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Effect Of Marangoni Convection On Dendritic SolidificationNabavizadeh, Seyed Amin 12 November 2021 (has links)
No description available.
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Modelling of brine transport mechanisms in Antarctic sea iceCook, Andrea 12 July 2021 (has links)
It is evident that the sea ice cycle, from its formation to its melt, is governed by a complex interaction of the ocean, atmosphere and surrounding continents. Once sea water begins to freeze, physical, biological and chemical processes have implications on the evolution of the sea ice morphology [38]. The distinguishing factor between fresh and sea water ice is brine inclusions that get trapped within the ice pores during freezing. Salt inclusions within frozen ice influence the salinity as well as the physical properties of the sea ice [23]. These brine inclusions form part of a dynamic process within the ice characterized by the movement of brine and phase transition which are the foundation of many of its physical properties [23]. Brine removal subsequently begins to occur due to vertical gravity drainage into the underlying ocean water. This study introduces the application of a biphasic model based on the Theory of Porous Media (TPM) which considers a solid phase for the pore structure of the ice matrix as well as a liquid phase for the brine inclusions, respectively. This work explores the use of the TPM framework towards advancing the description and study of the various desalination mechanisms that are significant in aiding the salt flux into the Southern Ocean. This will foster understanding of brine rejection and how it is linked to the porous microstructure of Antarctic sea ice
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Etude comparative des méthodes d'origine particulaire SPH et LBM pour la simulation d'écoulements polyphasiques intermittents dans des conduites / Comparative study of particle-based methods SPH and LBM for the simulation of multiphase slug flows in pipesDouillet-Grellier, Thomas 07 October 2019 (has links)
L’objectif de cette thèse est d’étudier les apports et les limitations de deux méthodes d’origine particulaire, SPH et LBM, dans le cadre de la simulation des écoulements à bouchons dans des conduites. Dans l’industrie pétrolière, ce type d’écoulement, que l’on retrouve par exemple dans les pipelines qui acheminent le pétrole et le gaz jusqu’aux raffineries, est connu pour endommager les installations et pour réduire l’efficacité du transport des fluides. Il est donc important de bien comprendre leur formation. Nous avons donc implémenté ces deux méthodes, ainsi que leurs variantes polyphasiques, et avons mené une campagne de validation et de comparaison afin de sélectionner la méthode la plus adéquate, pour poursuivre ensuite avec des simulations de cas plus appliqués et réalistes. Les contributions présentées se concentrent principalement sur trois axes. Tout d’abord, il a fallu construire les codes de calcul nécéssaires, les valider puis comparer des différentes formulations polyphasiques disponibles pour SPH et LBM. Ensuite, nous avons développé des conditions aux limites d’entrée/sortie adaptées au contexte polyphasique pour être en mesure d’injecter les fluides avec des vitesses imposées et de ler évacuer du domaine avec un pression donnée. Enfin, nous avons simulé différents cas d’écoulements à bouchons académiques avec SPH et LBM, puis sur des cas appliqués avec des géométries réalistes et des ratios de densité et de viscosité de type air/eau avec SPH seulement. / The main objective of this thesis is to study the contributions and limitations of two particle- based methods, SPH and LBM, for the simulation of slug flows in pipes. In the petroleum industry, these flow regimes, found for example during the transportation of oil and gas from reservoirs to refinery facilities through pipelines, are highly undesirable because they are known to damage facilities and to reduce flow efficiency. Therefore, it is important to understand its formation. We have implemented both methods, as well as their multiphase variants, and have led a validation and comparison campaign in order to to select the most suited method and to continue with simulations of more applied and realistic cases. The main contributions of this work can summarized in 3 points. First, we had to write the necessary computation codes, validate them and compare the different multiphase formulations available for SPH and LBM. Then, we have developed inlet/outlet boundary conditions adapted to the multiphase context so that we are able to inject fluids with prescribed velocities and let them exit he domain with a given pressure. Finally, we have simulated different academic test cases of slug flows with SPH and LBM and then on applied cases with realistic geometries and air-water like density and viscosity ratios with SPH only.
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Numerical Study on Indoor Climate Using Single-Phase and Multiphase Models / 単相および多相場モデルによる室内気候の数値解析的研究Chamika, De Costa 24 September 2015 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19280号 / 工博第4077号 / 新制||工||1629(附属図書館) / 32282 / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 牛島 省, 准教授 米山 望, 准教授 山上 路生 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM
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A Continuum Mechanics Approach to Modeling and Simulating Engineering Materials Undergoing Phase Transformation using the Evolving Micro-Structural Model of InelasticityAdedoyin, Adetokunbo Adelana 17 May 2014 (has links)
Heat treatment for the purpose of material strengthening is accompanied by residual stresses and distortion. During these processing steps, steel alloys experience a phase change that in turn modify their overall mechanical response. To properly account for the cumulative composite behavior, the mechanical response, transformation kinetics and subsequent interaction of each phase have to be properly accounted for. Of interest to material designers and fabricators is modeling and simulating the evolutionary process a part undergoes for the sake of capturing the observable residual stress states and geometric distortion accumulated after processing. In an attempt to capture the aforementioned physical phenomena, this investigation is premised upon a consistent thermodynamic framework. Following this, the single phase Evolving Microstructural Model of Inelasticity state variable model is extended to accommodate the occurrence of multiphases, affirming that the interaction between coexisting phases is through an interfacial stress. Since the efficacy of a multiphase model is dependent on its ability to capture the behavior of constituents phases and their subsequent interaction, we introduce a physically based self-consistent strain partitioning algorithm. With synthesis of the aforementioned ideas, the additional transformation induced plasticity is numerically accounted for by modifying each phase’s flowrule to accommodate an interfacial stress. In addition, for simulating the cohabitation of two phases, the mechanical multiphase model equations is coupled with a previously developed non-diffusional phase transformation kinetics model. A qualitative assessment of the material response based on a Taylor, Sachs and self-consistent polycrystalline approximation is carried out. Further analysis of the multiphase model and its interaction with transformation kinetics is evaluated.
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Multiscale Kinetic Modelling for Chemical Looping Applications: From Atomistic to ContinuumChen, Yu-Yen January 2021 (has links)
No description available.
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Multiphase Flow in Mixed-wet Porous MediaIrannezhad, Ashkan January 2023 (has links)
Multiphase flow in porous media is important in a wide range of industrial and environmental processes. It is well-known that the fluids’ relative affinity to the porous media (i.e., wettability) is a crucial factor controlling multiphase flow in porous media. Despite having a good understanding of multiphase flow in porous media under uniform wettability conditions, our knowledge of how fluids flow in mixed-wet porous media is more limited. Mixed-wet porous media (i.e., porous media with spatially heterogeneous wettability) is prevalent in nature, from groundwater aquifers to oil-bearing rocks. This Thesis aims to better understand the complexities of multiphase flow in mixed-wet porous media. The study begins with investigating fluid-fluid displacement in mixed-wet microfluidic flow cells. We performed experiments over a range of capillary numbers and mixed-wettability conditions, and our results show that the fluid-fluid interface in mixed-wet pores resembles an S shaped saddle with very low capillary pressure. In the next step, we derive analytical expressions for fluid-fluid interface evolution through mixed-wet pore throats. These analytical expressions are incorporated into a dynamic pore network model, which enables us to develop a numerical framework capable of simulating fluid-fluid displacement in mixed-wet porous media. Next, we leverage our model to simulate multiphase flow in simple mixed-wet porous micro-models consisting of distinct water-wet and oil-wet regions whose fractions are systematically varied to yield a variety of displacement patterns over a wide range of capillary numbers. Our simulations reveal that mixed-wettability impacts are most prominent at low capillary numbers, and it depends on the complex interplay between the wettability fraction and the intrinsic contact angle of the water-wet regions. We also investigate the dynamics of multiphase flow in mixed-wet porous media under quasi-static conditions and discover that it exhibits self-organized criticality (SOC). Finally, we determine the correlation between spatial and temporal aspects of this dynamical system. / Thesis / Doctor of Science (PhD)
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Computer simulation of general systems of interlinked multistaged separatorsChan, Willie K. January 1982 (has links)
Thesis: M.S., Massachusetts Institute of Technology, Department of Chemical Engineering, 1982 / Bibliography: leaves 59-60. / by Willie K. Chan. / M.S. / M.S. Massachusetts Institute of Technology, Department of Chemical Engineering
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Analysis And Design Optimization Of Multiphase ConverterZhang, Kejiu 01 January 2013 (has links)
Future microprocessors pose many challenges to the power conversion techniques. Multiphase synchronous buck converters have been widely used in high current low voltage microprocessor application. Design optimization needs to be carefully carried out with pushing the envelope specification and ever increasing concentration towards power saving features. In this work, attention has been focused on dynamic aspects of multiphase synchronous buck design. The power related issues and optimizations have been comprehensively investigated in this paper. In the first chapter, multiphase DC-DC conversion is presented with background application. Adaptive voltage positioning and various nonlinear control schemes are evaluated. Design optimization are presented to achieve best static efficiency over the entire load range. Power loss analysis from various operation modes and driver IC definition are studied thoroughly to better understand the loss terms and minimize the power loss. Load adaptive control is then proposed together with parametric optimization to achieve optimum efficiency figure. New nonlinear control schemes are proposed to improve the transient response, i.e. load engage and load release responses, of the multiphase VR in low frequency repetitive transient. Drop phase optimization and PWM transition from long tri-state phase are presented to improve the smoothness and robustness of the VR in mode transition. During high frequency repetitive transient, the control loop should be optimized and nonlinear loop should be turned off. Dynamic current sharing are thoroughly studied in chapter 4. The output impedance of the multiphase v synchronous buck are derived to assist the analysis. Beat frequency is studied and mitigated by proposing load frequency detection scheme by turning OFF the nonlinear loop and introducing current protection in the control loop. Dynamic voltage scaling (DVS) is now used in modern Multi-Core processor (MCP) and multiprocessor System-on-Chip (MPSoC) to reduce operational voltage under light load condition. With the aggressive motivation to boost dynamic power efficiency, the design specification of voltage transition (dv/dt) for the DVS is pushing the physical limitation of the multiphase converter design and the component stress as well. In this paper, the operation modes and modes transition during dynamic voltage transition are illustrated. Critical dead-times of driver IC design and system dynamics are first studied and then optimized. The excessive stress on the control MOSFET which increases the reliability concern is captured in boost mode operation. Feasible solutions are also proposed and verified by both simulation and experiment results. CdV/dt compensation for removing the AVP effect and novel nonlinear control scheme for smooth transition are proposed for dealing with fast voltage positioning. Optimum phase number control during dynamic voltage transition is also proposed and triggered by voltage identification (VID) delta to further reduce the dynamic loss. The proposed schemes are experimentally verified in a 200 W six phase synchronous buck converter. Finally, the work is concluded. The references are listed.
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Effects of Two-Phase Flow in a Multistage Centrifugal CompressorHalbe, Chaitanya Vishwajit 19 October 2016 (has links)
The performance of a vapor compression system is known to be affected by the ingestion of liquid droplets in the compressor. In these multiphase flows, the liquid and the vapor phase are tightly coupled. Therefore the interphase heat, mass and momentum transfer as well as droplet dynamics including droplet breakup and droplet-wall interactions play a vital role in governing these flows. Only thermodynamic analyses or two-dimensional mean-line calculations are not sufficient to gain an in-depth understanding of the complex multiphase flow field within the compressor. The objective of this research was to extend the current understanding of the operation of a multistage centrifugal compressor under two-phase flow conditions, by performing three-dimensional computational analysis.
In this work, two-phase flow of a single constituent (refrigerant R134a) through a two-stage, in-line centrifugal compressor was analyzed using CFD. The CFD model accounted for real gas behavior of the vapor phase. Novel user defined routines were implemented to ensure accurate calculations of interphase heat, mass and momentum transfer terms and to model droplet impact on the compressor surfaces. An erosion model was developed and implemented to locate the erosion "hot spots" and to estimate the amount of material eroded.
To understand the effects of increasing liquid carryover, the mass flow rate of the liquid phase was increased from 1% to 5% of the vapor mass flow rate. The influence of droplet size on the compressor performance was assessed by varying the droplet diameter at the inlet from 100 microns to 400 microns. The results of the two-phase flow simulations were compared with the simulation involving only the vapor phase.
Liquid carryover altered the flow field within the compressor, and as a result, both impellers were observed to operate at off-design conditions. This effect was more pronounced for the second impeller. The overall effects of liquid carryover were detrimental to the compressor performance. The erosion calculations showed maximum erosion potential on the blade and shroud of the first impeller.
The results from this investigation provided new and useful information that can be used to support improved design solutions. / Ph. D.
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