen en una desestabilització morfològica de la interfase sòlid-líquid que es produeix a mesura que el front avança. Per aquest motiu, l'estudi del comportament dinàmic de la interfase resulta essencial per entendre els mecanismes que intervenen en la creació d'aquests patrons. Els processos de solidificació solen descriure's mitjançant problemes de contorn mòbil. Aquestes formulacions consten d'equacions per a la difusió del calor i de massa en les fases sòlida i líquida, que s'han de resoldre imposant l'acompliment de diverses condicions de contorn mòbils a la interfase. Els problemes de contorn mòbil, malgrat contenir tots els elements que intervenen en la dinàmica i ser de molta utilitat en l'àmbit de l'enginyeria, requereixen un cost computacional que no permet simular sistemes reals en règims interfacials complexos.
Els mètodes de camp de fase (phase-field methods), van aparèixer a principis dels anys vuitanta com una eina computacional que permetia l'estudi de fenòmens interfacials de caire general. Aquests mètodes descriuen la forma de la interfase mitjançant un camp continu que pren valors diferents i constants en les dues fases. La dinàmica d'aquest camp és llavors acoblada al camp de difusió de calor o massa que determina l'avanç del front de solidificació. Un dels avantatges d'aquests mètodes és que la seva simulació no requereix d'algorismes de seguiment de la interfase (front tracking algorithsms).
És ben conegut que les característiques principals de les microestructures en solidificació, es determinen durant els transitoris inicials en els que els corrents de massa i calor s'adapten a la evolució dinàmica del front. Un dels objectius en aquesta tesi és el de fer servir mètodes de camp de fase per descriure de forma quantitativa aquests transitoris. Per comprovar la validesa del nostre procediment, es realitza una comparació quantitativa entre els resultats numèrics obtinguts i diferents prediccions analítiques derivades del problema de contorn mòbil.
Per un altra banda, la desestabilització del front es veu afectada per la presència de fluctuacions al sistema. Aquestes pertorbacions microscòpiques poden tenir el seu origen a les fluctuacions termodinàmiques internes, o bé ser conseqüència de imperfeccions experimentals que actuen com a font externa de soroll. El segon objectiu d'aquesta tesi és la introducció de fluctuacions en mètodes de camp de fase, de forma que es pugui estudiar l'amplificació dinàmica de les pertorbacions microscòpiques que acaben donant lloc a estructures macroscòpiques.
Per finalitzar, analitzem el problema de la selecció en solidificació direccional. Estudiem els règims lineal i no-lineal, tot determinant les condicions, el moment i la forma en que apareixen les estructures dendrítiques i cel·lulars.
Crystal growth is a non-equilibrium process which involves physical mechanisms at very different scales. When a solidification front advances, mass and heat diffusion processes are combined with interfacial phenomena like capillarity or kinetic attachment. A complex interplay between these mechanisms gives rise to complex interfacial structures like snowflakes or cellular patterns.
The formation of microstructures in solidification has both a scientific and a technological interest. On one hand, the study of the different interfacial structures constitutes a fundamental problem in the field of non-equilibrium pattern-forming systems. On the other side, from a technological point of view, the presence of microstructures determines the final mechanical and electrical properties of the processed material.
Directional solidification is a controlled solidification technique which reproduces the conditions occurring in some important metallurgical processes like material casting or zone melting refining procedures. In a directional solidification experiment, the alloy sample is pulled at a constant velocity towards the cold region of an externally-imposed temperature gradient. Depending on the growth conditions, a morphological destabilization of the solid-liquid interface occurs during early transient stages. These initial transients are associated to a solute redistribution process due to the adaptation of the concentration field to the forced motion of the sample. The main objective of this thesis is to study the dynamical evolution of the morphological deformations of the front from these initial transients to the final stages where the properties of the interfacial pattern are determined.
An important point in this process is that the internal fluctuations of the system play the role of an initiation mechanism for the morphological deformations of the front. During the initial transients, some of these microscopic perturbations are amplified by several orders of magnitude, and a range of wavelengths becomes morphologically unstable. The interfacial deformations of the front can be then characterized by means of power spectrum techniques.
In order to study the dynamical evolution of the solidification front in directional solidification, we have used both theoretical and computational approaches:
The main computational technique used in this thesis is the phase-field approach, which is a powerful method to simulate complex interfacial phenomena. The model equations describe the evolution of a continuous field , which takes different constant values at the solid and liquid bulks of the system. This field is then coupled with equations for the mass diffusion, and allows performing numerical studies without simulating the standard Stefan-like moving boundary problem. The phase-field method provides a diffuse interface description in which the transition from solid to liquid happens in a region of a certain thickness. The interface thickness introduces a new length in the simulations which must be taken into account to recover quantitative results.
One major point in this thesis concerns with the introduction of fluctuations in phase-field methods. In the particular case of variational phase-field formulations -in which the model equations can be derived from a single free energy functional for the whole system-, the introduction of fluctuations can be done by applying the Fluctuation-Dissipation theorem. Variational formulations, however, although their appealing structure, present a poor computational efficiency and cannot be used to obtain quantitative results. To this extent, we have derived a general approach which does not relay in the Fluctuation-Dissipation assumption and permits to introduce fluctuations in both variational and non-variational phase-field formulations.
Well-established analytical techniques like boundary integral methods for the transient front position and linear stability analysis of the interface during the transient have been used as theoretical predictions for the computational results.
The dynamical evolution of the solidification front can be divided in two stages: A linear regime where the initial noise is amplified, and a non-linear coarsening process where the final properties of the interfacial pattern are selected. We have studied these different stages of the solidification process by using the phase-field approach, and good agreement is obtained when comparing with well-established theoretical and experimental predictions.
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Nguyen, Hong Trung. "Coarse-grained Modeling Studies of Polymeric and Granular Systems." Scholar Commons, 2018. http://scholarcommons.usf.edu/etd/7202.
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This Dissertation is devoted to computational study of the solidification, dynamics and mechanics of model semiflexible polymers with variable chain flexibility as well as a computational investigation of the clogging phenomena observed in granular materials.
Chain stiffness is an intrinsic factor that governs single-chain flexibility. It plays a critical role in the physics of polymeric materials. In this work, we employ a coarse-grained polymer model in which chain stiffness can be tuned by a single parameter (bending stiffness kb) that yields chain shape ranging from coil-like to rod-like in the flexible and very stiff limit respectively. In chapter 2, we focus on how chain stiffness affects how polymer melts solidify under thermal cooling. We observe a strong dependence of the solid-state morphology (formed after cooling) upon chain flexibility. In the flexible limit, we find that monomers possess crystalline order while chains retain random-walk like structure. In higher stiffness regime glass formation is obtained while nematic ordering typical of lamellar precursors coexists with close-packing in the rod-like limit. Surprisingly we observe various structures ranging from spiral, to multi-domain nematic phases in the intermediate values of kb.
In chapter 3 we go a step further to relate the solidification behaviors of chains discussed in chapter 2 to their melt dynamics. We probe the microstructure and the dynamics of flexible, intermediate-stiffness and rod-like chains. We find that melts of flexible and stiff chains that crystallize under cooling show simple and fast dynamics with Arrhenius temperature dependence. Interestingly, the intermediate-stiffness chains exhibit Vogel-Fulcher dynamical relaxation typical of fragile glass-formers even though their ground states is a nematic-close-packed crystal. There is no compelling argument based on static micro-structure change explaining this dynamical arrest to be found. However, we find that the dynamics of intermediate-stiffness chains is dominated by the stringlike cooperative motion that correlates along their chain backbones. This cooperative rearrangement which is absent in other systems appears to be the main cause of the dynamical arrest observed for intermediate-stiffness chains.
In chapter 4, we turn to another class of materials where the negligible contribution of thermal fluctuations gives rise to an interesting phenomenon, i.e. the clogging transition. Clogging is a probabilistic event that occurs through a transition from a homogeneous flowing state to a heterogeneous or phase separated jammed state. The granular system under study is an assemble of bidisperse disks externally driven through a two dimensional periodic substrate. We find that the probability for clogging strongly depend on particle packing, obstacle number and the driving direction. Surprisingly, under relevant conditions we observe a size-specific clogging transition in which the smaller species get trapped while the larger species keep flowing.
Chapter 5 returns to discuss the polymer solidification in the context of isostaticity. Results from the simulations of semiflexible polymers described in chapter 2 allow us to derive a generalized isostaticity criterion that can be applied to finite-stiffness chains. The new criterion is based on the characteristic ratio C which characterizes the slow freezing out of configurational freedom of chains as chain stiffness increases. The results of the average coordination number at solidification Z(Ts) suggest a link between jamming in athermal systems and solidification in their thermal counterparts.
Finally, in chapter 6 we study the effect of chain stiffness on the mechanical response of glassy polymers. We investigate shear deformation of three systems with a different degree of entanglement. We find that loosely entangled chains display strong shear banding and undergo fracture via chain pullout. In contrast, tightly entangled chains fail at high enough strain along a well-defined plane via chain scission shortly after chains are pulled taut. We explain these chain-stiffness-dependent behaviors qualitatively using the segmental packing efficiency argument and quantitatively using modern plasticity measures
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Erdiller, Emrah Salim. "Investigation Of Solidification And Crystallization Of Iron Based Bulk Amorphous Alloys." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/3/1096585/index.pdf.
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The aim of this study is to form a theoretical model for simulation of glass forming ability of Fe �
Based bulk amorphous alloys, to synthesize Fe &
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based multicomponent glassy alloys by using the predictions of the theoretical study, and to analyze the influence of crystallization and solidification kinetics on the microstructural features of this amorphous alloys. For this purpose, first, glass forming ability of Fe &
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(Mo, B, Cr, Nb, C) &
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X ( X = various alloying elements, selected from the periodic table) ternary alloy systems were simulated for twenty different alloy compositions by using the electronic theory of alloys in pseudopotential approximation and regular solution theory. Then, by using the results of the theoretical study, systematic casting experiments were performed by using centrifugal casting method. The alloying elements were melted with induction under argon atmosphere in alumina crucibles and casted into copper molds of different shapes. Characterization of the cast specimens were performed by using DSC, XRD, SEM, and optical microscopy. Comparison of equilibrium and nonequilibrium solidification structures of cast specimens were also performed so as to verify the existence of the amorphous phase. Good agreement of the results of experimental work, with the predictions of the theoretical study, and the related literature was obtained.
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NIRMALANANDHAN, VICTOR SANJIT. "HEAT TRANSFER AUGMENTATION FOR EXTERNAL ICE-ON-TUBE TES SYSTEMS USING POROUS COPPER MESH TO INCREASE VOLUMETRIC ICE PRODUCTION." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1100796827.
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Sheridan, Luke Charles. "An Adapted Approach to ProcessMapping Across Alloy Systems and Additive Manufacturing Processes." Wright State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=wright1471861921.
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Asavapisit, Suwimol. "Solidification system for metal containing hazardous wastes." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287950.
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Lin, JiaCheng, and HaoRan Teng. "Influence of Nucleation Techniques on the Degree of Supercooling and Duration of Crystallization for Sugar Alcohol as Phase Change Material : Investigation on erythritol-based additiveenhanced Composites." Thesis, KTH, Energiteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-257758.
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Utilizing Phase Change Materials (PCM) for Latent Thermal Energy Storage (LTES) applications have previously been extensively researched as a measure to reduce greenhouse gas emissions from energy consumption. In order to make use of the waste heat from industrial processes for LTES purposes, a new demand emerged for PCMs capable of phase change in mid-temperature ranges of 100 °C - 200 °C. This higher temperature requirement made most of the previously studied material inapplicable as they had much lower melting and solidification temperatures. With this in mind, a new generation of PCMs consisting of Sugar Alcohols (SA) has been proposed. Erythritol is seen as an especially promising SA with good thermophysical properties for LTES purposes. However, it has been shown to suffer from severe supercooling, which makes it unreliable in real applications. To eradicate this issue, two additives, Graphene Oxide (GO) and Polyvinylpyrrolidone (PVP) at varying mass fractions were mixed with pure erythritol to form a composite which was studied using the Temperature-history (T-history) method to determine its effectiveness in reducing supercooling. Results show that at its most effective mass fraction, GO reduces supercooling by 28 o C and a 31 o C reduction is seen by the addition of PVP. The impacts on the duration of crystallization was also documented and analyzed using the same method. It was observed that the duration of crystallization was increased with increasing mass fractions of the additives. Other important properties of the composites were also studied in order to determine the overall feasibility for industrial applications. It includes analysis of the storage capacity through latent heat, changes in viscosity along with impacts on thermal diffusivity of the composites.Att använda fasändringsmaterial (PCM) för termisk energilagring i form av latent värme (LTES) har tidigare extensivt forskats och undersökts som en lösning för att minska utsläppen av växthusgaser från energiförbrukning. För att utnyttja spillvärme från industriella processer för LTES-ändamål uppstod en efterfrågan på PCM som ändrar fas i temperaturer mellan 100 °C - 200 °C. Detta krav på högre temperatur gjorde att de flesta av de tidigare aktuella materialen inte kunde tillämpas eftersom de hade mycket lägre smält- och kristalliseringstemperaturer. Med detta i åtanke har en ny generation av PCM bestående av sockeralkoholer (SA) föreslagits. Erytritol ses som ett särskilt lovande SA med goda egenskaper för LTES-ändamål. Den har dock visat sig drabbas av svår underkylning, vilket gör den opålitligt i verkliga tillämpningar. För att utrota detta problem blandades två tillsatser, Graphene Oxide (GO) och Polyvinylpyrrolidone (PVP) vid olika massfraktioner med ren erytritol för att bilda en komposit som studerades med metoden Temperature-history (T-history) för att bestämma dess effektivitet på att minska underkylningen. Resultaten visar att GO på sin mest effektiva massfraktion minskar underkylningen med 28 o C och tillsats av PVP lyckats minska den med som mest 31 o C. Påverkningarna på varaktighet av kristallisering dokumenterades och analyserades med samma metod. Det var observerad att varaktigheten av kristallisering ökades med ökande massfraktioner av tillsatserna. Även andra viktiga egenskaper hos kompositerna studerades för att avgöra rimligheten att använda dessa för industriella tillämpningar. Det inkluderar analys av lagringskapaciteten genom latent värme, förändringar i viskositet tillsammans med påverkan på kompositernas termiska diffusivitet.
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DeZego, Shawn Edward. "Experimental investigation of convective effects during solidification of a binary system in the continuous cast." FIU Digital Commons, 1996. http://digitalcommons.fiu.edu/etd/2789.
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A laboratory scale continuous casting facility is constructed to experimentally study the solidification of a binary system. Both initial and boundary conditions are varied in a parametric analysis to determine effects that these conditions have on convective transport in the critical liquid region of the continuous cast. A transparent Ammonium-Chloride and Water (NH4Cl-H20) solution is used to simulate cubic alloy solidification due to its dendritic microstructure. A hybrid Schlieren system is constructed to perform flow visualizations of heat and species transport for both eutectic and noneutectic solidification. Thermal and solutal profiles are measured via thermocouple grids and a multisensor fiber optic machine. Morphology images are also captured to serve as a photographic record of the two-phase region width along with tracking of the solidus and liquidus interfaces with respect to the mold walls. This data is used to substantiate origins and causes of defects known as macrosegregation in final casts.
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Jureidini, Imad Maurice. "Design and performance of a compact high-energy computed tomography system for the study of metal solidification." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/50534.
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Chen, Chih-Chang. "Evaluation of weld solidification cracking in aluminum alloys A1- 2219 and A1-2090 using the Gleeble 1500 system /." The Ohio State University, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487687115924536.
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KUROWSKI, PASCAL. "Etude experimentale d'un systeme hors d'equilibre fortement non-lineaire : fronts cellulaires en solidification directionnelle d'un alliage dilue (cbr#4)." Paris 7, 1990. http://www.theses.fr/1990PA077055.
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Lorsqu'on solidifie un alliage binaire dilue par tirage dans un gradient de temperature (solidification directionnelle), l'interface solide-liquide presente au-dela d'une vitesse critique v#c une deformation cellulaire periodique. Quand on augmente la vitesse de tirage, ces cellules se transforment en dendrites a tres grande vitesse. Nous utilisons des echantillons minces transparents de tetrabromomethane (cbr#4), contenant environ 0,15% d'impuretes (br#2). Nous avons etudie les formes des cellules et la dispersion de leur largeur, depuis le seuil d'apparition d'instabilite jusqu'aux premiers branchements dendritiques. Nous avons mis en evidence deux regimes selon l'ecart relatif au seuil: 1) un regime cellulaire jusqu'a des ecarts relatifs au seuil d'environ 5. La dispersion des largeurs cellulaires est faible et est du meme ordre de grandeur que celle due au bruit experimental (10 a 15%); la longueur d'onde moyenne varie en v##0#,#4; les cellules obeissent a une loi d'echelle: des cellules de differente largeur, reduites en unite de se superposent pour un meme ecart relatif au seuil; 2) un regime predendritique pour des ecarts relatifs au seuil de plus de 8; la dispersion des largeurs de cellules le long d'un front donne augmente de facon spectaculaire (la longueur cellulaire pouvant varier d'un facteur 3); on observe sur un meme front coexistence de cellules de morphologie differente: des cellules etroites qui ont les memes proprietes que dans le regime cellulaire et les cellules plus larges qui sont plus pointues; a partir d'un ecart au seuil 10, les premiers branchements dendritiques apparaissent uniquement sur les cellules les plus larges. L'apparition des branches est un phenomene local qui a lieu pour des nombres de peclet superieurs a 2-3 et le passage cellules-dendrites n'est pas une bifurcation globale
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Gaubil, Michel. "Etude de la solidification de materiaux refractaires appartenant au systeme quaternaire al#2o#3-zro#2-sio#2-na#2o." Orléans, 1996. http://www.theses.fr/1996ORLE2022.
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Les ceramiques refractaires electrofondues que nous avons etudiees sont des materiaux elabores par solidification et refroidissement de fontes d'oxydes liquides. Ils sont destines a la construction de fours de fusion du verre et leurs compositions appartiennent au systeme quaternaire al#2o#3 - zro#2 - sio#2 - na#2o. Les chemins de solidification des fontes industrielles ont ete determines en utilisant conjointement l'atd haute temperature, la drx et des analyses micrographiques. Afin de faciliter l'interpretation des resultats, nous avons etudie en parallele des produits de synthese de compositions voisines, appartenant au systeme ternaire al#2o#3 - zro#2 - sio#2 et au systeme quaternaire al#2o#3 - zro#2 - sio#2 et na#2o. La solidification des fontes refractaires conduit a la cristallisation primaire de la zircone, a la cristallisation de l'eutectique corindon zircone ou a la cristallisation separee de zircone et de corindon selon la concentration en na#2o et enfin a la formation d'une phase vitreuse interstitielle. La presence de na#2o meme en faible quantite dans le produit inhibe la formation de mullite. La phase vitreuse interstitielle conditionne un certain nombre de proprietes du materiau. C'est un materiau polyphase compose pour partie d'une phase vitreuse au sens reel du terme qui contient la totalite de l'oxyde de sodium, la quasie totalite de la silice, une fraction de l'alumine initiale du produit et une faible proportion de zircone. Les experiences rmn #2#9si et #2#7al haute resolution sur les echantillons industriels ont apporte des informations importantes concernant la structure a l'echelle microscopique. La comparaison avec des phases synthetiques de compositions similaires a la partie vitreuse a permis une meilleure comprehension du comportement de cette phase lors de la solidification du refractaire et au recuit. L'inhibition de la croissance des germes mullitiques au cours de la fabrication a ete associee a la presence des 1700c de cristaux de zircone et de corindon. Le suivie resolue dans le temps par analyse rmn #2#7al a tres hautes temperatures du refroidissement des echantillons de compositions proches de celles des refractaires industriels a mis en evidence un changement brusque de l'evolution de la structure locale du liquide surfondu avec la temperature. Ce comportement est associe au figeage progressif des coordinences iv, v et vi de l'aluminium dans le materiau vitrifie. Cette etude a par ailleurs montre que le processus de relaxation spin-reseau (#c) en rmn et celui du flux visqueux peuvent etre associes a des fluctuations microscopiques de meme nature. La presence de na#2o conduit a une depolymerisation du liquide surfondu et favorise la devitrification du verre. L'ensemble des resultats montrent que la zircone influence le comportement du liquide surfondu, l'evolution de la viscosite avec la temperature, la structure a l'echelle des phases vitreuses et la recristallisation des verres
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TOGUYENI, DAVID YEMBOINI. "Etude des changements de phase dans les systemes thermodynamique a deux especes chimiques : solidification, dissolution et fusion hors equilibre thermodynamique initial." Paris 6, 1994. http://www.theses.fr/1994PA066278.
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Cette these est consacree a l'etude des changements de phase, avec coexistence de deux phases initiales, dans les fluides a deux composants chimiques. Les transitions de phase etudiees sont la solidification avec equilibre thermodynamique initial, la dissolution et la fusion hors equilibre thermodynamique unidimensionnelles. Deux algorithmes sont developpes et utilises pour simuler la solidification des solutions aqueuses de chlorure de sodium. Une comparaison portant sur la rapidite de calcul et la precision des resultats des deux algorithmes est faite, puis les champs de temperature, de fraction massique (de solute) et la position du front solide-liquide sont analyses. En ce qui concerne les transitions de phase hors equilibre thermodynamique initial (fusion, dissolution), un processus d'initialisation du calcul est propose pour rendre compte de l'instauration de l'equilibre thermodynamique qui se produit au bout d'un temps inconnu a priori ; l'algorithme le plus rapide et le plus precis est ensuite utilise pour determiner les champs de temperature et de fraction massique dans les deux phases, aux instants posterieurs a l'instauration de l'equilibre thermodynamique, avec comme fluide binaire des solutions aqueuses de carbonate de sodium
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Chatelain, Marc. "Modélisation des phénomènes de transport solutal et étude d’un dispositif de brassage pour la purification du silicium photovoltaïque." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI105/document.
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Cette étude s’intéresse à la modélisation de la ségrégation des impuretés lors des procédés de solidification dirigée du silicium pour l’industrie photovoltaïque. Il s’agit d’un problème multi-physiques et multi-échelles qui nécessite des modèles efficaces pour pouvoir traiter des configurations industrielles en 3D. La première partie de l’étude porte sur le développement de fonctions de paroi solutales dans le but d’estimer la ségrégation sans résoudre numériquement la couche limite solutale. Un modèle analytique est alors utilisé pour estimer le paramètre convecto-diffusif à partir de la contrainte de frottement à l’interface solide/liquide. L’approche proposée consiste à coupler une simulation hydrodynamique de la convection dans la phase liquide et un calcul analytique de la ségrégation. Cette démarche est validée sur un cas de référence en 2D. Le modèle développé fournit une estimation pertinente de la concentration dans un lingot solidifié avec une vitesse imposée, y compris sur un maillage ne résolvant pas la couche limite solutale. La deuxième partie de l’étude concerne l’utilisation d’un système de brassage mécanique dans le but de favoriser la ségrégation des impuretés. Des simulations transitoires de brassage sont réalisées avec le logiciel FLUENT. Les résultats sont comparés à des mesures de champ de vitesse par PIV effectuées sur une maquette en eau, afin de valider le modèle hydrodynamique. La simulation de brassage est ensuite couplée à un calcul de ségrégation en régime quasi-permanent qui permet d’analyser l’influence de l’écoulement sur la couche limite solutale. Dans la dernière partie de l’étude, une simulation de solidification dirigée 3D instationnaire en régime de convection forcée, intégrant la thermique du four, est réalisée. Un modèle empirique de forces volumiques est alors proposé pour décrire l’écoulement lié au brassage dans le silicium liquide. Une première tentative d’estimation des ségrégations par l’approche analytique est ensuite mise en œuvreThe present study focuses on solute segregation during photovoltaic silicon directional solidification. This multi-physics problem involves various spatial and temporal scales. The numerical simulation of this process requires efficient models, especially for 3D industrial configurations. In the first part of the study, solute wall functions are derived from a scaling analysis in order to estimate the segregations without numerical resolution of the solute boundary layer. The method is based on the coupling of an hydrodynamic simulation of convection in the liquid phase and an analytical segregation computation. The developed analytical model provides an estimation of the convecto-diffusive parameter from the wall shear-stress at the solid/liquid interface. A reference case in 2D with imposed solidification rate is used for validation purposes. The developed model provides a meaningful estimation of concentration fields in the ingots. In a second part, we focus on segregation optimization by a mechanical stirrer. Transient stirring simulations, using a sliding mesh technique, are achieved with FLUENT commercial software. Results are compared to PIV velocity field measurements performed on an experimental setup using water. A segregation computation in a quasi-steady regime is then implemented in the stirring simulation. The effect of the stirring parameters are directly observed on the solute boundary layer at the solid/liquid interface. In a third part, a transient solidification simulation, including furnace thermal conditions, is performed in a 3D configuration with forced convection. The flow generated by the impeller is described thanks to an empirical model based on body forces. A first attempt is finally made to retrieve segregations in the ingot with the developed analytical method
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Hassan, Hamdy Abo Ali. "Etude et optimisation des transferts de chaleur en injection moulage : analyse de leur influence sur les propriétés finales." Thesis, Bordeaux 1, 2009. http://www.theses.fr/2009BOR13956.
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Les plastiques sont typiquement des polymères de grand poids moléculaire. Ils peuvent contenir des autres substances pour améliorer leurs performances et/ou pour réduire les prix. L'industrie plastique est l'une des industries qui a la croissance la plus rapide du monde : de nombreux produits de la vie quotidienne contiennent l'utilisation du produit plastique. Il y a différents procédés pour la mise en forme des polymères (soufflage, moulage par soufflage, moulage par compression, moulage par transfert, extrusion, moulage par injection) pour lesquels les matériaux utilisés, la qualité et la forme du produit fabriqué varient. En particulier, la demande des pièces moulées par injection augmente chaque année. Cela vient du fait que le moulage par injection est identifié comme une des techniques de fabrication les plus efficaces et économiques pour produire des pièces en plastique de formes précises et complexes. Il y a trois étapes significatives dans le processus : premièrement, on remplit la cavité avec le polymère fondu à une température et à une pression d'injection élévées (étape de remplissage et bien remplissage). Deuxièmement la chaleur de la pièce en polymère est évacuée par le système de refroidissement (étape de refroidissement). Troisièmement, après que la partie solidifiée a été éjectée, le moule est fermé et le prochain cycle d'injection commence (étape d'éjection)Plastics are typically polymers of high molecular weight, and may contain other substances to improve performance and/or reduce costs. Plastic industry is one of the world?s fastest growing industries; almost every product that is used in daily life involves the usage of plastic. There are different methods for polymer processing (thermoforming, blow molding, compression molding of polymers, transfer molding of polymers, extrusion of polymers, injection molding of polymers, etc.) which differ by the method of fabrications, the used materials, the quality of the product and the form of the final product. Demand for injection molded parts continues to increase every year because plastic injection molding process is well known as the most efficient manufacturing techniques for economically producing precise plastic parts and complex geometry at low cost and a large quantity. The plastic injection molding process is a cyclic process where polymer is injected into a mold cavity, and solidifies to form a plastic part. There are three significant stages in each cycle. The first stage is filling the cavity with hot polymer melt at high injection pressure and temperature (filling and post-filling stage). It is followed by cooling the injected polymer material until the material is completely solidified (cooling stage), finally the solidified part is ejected (ejection stage)
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Silva, Rondinei Almeida da. "Uma Análise Matemática de um Sistema Não Isotérmico do Tipo Allen-Cahn." Universidade Federal de Viçosa, 2014. http://locus.ufv.br/handle/123456789/4934.
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In this present Work We study a model Of phase ñeld rnodeling the evolution of solidiñcation process that Occurs in Certain binary alloys. We obtain existence Of solution and results under the hypotheses of regularity the nonlinearities are Lipschitz and limited. The non-linearity involved in the phase ñeld equation is a potential double-well type. We use throughout the Work the ñxed point theorern Of Leray-Schauder and the Galerkin method.
No presente trabalho estudamos urn modelo de Campo de fase que modela a evolução dos processos de solidiñcação que Ocorre ern Certas ligas binárias. Obte- rnos a existência de solução e resultados de regularidade sob as hipóteses das não linearidades serern Lipschitz e limitadas. A não linearidade envolvida na equação de Campo de fase é urn potencial do tipo poç0-duplo. Utilizamos ao longo do trabalho 0 teorerna do ponto ñXO de Leray-Schauder e 0 rnétodo de Galerkin.
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Candioto, Katia Cristiane Gandolpho. "Solidificação rápida e avaliação de estabilidade de fases de ligas Ti-Si-B." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/97/97134/tde-03102012-115808/.
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Materiais com fases intermetálicas têm sido avaliados para aplicações estruturais em altas temperaturas devido à baixa massa específica e interessantes propriedades de resistência mecânica e resistência à oxidação de vários compostos. As ligas de Ti são reconhecidas pela sua excelente combinação de alta-resistência, baixa massa específica e alta resistência à corrosão. Tendo em vista a importância de estudos em temperaturas na faixa de 700 a 1000 oC para futuras aplicações, avaliou-se neste trabalho as relações de fases do sistema Ti-Si-B na região rica em Ti nesta faixa de temperatura. Sabendo-se que a utilização de técnicas de solidificação rápida permite a obtenção de ligas com maior homogeneidade química e microestruturas finas, utilizou-se a técnica \"splat-cooling\" de solidificação rápida para produção das amostras, no sentido de obter microestruturas de equilíbrio em tempos e temperaturas menores nos tratamentos térmicos. As técnicas de microscopia, difração de raios X, análise térmica e dureza foram utilizadas para caracterização dos materiais. O processo de solidificação rápida (\"splat cooling\") promoveu refinamento de microestrutura e formação de fase amorfa em diversas composições de liga com temperaturas de início de cristalização (Tx) na faixa de 524 a 641oC. Foram confirmadas a estabilidade das fases αTi, Ti6Si2B e Ti3Si a 700oC e 1000oC. Os valores de dureza dos discos solidificados rapidamente ficaram na faixa de 434 HV a 1207 HV.Materials with intermetallic phases have been evaluated for structural applications at high temperatures due to low specific mass and attractive mechanical properties as high-strength and oxidation resistance of various compounds. Ti alloys are recognized for their excellent combination of high-strength, low specific mass and high oxidation resistance. About future applications, studies at temperatures ranging from 700 to 1000 oC are important, we evaluated in this work the phase relationships of the system Ti-Si-B in the Ti-rich region in this temperature range. Knowing that the use of rapid solidification techniques results in alloys with higher chemical homogeneity and fine microstructure, the \"splat-cooling\" technique was used to produce the samples, in order to obtain stable microstructures in lower times and temperatures at the heat treatment. Microscopy, X-ray diffraction, thermal analysis and hardness measurement techniques were used for the materials characterization. The rapid solidification - splat cooling promoted the refinement of microstructure and even the formation of amorphous phase in the microstructure of materials with initial temperatures of crystallization (Tx) in the range from 524 to 641oC. We confirmed the stability of the phases αTi, Ti6Si2B and Ti3Si at 700oC and 1000oC. The hardness of the rapidly solidified discs were in the range of 434 HV to 1207 HV.
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Stodolovská, Šárka. "Vývoj nového chemicky odolného nátěrového systému s obsahem druhotných surovin." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2021. http://www.nusl.cz/ntk/nusl-432472.
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New types of highly chemically resistant coating systems, primarily designed for concrete and metal substrates are designed and experimentally verified within the diploma thesis. Secondary raw materials, including solidified hazardous waste, are used as microfillers. The developed coating system is solved in two quality levels – PREMIUM and ECOLOGY. The level of PREMIUM is mainly designed for environments where extreme chemical stress is occurring. The polymer coating systém ECOLOGY can be used in environments where aggressive chemical media also act, however the ecological foot of the input raw materials is most important. The diploma thesis is dealing with current issues in the practice and it is the part of the research project.
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Poirot, Isabelle. "Etude du neptunium dans un verre borosilicate." Grenoble 2 : ANRT, 1986. http://catalogue.bnf.fr/ark:/12148/cb376004621.
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Schlieter, Antje. "Korrelation mikrostruktureller und mechanischer Eigenschaften von Ti-Fe-Legierungen." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-91907.
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The effect of solidification conditions on microstructural and mechanical properties of eutectic TiFe alloy cast under different conditions was examined. Samples exhibit different ultrafine eutectic structures (β-Ti(Fe) solid solution + TiFe). Different cooling conditions lead to the evolution of ultrafine eutectic oval-shaped colonies or elongated lamellar colonies with preferred orientation. Isotropic as well as anisotropic mechanical properties were obtained. Alloys exhibit compressive strengths between 2200 and 2700 MPa and plastic strains between 7 and 19 pct. in compression.
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El, Ghani Nouhayla. "Modélisation expérimentale du transfert de masse en croissance cristalline par des méthodes électrochimiques en présence d'ultrasons." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI037.
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Le brassage acoustique présente une alternative prometteuse pour l'amélioration des procédés de purification pendant la solidification du silicium photovoltaïque. Dans cette étude, on s'intéresse à la caractérisation de l'efficacité d'un brassage par acoustic streaming pour favoriser le phénomène de ségrégation. Nous avons ainsi développé une approche expérimentale originale basée sur des démonstrateurs en eau des phénomènes présents lors de la solidification. Cette démarche s'appuie sur une analogie entre d'une part la diffusion solutale des impuretés à travers la couche limite, au niveau du front de solidification, pendant le processus de croissance cristalline dans les fours de solidification, et d'autre part la diffusion des ions à travers la couche limite à la surface de l'électrode dans une cellule électrochimique. En effet, l'application des méthodes d'électrochimie analytique (polarographie), nous a permis de caractériser le transfert de masse au voisinage d'une paroi et de suivre son amélioration sous l'effet d'un jet impactant généré par une source acoustique continue au sein du fluide. La cohérence des résultats expérimentaux avec des simulations hydrodynamiques a été également examinée. En vue d'étendre les résultats obtenus dans l'eau à d'autres fluides notamment les métaux en phase liquide, on présente, dans la dernière partie de ce manuscrit, les différents paramètres de similitude permettant une description complète de l'expérience en fonction du fluide choisi : la géométrie, l'acoustique et l'hydrodynamique. Nous présenterons ensuite, le cas particulier d'un dispositif expérimental utilisant du galinstanAcoustic streaming presents a promising stirring technology in order to improve photovoltaic silicon purification during the solidification process. In the present study, we focus on the characterization of the efficiency of acoustic stirring to enhance segregation phenomena. We present an original experimental approach based on water demonstrators of the phenomena occuring during solidification. This approach is based on an analogy between on the one side the solute diffusion of impurities through the boundary layer, near the solidification front during the crystal growth process in solidification furnaces, and on the other side the diffusion of ions in an electrochemical cell on the surface of the electrode. We used analytical electrochemistry methods (polarography) to accurately characterize the solute boundary layer in the vicinity of the electrodes. Furthermore, we report the evolution of mass transfer in the presence of an impacting jet generated by a continuous acoustic source within the fluid. The consistency of the experimental results with hydrodynamic simulations was also examined. In order to extend the results obtained in water to other fluids, notably metals in the liquid phase, we present, in the last part of this manuscript, the different parameters allowing a complete description of the experiment for a particular fluid : geometry, acoustics and hydrodynamics parameters. We will then present the particular case of an experimental device using galinstan
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Shuleshova, Olga. "Equilibrium and metastable solidification in Ti-Al-Nb and Al-Ni systems." Doctoral thesis, 2009. https://tud.qucosa.de/id/qucosa%3A25328.
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The presented work reports on the solidification studies in two alloy systems: the niobium bearing γ-TiAl, relevant for the automotive and aero-engine applications, and aluminium rich Raney-Ni, precursor alloys for catalyses used in the chemical industry. The time-resolved observations of equilibrium liquid-solid phase transformations, as well as non-equilibrium solidification from the undercooled melt, are performed by combination of in situ structural studies using high-energy X-rays at a synchrotron source and the electromagnetic levitation technique. Containerless processing assured the contamination-free environment leading to high undercooling levels even at moderate cooling rates.
For the critical part of the Ti-Al-Nb phase diagram an equilibrium involving the liquid phase is deduced from the phase transformations gathered on heating periods of levitation experiment. New experimental data on the partial liquidus and solidus surfaces are delivered as well as the information on the nature of the reactions along the univariant lines. These data provide a valuable contribution to the reassessment of the thermodynamic description. The primary phase selection as function of undercooling is studied in ternary Ti-Al-Nb alloys. The metastable formation of the cubic β phase within the primary solidification region of the hexagonal α phase is observed with increasing melt undercooling. Furthermore, the microstructure evolution of the β solidifying Ti-46Al-8Nb alloy discloses the transition to the thermal growth mode for ∆T>200−250 K, accompanied by complete solute trapping. Supplemented with the data on the solidification velocity determined as function of melt undercooling, this results are discussed within the local non-equilibrium model of the free dendrite growth.
The in situ observations of the non-equilibrium solidification of the binary Al-Ni system give insight into multiple phase transformation sequence. The achieved undercooling levels up to 320 K for the aluminium alloys containing 18–31.5 at.% Ni did not alter the primary phase selection. However, during further cooling of L+Al3Ni2 semisolid samples the peritectic formation of a metastable decagonal quasicrystalline phase is observed providing a critical undercooling below the peritectic temperature of Al3Ni phase is reached. On further cooling the metastable phase subsequently transforms into the equilibrium Al3Ni. A similar solidification pathways are expected for the Raney-Ni alloys produced by gas atomisation, where the associated high cooling rates allowed to retain the metastable phase at room temperature.
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Lewis, Daniel J. "Solidification modeling in ternary alloys using the Bi-Pb-Sn system as an example /." Diss., 2001. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3010414.
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Lopez, Luis Felipe active 21st century. "Cyber-enabled manufacturing systems (CeMS) : model-based estimation and control of a solidification process." Thesis, 2014. http://hdl.handle.net/2152/28082.
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Vacuum arc remelting is a secondary melting process used to produce a variety of segregation sensitive and reactive metal alloys. The present day VAR practice for superalloys involves, typically, melting electrodes of 17'' into ingots of 20'' in diameter. Even larger diameter forging stock is desirable. However, beyond 20'' ingots of superalloys are increasingly prone to segregation defects if solidification is not adequately controlled. In the past years a new generation of model-based controllers was developed to prevent segregation in VAR by controlling melt rate, or the total amount of power flowing into the liquid pool. These controllers were seen as significant improvements in the industry of remelting processes, but these controllers were still focusing on the melting sub-process and ignoring ingot solidification. Accurate control of the liquid pool profile is expected to result in segregation-free ingots, but unfortunately a controller capable of stabilizing the solidification front in VAR is currently not available. The goal of the proposed research is to develop a cyber-enabled controller for VAR pool depth control that will enhance the capabilities of current technologies. More specifically, the objectives of this research are threefold. Firstly, a control-friendly model is proposed based on a high-fidelity ingot solidification model and is coupled to a thermal model of electrode melting. Secondly, sequential Monte Carlo estimators are proposed to replace the traditional Kalman filter, used in the previous VAR controllers. And finally, a model predictive controller (MPC) is designed based on the proposed reduced-order model. The time-critical characteristics of these methods are studied, and the feasibility of their real-time implementation is reported.text
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Shuleshova, Olga [Verfasser]. "Equilibrium and metastable solidification in Ti-Al-Nb and Al-Ni systems / vorgelegt von Olga Shuleshova." 2009. http://d-nb.info/1007106980/34.
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Chen, Yung-Fu, and 陳永福. "Improvement on Numerical Simulation Systems for Mold Filling and Solidification in Casting and Their Experimental Verifications." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/72220879613207583183.
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博士國立成功大學
材料科學(工程)學系
85
The purposes of this study are to improve the simulation systems for mold filling and solidification in casting and to verify the improvements on the accuracy of the simulation system with experimental measurements. For the im-provement on mold filling simulation, a technique named partial cell method is adoptedto improve the system*s capability of treating complex geometry. The conventionalfinite difference method has the weakness of limited capability to treat com-plex geometry. The partial cell method alIn this study, a mathematical model to simulate the filling phenomena in casting is based on SOLA-VOF 2D techniqueand then modified by the incorporation of a partial cell method and expansion to three dimensions. The pressure field of fluid is solved by the Successive Over-relaxation (SOR) method. The effective specific heat method is adaptedwith the measured latent heat released mode to calculate for the solidificationheat tr-ansfer. The measurement of latent heat release mode is conducted by the ComputeFor the improvement on mold filling simulation, a mathematical modelnamed PTC 3D based on the partial cell method has been successfully developed.The simu-lation results for a circular plate sand casting by the partial cellmethod is shown to be more accurate than those by the conventional rectangularcell method. Furthermore, the efficiency of calculation of partial cell is five times higher than that of the rectangular cell method. The mold filling simulations for die casting and EPC are also conducted. As the computed fillingpatterns are compared to the measured patterns, the consistency is quite satisfactory. For thee improvement on solidification simulation, the latent heat rereleased modes for near-pure aluminum, A356.2, A390, and A413 (near eutectics) aluminum alloys under different cooling rates are obtained through CA-CCA measurements.The relationship of solid fraction with temperature in mushy region isrepresented by the functional form of Huang.For A356.2 and A390 alloys, the liquidus tem- perature and solidus temperature, eutectic temperature, and maximumsolid fraction at the eutectic temperature, decrease as cooling rate increases. This is not true,however, for cooling rate higher than 9.5 oC/second. Two nonlinearity fac-tors, ne and np required to define the function are found toincrease as coolingrate increases. The solid density of A356.2 aluminum alloy lowers linearly from 2.581 to 2.535 g/cm3 when temperature ranged from 250 to 400 oC, while thedensity of the alloy is changed between 2.530~2.535 g/cm3 as temperature raisedfrom 400 to 580 oC. The liquid density of the alloy is nealy constant and varied within the range between 2.490 and 2.517 g/cm3 as temperature raised from 615 to 750 oC. The effect of latent heat released mode and high temperaturedensity of casting alloy on the accuracy of solidification simulation for thesand casting with a chill is also conducted in this study. The comparisons show that the accuracy of simulation by the incorporation of the two measured properties is significantly higher than these with constant values for the twothermal properties.
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Yu, Chia-Li, and 余佳俐. "The Numerical Simulation of Binary Solidification System with." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/58168710755976025383.
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碩士國立臺灣大學
機械工程學系
85
This study numerically investigate the binary solidification system which is cooled from the side wall. The binary solution is in a two-dimensional rectangular cavity with upper and lower adiabatic walls and two isothermal side walls. The single-phase numerical method and volume-average method are used to derive the governing equations. The mushy zone is assumed isotropic and the concentration of crystals is assumed uniform. After comparing with the experimental results, it is proved that the n The surface tension effect is obvious in the binary solidification system with a free surface. From the numerical results, several interesting conclusion can be attained: (1) Higher cooling temperature prevents the remelting phenomena in the mushy zone because of the interdendrite solution reduction. (2) Lower warm temperature changes the characteristic of the solidification flow field. (3) Under the microgravity condition, the remelting phenomena still occurred because of the surface tension. (4)Under the normal gravity condition, mushy zone thickness increases from top to bottom
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吳慶郎. "Simulation of solidification in eutectic nodular cast iron system." Thesis, 1988. http://ndltd.ncl.edu.tw/handle/59909604391109681403.
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Graves, Jeffrey A. "Undercooling and solidification behavior in the InSb-Sb system." 1985. http://catalog.hathitrust.org/api/volumes/oclc/12383855.html.
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Thesis (M.S.)--University of Wisconsin--Madison, 1985.Typescript. Metallurgical Engineering. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 206-212).
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YING, ZONG-JIE, and 應宗傑. "Transient heat transport in solidification of a binary hypoeutectic system." Thesis, 1989. http://ndltd.ncl.edu.tw/handle/46790240773932981142.
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Lin, Yu-Yi, and 林育毅. "The Design of the Argon Tube in Polysilicon Directional Solidification System." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/267kcp.
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碩士國立高雄應用科技大學
機械與精密工程研究所
103
The crystal growth experiment is a time-consuming and costly activity, in which the existing physical basis is used and cross-comparison of the calculation results obtained through numerical analysis and the results through the actual process to improve the approaches of Trial and Error of the growth plant to some extent. The increase of axial differential temperature in crystal growth would make the growth rate rise. The radial differential temperature would change the distribution of thermal stress, indirectly affecting the quality of crystal. Promoting the growth rate and quality of crystal and maintaining the temperature field distribution of high axial differential temperature and low radial differential temperature will be the focus in improvement. In this study, numerical analysis is used to conduct the simulation of the growth process of multicrystalline ingot solidification. The prototype is the directional-solidification crystal growth furnace (DSS450) produced by GT Advanced Technologies and the commercially-used software package ANSYS-FLUENT to conduct the modeling of finite elements. Also, the Finite Volume Method (FVM) is used. In simulation, the factors of the heat transfer model, the flow field model, and thermal radiation are considered. The opening angles of the intake port channel of Argon gas are adjusted, being respectively 20°, 60°, and 140°. The settings of simulation parameters include the Argon gas flow and the actual manufacturing process of time reference in heating. The temperature of all parts in the crystal growth furnace is 1685K and the temperature inside the Si molten bath is 1750K. Finally, the growth state of crystal is simulated and analyzed in a transient mode. Based on the results, the changes of the solid-liquid interface and the temperature field of crystal are explored. The results showed that in the initial stage of multicrystalline ingots’ growth, the small Argon gas channel opening is good for convex formation of the solid-liquid interface. This phenomenon makes the impurities in multicrystalline ingots pushed to the surrounding. After the middle stage, the opening of the Argon gas flow channel can be enlarged to favor the overall growth of crystal, process time reduction, and cost savings. When the opening angle of the Argon gas flow channel is 20°, axial differential temperature would be higher, causing the growth of crystal accelerated. In the initial stage of crystal growth, the prototype furnace is used for radial differential temperature. In the middle stage, 60° is used. In the late stage, the use of 60° would have lower radial differential temperature to avoid crystal grains growing from the Crucible wall.
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Chen, Hao Long, and 陳皓隆. "Rapid melting and solidification of Bi system superconductors by CO2 laser." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/57725478597831971902.
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Liu, Chun-Kai, and 劉君愷. "Heat and mass transport phenomena during solidification of a binary system." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/53626125190128821307.
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博士國立臺灣大學
機械工程學系
85
Solidification of binary system has many important applications in natural, industrial and manufacturing fields. In present study, heat and mass transport phenomena during solidification of binary system are studied by experimental, numerical method as well as scale analysis. The research focused on a rectangular cavity containing an ammonium chloride-water solution with cooling from sidewall. Experiments are performed to visualize phase change and convection processes by shadowgraph method. A CCD camera is used to record the whole process. Besides, the two-wavelength holographic interferometry method is used to measure the temperature and concentration in whole flow field at the same time. Three concentrations and different temperatures are studied in experiments. Three stages can be seen in the flow field while initial concentration is in preeutectic region. They are the density stratificatioA set of conservation equations is derived for the latent heat release, microsegregation and fluid flowing in microscopic. An effective numerical method combining APPLE algorithm, Weighting function scheme and SIS method is used. The numerical results show agreement with experiments very well. Because the microsegregation is considered, Scheil assumption is more suitable than level rule in describing complex transport phenomena in mushy zone. The variation of flow field and mass transfer in different stages can be realized from stream function, temperature and concentration distributions. Furthermore, double double-diffusive layer thickness, local and average Nusselt numbers are also systematically discussed. Finally, some physical variants like the velocity in mushy zone, mushy zone thickness, velocity near high temperature boundary and heat transfer coefficient of high temperature boundary are derived from scale analysis.
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LIN, CHENG-HUA, and 林政華. "The Study of Array Ultraviolet Light-Emitting Diode Solidification System Optimization." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/05270074124431565471.
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碩士國立暨南國際大學
光電科技碩士學位學程在職專班
105
With the increase in luminous efficiency and reliability, and with the decrease in manufacturing costs, LEDs have been popularly used in daily life lighting, and would be used in the key application of industrial processes. Additionally, the focus of LEDs has also been gradually evolved from the process technology development of unit part materials to research and development of packaging technology, steady lighting circuits and high lighting reliability, which would allow circuit stability control of lighting devices to become the development focus. This study was divided into three parts, aimed mainly to investigate the steady light state of high power ultraviolet light-emitting diodes for the auto constance current control system and auto constance electric power control system. The first part of this study was to devise a programmable module capable of automatically sensing lighting power and detecting voltage, light intensity and space temperature of LEDs in a real-time manner to replace measuring devices with a single function of measuring light intensity. Experimental results indicated that this module could be used to obtain variations of optical power and electric power of LEDs through steady long-term monitoring. The second part explored the difference between the steady and unsteady light states of the auto constant current control system and auto constant electric power control system. This study enabled us to continuously read light intensity and irradiation area temperature through a programmable automatic detector, and enabled those who applied the circuit control system to derive the best operating region and to define the irradiation process parameters of LEDs based on the model in this study. The third part delved into the semiconductor packaging processed by using irradiation from high power light emitting diodes, employing the difference between the irradiation-caused steady and unsteady states of the auto constant current control system and auto constant electric power control system, where the temperature of each working area was compared, and experimental reliability tests specified in automotive electronics were included. The first and third parts of the experimental conclusions could be corroborated. This study further verified that the steady lighting interval of the auto constant electric power control system is superior to that of the auto constant current control system and more suitable for use in the automotive electronics, which require high stability quality.
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Yang, Yao-Chung, and 楊耀中. "The Simulation Analysis of Silicon Ingot Growth in Directional Solidification System." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/72307749509741474711.
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碩士國立高雄應用科技大學
機械與精密工程研究所
101
Solar cell is mainly in polycrystalline silicon wafers, this research focuses on (Directional Solidification System,DSS) to fabricate polycrystalline silicon ingot. In the process of crystal growth, if silicon ingot axial temperature gradient increases, the crystal grains to grow vertically. The radial temperature gradient decrease can prevent crystal grains from growing on the walls of the crucible. Furthermore, the rate of heat radiation of crystal growth affects the output power of the heater, and the solid-liquid interface state affects the impurity concentration and stress distribution of the silica block. This research used GT-Solar to produce directional solidification crystal growth furnace as the prototype for the finite element model analysis. Through changing parameters of argon gas flow, heat radiation pad, and heater, as well as the temperature field, this research aims to improve temperature gradient, heat radiation rate, and solid-liquid interface state. The numerical analysis method was based on the finite volume method fluent as a tool, the main task was to analyze the thermal field of the directional solidification process through the solidify/molten model, with consideration given to the effects of heat conduction, heat convection, heat radiation, and argon gas flow in the process. The results from the analysis then adjust furnace interior parts so as to optimize the crystal growth process. Results show that using a larger flow of argon gas at the initial stage of the crystal growing process, and using a lower flow of argon gas at the latter stage of crystal growth induce more evenly distributed temperature at the solid-liquid interface, improve the quality of the polycrystalline silicon block. An increase in the thickness of the graphite heat radiation block cannot increase the vertical temperature of the silicon ingot and temperature evenness at the bottom efficiently, so that silicon ingot after processing that a reason about the photoelectric conversion efficiency of polycrystalline silicon wafers cannot effectively increased. Increasing the length of the heater to the same length parallel of the crucible effectively reduces crystal growth on the wall of the crucible and achieves better polycrystalline structure; the density of defects is lowered and therefore achieves higher quality polycrystalline silicon wafers. Periphery of the crucible install non-contact heat can block radiant heat transfer to the graphite thermal block, the axial temperature gradient increases and the radial temperature gradient decreases. Grain can be more vertically upward growth from the bottom of the crucible, so that the photoelectric conversion efficiency of polycrystalline silicon wafers can increase drastically.
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張福平. "Solutal Instability of a Binary Alloy in a Rotating System with Solidification." Thesis, 1989. http://ndltd.ncl.edu.tw/handle/20294536245452234994.
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碩士逢甲大學
機械工程研究所
77
A fluid layer, composed of a homogeneous binary mixture of light solute and heavy solvent, in a rotating system is sub jected to a cooling rom above or below. the freezing process is supposed to take place at the lower boundary. the freezing interface advances toward the liquid fluid under a controlled averaged speed with its perturbed position unknown. Since there exists a density jump between the solidified material and the liquid fluid, some amount o the liquid mixture, containing more light solute, is then self-inducedly squeezed out of the solidified material during the phase change and rejected into the fluid layer as being a gravitational potential energy for driving a possible convection. Stationary solutal instabilities are solely considered. The thickness of the fluid layer is chosen to be equal to D/V, in which viscous effects become important. The critical solute Rayleigh number R*s and wave-number a* are found to increase with the segregation coefficient r, the Schmidt number Sc, for small values of Ta, and the Taylor number Ta, and decrease with Sc, for large values of Ta. For a much larger thickness of the fluid layer, since the solutal diffusion becomes important, the critical values will decrease with the Schmidt number Sc.
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SUN, LI-DE, and 孫立德. "Solutal convective stability during solidification of a binary alloy in a rotating system." Thesis, 1989. http://ndltd.ncl.edu.tw/handle/60079239259748847604.
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Lin, Ting-Kang, and 林廷剛. "Numerical Simulations on Thermo-fluid Fields and Dopant Distributions in a Directional Solidification System." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/39442267358528156205.
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碩士國立交通大學
機械工程系所
103
Manufactures of multi-crystalline silicon ingots by means of the directional solidification system (DSS) is important to the solar photovoltaic (PV) cell industry. The quality of the ingots is highly related to the shape of the crystal-melt interface and the distributions of dopants during the crystal growth process. We performed numerical simulations to thoroughly analyze the transient thermo-fluid field and its effects to the shape evolution of the crystal-melt interface as well as the transportation of dopants, including oxygen, carbon, boron and phosphorous in transient processes. In addition, the transportation of dopants also is affected by segregation effect. Accuracy of the results is supported by comparing the evolutions of crystal heights with the benchmark experimental measurements. The excellent agreements demonstrate the applicability of the present numerical methods in capturing the key features for a practical and complex system of directional solidification system.
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JIANG, KE-DA, and 江可達. "Convective and morphological stability during solidification of a binary alloy in a rotating system." Thesis, 1989. http://ndltd.ncl.edu.tw/handle/61925590424475948775.
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Kang, Min-Chieh, and 康閔傑. "The Study of Impurities Distribution in Silicon Ingot with Growth Processby Directional Solidification System." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/13506860224948781222.
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碩士國立高雄應用科技大學
機械與精密工程研究所
103
In this paper the numerical analysis method focuses on impurity concentration diffusion by the process of crystal growth. This research used GT-Solar’s (Directional Solidification System,DSS) to simulate the prototype. Use Ansys Fluent modular software with governing equations include energy model、flow field model、aolidification & melting model、heat transfer model、species transport model and finite volume method , the results and process data of eversol technology companies to verify. This paper discusses oxygen, carbon, boron, phosphorus, iron, titanium in an argon and silicon melt for study of the impurity concentration distribution. In this study modeling of crystal growth furnace into a two-dimensional asymmetric structure further finite element simulation analysis. Simulation of the internal state of the furnace using transient analysis.To raise the insulation cage, which allows the furnace inside and outside temperature thermal convection, process 40 hours. Parameters contains argon gas flow used in the simulation, that reference to the real process. The silicon melt sets oxygen、carbon、boron、phosphorus、iron and titanium. In the whole process, the furnace pressure is kept 200mbar.Crystal growth furnace wall temperatures are 1000K, because that uses water-cooling system.Crystal growth furnace temperature is 1685K.Molten metal inside temperature is 1750K. Results show that using a larger flow of argon gas at the initial stage of the crystal growing process can take away impurities within the 5 hours. Inlet input a lower flow of argon gas at the latter stage of the crystal growing process after about 30 hours will be distributed temperatures,and improve the quality of the polycrystalline silicon back. Outlet output exhaust volume to increase over time,allows the impurity concentration in the gas phase for crystal growth furnace be reduced. In the amount of liquid silicon impurity concentration is oxygen, carbon, boron, phosphorus, iron, titanium sequentially. Oxygen and boron impurity are subject to segregation coefficient relationship, some impurities remain in the silicon ingot. In which oxygen impurity and because of the quartz crucible release oxygen impurity,so that the silicon ingot there will be a higher concentration area at the top of the crucible. Carbon, phosphorus, iron and titanium impurities can be directional solidification methods to achieve the purpose of purified polysilicon ingot.