In the reservoir conditions, a petroleum fluid is defined by its thermodynamic and volumetric properties and by its physicochemical properties. Their behaviors are modeled from experimental data in order to properly simulate the processing of these fluids during the production.   With the advent of new regulations and rigidity that exist at the custom regulations today, research centers have great difficulty in obtaining large amounts of samples. For these reason, although there are several methods to characterize the different components of crude oil, the laboratories are turning increasingly to techniques that requires lower amounts of samples: micro-distillation, gas chromatography (GC).   The micro-distillation is a fast and completely computerized technique made to substitute the standard distillation for analysis of liquid petroleum products. Advantages of the method compared to the standard distillation are the reduction of working time by at least a factor of 4, the small sample volumes required for distillation (few micro liters). [24]   This report is aimed to create a simple model that can predict yield curves of physical distillation, without using the micro-distillation technique. The results obtained through gas chromatography (GC) analysis by laboratory technicians enable the modeling of the fluid behavior. Having identified and treated practically all aspects of micro-distillation through simulations with PRO/II, I found out that, regardless of the setting and the thermodynamic method used, there are always significant differences between simulation results and those of the micro-distillation.   The result shows that it’s still difficult to create a model which can replace micro-distillation and gas chromatography (GC) because of the huge gap between the simulation results and micro-distillation. Furthermore, the dynamics revealed that the micro distillation is not accurate. I had hoped to get additional results by studies the correlations with more samples, but that did not turn out to be the case. Regardless of that, I think that it would be interesting to study more samples and use another simulator to properly represent micro distillation. This could be an interesting topic for further studies. / Under de föhållanden som reservoarens miljö erbjuder, definieras en petroleumvätska av dess termodynamiska och volymetriska egenskaper och av dess fysikalisk-kemiska egenskaper. För att korrekt simulera bearbetningen av dessa vätskor under produktion, deras beteende modelleras från experimentella data Med tillkomsten av nya regler och oflexibilitet som finns på tullbestämmelser vid gränserna idag, har forskningscenter stora svårigheter att få större mängder prover levererade. Av den anledningen, trots att det finns flera metoder för att karakterisera de olika komponenterna av råolja, tvingas laboratorier att vända sig mer och mer till alternativa analysmetoder som kräver mindre provvolymer: mikrodestillation, gaskromatografi, etc.   Mikrodestillation, som är en snabb och helt datoriserad teknik, visar sig kunna ersätta standarddestillation för analys av flytande petroleumprodukter. Fördelar med metoden jämfört med standarddestillering är minskad arbetstidsåtgång med minst en faktor 4. Därtill krävs endast en begränsad provvolym (några mikroliter) i jämförelse med standarddestillation.  [24]   Denna rapport syftar till att skapa en enkel modell som kan förutsäga avkastningskurvan av fysisk destillation, utan att använda mikrodestillationsteknik. De resultat som erhölls genom gaskromatografiska analyser möjliggjorde modelleringen av det vätskebeteendet hos det analyserade provet. Efter att ha identifierat och behandlat praktiskt taget alla viktiga aspekter av mikro destillation genom simuleringar med PRO/II, fann jag att, oberoende av inställningen och den termodynamiska metod som används,  det alltid finns stora skillnader mellan simulering och mikro destillation.   Resultatet visar att det fortfarande är svårt att skapa en modell som kan ersätta mikrodestillering och gaskromatografi på grund av differensen mellan simuleringsresultaten å ena sidan, och resultaten från mikrodestillering å andra sidan. Dessutom visade resultaten att mikrodestillation som analysmetod inte ger tillförlitliga resultat. Min förhoppning var att få ytterligare användbara resultat genom att studerar potentiella korrelationer emellan fler prover, men detta visade sig inte vara fallet. Jag anser att det skulle vara intressant att studera fler prover och använda en annan simulator för att bättre representera mikrodestillation. Detta skulle kunna vara ett intressant ämne för vidare studier.

<p>Advancements in future technologies such as artificial intelligence, electric vehicles, and renewable energy create a consistent need for more powerful and smaller electronic devices and systems. As a result, thermal management components such as heat sinks need to remove higher heat loads from more compact spaces to keep electronics within their operational temperature limits. Constraints imposed by conventional manufacturing processes restrict the design of heat sinks to simple geometries with limited cooling performance. Recent widespread commercialization of metal additive manufacturing (AM) tools offers new potential for leveraging the design freedom of these manufacturing technologies to design and fabricate heat sinks with improved performance. </p> <p>In AM, three dimensional parts are created through layer-by-layer depositing of materials, which allows fabrication of complex geometries that would be impossible or too costly using conventional subtractive methods. Many novel heat sink geometries have been proposed in literature which incorporate features such as manifolds, flow mixers, and curved channels using engineering intuition to reduce pressure drop or enhance heat transfer. Although such designs have been shown to offer improved performance, mathematical design algorithms such as topology optimization (TO) have been shown to outperform engineering intuition. Topology optimization optimizes the material distribution within a given design space, guided by physics-based simulations, to achieve a user-defined objective such as minimization of thermal resistance. Previous TO approaches have used penalization methods to ensure the final designs are composed of macroscopic and non-porous features due to the past precedent of fabrication capabilities. This traditional penalization approach is well-suited to the constraints of conventional manufacturing methods; however, microstructures and porous features are easily fabricable with additive manufacturing. There is a need to develop TO approaches that are better suited for leveraging AM for the design of heat sinks. In this thesis, a homogenization approach to topology optimization is proposed wherein the material distribution is represented as parametrized microstructures. This formulation allows design of thermal management components that have sub-grid features and leverages AM for fabrication. The focus of this thesis is the development of the homogenization approach for TO of heat sinks, as well as the exploration of the design problems it can address, the performance benefits made available, and the two-phase flow physics that it uniquely allows to be incorporated into the topology optimization process.</p> <p>A topology optimization algorithm using the homogenization approach is developed by representing the material distribution as arrays of pin fins with varying gap sizes. To this end, the pin fins are modeled as a porous medium with volume-averaged effective properties. Height-averaged two-dimensional flow and non-equilibrium thermal models for porous media are developed for transport in the pin fin array. Through multi-objective optimization, TO designs are generated for an example case involving a hotspot over a uniform background heat input. The resulting topologies have porous-membrane-like designs where the liquid is transported through a fractal network of open, low-hydraulic-resistance manifold pathways and then forced across tightly spaced arrays of pin fins for effective heat transfer. The TO designs are revealed to offer significant performance improvements relative to the benchmark straight microchannel (SMC) heat sink with features optimized under the same multi-objective cost function. A series of microchannel heat sinks are fabricated using direct metal laser sintering to investigate the printing capabilities and to experimentally demonstrate the performance of topology optimized designs. Advantages of the homogenization approach over the penalization approach can be summarized as follows: (1) reduced computational costs due to its ability to create sub-resolution features, (2) intrinsically fabricable parts using available metal AM tools, and (3) easier to use due to significantly reduced number of hyperparameters (e.g., penalization factors) that are controlled by the user. </p> <p>Topology optimization has been applied to thermal management methods involving single-phase flows such as natural convection, forced air cooling, and pumped liquid cooling. Compared to these conventional heat sink technologies, flow boiling offers very high heat transfer coefficients and effective heat capacities, making it a promising candidate for future cooling electronics applications. The final goal of this thesis is to enable topology optimization of flow boiling heat sinks. However, TO of flow boiling heat sinks has been avoided due to difficulties in modeling the boiling phenomena; of note, there are no examples of TO being applied to the design of heat sink under flow boiling throughout the literature. Multi-dimensional two-phase flow models require prior knowledge of friction factor and heat transfer coefficients. Correlations are available in literature but are not universal and depend significantly on channel/fin geometries, surface roughness, and operating conditions. Given that traditional penalization-based TO approach results in fin and channel geometries with unknown shapes, dimensions, and alignment before the optimization is completed, this prohibits their use for optimization of flow boiling heat sinks. However, the homogenization approach to topology optimization developed in this thesis enables the optimization of flow boiling heat sinks. As it relies on user-defined microstructures with known shapes, alignments, and ranges of geometric dimensions, a universal correlation for flow boiling in microchannels is not needed. Instead, correlations for the user-defined microstructures are sufficient to simulate flow boiling in TO designs generated using the homogenization approach. To this end, a predefined microstructure geometry is chosen for which two-phase flow correlations exist and therefore topology optimization can be performed. Topology optimized heat sink designs under flow-boiling are generated and investigated at various heat inputs, topology optimization grid sizes, and maximum vapor quality constraints. Topology optimized heat sinks designed for single-phase versus two-phase flow are compared.  There are significant differences in hydraulic and thermal responses of the single-phase and two-phase designs due to high effective heat capacity rates and high heat transfer coefficients of flow boiling. The algorithm demonstrated in this work extends the capabilities of topology optimization to two-phase flow physics, and thereby enables the design of various two-phase flow components such as evaporators, condensers, heat sinks, and cold plates.</p> <p>The flow and heat transfer of the TO algorithm for microchannel heat sinks under flow boiling use a two-phase mixture model featuring an effective porous medium formulation. However, closure of the governing equations requires empirical correlations for pressure drop and heat transfer that are specific to the operating conditions, microstructure geometry, and surface finish. Therefore, it must be demonstrated these available correlations can be successfully calibrated over a range of microstructural variations present within the homogenization framework, so as to attain the required prediction generality and accuracy needed to ensure the resulting designs achieve Pareto-optimality. To this end, a set of uniform pin fin calibration samples are additively manufactured and experimentally tested under flow boiling at various flow rates and heat inputs for model calibration. All of the unknown/free coefficients in the adopted correlations are determined by minimizing the error between the model predictions and the experimental measurements using gradient-based optimization. The calibrated topology optimization algorithm is then used to generate a Pareto-optimal set of heat sinks optimized for minimum pressure drop and thermal resistance during flow boiling. Experimental characterization of these additively manufactured heat sinks, unseen during the model coefficient calibration process, reveals that the measured Pareto optimality curve matches that predicted by the topology optimization algorithm. Lastly, a heat sink design is generated for a design space involving multiple hot spots and background heating to showcase the capability of the experimentally calibrated two-phase topology optimization algorithm at handling complex boundary conditions. The optimized heat sink intelligently distributes an adequate amount of coolant flow to each of the heated regions to avoid local dry-out. This work demonstrates a complete framework for two-phase topology optimization of heat sinks through experimental calibration of flow boiling correlations to the porous medium used by the homogenization approach. </p> <p>The major contribution of this thesis is the development of a homogenization approach for TO of additively manufactured microchannel heat sinks under single- and two-phase flows. Not only does the homogenization approach provide several advantages over the traditional penalization approaches such as reduced computational costs, intrinsic fabricability using AM, and ease of use, but it also enables TO of heat sinks under flow boiling and potentially TO of other two-phase thermal management components. The work discussed in this thesis serves a comprehensive end-to-end guide on TO of microchannel heat sinks using the homogenization approach with experimental demonstrations for validation.</p>

<p dir="ltr">The research focuses on improving core simulation procedures in Boiling Water Reactors (BWRs) by leveraging machine learning techniques. Aimed at better fuel planning and enhanced safety, a machine learning model has been developed to predict errors in existing low-fidelity, diffusion-based core simulators. The machine learning models have demonstrated the capability to accurately and efficiently predict errors in core eigenvalue and power distribution in BWR Operations. This results in a significant improvement over conventional simulation methods in nuclear reactors without increasing computational complexity.</p>

Fluid inclusion and mineralogical features indicative of boiling have been characterized in 855 samples from epithermal precious metals deposits along the Veta Madre at Guanajuato, Mexico. Features associated with boiling that have been identified at Guanajuato include colloform texture silica, plumose texture silica, moss texture silica, ghost-sphere texture silica, lattice-bladed calcite, lattice-bladed calcite replaced by quartz and pseudo-acicular quartz after calcite and coexisting liquid-rich and vapor-rich fluid inclusions. Most samples were assayed for Au, Ag, Cu, Pb, Zn, As and Sb, and were divided into high-grade and low-grade samples based on the gold and silver concentrations. For silver, the cutoff for high grade was 100 ppm Ag, and for gold the cutoff was 1 ppm Au. The feature that is most closely associated with high grades of both gold and silver is colloform texture silica, and this feature also shows the largest difference in grade between the presence or absence of that feature (178.8 ppm Ag versus 17.2 ppm Ag, and 1.1 ppm Au versus 0.2 ppm Au). For both Ag and Au, there is no significant difference in average grade as a function of whether or not coexisting liquid-rich and vapor-rich fluid inclusions are present. The textural and fluid inclusion data obtained in this study were analyzed using the binary classifier within SPSS Clementine. The models that correctly predicted high versus low grade samples most consistently (~70-75% of the tests) for both Ag and Au were the neural network, the C5 decision tree and Quest decision tree models. For both Au and Ag, the presence of colloform silica texture was the variable with the greatest importance, i.e., the variable that has the greatest predictive power. Boiling features are absent or rare in samples collected along a traverse perpendicular to the Veta Madre. This suggests that if an explorationist observes these features in samples collected during exploration that an environment favorable to precious metal mineralization is nearby. Similarly, good evidence for boiling is observed in the deepest levels of the Veta Madre that have been sampled in the mines and drill cores, suggesting that additional precious metal reserves are likely beneath the deepest levels sampled. / Master of Science

L’ébullition est un mode de transfert de chaleur intervenant dans de nombreux systèmes thermiques ou énergétiques de par son efficacité. Dans certains, elle se produit à basse pression. La pression statique induite par la colonne de liquide au-dessus de la surface de formation des bulles n’est alors pas négligeable devant la pression de saturation à la surface libre. Dès lors, la pression et le sous-refroidissement induit ne peuvent plus être considérés homogènes autour des bulles, d’où des inhomogénéités des propriétés thermophysiques dans le fluide. Les influences relatives des forces s’exerçant sur une bulle pendant sa croissance sont modifiées par rapport aux pressions plus élevées : une dynamique de bulles différente apparaît. Ces conditions particulières affectent également les transferts thermiques. L’influence de la pression sur l’ébullition en vase a été étudiée expérimentalement dans le régime de bulles isolées en site unique. L’eau a d’abord été testée sur une large gamme de pressions subatmosphériques. Quatre comportements de dynamique de bulles ont été identifiés d’après la visualisation par caméra rapide. Plusieurs paramètres de la dynamique ont été quantifiés grâce à un traitement d’images adapté appliqué aux vidéos. Pour généraliser le concept d’ébullition à « basse pression » et mieux en appréhender les phénomènes fondamentaux, de nouveaux essais ont été réalisés avec un second fluide, le cyclohexane, choisi pour sa similitude thermodynamique avec l’eau bouillant en deçà de la pression atmosphérique. La comparaison des comportements des deux fluides a permis d’identifier certains paramètres responsables des spécificités du phénomène. En outre, de nouvelles fonctionnalités sont apportées au dispositif expérimental pour – notamment – effectuer la mesure rapide du flux transféré sous la bulle pendant sa croissance, synchroniser ces mesures thermiques avec l’acquisition d’images et étudier des surfaces d’ébullition structurées. Les résultats obtenus sont encourageants pour l’analyse des comportements spécifiques de l’ébullition à basse pression et ses applications. / Boiling is an efficient heat transfer mode used in numerous thermal or energy systems. In some systems boiling takes place at low pressure. The static head of the liquid column over the wall where bubbles nucleate is then not negligible against the saturation pressure at the free surface level. The pressure and the induced subcooling degree therefore cannot be considered as homogeneous around growing bubbles, resulting in non-homogeneous thermophysical properties in the fluid. The relative influence of the forces acting on a growing bubble differs from higher pressure conditions, yielding specific bubble dynamics features. Heat transfer is consequently also affected. The effect of the pressure on pool boiling was experimentally investigated during the isolated bubbles regime taking place from a single activated nucleation site. Experiments were first conducted with water for a wide range of subatmospheric pressures. Four distinct bubble dynamics behaviors were identified through high-speed camera visualizations. An adapted image processing of the recordings enabled the measurement of several bubble dynamics characteristics. In order to generalize the concept of pool boiling at "low pressure" and to get a better understanding of the related fundamental phenomena, new experiments were performed with a second fluid, cyclohexane, chosen from original thermodynamic similarity with water boiling at pressures lower than atmospheric. The comparison of fluids’ behaviors made possible the identification of parameters governing the specific phenomena occurring during boiling at low pressure. Besides, the experimental facility was improved to provide new functionalities. The high-speed measurement of the heat flux transferred under the growing bubble, its synchronization with the high-speed videos images and the study of boiling on enhanced surfaces are in particular made possible. Results are encouraging for a better understanding of the specific behaviors of low pressure boiling and for its future implementation in practical applications.

Large-scale bed features are often encountered in coastal waters, and include sandbanks and spoil heaps. The morphodynamic development of such features involves complicated nonlinear interactions between the flow hydrodynamics, sediment transport, and bed profile. Numerical modelling of the morphodynamic evolution and migration of large-scale bed features is necessary in order to understand their long-term behaviour in response to changing environmental conditions. This thesis describes detailed measurements of the morphodynamics of sand mounds in unidirectional and oscillatory (tidal) flows, undertaken at the U.K. Coastal Research Facility (UKCRF). High quality data were collected, including water velocities, water levels and overhead images. The parameters tested are: three types of mound shape (circular and elliptical in plan shape, and Gaussian, cosine and triangular in cross-section); underlying fixed or mobile bed conditions; and initial crest height (submerged, surface-touching and surface-piercing). Peak flow velocities are about 0.5 m/s, the sand median grain size is 0.454 mm, and transport occurring mostly as bedload. When analysing the data, the bed contours are determined by digitising the shoreline at different water levels. From these plots, the volume, height, and centroid position of the mound are calculated. A large-scale fit method, based on a Gaussian function has been used to separate small-scale ripples from the large-scale bed structure during the evolution of an isolated sand mound or spoil heap. The bed profile after the ripples are removed is comparable to typical predictions by shallow-flow numerical solvers. The UKCRF experiments investigated the morphodynamic response of a bed mound to hydrodynamic forcing: shape changes, migration rates, volume decay and sediment transport rates. The measured migration rate and decay of a submerged sand mound in the UKCRF are found to be in satisfactory agreement with results from various theoretical models, such as the analytical solution derived by De Vriend. Numerical predictions of mound evolution by a commercial code, PISCES, are also presented for a fully submerged sand mound; the bed evolution is reasonably similar to that observed in the UKCRF. The data provided as a result of the research reported in this thesis provide insight into the behaviour of sand mounds in steady and unsteady flows at laboratory scale, and should also be useful for benchmark (validation) purposes to numerical modellers of large-scale morphodynamics.

Les composites Carbone/Carbone haute densité sont généralement obtenus par voie gazeuse ou liquide (sous une pression de pyrolyse de 100 MPa), suivant des procédés contraignants. L’imprégnation de préformes fibreuses par des brais liquéfiés, sous une pression limitée à 10 MPa, permettrait de réduire certaines contraintes d’élaboration à condition de trouver des procédés pour améliorer les rendements de densification. La solution proposée dans le cadre de cette thèse est d’augmenter fortement la densité en une première étape, grâce à des techniques de densification moins classiques. Une étude bibliographique approfondie a permis de déterminer les caractéristiques importantes des brais, les différents paramètres influençant les densifications par voie liquide et des techniques de pré-densification. La cohérence entre les résultats de plusieurs techniques de caractérisation des brais, est mise en évidence lors du suivi expérimental de l’évolution de divers brais vers un carbone graphitique, sous pression modérée. Cette étude expérimentale concernant les précurseurs de matrice aboutit à la sélection d’un brai remplaçant au brai de référence A240 et au choix des paramètres du protocole de pyrolyse sous pression modérée. L’influence du réseau poreux de la préforme sur le comportement du brai pendant la densification est soulignée en comparant les rendements de densification dans une préforme 3D orthogonale et dans une préforme aiguilletée. L’intérêt des densifications mixtes (avec caléfaction, imprégnation de poudres ou de brai mésophasique) est jugé par rapport à la densité et à la microstructure des composites obtenus. Les procédés originaux de densification hybride réalisés sur les préformes aiguilletées se révèlent efficaces, puisqu’une densité apparente supérieure à 1,80 et une porosité inférieure à 15% est atteinte après quatre cycles de densification par du brai isotrope. Des mesures thermiques sur les composites C/C obtenus illustrent la relation entre microstructure et conductivité thermique. Il semble ainsi possible de moduler les propriétés macroscopiques des composites C/C grâce à l’utilisation de procédés permettant d’élaborer des composites C/C à matrices carbonées mixtes. / High density Carbon/Carbon composites are usually prepared by chemical vapor impregnation or by liquid pitch impregnation under high pressure (100 MPa). As these processes are complex and costly, an alternative moderate pressure (P < 10 MPa) impregnation process may be attractive, provided the densification yield is strongly improved. This doctoral work proposes an original process, including a pre-densification step, which leads to a significant increase of the C/C composite final density. Essential characteristics of pitches, various parameters influencing liquid pitch densification and processes for the pre-densification step are determined from bibliographical study. Consistent changes of the different physico-chemical characteristics are observed throughout the evolution of pitches to graphitic carbon, under moderate pressure. This experimental study on matrix precursors leads to the selection of a particular pitch as substitute of A240 pitch and to the determination of a specific pyrolysis procedure under moderate pressure. Influence of porous network in preforms on the pitch behaviour during densification is outlined by the comparison of densification yields in both an orthogonal 3D preform and a needled preform. Hybrid densification processes (with film-boiling process, powder impregnation, mesophasic pitch impregnation) are evaluated through the final density and the microstructure of elaborated composites. High density C/C composites, with an apparent density higher than 1.80 g.cm-3 and an open porosity lower than 15%, have been prepared from a pre-densified needled preform, after four densification cycles with liquid isotropic pitch, under moderate pressure. Thermal properties measurements on these C/C composites confirm the strong relationship between microstructure and thermal conductivity. It seems possible to tailor the macroscopic properties of C/C composites, thanks to hybrid carbonaceous matrices.

A contínua mudança na qualidade da carga de alimentação das unidades de destilação atmosférica introduz incertezas na operação do processo de refino. A caracterização precisa do petróleo bruto, cuja composição varia devido à sua natureza intrínseca e às condições de transporte e armazenamento nas refinarias, poderia auxiliar na redução destas incertezas. O processo clássico de caracterização, baseado nas curvas de destilação TBP (True Boiling Point, Ponto de Ebulição Verdadeiro), ainda não permite detectar essas mudanças de modo mais dinâmico, o que reduz a precisão da simulação do processo e, portanto, uma menor confiabilidade nas condições de operação determinadas a partir dela. No Brasil, petróleo pesado é produzido de forma predominante, que é misturado freqüentemente com petróleo leve importado antes do refino. Como conseqüência, nas refinarias brasileiras as características do petróleo mudam em média, a cada três dias, sendo esta taxa de variação incompatível com a determinação das curvas de destilação TBP. A análise SimDis (Simulated Distillation, Destilação Simulada) é atualmente a técnica de laboratório alternativa para aproximar as curvas de destilação. Porém, ainda apresenta algumas características que a tornam tão limitantes quanto a análise TBP. A espectroscopia NIR (Near InfraRed, Infravermelho Próximo), tem se consagrado como uma técnica analítica rápida e viável em inúmeras aplicações industriais na determinação de diversos parâmetros qualitativos. Neste trabalho, metodologias inovadoras de caracterização são desenvolvidas visando reproduzir com maior dinamismo o processo de refino. A reprodução das curvas de destilação das cargas ao processo de destilação atmosférica da Refinaria de Capuava (RECAP ? Petrobras S.A.) através do seu espectro NIR tem sido o ponto de partida no desenvolvimento do trabalho. Métodos de calibração multivariada e redes neurais foram utilizados na construção de algoritmos computacionais que permitem a previsão dos perfis de destilação do petróleo processado, os quais foram utilizados na simulação do processo para avaliar o impacto da aplicação desta metodologia. A boa qualidade da reprodução das propriedades físico-químicas do petróleo através do NIR foi comprovada, uma vez que os modelos construídos foram condicionados às características da matéria analisada. Quanto à reprodução do cenário real do processo através da simulação, os resultados obtidos são promissores, mostrando que a caracterização da carga é útil para reproduzir mudanças no processamento. Porém, alguns aspectos precisam ainda ser aprofundados visando o melhor desempenho das metodologias. Contudo, os resultados desta pesquisa reforçam a relevância do papel da espectroscopia NIR, juntamente com técnicas clássicas de laboratório utilizadas, numa nova concepção de caracterização, que tem na rapidez e confiabilidade os seus principais aliados e pode ser aplicada na simulação de um processo visando uma melhor qualidade de operação. / The continuous variation in the quality of the feed petroleum to atmospheric distillation unities brings uncertainty to the operation of the refining process. The characterization of the crude oil, whose composition varies due to its intrinsic nature and the transport conditions and storage in refineries, could be useful in reducing the uncertainty. The classic process of characterization, based on TBP distillation curves (True Boiling Point), still does not permit to detect these changes in a more dynamic manner, which reduces the precision of the process simulation and, consequently, less confidence in the operation conditions determined from it. In Brazil, heavy petroleum is produced predominantly, which is typically blended with light imported petroleum before refining. As a consequence, in Brazilian refineries the characteristics of the petroleum change, on the average, about every three days. This rate of the petroleum change is incompatible with the determination of TBP curves. Nowadays, SimDis analysis (Simulated Distillation) is an alternative laboratory technique able to approximate the distillation curves. However, it still presents some limiting characteristics like those of TBP analysis. In the last decades, the NIR spectroscopy (Near InfraRed) has showed to be a both fast and feasible analytical technique for innumerous industrial applications in the determination of various qualitative parameters. In the present work, an innovative characterization methodology is developed aiming to reproduce more dynamically the refining process. The reproduction of distillation curves of the feed to the atmospheric distillation process of the Refinery of Capuava (RECAP ? Petrobras S.A.) from its NIR spectral determination has been the initial point for the development. Multivariate calibration methods and neural networks have been used in the construction of computational algorithms that allow the prediction of distillation profiles of the petroleum processed. These profiles were applied in process simulation in order to evaluate the impact of the application of this methodology. The good quality of the physicochemical properties of petroleum reproduction using NIR was confirmed, it is due to the fact that constructed models were conditioned to the characteristics of the samples analyzed. With respect to the reproduction of the real process behavior through simulation, the results obtained are promising, which show that the feed characterization is useful in order to reproduce process variations. However, some aspects need to be analyzed deeply in order to improve the performance of the methodologies. Finally, the results of this research strengthen the role of NIR spectroscopy together with classic laboratory techniques used in a new characterization concept, whose major advantages are the rapidity and the trustworthiness of its predictions, that can be applied in order to improve the quality of the simulation of a process.

A presente tese trata da análise experimental do efeito da geometria da seção transversal do canal e do desempenho de refrigerantes de reduzido GWP (Global Warming Potential) durante a ebulição convectiva em canais de reduzidas dimensões. A tese inclui ainda um estudo extenso e crítico da literatura sobre métodos de previsão da perda de pressão e do coeficiente de transferência de calor, e sobre estudos experimentais em canais não-circulares e de refrigerantes com reduzido GWP na ebulição convectiva em canais de dimensões reduzidas. Resultados para o coeficiente de transferência de calor e perda de pressão durante a ebulição convectiva foram obtidos para canais com geometrias de seção circular, quadrada e triangular para o refrigerante R134a. Nos testes utilizou-se canais com perímetros internos similares obtidos a partir da conformação de um tubo com diâmetro interno igual a 1,1 mm. No caso do canal circular, dados foram também levantados para os HFOs R1234ze(E) e R1234yf e o hidrocarboneto R600a, fluidos com reduzido GWP. Ensaios foram executados para amplas faixas de fluxos de calor e velocidades mássicas, temperaturas de saturação de 31 e 41°C e títulos de vapor entre 0 e 0,95. Aspectos relacionados aos efeitos da geometria e do fluido refrigerante foram minuciosamente investigados através da análise paramétrica dos resultados. Com base na comparação do banco de dados coletado com os métodos de previsão disponíveis na literatura, constatou-se que estes proporcionam previsões satisfatórias apenas para condições experimentais especificas. Portanto, novos métodos de previsão da perda de pressão e do coeficiente de transferência de calor foram desenvolvidos com base nos dados levantados no presente estudo. Os métodos propostos preveem satisfatoriamente o banco de dados do presente estudo e resultados independentes disponíveis na literatura. Adicionalmente, com base nos resultados levantados, verificou-se que dissipadores de calor baseados em multi-microcanais com canais de seção triangular apresentam desempenho superior comparados a dissipadores com canais quadrados e circulares. / The present thesis concerns an experimental study on the effects of cross-sectional geometry and low GWP refrigerants on the thermal-hydraulic performance for convective boiling inside micro-scale channels. Experimental results for heat transfer coefficient and pressure drop gradient during convective boiling were obtained for circular, square and triangular channels for the fluid R134a. The evaluated channels present the same external perimeter and equivalent diameters of 1.1, 0.977 and 0.835 mm, respectively. In the case of the circular geometry, experimental results were also acquired for the HFOs R1234ze(E) and R1234yf and the hydrocarbon R600a (isobutane), which are fluids with low GWP and null ODP. Experiments were performed for a wide range of heat fluxes and mass velocities, saturation temperatures of 31 and 41°C and vapor qualities up to 0.95. The experimental data were carefully analyzed and discussed based on a parametrical analysis focusing on the effect of the cross-sectional geometry and the working fluid. Subsequently, the experimental data were compared against the most quoted predictive methods from literature. In general, it was verified that none of the predictive methods were able to accurately capture the experimental trends of the overall database. So, new predictive methods for the pressure drop and heat transfer coefficient were developed based on the broad database obtained in the present study. The proposed methods provided satisfactory results not only for the experimental database used for its development, but also for independent databases collected in the literature. Additionally, based on the data obtained in the present study and a performance analysis taken into account pressure drop, heat transfer coefficient and the channel packing factor, triangular cross sectional geometry is recommended for heat sinks.

Une étude expérimentale est menée afin de comprendre le phénomène de nucléation lors de l'ébullition. Cette étude est menée sur des surfaces polies miroir ou ultra-polies en aluminium, l’acétone étant le fluide de travail. L'analyse est réalisée en fonction de la topographie de la surface liée au degré de polissage et en fonction du revêtement de la surface dans le but de modifier sa mouillabilité. L’étude a mis en avant trois catégories de comportement, fonctions de l’état de surface : les surfaces nano lisses, les surfaces nano lisses avec défauts et les surfaces rugueuses. Les bonnes caractéristiques obtenues avec des échantillons nano lisses comportant des défauts aléatoirement répartis ont conduit à la réalisation d’échantillons nano lisses avec des défauts de position et de taille contrôlés. Les résultats obtenus avec ces derniers échantillons présentent les meilleures performances. Une amélioration supérieure à un facteur deux par rapport aux surfaces rugueuses est observée, ce qui représente un gain substantiel. Bien qu’il soit le fondement de la plupart des modèles théoriques, le nucléus à l’origine de la formation d’une bulle n’a jamais été observé expérimentalement car sa taille dépasse la capacité des moyens de mesure traditionnels. Dans ce mémoire, une méthode optique - basée sur la résonnance de plasmons sur des surfaces comportant un réseau de diffraction - est utilisée dans le but d’étudier ce phénomène. Les expériences mettent en évidence la capacité de cette méthode à mesurer la variation de la température pariétale de l’échantillon avant le déclenchement de l’ébullition. Les mesures de résonance plasmon montrent qu’il n’y a pas de modification de la densité du fluide au voisinage de la paroi pour des surchauffes proches du déclenchement de l’ébullition. La nucléation est trop rapide pour être mesurée. Cependant, des premiers nuclei de condensation ont été détectés par cette méthode, ce qui constitue un résultat très prometteur. / An experimental study was conducted in order to understand the phenomenon of nucleation in boiling. This study was done on smooth surface or ultra-smooth surface made of aluminum, the working fluid is acetone. The analysis was realized as a function of the topography of the sample, roughness level, and as a function of nanocoating of the surface in order to modify the wettability. The study classed the sample in three categories, depending on the surface condition: the ultra-smooth surface, the ultra-smooth surface with defect and the rough surface. The good characteristics were obtained for the ultra-smooth sample with randomly distributed defects led to the fabrication of ultra-smooth sample with controlled artificial cavity. The results obtained with these latter samples present the best performances. A two-fold improvement over rough surfaces is observed, representing a substantial gain. Although it is the foundation of most theoretical models, the nucleus at the origin of the formation of a bubble has never been observed experimentally because its size exceeds the capacity of the traditional means of measurement. In this memory, an optical method - based on the resonance of plasmons on surfaces with a diffraction grating - is used to study this phenomenon. The experiments demonstrate the ability of this method to measure the temperature variation in the wall of the sample before boiling. Plasmon resonance measurements show that there is no change in the density of the fluid near the wall for overheating close to the boiling point. The nucleation is too fast to be measured. However, first nuclei of condensation were detected by this method, which is a very promising result.