La conception des moteurs aéronautiques est soumise à de nombreuses contraintes telles que les gains de performance ou les normes environnementales de plus en plus exigeantes. Face à ces objectifs souvent contradictoires, les nouvelles technologies de moteur tendent vers une augmentation de la température locale et globale dans les étages chauds. En conséquence, les parties solides comme les parois du brûleur sont soumises à des niveaux de température élevés ainsi que d’importants gradients de température, tous deux critiques pour la durée de vie du moteur. Il est donc essentiel pour les concepteurs de caractériser précisément la thermique locale de ces systèmes. Aujourd’hui, la température de paroi est évaluée par des essais de coloration. Pour limiter ces essais relativement chers et complexes, des outils numériques haute fidélité capables de prédire la température de paroi des chambres de combustion sont actuellement développés. Cet exercice nécessite de considérer tous les modes de transfert de chaleur (convection, conduction et rayonnement) ainsi que la combustion au sein du brûleur. Ce problème multi-physique peut être résolu numériquement à l’aide de différentes approches numériques. La méthode utilisée dans ce travail repose sur une approche partitionnée qui inclut la résolution de l’écoulement turbulent réactif par un code de simulation aux grandes échelles (LES), un solveur radiatif basé sur la méthode aux ordonnées discrètes ainsi qu’ un code de conduction solide.Les diverses questions et difficultés liées à la répartition des ressources informatiques ainsi qu’à la méthodologie de couplage employée pour traiter les disparités d’échelles de temps et d’ espace présentes dans chacun des modes de transfert de chaleur sont discutées. La performance informatique des applications couplées est étudiée à travers un modèle très simplifié ainsi que sur une application industrielle. Les paramètres importants sont identifiés et des pistes potentielles d’amélioration sont proposées. La méthodologie de couplage thermique est ensuite étudiée du point de vue physique sur deux configurations distinctes. Pour commencer, l’équilibre thermique entre un fluide réactif et un solide est étudié pour une configuration académique d’accroche flamme. L’influence de la température de paroi de l’accroche flamme sur la stabilisation de flamme est mise en évidence sur des simulations fluideseul. Ces résultats indiquent trois états d’équilibre théorique différents. La pertinence physique de ces trois états est ensuite évaluée à l’aide de diverses simulations de transfert de chaleur conjugué réalisées pour différentes solutions initiales et conductivités solides. Les résultats indiquent que seulement deux états d’équilibre ont un sens physique et que la bifurcation entre les deux états possibles dépend à la fois de la condition initiale et de la conductivité solide. De plus, pour la gamme de paramètres testés, la méthodologie de couplage n’a pas d’effet sur les solutions obtenues. Une méthodologie similaire est ensuite appliquée à une chambre de combustion d’hélicoptère pour laquelle le rayonnement est de plus pris en compte. Diverses simulations sont présentées afin d’évaluer l’impact de chacun des processus de transfert de chaleur sur le champ de température : une simulation fluide-seul adiabatique de référence, de transfert de chaleur conjugué, d’interaction thermique fluide-rayonnement ainsi qu’une simulation incluant toutes les physiques. Ces calculs montrent la faisabilité d’un couplage LES/conduction solide dans un contexte industriel et fournissent de bonnes tendances de distribution de température. Pour finir, pour cette géométrie de brûleur et la condition d’opération simulée, les divers résultats montrent que le rayonnement joue un rôle important dans la distribution des températures de paroi. De ce fait, les comparaisons aux essais de coloration sont globalement en meilleur accord quand les trois modes de transfert sont pris en compte / The design of aeronautical engines is subject to many constraints that cover performance gain as well as increasingly sensitive environmental issues. These often contradicting objectives are currently being answered through an increase in the local and global temperature in the hot stages of the engine. As a result, the solid parts encounter very high temperature levels and gradients that are critical for the engine lifespan. Combustion chamber walls in particular are subject to large thermal constraints. It is thus essential for designers to characterize accurately the local thermal state of such devices. Today, wall temperature evaluation is obtained experimentally by complex thermocolor tests. To limit such expensive experiments, efforts are currently performed to provide high fidelity numerical tools able to predict the combustion chamber wall temperature. This specific thermal field however requires the consideration of all the modes of heat transfer (convection, conduction and radiation) and the heat production (through the chemical reaction) within the burner. The resolution of such a multi-physic problem can be done numerically through the use of several dedicated numerical and algorithmic approaches. In this manuscript, the methodology relies on a partitioned coupling approach, based on a Large Eddy Simulation (LES) solver to resolve the flow motion and the chemical reactions, a Discrete Ordinate Method (DOM) radiation solver and an unsteady solid conduction code. The various issues related to computer resources distribution as well as the coupling methodology employed to deal with disparity of time and space scales present in each mode of heat transfer are addressed in this manuscript. Coupled application high performance studies, carried out both on a toy model and an industrial burner configuration evidence parameters of importance as well as potential path of improvements. The thermal coupling approach is then considered from a physical point of view on two distinct configurations. First, one addresses the impact of the methodology and the thermal equilibrium state between a reacting fluid and a solid for a simple flame holder academic case. The effect of the flame holder wall temperature on the flame stabilization pattern is addressed through fluid-only predictions. These simulations highlight interestingly three different theoretical equilibrium states. The physical relevance of these three states is then assessed through the computation of several CHT simulations for different initial solutions and solid conductivities. It is shown that only two equilibrium states are physical and that bifurcation between the two possible physical states depends both on solid conductivity and initial condition.Furthermore, the coupling methodology is shown to have no impact on the solutions within the range of parameters tested. A similar methodology is then applied to a helicopter combustor for which radiative heat transfer is additionally considered. Different computations are presented to assess the role of each heat transfer process on the temperature field: a reference adiabatic fluid-only simulation, Conjugate Heat Transfer, RadiationFluid Thermal Interaction and fully coupled simulations are performed. It is shown that coupling LES with conduction in walls is feasible in an industrial context with acceptable CPU costs and gives good trends of temperature repartition. Then, for the combustor geometry and operating point studied, computations illustrate that radiation plays an important role in the wall temperature distribution. Comparisons with thermocolor tests are globally in a better agreement when the three solvers are coupled.

Dans le contexte aéronautique, cette thèse, financée par Safran Helicopter Engine, s’intéresse à l’application de l’approche Simulations aux Grandes Échelles (SGE) pour les systèmes de refroidissement de turbine. Le système de refroidissement industriel complexe est divisé en cas académiques plus simples donnant accès à des caractérisations expérimentales de la dynamique et de la thermique. Le jet impactant est traité en tant que système interne et l’écoulement de protection au bord de fuite en tant que système externe. Après une brève introduction du contexte lié au refroidissement de turbine et des objectifs scientifiques, ce manuscrit est divisé en 3 parties. La 1ère partie traite d’un écoulement de jet impactant sur plaque plane représentatif de l’impact à mi-corde. Elle se concentre sur la validation et la qualification des outils et modèles ainsi que sur l’analyse physique de l’écoulement. Les différentes instationarités de l’écoulement sont reliées à la thermique de paroi à l’aide de diagnostics statistiques et d’analyses modales. La 2ème partie s’intéresse à l’impact sur paroi concave représentatif de l’impact au bord d’attaque. Cette étude se concentre principalement sur la caractérisation de l’effet de courbure pour le jet impactant. Contrairement, au consensus actuel sur l’effet de courbure, la réduction des transferts thermiques est observée pour le cas d’étude de cette thèse. Au vu de ces résultats, une discussion est proposée pour tenter d’expliquer cet écart. Finalement, la 3ème partie de ce manuscrit contient une application de la SGE à un système de protection du bord de fuite par film isolant. Dans ce dispositif, des effets de groupe sont mis en évidence. L’impact des choix de modélisation tels que l’hypothèse de périodicité dans la direction de l’envergure est alors évalué. Il est montré que cette hypothèse de périodicité influe sur la prédiction locale de l’efficacité en forçant l’écoulement. En revanche, la prédiction de l’efficacité globale du système de protection n’est pas impactée. / This PhD thesis, funded by Safran Helicopter Engines, focuses on the application of the Large Eddy Simulation (LES) formalism to cooling systems present in high pressure turbine. The complex industrial problem is simplified into academic test cases for which experimental data are available for the validation process. The manuscript is divided into 3 parts dealing respectively with the impinging jet system on flat and concave plates and with the film cooling at the trailing edge equipped with a cutback on the pressure side. The 1st part deals with a jet impinging on a flat plate representing the impingement at mid-chord. This part focuses on the validation and qualification of the tools and models as well as on the physical analysis of the flow. The unsteadiness present in such an impinging jet flow are linked to the thermal behavior of the wall through the use of statistical analysis and modal decomposition of the flow field. The 2nd part is dedicated to the study of a jet impinging on a concave surface. This study aims at characterizing the effect of curvature for an impinging jet flow. The results found in this study disagreed with the current consensus attributing heat transfer enhancement on concave surface to Gortler instability. Hence, a discussion is proposed in an attempt to explain this discrepancy. Finally, the 3rd part reports an LES of the film cooling at the trailing edge. Group effects, due to the presence of internal ribs, are highlighted for the configuration studied here. These simulations use a spatial periodicity assumption to reduce the size of the computational domain. It is shown that this specific assumption is not suited as it forces the flow and modifies the group effect. The local results, in terms of adiabatic effectiveness, are found to be sensitive to such a forcing. However, the global behavior of the effectiveness is not impacted by this periodic boundary condition.

Em processos de combustão, uma determinação precisa dos parâmetros envolvendo transferência de calor influencia diretamente os demais fenômenos envolvidos. Dentre os mecanismos de transferência de calor presentes na combustão a radiação térmica é predominante, mas sua correta determinação impõe uma elevada complexidade, principalmente quando se trata da solução de meios participantes. O cálculo envolve propriedades de absorção que variam com a temperatura e o comprimento de onda, sendo então necessária a utilização de modelos espectrais para obter bons resultados com um baixo tempo computacional. Para o cálculo da transferência radiante, existem diversos modelos espectrais, desde modelos de simples implementação, como, por exemplo, o GG (gás cinza) e o WSGG (soma-ponderada-dos-gases-cinza), até modelos com um grau elevado de detalhamento, como o SLW (soma-ponderada-dos-gases-cinza baseado em linhas espectrais) e o CW (número de onda cumulativa). Como os modelos com maior grau de detalhamento são de complexa implementação, alguns autores preferem empregar modelos simplistas, como o GG (gás cinza), apenas por questões de conveniência, mesmo em detrimento da qualidade dos resultados. Uma forma de executar o cálculo da radiação térmica sem simplificações é levar em conta as absorções em cada comprimento de onda, sendo esses cálculos denominados integração linha-por-linha (LBL), por executar o cálculo da transferência radiante em cada linha de absorção, o que gera resultados benchmark, podendo ser utilizados para avaliar os diversos modelos existentes. Este trabalho tem por objetivo verificar e sintetizar a aplicação dos modelos espectrais, em configurações envolvendo concentração e temperatura não uniformes, onde são realizados cálculos em um meio contendo CO2, H2O e fuligem. São avaliados os modelos GG, WSGG, SLW e CW. Dentre os modelos avaliados, o que apresenta os melhores resultados para as condições apresentadas é o modelo WSGG. De forma a aprimorar o modelo WSGG, uma nova implementação para a solução de misturas é apresentada, a qual apresenta correlações para o H2O e para o CO2 geradas individualmente, possibilitando misturas com qualquer razão de concentração, mostrando que o modelo apresenta bons resultados em diversas situações e é uma boa opção para a solução de problemas de combustão. / In combustion processes a good determination of the heat transfer parameters are of great importance because of its direct influence in the computation of the chemical reactions rate in the process and, consequently, in the formation of the combustion products. Among the processes of heat transfer in combustion, thermal radiation is predominant, and their determination can be a very complex task, especially with participating medium. The analysis involves absorption properties that vary with the temperature and wavelength, and therefore it is necessary to use spectral models to ensure good results with low computational time. There are several spectral models developed along the years, since the simplistic models such as the GG (gray gas) and WSGG (weighted-sum-of-gray-gases), to more advanced methods such as the SLW (spectral line weighted-sum-of-gray-gases) and CW (cumulative wavenumber). Due advanced models are in general a hard task to implement, the option is to use simplified models, for example the GG, even working with considerably errors. In order to quantify these solutions, for temperature and concentration conditions of the absorbing species, it is necessary to implement the radiation heat transfer taking into account the absorption at each wavelength through line-by-line (LBL) integration, being this solution the exact one, or, the benchmark solution, which it is used to evaluate the spectral models. In this study, the LBL integration is carried out to evaluate some of the existing models in a non-isothermal and inhomogeneous medium containing CO2, H2O and soot. The work involves the GG, WSGG, SLW and CW spectral models. For the presented cases, the best results occur with WSGG model. In order to improve the WSGG model a new implementation for the mixture solution is presented, which solves the correlations for H2O and CO2 generated individually, enabling mixtures containing any concentration ratio, showing the good agreement of the spectral model at any condition, being the WSGG a good option to solve combustion problems.

Today, high performance steel as a construction material is treated as conventional steel in the European standards. Referring to the Eurocodes, the buckling curves for dimensioning of steel constructions only presents values up to steel grade S460, meaning that the full potential of high performance steel is not considered. If the amplitude of the residual stresses in high performance steel can be confirmed to be smaller than in conventional steel, more slender cross sections could be obtained when using high performance steel, HPS. One challenge with the residual stress patterns for HPS is its variation obtained in different studies, where new resulting residual stress patterns are found depending on plate thickness and manufacturing methods for the steel.   Residual stresses in steel are stresses not associated with external forces. The stresses are instead caused by internal forces, such as differencing temperature. Residual stresses can therefore be connected to stresses due to welding. Considering HPS, it is distinctive from conventional steel in the way that it has higher performance in tensile strength, toughness, weldability, corrosion and cold formability.   This study has been performed by Finite Element Modelling in the software Abaqus and by performing an experiment. The objective of this study was to find residual stress patterns and to compare the results with existing residual stress patterns according to the European Convention for Constructional Steel (ECCS) and the Swedish handbook for steel constructions provided by Boverket (BSK 07), but also to compare the results with previous studies.   The influence of temperature changes due to welding was studied for a L-section made of steel S690QL, where only the longitudinal stresses were considered during the research. The numerical analysis in Abaqus was performed using a DFlux subroutine, which is written in Fortran language. Furthermore, the analysis was divided into subparts; one heat transfer analysis and two three-dimensional stress analyses for two different boundary conditions, with the purpose of obtaining results in terms of temperature and stresses for further analysis. The experimental work was performed on three specimens using Gas Metal Arc Welding, where thermocouples and strain gages were used for measuring temperature and strains respectively.   Conclusions of this study were that the resulting residual stress pattern obtained the experiment was similar to the stress pattern for a L-section in BSK 07, while the resulting residual stress pattern obtained in the numerical analysis was mostly comparable to ECCS, but with similarities to BSK 07 and a previous study by Cherenenko & Kennedy (1990).  Moreover, the resulting residual tensile stresses obtained in the study had the same amplitude or lower than what is specified in BSK 07.

This thesis investigates the broad subject of thermal management problems currently encountered in Formula One race car design. A computationally economical tool, based on linear superposition, for predicting the temperature field arising from a set of thermal and inlet velocity boundary conditions was developed. Using a set of base analyses, the research showed that it is possible to superpose and scale these results in order to predict the temperature field for differing sets of boundary conditions. This method was shown to have a significant speed advantage over typical computational simulations. An experimental facility was designed and built to provide validation for aspects of the linear superposition approach. A method of measuring the cylinder wall heat flux has been developed using thin film gauge technology. The resulting sensor was designed to fit the mounting of existing instrumentation in order to avoid requiring large scale modifications to existing test facilities. The design makes use of modern rapid prototyping techniques in order to meet this mounting requirement and to provide a novel solution to routing the signal from the thin film gauge. In addition, the research investigated a method for predicting the cylinder wall temperature in real-time. The cylinder wall is subject to heat fluxes from in-cylinder gases during the engine cycle on the inner face and the effect of the coolant jacket on the outer face. Two separate methods were used to process these thermal boundary conditions respectively, before being superposed in order to form the whole solution. The computation time of the method is characterised in order to demonstrate its feasibility for real-time operation.

Made available in DSpace on 2014-06-11T19:25:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2002-12-19Bitstream added on 2014-06-13T19:32:43Z : No. of bitstreams: 1 ferrari_pr_me_rcla.pdf: 475478 bytes, checksum: 988b82c4b0d86391822af94333d12689 (MD5) / O descarte de resíduos industriais constitui-se num problema para os agentes produtores e para a sociedade. O volume de resíduo produzido é bastante grande e, normalmente, são poluidores ambientais. Pesquisadores afirmam que a determinação das propriedades térmicas de um solo e do resíduo, pode colaborar na decisão de incorporar este ao solo, visando melhorar sua capacidade de difundir a energia necessária ao processo de crescimento das plantas. O presente trabalho foi desenvolvido com o propósito de obter a medida da difusividade térmica de um solo incorporado um resíduo industrial de silicato, em várias proporções. O método utilizado foi aquele proposto por CLIVATI (1991), adaptado para as condições da pesquisa. A partir dos valores obtidos para a temperatura com o tempo, as difusividades térmicas das amostras foram determinadas, comparadas entre si e com a literatura. Dos resultados concluiu-se que amostras de solo com resíduo incorporado na proporção de 10%, em massa, apresentaram valores de difusividade térmica muito próximos daqueles obtidos para o solo. Tais resultados indicam a possibilidade de se descartar esse resíduo no solo, em condições semelhantes àquelas propostas neste trabalho. / The dump of industrial residue, constitutes a problem for the agents that produce them and for the society. The amount of residue produced is quite voluminous and they are generally environment polluters. Researchers state that the determination of the thermal properties of the soil and of the residue can cooperate in the decision to the incorporate the residue into the soil, thus improving its capacity to diffuse the necessary energy for the growth process of the plants. This work has been developed with the purpose of determining the value of the thermal diffusivity of a soil in which an industrial residue of silicate was incorporated in various proportions. The method used was the one proposed by CLIVATI (1991) and adequate for the actual conditions. From the values obtained for the temperature in time function, the thermal diffusivities of the samples were determined, compared among themselves and with the current literature. The obtained results allow us to conclude that the soil samples with the residue incorporated at the proportion of 10% in weight, presented values of thermal diffusivities very close to those obtained from the barren soil. These results point out for the possibility of dumping this residue into the soil, in the conditions closed to those proposed in this work.

Made available in DSpace on 2014-06-11T19:31:35Z (GMT). No. of bitstreams: 0 Previous issue date: 2004-12-17Bitstream added on 2014-06-13T20:42:04Z : No. of bitstreams: 1 gumerato_hf_dr_botfca.pdf: 735190 bytes, checksum: f1454b535f3ff650b6cf9e96b355f222 (MD5) / Universidade Estadual Paulista (UNESP) / Foi estudado processo de transferência de calor transiente por agitação intermitente em embalagens, visando a conservação de alimentos por tratamento térmico com processo mais econômico e que mantivesse a qualidade de alimentícios. Objetivou-se o desenvolvimento de um processo baseado em agitação intermitente de embalagens para aplicação em pasteurização ou esterilização. O estudo da transferência de calor transiente em sistema com movimento linear alternado foi realizado em embalagens metálicas, em 4 meios simulantes de diferentes viscosidades e massas específicas: 3 óleos orgânicos e água. Foram combinados efeitos de 5 tratamentos, sendo: meio simulante (4 níveis), espaços livres (3 níveis), freqüência de agitação (4 níveis), amplitude de agitação (2 níveis) e posições das latas (4 níveis). Os ensaios de aquecimento e resfriamento foram feitos em tanque com água a temperatura de 98°C e 17 a 20°C, respectivamente. Com os dados de penetração de calor em cada experimento foram calculados os parâmetros de penetração de calor fh, jh, fc e jc. Os resultados foram modelados utilizando-se grupos de números adimensionais e foram expressos em Nusselt, Prandtl, Reynolds e... / Transient heat transfer was studied by intermittent shake in cans with linear system, in order to preserve food by heat thermally processed, applying process more economic, and keeping high food quality. The objective was developing a process based on intermittent shake in cans to applying in pasteurisation or sterilisation process. Heat transfer was carried out in metallic cans filled four different simulate medium: water, Neutral oil 150 and 500 and Bright stock oil. It was arranged five treatments: simulate media (4 levels), head space (3 levels), agitation frequency (4 levels), length of agitation (2 levels) and cans positions (4 levels). The tests were carried out in hot water tank at temperature 98°C and cool at 17~20°C. Heat transfer parameters (fh, jh, fc and jc) for each test was calculated. Results were expressed applying dimensionless numbers equations for heat and cool. Data were computed pplying dimensionless numbers and were assign as Nusselt, Prandtl, Reynolds and trigonometric functions. Results obtained from linear shake system were compared with end-over-end agitation, and shake linear system showed more efficient. Shake linear system can be applied in pasteurisation or static retorts with simple internal structure fits...(Complete abstract, click electronic access below)

abstract: Self-heating degrades the performance of devices in advanced technology nodes. Understanding of self-heating effects is necessary to improve device performance. Heat generation in these devices occurs at nanometer scales but heat transfer is a microscopic phenomena. Hence a multi-scale modeling approach is required to study the self-heating effects. A state of the art Monte Carlo device simulator and the commercially available Giga 3D tool from Silvaco are used in our study to understand the self heating effects. The Monte Carlo device simulator solves the electrical transport and heat generation for nanometer length scales accurately while the Giga 3D tool solves for thermal transport over micrometer length scales. The approach used is to understand the self-heating effects in a test device structure, composed of a heater and a sensor, fabricated and characterized by IMEC. The heater is the Device Under Test(DUT) and the sensor is used as a probe. Therefore, the heater is biased in the saturation region and the sensor is biased in the sub-threshold regime. Both are planar MOSFETs of gate length equal to 22 nm. The simulated I-V characteristics of the sensor match with the experimental behavior at lower applied drain voltages but differ at higher applied biases. The self-heating model assumes that the heat transport within the device follows Energy Balance model which may not be accurate. To properly study heat transport within the device, a state of the art Monte Carlo device simulator is necessary. In this regard, the Phonon Monte Carlo(PMC) simulator is developed. Phonons are treated as quasi particles that carry heat energy. Like electrons, phonons obey a corresponding Boltzmann Transport Equation(BTE) which can be used to study their transport. The direct solution of the BTE for phonons is possible, but it is difficult to incorporate all scattering mechanisms. In the Monte Carlo based solution method, it is easier to incorporate different relevant scattering mechanisms. Although the Monte Carlo method is computationally intensive, it provides good insight into the physical nature of the transport problem. Hence Monte Carlo based techniques are used in the present work for studying phonon transport. Monte Carlo simulations require calculating the scattering rates for different scattering processes. In the present work, scattering rates for three phonon interactions are calculated from different approaches presented in the literature. Optical phonons are also included in the transport problem. Finally, the temperature dependence of thermal conductivity for silicon is calculated in the range from 100K to 900K and is compared to available experimental data. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2016

abstract: The proposed research mainly focuses on employing tunable materials to achieve dynamic control of radiative heat transfer in both far and near fields for thermal management. Vanadium dioxide (VO2), which undergoes a phase transition from insulator to metal at the temperature of 341 K, is one tunable material being applied. The other one is graphene, whose optical properties can be tuned by chemical potential through external bias or chemical doping. In the far field, a VO2-based metamaterial thermal emitter with switchable emittance in the mid-infrared has been theoretically studied. When VO2 is in the insulating phase, high emittance is observed at the resonance frequency of magnetic polaritons (MPs), while the structure becomes highly reflective when VO2 turns metallic. A VO2-based thermal emitter with tunable emittance is also demonstrated due to the excitation of MP at different resonance frequencies when VO2 changes phase. Moreover, an infrared thermal emitter made of graphene-covered SiC grating could achieve frequency-tunable emittance peak via the change of the graphene chemical potential. In the near field, a radiation-based thermal rectifier is constructed by investigating radiative transfer between VO2 and SiO2 separated by nanometer vacuum gap distances. Compared to the case where VO2 is set as the emitter at 400 K as a metal, when VO2 is considered as the receiver at 300 K as an insulator, the energy transfer is greatly enhanced due to the strong surface phonon polariton (SPhP) coupling between insulating VO2 and SiO2. A radiation-based thermal switch is also explored by setting VO2 as both the emitter and the receiver. When both VO2 emitter and receiver are at the insulating phase, the switch is at the “on” mode with a much enhanced heat flux due to strong SPhP coupling, while the near-field radiative transfer is greatly suppressed when the emitting VO2 becomes metallic at temperatures higher than 341K during the “off” mode. In addition, an electrically-gated thermal modulator made of graphene covered SiC plates is theoretically studied with modulated radiative transport by varying graphene chemical potential. Moreover, the MP effect on near-field radiative transport has been investigated by spectrally enhancing radiative heat transfer between two metal gratings. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2016

abstract: Fluids such as steam, oils, and molten salts are commonly used to store and transfer heat in a concentrating solar power (CSP) system. Metal oxide materials have received increasing attention for their reversible reduction-oxidation (redox) reaction that permits receiving, storing, and releasing energy through sensible and chemical potential. This study investigates the performance of a 111.7 MWe CSP system coupled with a thermochemical energy storage system (TCES) that uses a redox active metal oxide acting as the heat transfer fluid. A one-dimensional thermodynamic model is introduced for the novel CSP system design, with detailed designs of the underlying nine components developed from first principles and empirical data of the heat transfer media. The model is used to (a) size components, (b) examine intraday operational behaviors of the system against varying solar insolation, (c) calculate annual productivity and performance characteristics over a simulated year, and (d) evaluate factors that affect system performance using sensitivity analysis. Time series simulations use hourly direct normal irradiance (DNI) data for Barstow, California, USA. The nominal system design uses a solar multiple of 1.8 with a storage capacity of six hours for off-sun power generation. The mass of particles to achieve six hours of storage weighs 5,140 metric tonnes. Capacity factor increases by 3.55% for an increase in storage capacity to eight hours which requires an increase in storage volume by 33% or 737 m3, or plant design can be improved by decreasing solar multiple to 1.6 to increase the ratio of annual capacity factor to solar multiple. The solar reduction receiver is the focal point for the concentrated solar energy for inducing an endothermic reaction in the particles under low partial pressure of oxygen, and the reoxidation reactor induces the opposite exothermic reaction by mixing the particles with air to power an air Brayton engine. Stream flow data indicate the solar receiver experiences the largest thermal loss of any component, excluding the solar field. Design and sensitivity analysis of thermal insulation layers for the solar receiver show that additional RSLE-57 insulation material achieves the greatest increase in energetic efficiency of the five materials investigated. / Dissertation/Thesis / Masters Thesis Civil and Environmental Engineering 2017