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Development of a cascaded latent heat storage system for parabolic trough solar thermal power generationMuhammad, Mubarak Danladi 09 1900 (has links)
Concentrated solar power (CSP) has the potential of fulfilling the world’s
electricity needs. Parabolic-trough system using synthetic oil as the HTF with
operating temperature between 300 and 400o C, is the most matured CSP
technology. A thermal storage system is required for the stable and cost
effective operation of CSP plants. The current storage technology is the indirect
two-tank system which is expensive and has high energy consumption due to
the need to prevent the storage material from freezing. Latent heat storage
(LHS) systems offer higher storage density translating into smaller storage size
and higher performance but suitable phase change materials (PCMs) have low
thermal conductivity, thus hindering the realization of their potential. The low
thermal conductivity can be solved by heat transfer enhancement in the PCM.
There is also lack of suitable commercially-available PCMs to cover the
operating temperature range. In this study, a hybrid cascaded storage system
(HCSS) consisting of a cascaded finned LHS and a high temperature sensible
or concrete tube register (CTR) stages was proposed and analysed via
modelling and simulation. Fluent CFD code and the Dymola simulation
environment were employed.
A validated CFD phase change model was used in determining the heat
transfer characteristics during charging and discharging of a finned and unfinned
LHS shell-and-tube storage element. The effects of various fin
configurations were investigated and heat transfer coefficients that can be used
for predicting the performance of the system were obtained. A model of the
HCSS was then developed in the Dymola simulation environment. Simulations
were conducted considering the required boundary conditions of the system to
develop the best design of a system having a capacity of 875 MWhth, equivalent
to 6 hours of full load operation of a 50 MWe power plant.
The cascaded finned LHS section provided ~46% of the entire HCSS capacity.
The HCSS and cascaded finned LHS section have volumetric specific
capacities 9.3% and 54% greater than that of the two-tank system, respectively.
It has been estimated that the capital cost of the system is ~12% greater than
that of the two-tank system. Considering that the passive HCSS has lower
operational and maintenance costs it will be more cost effective than the twotank
system considering the life cycle of the system. There is no requirement of
keeping the storage material above its melting temperature always. The HCSS
has also the potential of even lower capital cost at higher capacities (>6 hours
of full load operation).
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A study of the polymorphism of 4-methyl-2-nitroacetanilide and related compoundsYeadon, Alan January 1985 (has links)
The full crystal structures of three polymorphs of 4-methyl-2-nitroacetanilide (MNA) are described. The white form (MNA-l), is the most stable form. The least stable form is the amber farm (MNA-2). The yellow form (MNA-3) has been found to change in a topotactic manner into the white form. The relationships between the three polymorphs are discussed and possible mechanisms to account for the topotactic phase changes are presented. The polymorphs show different i.r. and Raman spectra in the solid state. These spectra, and those of deuterated analogues are interpreted and their differences explained. A study of the proton and 13-C n.m.r. spectra show that the conformation of flexible MNA molecules is markedly dependent on the nature of the solvent. The ability of other o-nitroacetanilides to exist in a white (intermolecular) and yellow (intramolecular hydrogen bonded) forms has been examined. Finally, details of the synthesis of these compounds and an account of the examination of MNA polymorphs by differential scanning calorimetry (d.s.c) are described. A description of computer programs used, including one in BASIC which will enable the contents of unit cell(s) to be viewed, is given.
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Numerical Investigation Of SolidificationAlrmah, Masoud Ahmed 01 June 2005 (has links) (PDF)
Finite element solution of solidification process in 2-D Cartesian and axisymmetric geometries is investigated. The use of finite element may result in spurious increase of temperature in the field and the selection of the mushy zone range when used as a numerical tool along with the selection of the mesh size results in large errors in the predicted solidification time.
The approach works best for problems where the mushy zone range is finite and the thermal conductivities of both phases are high.
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[en] SOLIDIFICATION OF A BINARY SUBSTAME INSIDE A VERTICAL ANNULAR CAVITY / [pt] SOLIDIFICAÇÃO DE MISTURA BINÁRIA EM CAVIDADE ANULAR VERTICALCLEYTON SENIOR STAMPA 18 April 2002 (has links)
[pt] Neste trabalho realizou-se um estudo básico numérico-
experimental, em geometria anular vertical, sobre a
solidificação de um hidrato de sal, cuja mudança de fase se
dá analogamente à de ligas metálicas binárias. O sistema
escolhido foi a substância NH4CL-H2O, e o processo de
solidificação foi estudado em três cavidades, de diferentes
razões de aspecto, usando-se soluções de diferentes
concentrações iniciais. Em todos os experimentos, idênticas
condições inicial e de contorno foram adotadas. Para tal,
foi montado um aparato experimental que permitiu a
visualização do crescimento da estrutura de sólido junto à
parede fria e medições locais de temperatura e
concentração. As concentrações iniciais foram escolhidas
com o intuito de formar uma base de dados experimentais que
descrevesse suficientemente o comportamento do sistema
durante a solidificação, no qual determinados resultados
foram utilizados na comparação com as previsões numéricas.
O problema numérico foi resolvido bidimensionalmente,
utilizando-se o método de volumes finitos e,
analiticamente, foi aplicada às equações de conservação a
técnica de obtenção de valores médios em volume. Além da
comparação efetuada entre os resultados numéricos e
experimentais sobre a evolução temporal das temperaturas e
concentrações, também investigou-se o comportamento da
solidificação. Adicionalmente, foi avaliada a influência da
razão de aspecto, sob a luz da transferência de calor para
a parede fria da cavidade e do crescimento da frente de
solidificação, ao longo do tempo. Na parte experimental foi
desenvolvida uma técnica de medição da concentração,
utilizando-se termopares acoplados a fibras ópticas, que
permitiu medir esta grandeza, simultaneamente, em pontos
escolhidos no domínio, em tempo real, causando mínima
perturbação no meio. / [en] In the present work a basic numerical-experimental study
was carried out, in vertical annular geometry, about the
solidification of a salt hydrate, whose change of phase
takes place similarly to the binary metallic alloys. It was
chosen the NH4CL-H2O binary system, and the solidification
process was studied in three cavities of different aspect
ratios, utilizing solutions of distinct initial
concentrations. In all the experiments, identical initial
and boundary conditions were adopted. For that, an
experimental apparatus was set up to be allowed not only
the visualization of solid structure growth, that attaches
the cold wall, but also local measurements of temperature
and concentration. The initial concentration values were
chosen to provide an experimental data base that depicted
sufficiently the system behavior during the solidification
process, in which part of them were used in the comparison
with numerical predictions. The numerical problem was
solved bi-dimensionally, utilizing the finite volume
method and, analytically, it was applied the averaging
volume technique to the conservation equations. Besides the
comparison between numerical and experimental results about
temperature and concentration transients, it was also
investigated the solidification behavior. Additionally, it
was evaluated both the temporal influence of the aspect
ratio against the heat transfer to the cold wall of the
cavity, and about the solidification front progress.
Further, in the experimental part of this study, it was
developed a technique for the determination of the
concentration in any point of interest, making use of
thermocouples attached to optical fiber sensors, that
allowed to make several measurements simultaneously, in
real time, causing minimal disturbance in the medium.
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[en] NUMERICAL FINITE ELEMENT ANALYSIS OF RESIDUAL STRESSES GENERATED BY TREATED PHASE CHANGES IN THERMICALLY STELLS / [pt] ANÁLISE NUMÉRICA POR ELEMENTOS FINITOS DE TENSÕES RESIDUAIS GERADAS POR MUDANÇA DE FASE EM AÇOS TRATADOS TERMICAMENTEMARCELLO GOULART TEIXEIRA 20 May 2002 (has links)
[pt] O objetivo deste trabalho é fazer uma modelagem numérica
por elementos finitos de tensões residuais em peças de liga
ferro-níquel e aço carbono submetidas a tratamentos
térmicos,considerando mudanças de fase.Com este objetivo,
foram desenvolvidos códigos computacionais orientados a
objetos para análise térmica não-linear acoplado à análise
da micro-estrutura. Códigos implementados em POO também
foram criados para análise elasto-plástica, onde a
distribuição de temperatura e as frações parciais dos
constituintes são dados de entrada. As propriedades termo-
mecânicas do material são consideradas dependentes tanto da
temperatura quanto da fração parcial de cada constituinte.
No tratamento térmico está sendo considerado a formação de
martensita segundo o esquema de Koistinen e Marburger
(1959). É abordado também a formação difusional de perlita
e bainita, segundo o esquema proposto por Avrami (1939).
Por fim, é apresentado um novo modelo para calcular os
parâmetros cinéticos das transformações difusionais
austenita-perlita e austenita-bainita. / [en] The objective of this thesis is to perform a finite element
analysis of residual stress in Fe-Ni alloys and carbon
steel heat-treated pieces, considering phase changes.
To achieve this goal, a object oriented computer code for
the non-linear thermal analysis coupled with a code for a
micro-structural analysis were developed. OPP codes were
also created for an elasto-plastic analysis, with
temperature distribution and constituents partial fraction
as input data. The material properties are considered
dependent on both the temperature and the partial fraction
for all analyses.In the thermal treatment, the martensite
transformation according to Koistinen and Marburger (1959)
scheme and the diffusional formation of pearlite and
bainite according to Avrami (1939) are considered.
Finally, a new model to calculate the kinetics parameters
of the diffusional austenite-pearlite and austenite-bainite
transformations is presented.
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Application of Phase Change Material in Buildings: Field Data vs. EnergyPlus SImulationJanuary 2010 (has links)
abstract: Phase Change Material (PCM) plays an important role as a thermal energy storage device by utilizing its high storage density and latent heat property. One of the potential applications for PCM is in buildings by incorporating them in the envelope for energy conservation. During the summer season, the benefits are a decrease in overall energy consumption by the air conditioning unit and a time shift in peak load during the day. Experimental work was carried out by Arizona Public Service (APS) in collaboration with Phase Change Energy Solutions (PCES) Inc. with a new class of organic-based PCM. This "BioPCM" has non-flammable properties and can be safely used in buildings. The experimental setup showed maximum energy savings of about 30%, a maximum peak load shift of ~ 60 min, and maximum cost savings of about 30%. Simulation was performed to validate the experimental results. EnergyPlus was chosen as it has the capability to simulate phase change material in the building envelope. The building material properties were chosen from the ASHRAE Handbook - Fundamentals and the HVAC system used was a window-mounted heat pump. The weather file used in the simulation was customized for the year 2008 from the National Renewable Energy Laboratory (NREL) website. All EnergyPlus inputs were ensured to match closely with the experimental parameters. The simulation results yielded comparable trends with the experimental energy consumption values, however time shifts were not observed. Several other parametric studies like varying PCM thermal conductivity, temperature range, location, insulation R-value and combination of different PCMs were analyzed and results are presented. It was found that a PCM with a melting point from 23 to 27 °C led to maximum energy savings and greater peak load time shift duration, and is more suitable than other PCM temperature ranges for light weight building construction in Phoenix. / Dissertation/Thesis / M.S. Mechanical Engineering 2010
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Direct numerical simulation of free-surface and interfacial flow using the VOF method : cavitating bubble clouds and phase change / Simulation numérique directe de l'écoulement en surface libre et de l'écoulement interfacial à l'aide de la méthode VOF : cavitation des nuages de bulles d'air et changement de phaseMalan, Leon 24 October 2017 (has links)
La présente étude se fonde sur la méthode du volume de fluide (en anglais VOF pour Volume-of-Fluid), proposée à l'origine par Hirt et Nicols. L'objectif de la première partie de ce travail est l'étude hydrodynamique de la cavitation isotherme dans les grands nuages de bulles. Cette étude s'inscrit plus généralement dans un large effort de recherche en micro--écaillage mené par le CEA. Une méthode capable de traiter la présence de cavités de vapeur de volume variable ou encore de pores a été formulée et implémentée dans un code existant, PARIS. L'écoulement est idéalisé en supposant un liquide parfait, des effets thermiques négligeables et une pression de vapeur nulle. Une étude innovante est présentée, traitant de l'interaction du nuage de bulles dans un liquide en expansion par simulation numérique directe. Les résultats des simulations révèlent l'existence d'un concours de cavités dans un certain régime caractérisé par le nombre de Weber.Dans la deuxième partie de l'étude, le système d'équations à résoudre est modifié et généralisé afin de décrire l'écoulement incompressible d'un fluide diphasique tout en incluant la possibilité d'un changement de phase à l'interface. Une nouvelle méthode VOF est proposée, dans laquelle une nouvelle technique d'advection de la fonction VOF permet de traiter à la fois la conservation de la masse et de l'énergie sous une forme conservative. Les expériences numériques démontrent la précision, la robustesse et la généralité de la méthode proposée, et témoignent d'un développement fondamental important pour l'application des méthodes VOF à la modélisation des changements de phase. / Direct numerical simulation of two-phase ow is used extensively for engineering research and fundamental fluid physics studies [54, 81]. This study is based on the Volume-Of-Fluid (VOF) method, originally created by Hirt and Nicols [30]. This method has gained increased popularity, especially when geometric advection techniques are used coupled with a planar reconstruction of the interface [14, 89]. The focus of the first part of this work is to investigate the hydrodynamics of isothermal cavitation in large bubble clouds, which originated from a larger study of micro-spalling [61], conducted by the French CEA. A method to deal with volume-changing vapour cavities, or pores, was formulated and implemented in an existing code, PARIS . The ow is idealized by assuming an inviscid liquid, negligible thermal effects and vanishing vapour pressure. A novel investigation of bubble cloud interaction in an expanding liquid using direct or detailed numerical simulation is presented. The simulation results reveal a pore competition, which is characterised by the Weber number in the ow. In the second part of the study the governing equations are extended to describe incompressible ow with phase change [79]. The description of the work commences with the derivation of the governing equations. Following this, a novel, geometric based, VOF solution method is proposed. In this method a novel way of advecting the VOF function is invented, which treats both mass and energy conservation in conservative form. New techniques include the advection of the interface in a discontinuous velocity field. The proposed algorithms are consistent and elegant, requiring minimal modifications to the existing code. Numerical experiments demonstrate accuracy, robustness and generality. This is viewed as a significant fundamental development in the use of VOF methods to model phase change.
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[en] SUPERCOOLING OF THE WATER IN CYLINDRICAL CAPSULES: PARAMETERS OF INFLUENCE / [pt] SUPER-RESFRIAMENTO DA ÁGUA EM CÁPSULAS CILÍNDRICAS: PARÂMETROS DE INFLUÊNCIAHUGO GUILLERMO JIMENEZ PACHECO 11 November 2008 (has links)
[pt] Um dispositivo experimental foi desenvolvido para o estudo
do superresfriamento
da água em cápsulas cilíndricas visando sua utilização em
processos
de termoacumulação. A bancada experimental é constituída
basicamente por:
seção de teste, sistema de resfriamento, sistema de
visualização, sistema de
aquisição e armazenamento de dados. A temperatura do fluido
externo, ou fluido
de transferência (FT), uma solução aquosa de álcool a 50%
por volume,
foimantida constante por um banho de temperatura controlada
durante cada teste.
O trabalho foi dividido em quatro etapas. A primeira trata
do estudo estatístico do
super-resfriamento e da nucleação, em que foram utilizados
3 materiais distintos
(alumínio, acrílico e PVC) para cápsulas de 30 e 80 mm de
diâmetro com
diferentes tipos de rugosidade, e diferentes temperaturas
do FT. A segunda etapa
investiga a Taxa de Resfriamento, parâmetro que quantifica
a queda da
temperatura e influencia fortemente o super-resfriamento e
a nucleação. Na
terceira etapa, foi estudada a influência da rugosidade da
parede interna da
cápsula. Nesta etapa, quatro cápsulas de alumínio
distintas, com diferentes
rugosidades, foram utilizadas. Finalmente, na quarta etapa
foram realizadas
visualizações do fenômeno de nucleação. Os resultados
obtidos indicam que o
material da cápsula (condutividade e rugosidade) e a
temperatura do FT têm
grande influência nos fenômenos de super-resfriamento e
nucleação da água em
cápsulas cilíndricas, afetando fortemente o processo de
mudança de fase. / [en] An experimental device was developed for the super-cooling
water in
cylindrical capsules study, seeking its use in term-
accumulation processes. The
experimental set is constituted basically by: test section,
cooling system, visualization
system, and data logger system.
The temperature of the external fluid, or transfer fluid
(FT), an alcohol aqueous
solution with 50% per volume, it was maintained
unchangeably with a bath
controlled temperature during each test. The work was
divided in four stages. The first
one is about the statistical study of the super-cooling and
nucleation, where 3 distinct
materials were used (aluminum, acrylic and PVC) for
capsules of 30 and 80 mm
diameter, different roughness type, with different
temperatures of FT. The second
stage investigates the Cooling Rate, parameter that
quantifies the falling of the
temperature and it influences strongly the super-cooling
and the nucleation process. In
the third stage, the influence of the internal wall of the
capsule was studied. In this
stage, four different capsules of aluminum, with different
roughness were used.
Finally, in the fourth stage, visualizations of the
nucleation phenomenon were
accomplished. The obtained results indicate that the
capsule material (conductivity
and roughness) and the FT temperature has great influence
in the phenomena of
super-cooling and nucleation of the water in cylindrical
capsules, affecting, strongly,
the process of phase change.
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Development of a Concentrating Solar Water Heater with Phase Change Energy StorageJanuary 2015 (has links)
abstract: The complicated, unpredictable, and often chaotic hot water usage pattern of typical households severely limits the effectiveness and efficiency of traditional solar hot water heater systems. Similar to large scale concentrating solar power plants, the use of thermal energy storage techniques to store collected solar energy as latent heat has the potential to improve the efficiency of solar hot water systems. Rather than being used to produce steam to generate electricity, the stored thermal energy would be used to heat water on-demand well after the sun sets. The scope of this thesis was to design, analyze, build, and test a proof of concept prototype for an on-demand solar water heater for residential use with latent heat thermal energy storage. The proof of concept system will be used for future research and can be quickly reconfigured making it ideal for use as a test bed. This thesis outlines the analysis, design, and testing processes used to model, build, and evaluate the performance of the prototype system.
The prototype system developed to complete this thesis was designed using systems engineering principles and consists of several main subsystems. These subsystems include a parabolic trough concentrating solar collector, a phase change material reservoir including heat exchangers, a heat transfer fluid reservoir, and a plumbing system. The system functions by absorbing solar thermal energy in a heat transfer fluid using the solar collector and transferring the absorbed thermal energy to the phase change material for storage. The system was analyzed using a mathematical model created in MATLAB and experimental testing was used to verify that the system functioned as designed. The mathematical model was designed to be adaptable for evaluating different system configurations for future research. The results of the analysis as well as the experimental tests conducted, verify that the proof of concept system is functional and capable of producing hot water using stored thermal energy. This will allow the system to function as a test bed for future research and long-term performance testing to evaluate changes in the performance of the phase change material over time. With additional refinement the prototype system has the potential to be developed into a commercially viable product for use in residential homes. / Dissertation/Thesis / Masters Thesis Engineering 2015
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Thermal Storage and Transport in Colloidal Nanocrystal-Based MaterialsJanuary 2015 (has links)
abstract: The rapid progress of solution-phase synthesis has led colloidal nanocrystals one of the most versatile nanoscale materials, provided opportunities to tailor material's properties, and boosted related technological innovations. Colloidal nanocrystal-based materials have been demonstrated success in a variety of applications, such as LEDs, electronics, solar cells and thermoelectrics. In each of these applications, the thermal transport property plays a big role. An undesirable temperature rise due to inefficient heat dissipation could lead to deleterious effects on devices' performance and lifetime. Hence, the first project is focused on investigating the thermal transport in colloidal nanocrystal solids. This study answers the question that how the molecular structure of nanocrystals affect the thermal transport, and provides insights for future device designs. In particular, PbS nanocrystals is used as a monitoring system, and the core diameter, ligand length and ligand binding group are systematically varied to study the corresponding effect on thermal transport.
Next, a fundamental study is presented on the phase stability and solid-liquid transformation of metallic (In, Sn and Bi) colloidal nanocrystals. Although the phase change of nanoparticles has been a long-standing research topic, the melting behavior of colloidal nanocrytstals is largely unexplored. In addition, this study is of practical importance to nanocrystal-based applications that operate at elevated temperatures. Embedding colloidal nanocrystals into thermally-stable polymer matrices allows preserving nanocrystal size throughout melt-freeze cycles, and therefore enabling observation of stable melting features. Size-dependent melting temperature, melting enthalpy and melting entropy have all been measured and discussed.
In the next two chapters, focus has been switched to developing colloidal nanocrystal-based phase change composites for thermal energy storage applications. In Chapter 4, a polymer matrix phase change nanocomposite has been created. In this composite, the melting temperature and energy density could be independently controlled by tuning nanocrystal diameter and volume fractions. In Chapter 5, a solution-phase synthesis on metal matrix-metal nanocrytal composite is presented. This approach enables excellent morphological control over nanocrystals and demonstrated a phase change composite with a thermal conductivity 2 - 3 orders of magnitude greater than typical phase change materials, such as organics and molten salts. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2015
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