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1
Chavez, Cervantes Mariana [Verfasser], und Isabella [Akademischer Betreuer] Gierz. „Photo-Carrier Dynamics and Photo-Induced Melting of Charge Density Waves in Indium Wires / Mariana Chavez Cervantes ; Betreuer: Isabella Gierz“. Hamburg : Staats- und Universitätsbibliothek Hamburg, 2020. http://d-nb.info/1212585143/34.
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2
Nduwimana, Alexis. „Confinement effect on semiconductor nanowires properties“. Diss., Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19865.
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Thesis (Ph.D)--Physics, Georgia Institute of Technology, 2008.Committee Chair: Chou, Mei-Yin; Committee Member: First,Phillip; Committee Member: Gao, Jianping; Committee Member: Landman, Uzi; Committee Member: wang, Xiao-Qian.
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Khillarkar, Dipendra B. „Melting of a phase change material in horizontal annuli“. Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=21307.
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Numerical experiments were carried out to determine tube geometries for more efficient thermal storage. A finite element simulation code developed earlier, which solves the two dimensional governing conservation equations was employed to examine the thermal performance of horizontal annuli of the following configurations: (a) Square external tube with a circular tube inside---Annulus Type A; (b) Circular external tube with a square tube inside---Annulus Type B. Effects of the Rayleigh number as well as heating of the inside, outside or both walls at a temperature above the melting point of the material were studied. Flow and temperature patterns within the melt, local heat flux distributions at the heating surface and the cumulative energy charged as a function of time are presented and discussed.To enhance the heat transfer rate during melting in horizontal annular containers various innovative passive methods were examined. Eccentric annular configurations are identified as superior to concentric tubular geometries due to the vertically upward orientation of the buoyancy force in the melt phase at higher Rayleigh numbers. In addition to this the effect of flipping the container at pre-selected times after initiation of melting as a measure to increase the heat transfer rate during the last stage of the melting process is also examined and discussed.
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Khillarkar, Dipendra B. „Melting of a phase change material in horizontal annuli“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0025/MQ50629.pdf.
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Gong, Zhen-Xiang. „Time-dependent melting and freezing heat transfer in multiple phase change materials“. Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=42043.
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Based on an analysis of the causes of non-convergence in the effective heat capacity methods a new conservative effective heat capacity method is developed for general phase change heat transfer problems. Numerical experiments verified the accuracy and efficiency of the new method.A multi-layer phase change material (PCM) heat transfer module is proposed for latent heat energy storage. Cyclic heat transfer in the module was modelled using the finite element technique. A parametric study was performed to investigate the energy charge/discharge rates for the new design.
A second-law thermodynamic analysis was carried out for thermal energy storage using multiple PCMs. The exergy efficiency of energy storage units using two, three as well as five different PCMs was analyzed and compared with that using a single PCM.
A novel cone-cylinder design configuration is proposed for a shell-and-tube latent heat energy storage exchanger. A finite element model was developed to simulate the coupled convection and cyclic melting/freezing phase change heat transfer occurring outside the tube. The advantages of the new configuration are examined and discussed with the help of numerical experiments. Following the new design configuration a novel multi-exchanger energy storage system is proposed. Finite element simulation results validated and extended the thermodynamic analytical results.
A new solar thermal storage unit using multiple PCMs was proposed and analyzed by a finite element model. A parametric study was carried out to investigate the advantages of the new design when compared with conventional single PCM designs.
Finally, a finite element model for melting and freezing heat transfer including free convection in the melt region was developed. The streamline upwind/Petrov-Galerkin method was employed to enhance both the stability and accuracy of the numerical solution. Using this finite element model simulations were carried out for melting of a PCM in a rectangular cavity heated from below. Flow patterns and local heat flux distributions at the heating surface are presented and discussed. In addition, melting of a PCM in a rectangular cavity with an isothermal vertical wall was simulated. To enhance the heat transfer rate during the last stage of the melting process, inverting the PCM container is shown to be an effective technique; this idea was examined with a parametric study.
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Gong, Zhen-Xiang. „Time-dependent melting and freezing heat transfer in multiple phase change materials“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ29948.pdf.
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Yang, Jia. „Melting and solidification models and thermal characteristics of microencapsulated phase change materials“. Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/58140/.
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Microencapsulated phase change material (MPCM) as a new thermal energy storage material and a heat transfer medium have attracted considerable attention in the thermal energy storage field. Solidification and melting models of a single PCM particle are constructed in this thesis. An effective numerical method for the problem of a spherical particle with a moving boundary was developed and validated by an iterative analytical series solution. A new liquid-solid interface model was proposed for modelling the effect of binary phase composition on the solidification of an alloy and a mixture PCM particle based on solid fraction. A full two-phase melting model of differentlysized micro/nano particles was also built. The initial melting point of particles is defined and depends on the minimum melting temperature of particles measured by DSC, the particle size and the Gibbs-Thomson equation. The model can predict the melting time of micro-particles flowing in a heat transfer channel, which agrees with the group melting behaviour of MPCM as observed by experiments. A test rig was built to explore the melting heat transfer behaviour of microcapsule phase change slurry (MPCS) flowing through a circular tube for a given constant heat flux. DPNT06-0182 slurries were investigated on the test rig. The experimental results indicate that the flow rate is a key factor in determining heat transfer coefficients of slurries. For the same energy efficiency, and in the situation of low flow rate and phase change, the pressure drop and local heat transfer coefficients of 10% DPNT slurry are lower compared with water, but the most heat energy is stored during the passage through the heated test section. However, in the case of high flow rates and no phase change, the local heat transfer coefficients of 10% DPNT slurry are higher with comparison to water under turbulent flows.
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Wright, Sarah Kelly. „Melting Marvels: Tourist Responses to Climate Change and Glacial Melt in the Peruvian Andes“. Columbus, Ohio : Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1243370470.
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Wei, Xiupeng. „Multiscale modeling and simulation of material phase change problems: ice melting and copper crystallization“. Thesis, University of Iowa, 2010. https://ir.uiowa.edu/etd/904.
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The primary objective of this work is to propose a state-of-the-art physics based multiscale modeling framework for simulating material phase change problems. Both ice melting and copper crystallization problems are selected to demonstrate this multiscale modeling and simulation. The computational methods employed in this thesis include: classical molecular dynamics, finite element method, phase-field method, and multiscale (nano/micro coupling) methods.
Classical molecular dynamics (MD) is a well-known method to study material behaviors at atomic level. Due to the limit of MD, it is not realistic to provide a complete molecular model for simulations at large length and time scales. Continuum methods, including finite element methods, should be employed in this case.
In this thesis, MD is employed to study phase change problems at the nanoscale. In order to study material phase change problems at the microscale, a thermal wave method one-way coupling with the MD and a phase-field method one-way coupling with MD are proposed. The thermal wave method is more accurate than classical thermal diffusion for the study of heat transfer problems especially in crystal based structures. The second model is based on the well-known phase-field method. It is modified to respond to the thermal propagation in the crystal matrix by the thermal wave method, as well as modified to respond to temperature gradients and heat fluxes by employing the Dual-Phase-Lag method. Both methods are coupled with MD to obtain realistic results.
It should be noted that MD simulations can be conducted to obtain material/thermal properties for microscopic and/or macroscopic simulations for the purpose of hierarchical/sequential multiscale modeling. These material parameters include thermal conductivity, specific heat, latent heat, and relaxation time. Other type of interfacial parameters that occur during the phase change process, such as nucleus shape, interfacial energy, interfacial thickness, etc., are also obtained by MD simulation since these have so far been too difficult to measure experimentally.
I consider two common phase change phenomena, ice melting and copper crystallization, in this thesis. For the case of ice melting, MD is first employed to study its phase change process and obtain thermal properties of ice and water. Several potential models are used. I conduct simulations of both bulk ice and ice/water contacting cases. It is found that various potential models result in similar melting phenomena, especially melting speed. Size effects are also studied and it is found that the melting time is longer for larger bulk ice segments but that the average melting speed is size dependent. There is no size effect for the melting speed at ice/water interface at the nanoscale if the same temperature gradient is applied. The melting speed of ice should depend on the temperature gradient. To study ice melting at the microscale, the thermal wave model is employed with parameters obtained from MD simulations. It is found that ice melting speed is scale, for both length scale and time scale, dependent.
For the case of copper crystallization, an EAM potential is first employed to conduct MD simulations for studying the copper crystallization process at the nanoscale. I obtain thermal properties and interfacial parameters, including thermal diffusion coefficient, latent heat, relaxation time, interfacial thickness, interfacial energy and the anisotropy coefficients, and nucleus shape etc. A central symmetry parameter is used to identify an atom in solid state or liquid state. And then an initial nucleus shape is obtained and used as the input for microscale simulation, in which the phase-field method is used to study copper crystallization at the microscale.
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Sridharan, Prashanth. „Aspect Ratio Effect on Melting and Solidification During Thermal Energy Storage“. Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4777.
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The present work investigates, numerically, the process of melting and solidification in hollow vertical cylinders, filled with air and phase change material (PCM). The PCM used is sodium nitrate, which expands upon melting. Therefore, a void must be present within the cylinder, which is filled with air. The influence of cylinder shape on melting time is determined. The numerical model takes both conductive and convective heat transfer into account during the melting process. The Volume-of-Fluid (VOF) model is used to track the interface between the PCM and air as the PCM melts. Three dimensionless numbers represent the characteristics of the problem, which are the Grashof, Stefan, and Prandtl numbers. The Stefan and Prandtl numbers are held constant, while the Grashof number varies. Inner Aspect Ratio (AR) is used to characterize the shape of the cylinder, which is defined as the ratio of the height to the diameter of the vertical cylinder. In this study, a range of AR values from 0.23 to 10 is investigated. Cylinders with small AR, corresponding to high Grashof numbers, lead to lower melting times compared with cylinders with high AR. The molten PCM velocity was also influenced greatly by this difference between solid PCM shape between high and low AR cases. Cylinders with small AR, corresponding to high Grashof numbers, lead to higher solidification times compared with cylinders with high AR. It was found that the velocity decreased during the solidification process, but the shape of the cylinder had an effect on the decrease. Natural convection velocity was found to decrease during the solidification process and, therefore, its effects diminish as solidification proceeds.
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Vogel, Julian [Verfasser], und André [Akademischer Betreuer] Thess. „Influence of natural convection on melting of phase change materials / Julian Vogel ; Betreuer: André Thess“. Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2019. http://d-nb.info/1188241273/34.
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Sebetci, Ali. „The Structure, Energetics And Melting Behavior Of Free Platinum Clusters“. Phd thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/1209980/index.pdf.
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The Voter and Chen version of an embedded-atom model, derived by fitting to experimental data of both the diatomic molecule and bulk platinum simultaneously, has been applied to study the locally stable structures, energetics, growth patterns and melting behavior of free platinum clusters in the size range of N=2-56 and N=75. Using the constant-energy molecular dynamics simulations, thermal and conjugate-gradient minimization techniques, the global minima and the other locally stable structures have been distinguished from those stationary structures that correspond to saddle points of the potential energy surface. The number of isomers and the probabilities of sampling different basins of attractions of the clusters from 2 to 22 atoms are obtained. The energy spectra of these clusters have been analyzed. The correlations between the total energy of the 75-atom cluster and the isomer number and the energy-spectrum-width of the isomers are investigated. The number of isomers of 75-atom cluster as a function of the total energy is presented, and the isomer probability distribution is discussed. The melting behavior of Pt_N clusters in the size range of N=12-14, 54-56, and N=75 has been studied. An atom-resolved analysis method including physical quantities such as the root-mean-square bond-length fluctuations and the coordination numbers for indivudual atoms as the functions of the temperature has been presented. Comparisons have been made with the results of previous calculations using electronic structure and empirical potential methods. The results show that the global minima have structures based on either octahedral, decahedral or icosahedral packing.
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Bakker, P., A. Schmittner, J. T. M. Lenaerts, A. Abe-Ouchi, D. Bi, den Broeke M. R. van, W. L. Chan et al. „Fate of the Atlantic Meridional Overturning Circulation: Strong decline under continued warming and Greenland melting“. AMER GEOPHYSICAL UNION, 2016. http://hdl.handle.net/10150/622754.
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The most recent Intergovernmental Panel on Climate Change assessment report concludes that the Atlantic Meridional Overturning Circulation (AMOC) could weaken substantially but is very unlikely to collapse in the 21st century. However, the assessment largely neglected Greenland Ice Sheet (GrIS) mass loss, lacked a comprehensive uncertainty analysis, and was limited to the 21st century. Here in a community effort, improved estimates of GrIS mass loss are included in multicentennial projections using eight state-of-the-science climate models, and an AMOC emulator is used to provide a probabilistic uncertainty assessment. We find that GrIS melting affects AMOC projections, even though it is of secondary importance. By years 2090-2100, the AMOC weakens by 18% [-3%, -34%; 90% probability] in an intermediate greenhouse-gas mitigation scenario and by 37% [-15%, -65%] under continued high emissions. Afterward, it stabilizes in the former but continues to decline in the latter to -74% [+4%, -100%] by 2290-2300, with a 44% likelihood of an AMOC collapse. This result suggests that an AMOC collapse can be avoided by CO2 mitigation.
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Guventurk, Abdulkadir. „Impacts Of Climate Change On Water Resources On Eastern Mountainous Region Of Turkey“. Master's thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615706/index.pdf.
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Temperature and precipitation are the most important indicators of climate change. Especially for the basins fed by snow, the shifts of melting to earlier times, affects the streamflow. Increase in temperature causes to shifts of melting of snow to shift to earlier times so that hydrologic regime of the river system changes, and leads to changes in climatic conditions of the region.
In this study the shifts of snow melting times are analyzed for the selected 15 streamflow stations located in Euphrates, Tigris, Aras, and Çoruh basins in Eastern Anatolia of Turkey along with period from 1970 to 2010. The shifts in snowmelt runoff are determined by Center Time (CT) method. Meteorological stations representing the stream gauge stations regarding the basin characteristics are also selected to be used in the analyses. In order to relate CT shifts to temperature and precipitation changes, trend analysis are applied to temperature, precipitation and streamflow data. In addition to these, days with daily average temperature less than freezing and wet days below freezing until CT for each station pair between stream gauge and meteorological stations and each year are also analyzed. These days till CT within a year for each station pair can be indirectly linked to snowy days and accumulated snow amount. Complete analyses show significant warming at each station in the region and no important trends in annual precipitation. However at a few stations meaningful seasonal changes in precipitation are observed. Regional warming and associated changes in precipitation and snowmelt runoff cause significant shifts to earlier times of snowmelt runoff. In the region eight out of fifteen stream gauge stations in Euphrates, Tigris and Aras basins showed significant time shifts according to statistical trend tests.
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Бабушкин, Б. Д., und B. D. Babushkin. „Разработка web-приложения решения задачи оптимизации состава многокомпонентной плавильной шихты : магистерская диссертация“. Master's thesis, б. и, 2021. http://hdl.handle.net/10995/99885.
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Магистерская диссертация посвящена разработке web-приложения решения задачи оптимизации состава многокомпонентной плавильной шихты. В ходе работы рассмотрены основные этапы разработки программного обеспечения: анализ предметной области; создание архитектуры программного обеспечения; разработка алгоритмического обеспечения и справочной документации; подготовка дистрибутива. В процессе выполнения работы реализованы все цели и задачи, стоящие перед проектом. Основными пользователями системы являются специалисты инженерно-технологического персонала доменных цехов, студенты.
Научная новизна полученных в работе результатов заключается в применении нового метода эффективной организации и ведения специализированного алгоритмического и программного обеспечения решения задачи оптимизации расчета многокомпонентной плавильной шихты, ориентированного на повышение эффективности управления процессами получения качественных сплавов с использованием современных методов обработки информации: использование гибкой методологии разработки (Agile) и таск-трекера Atlassian JIRA для ведения проекта, взаимодействия с заказчиком во время разработки, отслеживания ошибок, визуального отображения задач и мониторинга процесса их выполнения; функциональное моделирование процессов для реализации web-приложения решения задачи оптимизации затрат на перевозку продукции на основе методологии IDEF0 и средства реализации Ramus Educational; использование методики коллективного владения программным кодом на основе сервиса (удаленного репозитория) Atlassian Bitbucket.
Практическая значимость результатов заключается в том, что разработанное программное обеспечение позволит: производить расчёт оптимального состава многокомпонентной плавильной шихты; инженерно-технологическому персоналу литейных цехов металлургических предприятий сократить время на выполнение расчетов состава многокомпонентной плавильной шихты за счет реализации эргономичного web-интерфейса; специалистам отдела сопровождения информационных систем предоставляет условия для снижения трудозатрат на сопровождение, совершенствование и развитие системы с учетом пожеланий пользователей.
Результаты работы могут быть использованы также в учебном процессе для обучения бакалавров и магистрантов по направлению «Информационные системы и технологии».The master's thesis is devoted to the development of a web application for solving the problem of optimizing the composition of a multicomponent melting mixture. In the course of the work, the main stages of software development were considered: analysis of the subject area; creation of software architecture; development of algorithmic support and reference documentation; distribution kit preparation. In the process of performing the work, all the goals and objectives of the project have been realized. The main users of the system are specialists of the engineering and technological personnel of blast-furnace shops, students. The scientific novelty of the results obtained in the work lies in the application of a new method of effective organization and maintenance of specialized algorithmic and software for solving the problem of optimizing the calculation of a multicomponent melting charge, focused on increasing the efficiency of control of the processes of obtaining high-quality alloys using modern information processing methods: use of flexible development methodology (Agile) and the Atlassian JIRA task tracker for project management, interaction with the customer during development, tracking errors, visual display of tasks and monitoring the process of their implementation; functional modeling of processes for the implementation of a web-application for solving the problem of optimizing the costs of transportation of products based on the IDEF0 methodology and Ramus Educational tools; using the method of collective ownership of the program code based on the service (remote repository) Atlassian Bitbucket. The practical significance of the results lies in the fact that the developed software will allow: to calculate the optimal composition of the multicomponent melting mixture; to the engineering and technological personnel of foundries of metallurgical enterprises to reduce the time for performing calculations of the composition of a multicomponent melting mixture by implementing an ergonomic web interface; for specialists of the information systems support department, it provides conditions for reducing labor costs for maintaining, improving and developing the system, taking into account the wishes of users. The results of the work can also be used in the educational process for training bachelors and undergraduates in the direction of "Information systems and technologies".
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Ramos, Archibold Antonio Miguel. „Thermal Assessment of a Latent-Heat Energy Storage Module During Melting and Freezing for Solar Energy Applications“. Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5433.
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Capital investment reduction, exergetic efficiency improvement and material compatibility issues have been identified as the primary techno-economic challenges associated, with the near-term development and deployment of thermal energy storage (TES) in commercial-scale concentrating solar power plants. Three TES techniques have gained attention in the solar energy research community as possible candidates to reduce the cost of solar-generated electricity, namely (1) sensible heat storage, (2) latent heat (tank filled with phase change materials (PCMs) or encapsulated PCMs packed in a vessel) and (3) thermochemical storage. Among these the PCM macro-encapsulation approach seems to be one of the most-promising methods because of its potential to develop more effective energy exchange, reduce the cost associated with the tank and increase the exergetic efficiency. However, the technological barriers to this approach arise from the encapsulation techniques used to create a durable capsule, as well as an assessment of the fundamental thermal energy transport mechanisms during the phase change.
A comprehensive study of the energy exchange interactions and induced fluid flow during melting and solidification of a confined storage medium is reported in this investigation from a theoretical perspective. Emphasis has been placed on the thermal characterization of a single constituent storage module rather than an entire storage system, in order to, precisely capture the energy exchange contributions of all the fundamental heat transfer mechanisms during the phase change processes. Two-dimensional, axisymmetric, transient equations for mass, momentum and energy conservation have been solved numerically by the finite volume scheme.
Initially, the interaction between conduction and natural convection energy transport modes, in the absence of thermal radiation, is investigated for solar power applications at temperatures (300 - 400°). Later, participating thermal radiation within the storage medium has been included in order to extend the conventional natural convection-dominated model and to analyze its influence on the melting and freezing dynamics at elevated temperatures (800 - 850°). A parametric analysis has been performed in order to ascertain the effects of the controlling parameters on the melting/freezing rates and the total and radiative heat transfer rates at the inner surface of the shell. The results show that the presence of thermal radiation enhances the melting and solidification processes.
Finally, a simplified model of the packed bed heat exchanger with multiple spherical capsules filled with the storage medium and positioned in a vertical array inside a cylindrical container is analyzed and numerically solved. The influence of the inlet mass flow rate, inner shell surface emissivity and PCM attenuation coefficient on the melting dynamics of the PCM has been analyzed and quantified.
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FERREIRA, MARCUS V. L. „Estudo in vitro da fusao de hidroxiapatita e esmalte em superficies de esmalte humano pelo laser de Nd: YAG“. reponame:Repositório Institucional do IPEN, 2000. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10856.
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Made available in DSpace on 2014-10-09T12:44:45Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T13:58:00Z (GMT). No. of bitstreams: 1 06997.pdf: 4582469 bytes, checksum: 7c5c05e2d6d13841e0e7d53eb604c3d2 (MD5)
Dissertacao (Mestrado Profissionalizante em Lasers em Odontologia)
IPEN/D-MPLO
Intituto de Pesquisas Energeticas e Nucleares, IPEN/CNEN-SP; Faculdade de Odontologia, Universidade de Sao Paulo
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Seiner, Lizárraga Lizardo. „Carey, Mark. In the Shadow of Melting Glaciers. Climate Change and Andean Society. New York: Oxford University Press, 2010, 273 pp“. Pontificia Universidad Católica del Perú, 2012. http://repositorio.pucp.edu.pe/index/handle/123456789/121552.
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Williams, Clare Carlisle. „A Multi-Proxy Approach to Understanding Abrupt Climate Change and Laurentide Ice Sheet Melting History Based on Gulf of Mexico Sediments“. Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5332.
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During the last deglaciation (ca. 24-10 ka thousand years ago (ka)), the North American Laurentide Ice Sheet (LIS) was a major source of meltwater to the Arctic Ocean, North Atlantic Ocean, and the Gulf of Mexico (GOM), and it is hypothesized that meltwater routing played an important role in regulating Late Quaternary millennial-scale climate variability, via its influence on Atlantic Meridional Overturning Circulation (AMOC). For example, the meltwater routing hypothesis predicts that a rerouting of meltwater from the GOM to the North Atlantic and/or Arctic Oceans resulted in a decrease of North Atlantic Deep Water (NADW) formation and subsequent cooling in the northern North Atlantic region, at the onset of the Younger Dryas (ca. 13 ka). The GOM was an important outlet for meltwater that likely originated from the southern margin of the LIS. Northern GOM sediments document episodic LIS meltwater input via the Mississippi River throughout the last deglaciation, and further study may provide insight to the evolution of LIS deglaciation and the hydrological response of meltwater flux to the marine depositional environment of GOM. Here, a multi-proxy geochemical study, based on marine sediments from Orca Basin, in northern GOM, aims to 1) reconstruct high-resolution records of deglacial (ca. 24-10 ka) LIS melting history to assess linkage between meltwater input to the GOM and deglacial climate change; 2) investigate the relationship between marine-based records of meltwater input and terrestrial evidence for continental deglaciation to reconstruct LIS drainage patterns within the Mississippi River watershed; and 3) reconstruct the redox state of Orca Basin sediments to evaluate the potential role of turbidity flows as a means of meltwater transport into the northern GOM. All data for this study is from core MD02-2550, a 9.09 m long giant box core, recovered from 2248 m water depth from the Orca Basin, approximately 300 km southwest of the modern Mississippi River delta. High sedimentation rates (45 cm/thousand years (kyr)) and 0.5 to 2 cm sampling resolution allow for sub-centennial sampling resolution. An anoxic hypersaline brine lake currently occupies the bottom 200 m of Orca Basin; yet, visible laminations and color changes that suggest episodic suboxic to anoxic sedimentary conditions during deglaciation, possibly related to LIS meltwater input and/or local biologic productivity.
In chapter one, paired d18O and Mg/Ca-sea-surface temperature (SST) analyses on two varieties of the surface-dwelling planktic foraminifera Globigerinoides ruber (G. ruber; (white and pink, separately)) are used to reconstruct deglacial changes in GOM seawater d18O (d18Osw). Once corrected for global ice volume, the ice volume-corrected d18Osw (d18Oivc-sw) record is primarily influenced by LIS meltwater. d18Oivc-sw records document negative excursions at ca. 19-18.2, 17.5-16.2, 15.3-14.8, and 13.7-13 ka, interpreted as four LIS melting events, followed by the cessation of meltwater at the onset of the Younger Dryas (12.9 ka). Additionally, LIS melting at ca. 17.5 ka suggests that enhanced seasonality in the North Atlantic produced mild summers sufficient for ice sheet retreat during the Mystery Interval (17.5-14.5 ka) despite extremely cold winters.
Because of the inherent difficulties in quantifying meltwater flux using d18Oivc-sw data, foraminiferal (G. ruber) Ba/Ca data are generated in chapter two to assess the influence of LIS meltwater on GOM salinity (a function of meltwater flux) during deglaciation. Ba concentrations in the Mississippi River are elevated relative to GOM seawater and are negatively correlated to sea-surface salinity. Because foraminiferal Ba/Ca (Ba/Caforam) exhibits a predictable relationship to the Ba/Ca of seawater (Ba/Casw), it may be used to calculate changes in salinity arising from deglacial variations in Mississippi River discharge. A complicating factor for Ba/Ca-based salinity interpretations is that Ba concentrations vary spatially throughout the Mississippi River watershed. For example, modern Missouri and Upper Mississippi River Ba concentrations (633 and 436 nM, respectively) are higher than that of the Ohio River (253 nM). Thus, GOM Ba/Ca variability could reflect changes in total Mississippi River input and/or shifts in the dominant region of LIS melting. Applying the modern spatial variability of Ba, we can gain insights into the pattern of ice retreat along the southern margin of the LIS during the last deglaciation.
d18Oivc-sw and Ba/Ca results suggest that meltwater, originating from the Great Lakes region, entered the GOM at ca. 19.0 ka and may have contributed to global sea level rise. A melting event at ca. 17.5 ka coincided with Lake Erie Lobe retreat and may have preconditioned the North Atlantic for AMOC instability during the Mystery Interval (ca. 17.5-14.5 ka). Elevated GOM Ba/Ca (ca. 15.6 to 14.0 ka) suggests greater meltwater input from the Ba-rich Missouri and Upper Mississippi River watershed during the second half of the Mystery Interval (ca. 16.1-14.5 ka), when wet climate conditions prevailed in the southwestern United States and Central America. Overall, Ba/Ca and d18Oivc-sw data suggest large variations in the delivery of meltwater to the Mississippi River and GOM during the last deglaciation.
In chapter three, a suite of redox sensitive trace metals (Mo, Re, U, Mn) from bulk sediment samples are analyzed to reconstruct the redox state of Orca Basin sediments, from the Last Glacial Maximum through the early Holocene (24-7 ka). Variations in the redox state of Orca Basin sediments during deglaciation may be due to changes in local biologic productivity, sediment transport, and/or regional/global physical oceanography. Laminated sediments enriched with authigenic Mo, Re, and U, suggest suboxic to anoxic conditions coincident with high total organic carbon fluxes and LIS meltwater input at ~17.0 ka. Low authigenic trace element concentrations, high quantities of terrigenous material, and abundant Cretaceous-age nannofossils in a 19-cm homogenous interval indicate a turbidite in Orca Basin at ca. 14.4 ka. This stratigraphic unit correlates with evidence from Pigmy Basin, and the Louisiana Shelf, suggesting increased meltwater flux may reflect LIS contribution to Meltwater pulse 1a (MWP-1a) sea level rise. Trace element records coupled with analyses of Orca Basin sedimentary structures will likely improve understanding of deglacial water column stratification, how meltwater entered the GOM (i.e. as a buoyant cap or at depth via sediment-laden hyperpycnal plumes), and the affects of glacial meltwater on marine biologic productivity.
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Ayasoufi, Anahita. „Numerical Simulation of Heat Conduction with Melting and/or Freezing by Space-Time Conservation Element and Solution Element Method“. See Full Text at OhioLINK ETD Center (Requires Adobe Acrobat Reader for viewing), 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=toledo1103147485.
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Dissertation (Ph.D.)--University of Toledo, 2004.Typescript. "A dissertation [submitted] as partial fulfillment of the requirements of the Doctor of Philosophy degree in Engineering." Bibliography: leaves 194-211.
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Kirchner, Kathleen. „A simulation study of simple ionic liquids near charged walls : the melting of the electric double layers and structural transitions at the interface“. Thesis, University of Strathclyde, 2013. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=25540.
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The temperature dependence of the electrical double layer (EDL) capacitance of high and low temperature ionic liquids (IL) is under excited debates within experimental, theoretical & computational communities for decades. Using a coarse-grain model of ILs with asymmetric sized ions we studied the EDL behaviour of ILs at an electrified interface to gain understanding in the temperature-effect. We improved the accuracy of the capacitance calculations by increasing the overall simulation time by an order of magnitude compared to former publications and discussed possible error sources. The analysis of different temperatures from 250K to 500K revealed a voltage dependent temperature-effect on the differential capacitance. To our opinion, the temperature dependence can be attributed to the formation of well ordered structures of the EDL at low temperatures, that are ‘melted’ at higher temperatures. The results provide an explanation for the contradicting experimental results published in the past years. By systematically analysing number density profiles, a charge induced structural transition has been revealed. At most surface charge densities under study, the electric double layer forms a multilayered structure. At transition points, a hexatic (also termed as Moiré-like) monolayer structure is formed by the counter-ions. These findings correlate very well with experimental observations on room temperature ionic liquids and metal melts by Freyland and co-workers (Phys. Chem. Chem. Phys., 2008, 10, 923-936). The ions of the hexatic layer screen the electrode charge completely, thereby annihilating the interaction between electrode and subsequent bulk ionic liquid. Moreover we can report the formation of herring-bone structures at higher surface charge densities, that form as the superposition of two hexatic layers.
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Kota, Krishna. „DESIGN AND EXPERIMENTAL STUDY OF AN INTEGRATED VAPOR CHAMBER – THERMAL ENERGY STORAGE SYSTEM“. Doctoral diss., University of Central Florida, 2008. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2816.
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Future defense, aerospace and automotive technologies involve electronic systems that release high pulsed waste heat like during high power microwave and laser diode applications in tactical and combat aircraft, and electrical and electronic systems in hybrid electric vehicles, which will require the development of an efficient thermal management system. A key design issue is the need for fast charging so as not to overheat the key components. The goal of this work is to study the fabrication and technology implementation feasibility of a novel high energy storage, high heat flux passive heat sink. Key focus is to verify by theory and experiments, the practicability of using phase change materials as a temporary storage of waste heat for heat sink applications. The reason for storing the high heat fluxes temporarily is to be able to reject the heat at the average level when the heat source is off. Accordingly, a concept of a dual latent heat sink intended for moderate to low thermal duty cycle electronic heat sink applications is presented. This heat sink design combines the features of a vapor chamber with rapid thermal energy storage employing graphite foam inside the heat storage facility along with phase change materials and is attractive owing to its passive operation unlike some of the current thermal management techniques for cooling of electronics employing forced air circulation or external heat exchangers. In addition to the concept, end-application dependent criteria to select an optimized design for this dual latent heat sink are presented. A thermal resistance concept based design tool/model has been developed to analyze and optimize the design for experiments. The model showed that it is possible to have a dual latent heat sink design capable of handling 7 MJ of thermal load at a heat flux of 500 W/cm2 (over an area of 100 cm2) with a volume of 0.072 m3 and weighing about 57.5 kg. It was also found that with such high heat flux absorption capability, the proposed conceptual design could have a vapor-to-condenser temperature difference of less than 10 0C with a volume storage density of 97 MJ/m3 and a mass storage density of 0.122 MJ/kg. The effectiveness of this heat sink depends on the rapidness of the heat storage facility in the design during the pulse heat generation period of the duty cycle. Heat storage in this heat sink involves transient simultaneous laminar film condensation of vapor and melting of an encapsulated phase change material in graphite foam. Therefore, this conjugate heat transfer problem including the wall inertia effect is numerically analyzed and the effectiveness of the heat storage mechanism of the heat sink is verified. An effective heat capacity formulation is employed for modeling the phase change problem and is solved using finite element method. The results of the developed model showed that the concept is effective in preventing undue temperature rise of the heat source. Experiments are performed to investigate the fabrication and implementation feasibility and heat transfer performance for validating the objectives of the design i.e., to show that the VCTES heat sink is practicable and using PCM helps in arresting the vapor temperature rise in the heat sink. For this purpose, a prototype version of the VCTES heat sink is fabricated and tested for thermal performance. The volume foot-print of the vapor chamber is about 6"X5"X2.5". A custom fabricated thermal energy storage setup is incorporated inside this vapor chamber. A heat flux of 40 W/cm2 is applied at the source as a pulse and convection cooling is used on the condenser surface. Experiments are done with and without using PCM in the thermal energy storage setup. It is found that using PCM as a second latent system in the setup helps in lowering the undue temperature rise of the heat sink system. It is also found that the thermal resistance between the vapor chamber and the thermal energy storage setup, the pool boiling resistance at the heat source in the vapor chamber, the condenser resistance during heat discharging were key parameters that affect the thermal performance. Some suggestions for future improvements in the design to ease its implementation and enhance the heat transfer of this novel heat sink are also presented.Ph.D.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering PhD
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Gunasekara, Saman Nimali. „Phase Equilibrium-aided Design of Phase Change Materials from Blends : For Thermal Energy Storage“. Doctoral thesis, KTH, Kraft- och värmeteknologi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-212440.
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Climate change is no longer imminent but eminent. To combat climate change, effective, efficient and smart energy use is imperative. Thermal energy storage (TES) with phase change materials (PCMs) is one attractive choice to realize this. Besides suitable phase change temperatures and enthalpies, the PCMs should also be robust, non-toxic, environmental-friendly and cost-effective. Cost-effective PCMs can be realized in bulk blends. Blends however do not have robust phase change unless chosen articulately. This thesis links bulk blends and robust, cost-effective PCMs via the systematic design of blends as PCMs involving phase equilibrium evaluations. The key fundamental phase equilibrium knowledge vital to accurately select robust PCMs within blends is established here. A congruent melting composition is the most PCM-ideal among blends. Eutectics are nearly ideal if supercooling is absent. Any incongruent melting composition, including peritectics, are unsuitable as PCMs. A comprehensive state-of-the-art evaluation of the phase equilibrium-based PCM design exposed the underinvestigated categories: congruent melting compositions, metal alloys, polyols and fats. Here the methods and conditions essential for a comprehensive and transparent phase equilibrium assessment for designing PCMs in blends are specified. The phase diagrams of the systems erythritol-xylitol and dodecane-tridecane with PCM potential are comprehensively evaluated. The erythritol-xylitol system contains a eutectic in a partially isomorphous system unlike in a non-isomorphous system as previous literature proposed. The dodecane-tridecane system forms a probable congruent minimum-melting solid solution, but not a maximum-melting liquidus or a eutectic as was previously proposed. The sustainability aspects of a PCM-based TES system are also investigated. Erythritol becomes cost-effective if produced using glycerol from bio-diesel production. Olive oil is cost-effective and has potential PCM compositions for cold storage. A critical need exists in the standardization of methods and transparent results reporting of the phase equilibrium investigations in the PCM-context. This can be achieved e.g. through international TES collaboration platforms.Energi är en integrerad del av samhället men energiprocesser leder till miljöbelastning, och klimatförändringar. Därför är effektiv energianvändning, ökad energieffektivitet och smart energihantering nödvändigt. Värmeenergilagring (TES) är ett attraktivt val för att bemöta detta behov, där ett lagringsalternativ med hög densitet är s.k. fasomvandlingsmaterial (PCM). Ett exempel på ett billigt, vanligt förekommande PCM är systemet vatten-is, vilket har använts av människor i tusentals år. För att tillgodose de många värme- och kylbehov som idag uppstår inom ett brett temperaturintervall, är det viktigt med innovativ design av PCM. Förutom lämplig fasförändringstemperaturer, entalpi och andra termofysikaliska egenskaper, bör PCM också ha robust fasändring, vara miljövänlig och kostnadseffektiv. För att förverkliga storskaliga TES system med PCM, är måste kostnadseffektivitet och robust funktion under många cykler bland de viktigaste utmaningarna. Kostnadseffektiva PCM kan bäst erhållas från naturliga eller industriella material i bulkskala, vilket i huvudsak leder till materialblandningar, snarare än rena ämnen. Blandningar uppvisar dock komplexa fasförändringsförlopp, underkylning och/eller inkongruent smältprocess som leder till fasseparation. Denna doktorsavhandling ger ny kunskap som möjliggör att bulkblandningar kan bli kostnadseffektiva och robusta PCM-material, med hjälp av den systematiskutvärdering av fasjämvikt och fasdiagram. Arbetet visar att detta kräver förståelse av relevanta grundläggande fasjämviktsteorier, omfattande termiska och fysikalisk-kemiska karakteriseringar, och allmänt tillämpliga teoretiska utvärderingar. Denna avhandling specificerar befintlig fasjämviktsteori för PCM-sammanhang, men sikte på att kunna välja robusta PCM blandningar med specifika egenskaper, beroende på tillämpning. Analysen visar att blandningar med en sammansättning som leder till kongruent smältande, där faser i jämvikt har samma sammansättning, är ideala bland PCM-blandningar. Kongruent smältande fasta faser som utgör föreningar eller fasta lösningar av ingående komponenter är därför ideala. Eutektiska blandningar är nästan lika bra som PCM, så länge underkylning inte förekommer. Därmed finns en stor potential för att finna och karakterisera PCM-ideala blandningar som bildar kongruent smältande föreningar eller fasta lösningar. Därigenom kan blandningar med en skarp, reversibel fasändring och utan fasseparation erhållas – egenskaper som liknar rena materialens fasändringsprocess. Vidare kan man, via fasdiagram, påvisa de blandningar som är inkongruent smältande, inklusive peritektiska blandningar, som är direkt olämpliga som PCM. Denna avhandling ger grundläggande kunskap som är en förutsättning för att designa PCM i blandningar. Genom en omfattande state-of-the-art utvärdering av fas-jämviktsbaserad PCM-design lyfter arbetet de PCM-idealiska blandningarna som hittills inte fått någon uppmärksamhet, såsom kongruenta smältande blandningar, och materialkategorierna metallegeringar, polyoler och fetter. Resultatet av arbetet visar dessutom att vissa PCM-material som ibland föreslås är direkt olämpliga då fasdiagram undersöks, bl a pga underkylning och även peritektiska system med fasseparation och degradering av kapaciteten (t ex Glauber-salt och natriumacetat-trihydrat). Denna avhandling specificerar och upprättar grundläggande teori samt tekniker, tillvägagångssätt och förhållanden som är nödvändiga för en omfattande och genomsynlig fasjämviktsbedömning, för utformning av PCM från blandningar för energilagering. Med detta som bas har följande fasdiagramtagits fram fullständigt: för erytritol-xylitol och för dodekan-tridekan, med PCM-potential för låg temperaturuppvärmning (60-120 °C) respektive frysning (-10 °C till -20 °C) utvärderas fullständigt. Erytritol-xylitol systemet har funnits vara eutektiskt i ett delvis isomorft system, snarare än ett icke-isomorft system vilket har föreslagits tidigare litteratur. Dodekan-tridekan systemet bildar ett system med kongruent smältande fast lösning (idealisk som en PCM) vid en minimumtemperatur, till skillnad från tidigare litteratur som föreslagt en maximumtemperatur, eller ett eutektiskt system. Teoretisk modellering av fasjämvikt har också genomförts för att komplettera det experimentella fasdiagrammet för systemet erytritol-xylitol. Efter granskning av de metoder som använts tidigare i PCM-litteraturen har här valts ett generiskt tillvägagångssätt (CALPHAD-metoden). Denna generiska metod kan bedöma vilken typ av material och fasändring som helst, till skillnad från en tidigare använda metoder som är specifika för materialtyper eller kemiska egenskaper. Denna teoretiska studie bekräftar termodynamiskt solvus, solidus, eutektisk punkt och erytritol-xylitol fasdiagrammet i sin helhet. Vad gäller hållbarhetsaspekter med PCM-baserad TES, lyfter denna avhandling fokus på förnybara och kostnadseffektiva material (t.ex. polyoler och fetter) som PCM. Som exempel har här undersökts erytritol och olivolja, med förnybart ursprung. Erytritol skulle kunna bli ett kostnadseffektivt PCM (163 USD/kWh), om det produceras av glycerol vilket är en biprodukt från biodiesel/bioetanolframställning. Olivolja är ännu ett kostnadseffektivt material (144 USD/kWh), och som här har påvisats innehålla potentiella PCM sammansättningar med lämpliga fasändringsegenskaper för kylatillämpningar. En övergripande slutsats från denna avhandling är att det finns ett behov av att standardisera tekniker, metoder och transparent resultatrapportering när det gäller undersökningar av fasjämvikt och fasdiagram i PCM-sammanhang. Internationella samarbetsplattformar för TES är en väg att koordinera arbetet.
QC 20170830
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Mickelson, Leah E. „Cyanine Dye Interactions with Quadruplex and Duplex DNA: Changes in Conformation, Stability, and Affinity“. Digital Archive @ GSU, 2011. http://digitalarchive.gsu.edu/chemistry_theses/38.
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There is a high demand for quadruplex-specific compounds that not only bind preferentially to quadruplex DNA over duplex DNA, but also bind to one quadruplex motif over other motifs. Quadruplex structures are recognized as common occurrences in cancer cells, and if a compound could stabilize this structure, it may serve as an effective anti-cancer treatment with minimal side effects. In this study, cyanine dyes’ interactions with DNA were analyzed with fluorescence titrations, UV-Vis thermal studies, circular dichroism titrations, and surface plasmon resonance (SPR) analysis. With these techniques, binding affinity, DNA stabilization, and conformational shifts were analyzed to determine if cyanine dyes could act as quadruplex-specific binding compounds for possible cancer treatments.
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Enderlin, Ellyn Mary. „Observations and Modeling of Greenland Outlet Glacier Dynamics“. The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1372609057.
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Arosemena, Arturo. „Numerical Model of MeltingProblems“. Thesis, KTH, Mekanik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-221141.
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In the present study, a finite volume method is employed to modelthe advection-diffusion phenomenon during a pure substance meltingprocess. The exercise is limited to a benchmark problem consisting ofthe 2D melting from a vertical wall of a PCM driven by natural convectionin the melt. Numerical results, mainly the temporal evolutionof average Nusselt number at the hot wall and the average liquid fraction,are validated by available literature data and the effect of thermalinertia in the heat transfer is considered as well. Finally, motivatedby recent publications and the model presented here, possible new researchtopics are proposed.
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Ha, Oai The. „Modeling and Numerical Investigation of Hot Gas Defrost on a Finned Tube Evaporator Using Computational Fluid Dynamics“. DigitalCommons@CalPoly, 2010. https://digitalcommons.calpoly.edu/theses/400.
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Defrosting in the refrigeration industry is used to remove the frost layer accumulated on the evaporators after a period of running time. It is one way to improve the energy efficiency of refrigeration systems. There are many studies about the defrosting process but none of them use computational fluid dynamics (CFD) simulation. The purpose of this thesis is (1) to develop a defrost model using the commercial CFD solver FLUENT to simulate numerically the melting of frost coupled with the heat and mass transfer taking place during defrosting, and (2) to investigate the thermal response of the evaporator and the defrost time for different hot gas temperatures and frost densities. A 3D geometry of a finned tube evaporator is developed and meshed using Gambit 2.4.6, while numerical computations were conducted using FLUENT 12.1. The solidification and melting model is used to simulate the melting of frost and the Volume of Fluid (VOF) model is used to render the surface between the frost and melted frost during defrosting. A user-defined-function in C programming language was written to model the frost evaporation and sublimation taking place on the free surface between frost and air. The model was run under different hot gas temperatures and frost densities and the results were analyzed to show the effects of these parameters on defrosting time, input energy and stored energy in the metal mass of the evaporator. The analyses demonstrate that an optimal hot gas temperature can be identified so that the defrosting process takes place at the shortest possible melting time and with the lowest possible input energy.
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Ehms, José Henrique Nazzi. „Comparação de modelos numéricos de malha fixa baseados em entalpia para os processos de fusão e de solidificação de PCM em esfera“. Universidade do Vale do Rio dos Sinos, 2018. http://www.repositorio.jesuita.org.br/handle/UNISINOS/7486.
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CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Armazenamento térmico apresenta grande potencial de utilização em diversas aplicações, como energia solar, climatização, conservação de alimentos ou aproveitamento de calor residual em processos industriais. O armazenamento térmico de calor latente é realizado com materiais de mudança de fase (PCM), através dos processos de fusão e solidificação. A representação destes processos através de simulação numérica é realizada com o acréscimo ao modelo matemático básico, composto pelas equações da conservação da massa, quantidade de movimento e energia, modelos para descrever o calor latente e a transição na velocidade entre as fases, tais como: Darcy STM (source term method), VVM (variable viscosity method) e SOM (switch-off method). No entanto, a grande maioria das pesquisas nesta área utiliza o primeiro método. Além disso, são poucos os estudos comparativos de diferentes métodos para descrever processos de mudança de fase. Assim, o objetivo do presente estudo é comparar os métodos Darcy STM, VVM e misto (utilizando elementos dos dois anteriores) na simulação numérica de processos de fusão e de solidificação do PCM RT27 no interior de uma esfera. O estudo foi realizado utilizando-se fluidodinâmica computacional, através do método dos volumes finitos. O Modelo numérico foi validado com resultados experimentais da literatura. Os resultados quantitativos e qualitativos de fração líquida mostram que o método Darcy STM é mais adequado ao processo de solidificação, enquanto o método VVM produz resultados mais próximos aos experimentais no processo de fusão. O custo computacional foi menor para o método Darcy STM e maior para o método VVM, enquanto o método misto apresenta custo computacional pouco inferior ao do método VVM. Na análise da camada líquida na fusão de contato, foram analisadas a velocidade descendente do sólido, a espessura da camada e a vazão na camada. Os resultados referentes a camada líquida indicaram significativa influência das configurações do método Darcy STM. No entanto, são pouco influenciados pelas configurações do método VVM.
Thermal energy storage presents great potential of utilization in several applications, such as solar energy, HVAC systems, food conservation or waste heat recovery in industrial processes. Latent heat thermal energy storage is realized with phase change materials (PCM), through solidification and melting processes. Representation of such processes through numerical simulation is performed with the addition to the basic numerical model, composed of the conservation equations of mass, momentum and energy, models to account the latent heat and the velocity transition between the phases, such as: Darcy STM (source term method), VVM (variable viscosity method) and SOM (switch-off method). However, the large majority of the research on such area employ the first method. Besides that, there are few comparative studies of different methods to describe phase change processes. Thus, the objective of the present work is compare Darcy STM, VVM and mixed method (using elements of the two prior) in the simulation of melting and solidification processes of PCM RT27 inside a sphere. The study was realized using computational fluid dynamics, with the finite volume method. The numerical model was validated with experimental results from literature. Quantitative and qualitative results of liquid fraction show that Darcy STM is most suitable to solidification process, while VVM produces results closer to experimental in the melting process. Computational cost was smaller for Darcy STM and greater for VVM, while mixed method presents computational cost slightly lower than the one of VVM. In the analysis of the liquid layer in close contact melting, were analyzed descending velocity of the solid, liquid layer thickness and the flow in the liquid layer. The results regarding the liquid layer denote significant influence of the configurations for Darcy STM. However, such results are little influenced by the configurations of VVM.
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Maréchal, William. „Utilisation de méthodes inverses pour la caractérisation de matériaux à changement de phase (MCP)“. Thesis, Pau, 2014. http://www.theses.fr/2014PAUU3014/document.
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Avec le développement des énergies intermittentes et la raréfaction des énergies fossiles, le sujet du stockage de l’énergie prend de plus en plus d’ampleur. Une des voies étudiée est le stockage thermique par utilisation de matériaux à changement de phase (MCP). Cette voie est en outre développée pour améliorer l’inertie thermique dans le secteur du bâtiment. Pour utiliser au mieux ces matériaux il est nécessaire de pouvoir prévoir leur comportement énergétique. Cela nécessite une connaissance précise des propriétés thermophysiques, et en premier lieu de la fonction enthalpie massique . Actuellement, il est souvent proposé d'approximer cette enthalpie par l'intégration directe des thermogrammes de la calorimétrie utilisant notamment la notion de capacité calorifique "équivalente". Cette approche est cependant fausse car le thermogramme n’est qu'une représentation en fonction du temps de phénomènes complexes faisant intervenir non seulement les propriétés énergétique du matériaux mais également les transferts thermiques au sein de la cellule du calorimètre. Il en résulte, par exemple, que la forme des thermogrammes, et donc l’enthalpie apparente, dépend de la vitesse de réchauffement et de la masse de l'échantillon ce qui n'est pas le cas de l'enthalpie des MCP qui ne dépend, à pression fixe, que de la température ou de la concentration (pour les solutions). On propose de comparer la sortie d’un modèle numérique direct avec des thermogrammes expérimentaux. L’objectif principal de cette thèse est alors d’utiliser ce modèle dans le cadre d’une méthode inverse permettant l’identification des paramètres de l’équation d’état permettant alors de calculer l’enthapie massique . Dans un premier temps, il est donc présenté le détail d'un modèle 2D dit enthalpique qui néglige la convection, validé par l'expérience, permettant de reconstituer les thermogrammes de corps purs ou de solutions binaires dont les enthalpies sont connues. Il en est déduit une étude de l'influence des différents paramètres ( , , , ...) sur la forme des thermogrammes pour en déduire leurs sensibilités. Une réduction de ce modèle est ensuite effectuée pour réduire le temps de calcul du modèle direct en vue de l’utilisation dans une méthode inverse. Cette dernière est décrite ainsi que les algorithmes d’optimisation correspondants (de Levenberg-Marquardt, génétique ou du simplexe qui s'est avéré le plus rapide) dans un second temps. Nous appliquerons ensuite cet algorithme pour identifier, à partir d'expériences, la fonction enthalpie de corps purs ou de solutions binaires. Les résultats obtenus montrent qu’il est possible d’identifier une fonction independante de la vitesse de réchauffement et de la masse, ce qui valide la méthode. Une analyse des différentes sources d’erreurs dans le processus d’identification et leurs influences sur le résultat permet d’évaluer la qualité de la fonction enthalpie que l’on identifie. Enfin, cette même approche a été utilisée pour analyser une expérience réalisée sur un échantillon d’un matériau composite utilisé dans le bâtiment (ciment avec inclusion de MCP micro-encapsulé). Dans ce cas encore, nos méthodes permettent une caractérisation énergétique pertinenteWith the development of intermittent sources of energy and the depletion of fossil fuels, the subject of energy storage is becoming an important topic. One of the studied options is tthe latent hermal storage using of phase change materials (PCM). One application for this type of energy storage is to improve the thermal insulation in buildings. To make the best use of these materials it is necessary to be able to predict their energy behavior. This requires a precise knowledge of their thermophysical properties, first of all of the specific enthalpy function of the material . Currently, it is often suggested to approximate the enthalpy by the direct integration of the thermograms obtained through calorimetry experiments (notion of "equivalent" calorific capacity). This approach is false because thermograms are only a time related representation of complex phenomena where thermal transfers arise in the cell of the calorimeter acting with the thermophysical properties. As a result, for example, the shape of thermograms depends on the heating rate and on the mass of the sample, which is not the case for the enthalpy of the PCM, which depends, at constant pressure, only on the temperature or on the concentration (for the solutions). We propose to compare the results given by a of a numerical direct model with experimental thermograms. The main objective in this thesis is then to use this direct model in an inverse method in order to identify the parameters of the equation of state, which enables us to calculate the specific enthalpy . First of all, the detail of an enthalpy model is presented, and then validated by comparison with experiments, allowing us to reconstruct the thermograms of pure substances or of salt solutions, of which the enthalpies are known. A study of the influence of the various parameters ( , , , .,..) on the shape of thermograms is also undertaken in order to deduce their sensibilities. A reduced model is then developed in order to reduce the calculating time of the direct model. This optimized model allows the use of inverse methods with acceptable durations. Several inverses algorithms are then presented: Levenberg-Marquardt, evolutionary and Simplex which has proved to be the fastest). We shall then apply this algorithm to identify, from calorimetric experiments, the enthalpy function of pure substances or of salt solutions. The results that we obtain show that it is possible to identify a function independent of the heating rate and of the mass, which validates the method. An analysis of the various sources of errors in the identification process and of their influences on the result allows us to estimate the quality of the enthalpy function that we identify
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Berlin, Katja. „In-situ transmission electron microscopy on high-temperature phase transitions of Ge-Sb-Te alloys“. Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19219.
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Das Hochtemperaturverhalten beeinflusst viele verschiedene Prozesse von der Materialherstellung bis hin zur technologischen Anwendung. In-situ Transmissionselektronenmikroskopie (TEM) bietet die Möglichkeit, die atomaren Prozesse während struktureller Phasenübergänge direkt und in Realzeit zu beobachten. In dieser Arbeit wurde in-situ TEM angewendet, um die Reversibilität des Schmelz- und Kristallisationsprozesses, sowie das anisotropen Sublimationsverhaltens von Ge-Sb-Te (GST) Dünnschichten zu untersuchen. Die gezielte Probenpräparation für die erfolgreiche Beobachtung der Hochtemperatur-Phasenübergänge wird hervorgehoben. Die notwendige Einkapselung für die Beobachtung der Flüssigphase unter Vakuumbedingungen und die erforderliche sauberer Oberfläche für den Sublimationsprozess werden detailliert beschrieben. Außerdem wird die Elektronenenergieverlustspektroskopie eingesetzt um die lokale chemische Zusammensetzung vor und nach den Übergängen zu bestimmen. Die Untersuchung der Grenzflächenstruktur und Dynamik sowohl beim Phasenübergang fest-flüssig als auch flüssig-fest zeigt Unterschiede zwischen den beiden Vorgängen. Die trigonale Phase von GST weist beim Schmelzen eine teilweise geordnete Übergangszone an der fest-flüssig-Grenzfläche auf, während ein solcher Zwischenzustand bei der Erstarrung nicht entsteht. Außerdem läuft der Schmelzvorgang zeitlich linear ab, während die Kristallisation durch eine Wurzelabhängigkeit von der Zeit mit überlagerter Start-Stopp-Bewegung beschrieben werden kann. Der Einfluss der Substrat-Grenzfläche wird diskutiert und die Oberflächenenergie von GST bestimmt. Die anisotrope Dynamik führt beim Phasenübergang fest-gasförmig der kubischen Phase von GST zur Ausbildung stabiler {111} Facetten. Dies erfolgt über die Bildung von Kinken und Stufen auf stabilen Terrassen. Die Keimbildungsrate und die bevorzugten Keimbildungsorte der Kinken wurden identifiziert und stimmen mit den Voraussagen des Terrassen-Stufen-Kinken Modells überein.High-temperature behavior influence many different processes ranging from material processing to device applications. In-situ transmission electron microscopy (TEM) provides the means for direct observation of atomic processes during structural phase transitions in real time. In this thesis, in-situ TEM is applied to investigate the reversibility of the melting and solidification processes as well as the anisotropic sublimation behavior of Ge-Sb-Te (GST) thin films. The purposeful sample preparation for the successful observation of the high-temperature phase transitions is emphasized. The required encapsulation for the observation of the liquid phase inside the vacuum conditions and the necessary clean surface for sublimation process are discussed in detail. Additionally electron energy-loss spectroscopy in the TEM is used to determine the local chemical composition before and after the phase transitions. The analysis of the interface structure and dynamic during the solid-to-liquid as well as the liquid-to-solid phase transition shows differences between both processes. The trigonal phase of GST exhibits a partially ordered transition zone at the solid-liquid interface during melting while such an intermediate state does not form during solidification. Additionally the melting process proceeds with linear dependence on time, whereas crystallization can be described as having a square-root time-dependency featuring a superimposed start-stop motion. The influence of the interface is addressed and the surface energies of GST are determined. The anisotropic dynamic of the solid-to-gas phase transition of the cubic GST phase leads to the formation of stable {111} facets. This happens via kink and step nucleation on stable terraces. The nucleation rates and the preferred kink nucleation sites are identified and are in accordance with the predictions of terrace-step-kink model.
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Robin, Christophe. „Pétrogenèse des komatiites de Barberton (Afrique du Sud)“. Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00607819.
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Les komatiites sont des roches volcaniques ultrabasiques caractéristiques de l'Archéen et du Protérozoïque. Nous présentons ici une étude de la pétrogénèse des komatiites de la ceinture de Barberton en Afrique du Sud. Celle-ci comprend un modèle de fusion original bâti à partir de la constatation expérimentale qu'à très forte profondeur (P>13GPa), les liquides komatiitiques sont plus denses que la péridotite solide et donc ne peuvent pas s'échapper de leur source. Nous proposons que la fusion des sources des komatiites de Barberton ait commencée à une pression supérieure à 13GPa dans le manteau mais que les liquides produits soient restés retenus dans les sources jusqu'à ce que celles-ci n'aient dépassé, au cours de leur remonté, la limite de densité à laquelle le liquide devient moins dense que le résidu solide (à ~13GPa). Alors, les liquides auraient commencé à quitter leur source, d'abord doucement, puis de plus en plus vite alors que la différence de densité entre le liquide et le résidu solide s'accroissait. Les komatiites appauvries en Al, qui sont les plus abondantes à Barberton, auraient été produites par les premiers liquides qui ont quitté la source peu après le franchissement de la limite de densité. Les liquides qui quittèrent ensuite cette même source à moins forte pression, auraient formé les komatiites enrichies en Al. Les komatiites non-appauvries en Al auraient été produites par le même mécanisme mais par des sources de température potentielle plus forte. Une étude parallèle des trois systèmes isotopiques Sm-Nd, Lu-Hf et Re-Os nous a permis de contraindre l'histoire chimique des sources de komatiites de Barberton. Les systèmes Sm-Nd et Lu-Hf indiquent des sources appauvries et le système Re-Os une source chondritique. Nous proposons que les sources des komatiites aient été appauvries par l'extraction de croûte, mais qu'ensuite, leur composition en Re et Os aient été ramenées à leur valeur chondritique par le dernier épisode massif d‟accrétion de la Terre : " le vernis tardif ".
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Vasudevamurthy, Madhusudan. „Betaine analogues and related compounds for biomedical applications“. Thesis, University of Canterbury. Chemical and Process Engineering, 2006. http://hdl.handle.net/10092/1096.
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Living cells accumulate compensatory solutes for protection against the harmful effects of extreme environmental conditions such as high salinity, temperature and desiccation. Even at high concentrations these solutes do not disrupt the normal cellular functions and at times counteract by stabilizing the cellular components. These properties of compensatory solutes have been exploited for stabilizing proteins and cells in vitro. Betaines are widespread natural compensatory solutes that have also been used in other applications such as therapeutic agents and polymerase chain reaction (PCR) enhancers. Some biomedical applications of novel synthetic analogues of natural betaines were investigated. Natural compensatory solutes are either dipolar zwitterionic compounds or polyhydroxyl compounds, and the physical basis of compensation may differ between these, so one focus was on synthetic betaines with hydroxyl substituents. The majority of the synthetic solutes stabilized different model proteins against stress factors such as high and low temperatures. The presence of hydroxyl groups improved protection against desiccation. The observed stabilization effect is not just on the catalytic activity of the enzyme, but also on its structural conformation. Synthetic compensatory solutes have a potential application as protein stabilizers. Dimethylthetin was evaluated as a therapeutic agent and found to be harmful in a sheep model. However, from the study we were able to generate a large-animal continuous ambulatory peritoneal dialysis (CAPD) model and showed that glycine betaine could be added to the dialysis fluid in chronic renal failure. Some synthetic compensatory solutes reduce the melting temperatures of DNA better than most natural solutes. Synthetic solutes were identified that have potential to enhance PCR and could replace some reagents marketed by commercial suppliers. Density, viscosity and molecular model data on the solutes showed correlations with the biochemical effects of the solutes, but no physical measurements were found that reliably predicted their potential for biotechnological applications.
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Miehe, Anja. „Numerical investigation of horizontal twin-roll casting of the magnesium alloy AZ31“. Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2014. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-149625.
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The horizontal twin-roll casting (TRC) process is an energy saving and cost-efficient method for producing near-net-shape sheets of castable metals for light-weight production. In order to investigate the TRC process numerically, a code is generated in OpenFOAM and the commercial software STAR-CCM+ is used. Both are validated with the Stefan problem, the gallium melting test case, and a continuous casting experiment for magnesium AZ31. Different solidification models are tested that are similar to solution domain definitions and solid-fraction temperature relations. The comparison with temperature measurements of the MgF GmbH Freiberg pilot plant and the final microstructure exhibits good correlation. Sensitivity studies are carried out for thermophysical properties of AZ31 as well as pilot plant parameters. Furthermore, the rolls are incorporated into the simulation to determine the effect of a location-dependent heat-transfer coefficient. Finally, the results are compared to a second pilot plant situated at the Helmholtz-Centre Geesthacht in order to explore differences and similaritiesDas horizontales Gießwalzen ist eine energiesparende und kostengünstige Methode zur Erzeugung von Flachprodukten, die im Leichtbau verwendet werden. Um dieses Verfahren numerisch zu untersuchen wurde ein Programmcode in OpenFOAM entwickelt und die kommerzielle Software STAR-CCM+ verwendet, wobei beide mit dem Stefan Problem, dem Schmelzen von Gallium und Messdaten des Stranggusses von Magnesium AZ31 validiert wurden. Verschiedene Erstarrungsmodelle werden ebenso getestet wie Variationen des Simulationsbereiches und Feststoff-Temperatur-Verläufe. Vergleiche mit Temperaturmessdaten der Pilotanlage MgF GmbH Freiberg und der finalen Mikrostruktur zeigen gute Übereinstimmungen. Sensitivitätsanalysen werden durchgeführt, um die Einflüsse von thermophysikalischen Eigenschaften und Anlagenparametern abzuschätzen. Des Weiteren werden die Walzen in die Simulation mit einbezogen, um den Effekt eines lokal veränderlichen Wärmeübergangskoeffizienten zu beurteilen. Schließlich werden die Ergebnisse mit denen einer zweiten Pilotanlage am Helmholtz-Zentrum Geesthacht verglichen
Le laminage de coulée continue horizontal possède une faible consommation d’énergie et est bon marché pour la production des feuilles de métaux coulables utilisés dans la construction légère. Afin d’examiner ce processus numériquement, un code est généré dans OpenFOAM et le logiciel commercial STAR-CCM+ est utilisé, tous les deux sont validés en utilisant le problème de Stefan, la fusion du gallium et la coulée continue verticale de magnésium AZ31. Plusieurs modèles de solidification sont testés, ainsi que la variation du domaine de simulation, et des rélations entre la teneur en matière solide et la température. Des comparaisons avec des résultats de mesures de la température à l’installation pilote de MgF GmbH Freiberg ainsi que la microstructure donnent des bons résultats. Des analyses de sensibilité sont effectuées afin d’évaluer l’influence des propriétés thermophysiques et des paramètres de l’installation. De plus, les cylindres sont intégrés dans la simulation pour estimer l’impact du coefficient de transfert de chaleur dépendant du lieu. Finalement, les résultats sont comparés avec ceux du Helmholtz-Centre Geesthacht
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Rakotondrandisa, Aina. „Modélisation et simulation numérique de matériaux à changement de phase“. Thesis, Normandie, 2019. http://www.theses.fr/2019NORMR051/document.
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Nous développons dans ce travail de thèse un outil de simulation numérique pour les matériaux à changement de phase (MCP), en tenant compte du phénomène de convection naturelle dans la phase liquide, pour des configurations en deux et trois dimensions. Les équations de Navier-Stokes incompressible avec le modèle de Boussinesq pour la prise en compte des forces de flottabilité liées aux effets thermiques, couplées avec une formulation de l’équation d’énergie suivant la méthode d’enthalpie, sont résolues par une méthode d’éléments finis adaptatifs. Une approche mono-domaine, consistant à résoudre les mêmes systèmes d’équations dans les phases solide et liquide, est utilisée. La vitesse est ramenée à zéro dans la phase solide, en introduisant un terme de pénalisation dans l’équation de quantité de mouvement, suivant le modèle de Carman-Kozeny, consistant à freiner la vitesse à travers un milieu poreux. Une discrétisation spatiale des équations utilisant des éléments finis de Taylor-Hood, éléments finis P2 pour la vitesse et éléments finis P1 pour la pression, est appliquée, avec un schéma d’intégration en temps implicite d’ordre deux (GEAR). Le système d’équations non-linéaires est résolu par un algorithme de Newton. Les méthodes numériques sont implémentées avec le logiciel libre FreeFem++ (www.freefem.org), disponible pour tout système d’exploitation. Les programmes sont distribués sous forme de logiciel libre, sous la forme d’une forme de toolbox simple d’utilisation, permettant à l’utilisateur de rajouter d’autres configurations numériques pour des problèmes avecchangement de phase. Nous présentons dans ce manuscrit des cas de validation du code de calcul, en simulant des cas tests bien connus, présentés par ordre de difficulté croissant : convection naturelle de l’air, fusion d’un MCP, le cycle complet fusion-solidification, chauffage par le bas d’un MCP, et enfin, la solidification de l’eauIn this thesis we develop a numerical simulation tool for computing two and three-dimensional liquid-solid phase-change systems involving natural convection. It consists of solving the incompressible Navier-Stokes equations with Boussinesq approximation for thermal effects combined with an enthalpy-porosity method for the phase-change modeling, using a finite elements method with mesh adaptivity. A single-domain approach is applied by solving the same set of equations over the whole domain. A Carman-Kozeny-type penalty term is added to the momentum equation to bring to zero the velocity in the solid phase through an artificial mushy region. Model equations are discretized using Galerkin triangular finite elements. Piecewise quadratic (P2) finite-elements are used for the velocity and piecewise linear (P1) for the pressure. The coupled system of equations is integrated in time using a second-order Gear scheme. Non-linearities are treated implicitly and the resulting discrete equations are solved using a Newton algorithm. The numerical method is implemented with the finite elements software FreeFem++ (www.freefem.org), available for all existing operating systems. The programs are written and distributed as an easy-to-use open-source toolbox, allowing the user to code new numerical algorithms for similar problems with phase-change. We present several validations, by simulating classical benchmark cases of increasing difficulty: natural convection of air, melting of a phase-change material, a melting-solidification cycle, a basal melting of a phase-change material, and finally, a water freezing case
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Benkreira, Hadj. „Step-change in Enhancing Extrusion as a Unit Operation“. 2005. http://hdl.handle.net/10454/861.
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YesExtrusion-a unit operation in polymer processing has been in extensive use since the great age of plastic technology. It is a simple operation that enables within one equipment the sequential conveying of solid polymer chips or powder, their melting, mixing, pumping and shaping via a die into a variety of high tonnage and/or value products. Pipes, bottles, films are the most common examples but the list of applications is endless from tiny micromoulded parts to large structural profiles. Extrusion is not limited to plastics but is used hot or cold to process soft solids like food, industrial and pharmaceutical pastes, as well as metals and ceramics. Most of the advances in extrusion processing have concentrated in improving the essential functions of extrusion: solid conveying, melting, pumping and mixing. The literature abounds with descriptions of such advances pushing the limits of the extrusion in an incremental way. In this paper, we describe step-changes in enhancing extrusion, which opens up new applications to better old technology-make them safer, cheaper and cleaner. The new designs presented in this paper have also the potential to develop new reactor technology for viscous fluids.
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Boswell, Steven M. „Enhanced Surface Melting of the Fennoscandian Ice Sheet during Stadials“. Thesis, 2018. https://doi.org/10.7916/D8572VRZ.
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Unexpected melting of Northern Hemisphere ice sheets during periods of regional cooling characterizes the climate of the last glacial period. While the Heinrich Events are the most well-studied example of this phenomenon, Samuel Toucanne and colleagues recently documented evidence of Fennoscandian Ice Sheet melting during Heinrich Stadials, the cold periods during which Heinrich Events occur. In this dissertation, I use the geographic provenance of sediments in the Bay of Biscay, a proxy for Fennoscandian Ice Sheet melting, along with other paleoclimate records to: (1) demonstrate the persistence of abrupt Fennoscandian Ice Sheet melting as a feature of the Pleistocene climate system, (2) develop a self-consistent explanation for the synchronous melting of ice sheets in the North Atlantic region, and (3) elucidate the timing of abrupt climate change in the Northern Hemisphere.
I begin by introducing a framework for inferring the subglacial transport distance of fine sediments from coupled provenance and grain size analyses. This chapter untangles the relationships between the source, size, transport history, and geochemical signature of glacigenic sediments in northern Europe, clarifying the geographical significance of sediment provenance in the Bay of Biscay. I then develop a new method for the spectral analysis of unevenly sampled time series. In the following chapter, I apply the new spectral method to time series of Fennoscandian Ice Sheet melting, Laurentide Ice Sheet melting, and solar activity changes during the last glacial period. Doing so reveals a coherence between ice sheet melting and solar activity and helps explain the quasi-periodic melting of ice sheets on millennial timescales. I then extend the neodymium isotope provenance record of Fennoscandian Ice Sheet melting through Marine Isotope Stage 6, demonstrating that enhanced summertime melting of the FIS during Heinrich Stadials is a recurring feature of glacial periods. In the final chapter, I document a relationship between the occurrence of abrupt ice sheet melting in the Northern Hemisphere and the precession of Earth’s spin axis to reveal an astronomical forcing of millennial-scale climate change.
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Ma, Shih-Hsien, und 馬世憲. „Effects of high melting point element dopant on the optical properties and microstructure of the GeSbSn phase change optical disk films“. Thesis, 2005. http://ndltd.ncl.edu.tw/handle/68538627836903880898.
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碩士國立臺灣大學
材料科學與工程學研究所
93
One of the main development in rewritable phase change optical disk is to find out high crystallization speed materials for high-speed phase change optical disk application. In this study, (GeSbSn)100-xMx thin films (M=Ta、Fe、Ru、Ni or Co) are deposited on nature-oxidized Si wafer and glass substrates by DC magnetron co-sputtering. From the thermal analysis, we choose (GeSbSn)100-xFex and (GeSbSn)100-xCox thin films to investigated the effects of Fe or Co on the optical properties and microstructures of these films, and investigate its possibility for rewritable phase change optical media application. Thermal analysis shows that doping Fe or Co into GeSbSn thin film can decrease the activation energy and phase change temperature of the film. This indicates that the crystallization speed of the GeSbSn film will be increased. The optical property analysis shows that (GeSbSn)100-xFex and (GeSbSn)100-xCox films have good absorption. The optical contrast of (GeSbSn)100-xCox film decreases with increasing Co conent as x = 8.20~16.75. The optical contrast of (GeSbSn)100-xFex film increases with Fe content as x in the range of 7.10~9.75 but decreases with Fe content when x=12.91~16.63. The X-ray diffraction analysis shows that the as-deposited (GeSbSn)100-xFex and (GeSbSn)100-xCox films are amorphous structure. After annealing at 250℃ for 30 min, the major crystalline phase of (GeSbSn)100-xFex film (x=0~9.75) is Sb. The Sb、Fe and FeSb crystalline phases are appeared as x>16.63. After same annealing condition, the Sb and SbCo3 crystalline phase are found in the (GeSbSn)100-xCox film (x>8.20). The TEM analysis shows that the average grain size of the GeSbSn film is about 27.9 nm after annealing at 250℃ for 30 min. After doping Fe, average grain size of the GeSbSn film is decreased, it decreases to 17.6 nm as 7.10 at.% Fe is added. However, the grain size is increased to about 30.1 nm when 16.63 at.% Fe is added. On the other hands, as 9.79 at.% Co is doped into the GeSbSn film, average grain size of the film is decreased to about 16.8 nm, and the grain shape is irregular. When 16.75 at.% Co is added, the grain grows irregularly, the grain size is in the range of 30 to 200 nm and the average size is about 96 nm.
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Gao, Jhih-Yoan, und 高志遠. „An Experimental Study on Melting Heat Transfer Behavior of a Phase-Change-Material Containing Al2O3 Nanoparticles in a Vertical Rectangular Enclosure“. Thesis, 2008. http://ndltd.ncl.edu.tw/handle/14467385561940503801.
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碩士國立成功大學
機械工程學系碩博士班
96
The present study considers a mixture of n-Octadecane and Al2O3 nanoparticles as a phase change nano material for the latent-heat thermal energy storage application Thermophysical properties of the PCM containing varies mass fractions of alumina particles were determined experimentally as a function of temperature. Moreover, melting heat transfer characteristics of the PCM dispersed with alumina particles were examined experimentally in a differentially heated vertical square enclosure with the relevant parameters in the ranges : Ra=1710000~5670000 ; Ste=0.037~0.108 and Sb=0.042~0.537. The heat transfer results indicate natural convection heat transfer in the melted region and thus the thermal energy storage efficiency tend to decrease markedly with increasing mass fraction of alumina particles in n-Octadecane.
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Achenbach, Hermann. „Historische und rezente Gletscherstandsschwankungen in den Einzugsgebieten des Cha Lungpa (Mukut-, Hongde- und Tongu-Himalaja sowie Tach Garbo Lungpa), des Khangsar Khola (Annapurna N-Abdachung) und des Kone Khola (Muktinath-, Purkhung- und Chulu-Himalaja)“. Doctoral thesis, 2011. http://hdl.handle.net/11858/00-1735-0000-0006-B2F4-3.
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Tombrink, Gerrit. „Der glazifluviale Formenschatz im Gletschervorfeld des Himalaya und der Versuch einer relativ-zeitlichen Einordnung“. Doctoral thesis, 2017. http://hdl.handle.net/11858/00-1735-0000-002E-E317-A.
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