Design of internal cooling channels for gas turbine blade is critical to system performance. To achieve maximum efficiency, i.e. maximum cooling with minimum coolant usage, intensive research is required to optimize heat transfer enhancement features. The present study aims at experimental and numerical investigation of two heat transfer augmentation techniques for internal cooling, viz. dimple and swirl induced jet impingement. Dimples are suitable candidates for high performance enhancement as they impose a low pressure drop penalty. The present study aims at experimentally measuring heat transfer on all the walls of diamond, triangular, square and cylindrical shaped dimples in a staggered configuration at three flow conditions in a high aspect ratio channel. A thermal-hydraulic performance factor was evaluated to characterize each dimple shape. Numerical simulations were conducted to visualize flow patterns which was correlated with heat transfer distribution. The results were in good agreement with previous studies. Triangular dimples showed the highest overall performance due to lowest pressure drop penalty, but heat transfer was low inside the dimples. In rotating channels, Coriolis Effect and centrifugal buoyancy significantly affect heat transfer distribution. There is a need to develop a cooling geometry that benefits from rotation and provides consistent cooling. A new geometry was derived from a past study, consisting of two channels divided by a wall with angled holes to provide jet impingement from inlet to outlet channel. Liquid crystal technique was used for heat transfer measurements. It was found that at high rotational speeds, heat transfer increased in the inlet channel, while it decreased in the outlet channel. Additional testing at even higher speeds may provide insight into replacing a traditional U-bend channel in a turbine blade. / Master of Science

Electric vehicles aim to carry the torch into a sustainable future. An optimized cooling system is crucial to an Electric Drive Unit (EDU). A smartly designed cooling system will deliver high-performance, efficient and long-lasting EDUs at lower costs. One way to achieve that is to have an integrated cooling system. When the electric motor and transmission share a common oil, the oil returning from the transmission side is aerated due to spraying and splashing. This aeration affects the pump performance and may reduce the cooling performance of the oil. Thus, this thesis is initiated to understand the impact of aeration on heat transfer.     Oil aeration is the presence of air in oil. This aeration depends on the air content and bubble sizes mixed in the oil. Typically, there is also some amount of dissolved air in any oil. Depending on the type of aeration, the oil will appear lighter than its usual colour and have a very foamy texture, showing a change in the properties of the fluid, for example density, viscosity and heat transfer.    An experimental setup is built in order to replicate and study the effect of aeration on local heat transfer. A flat channel with rectangular cross-section is designed with three parts – a bottom plate, a flow spacer channel and a top transparent plate. The oil and air are mixed before they enter the channel and then heated using thin film heaters. A groove within the bottom plate houses an insulating material, the thin film heater, a thermocouple touching the heater and a thermochromic liquid crystal sheet facing the fluid mixture. The thermocouple gives temperature readings from a single point between the heater and the insulating material. Meanwhile, the liquid crystal sheets come in different desired temperature ranges and change in colour from red to blue to show the surface temperatures over an area. So, the surface temperature of the mixed fluid flow can be recorded visually over an area with the thin film heater under it to calculate the heat transfer coefficients accordingly.    The drop in Nusselt number and heat transfer rates with increased aeration in the working fluid is the main highlight and result. The size of the air bubbles in the channel also determine how fast the heat transfer rate drops.

No description available.

Proper design of high performance industrial heat transfer equipment relies on accurate knowledge and prediction of the thermal boundary conditions. In order to enhance the overall gas turbine efficiency, advancements in cooling technology for gas turbines and related applications are continuously investigated to increase the turbine inlet temperature without compromising the durability of the materials used. For detailed design, local distributions are needed in addition to bulk quantities. Detailed local distributions require advanced experimental techniques whereas they are readily available using numerical tools. Numerical predictions using a computational fluid dynamics approach with popular turbulence models are benchmarked against a semi-empirical correlation for the friction in a circular channel with repeated-rib roughness to demonstrate some shortcomings of the models used. Numerical predictions varied widely depending on the turbulence modelling approach used. The need for a compatible experimental dataset to accompany numerical simulations was discussed. An exact, closed-form analytical solution to the enhanced lumped capacitance model is derived. The temperature evolution in a representative 2D turbulated surface is simulated using Fluent to validate the model and its exact solution. A case including an interface contact resistance was included as well as various rib sizes to test the validity of the model over a range of conditions. The analysis was extended to the inter-rib region to investigate the extent and magnitude of the influence of the metallic rib features on the apparent heat transfer coefficients in the inter-rib region. It was found that the thermal contamination is limited only to the regions closest to the base of the rib feature. An experimental setup was developed, capable of measuring the local heat transfer distributions on all four channel walls of a rectangular channel (with aspect ratios between 1 and 5) at Reynolds numbers up to 150,000. The setup utilizes a transient thermochromic liquid crystals technique using narrow band crystals and a four camera setup. The setup is used to test a square channel with ribs applied to one wall. Using the transient thermochromic liquid crystals technique and applying it underneath high conductivity, metallic surface features, it is possible to calculate the heat transfer coefficient using a lumped heat capacitance approach. The enhanced lumped capacitance model is used to account for heat conduction into the substrate material. Rohacell and aluminum ribs adhered to the surface were used to tandem to validate the hybrid technique against the standard technique. Local data was also used to investigate the effect of thermal contamination. Thermal contamination observed empirically was more optimistic than numerical predictions. Traditional transient thermochromic liquid crystals technique utilizes the time-to-arrival of the peak intensity of the green color signal. The technique has been extended to utilize both the red and green color signals, increasing the throughput by recovering unused data while also allowing for a reduction in the experimental uncertainty of the calculated heat transfer coefficient. The over-determined system was solved using an un-weighted least squares approach. Uncertainty analysis of the multi-color technique demonstrated its superior performance over the single-color technique. The multi-color technique has the advantage of improved experimental uncertainty while being easy to implement.

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La convection de Rayleigh-Bénard est étudiée expérimentalement dans une cellule circulaire. Des fluides à seuil modèles (gels aqueux de Carbopol) sont mis en œuvre. Leurs comportements rhéologiques et leurs perméabilités en relation avec leurs microstructures ont été finement caractérisés. Dans toute la thèse, les expériences ont été menées sans glissement à la paroi. L'influence du seuil d'écoulement et de la distance entre plaques chaudes et froides sur les transferts thermiques a été approfondie. Trois mécanismes sont discutés pour expliquer le déclenchement de la convection: i) les propriétés visco-élastiques au-dessous du seuil, ii) le fluage au-dessous du seuil, iii) une approche d'un milieu poreux pour les gels de Carbopol considérés comme une suspension de micro-gels. On montre que le nombre de seuil Y, représentant le rapport entre la contrainte du seuil et la contrainte de la poussée d'Archimède est un paramètre important gouvernant l'apparition de l'instabilité. Les valeurs critiques de Y^(-1) sont déterminées entre 60 et 90. La visualisation à l'aide des cristaux liquides thermo-chromiques a permis une vue globale de la cinématique. Les structures observées dans les différents états thermiques montrent l'évolution de la convection. Une analyse qualitative du champ de température est également présentée. Enfin, la simulation numérique dans une cellule carré avec un modèle d'Herschel-Bulkley régularisé dans la gamme des nombres sans dimension utilisée dans les expérience a permis de mettre en évidence les paramètres critiques et la morphologie des champs thermiques et cinématique. Les ordres de grandeurs du nombre de seuil critique prédit se comparent raisonnablement avec les valeurs expérimentales. / In this thesis, three main mechanisms proposed in a recent paper (Darbouli et al., Physics of fluids, 25(2) 2013) have been discussed to explain the onset of Rayleigh Bénard Convection in a yield fluid (Carbopol gels): i) the elasto-visco-plasticity behavior of the material below the yield stress, ii) a viscosity at low values of shear rates by creep measurements below the yield stress, iii) a microscopic viewpoint considering the fluid as a porous two phases system. No-slip conditions have been achieved for all the experiments. The results with different Carbopol gels have proved the importance of Y, the yield number which presents the report of the yield stress and the buoyancy effect, as the governing parameter. The critical value of Y^(-1) with no-slip condition has been found between 60 and 90. A visualization measurement with the utilization of thermochromics liquid crystals presents a global view from above. Different structures have been observed in different states of thermal conditions, which describe the evolution of the convection. For several cases the color of the liquid crystals can indicate the temperature field in the whole experiment cell. Numerical simulations with a Herschel-Bulkley model have also been discussed in this thesis. The dimensionless parameters are defined approaching the values obtained in the experiments, so that we can compare the numerical results with some of experimental ones.

Ces travaux sont issus d’une thèse CIFRE et de la collaboration entre la société Viessmann Faulquemont et le laboratoire de recherche l’Institut Jean Lamour. Ayant pour objectif de fortement réduire les problèmes liés aux hautes températures de stagnation dans les panneaux solaires thermiques, nous présentons une nouvelle génération d’absorbeur solaire intelligent à base de dioxyde de vanadium. Le dioxyde de vanadium, noté VO2, est un matériau présentant une transition métal-isolant (MIT) à une température critique (Tc) de 68°C. Cette transition s’accompagne d’une modification de la structure cristallographique. Le VO2 se trouve sous une forme monoclinique VO2(M) à basse température, et sous une forme rutile VO2(R) à haute température. Ce changement de structure s’accompagne d’une forte modification des propriétés optiques. La synthèse de ces films est réalisée à partir d’une couche de vanadium métallique déposée par pulvérisation. Un recuit d’oxydation-cristallisation est ensuite effectué pour obtenir une couche d’environ 400 nm de dioxyde de vanadium. Afin d’optimiser et d’augmenter la variation d’émissivité (Δε), la température et la durée du recuit sont étudiées. Dans un second temps, un dopage aluminium est réalisé afin d’augmenter l’effet de la transition thermochrome. Après optimisation, le passage au niveau industriel est un succès et des prototypes de taille 1 sont réalisés à partir de la couche thermochrome et de la couche standard afin d’être comparés dans des conditions normales d’utilisation / This work is a CIFRE thesis between VIESSMANN Faulquemont SAS society and the laboratory Institut Jean Lamour. In order to strongly reduce the problems associated with high stagnation temperature, we present a new generation of solar absorbent layers based on a smart thermochromic vanadium dioxide thin film. Vanadium dioxide (VO2) is a material which exhibit a metal insulator transition (MIT) at a critical temperature of 68°C (Tc). The transition is accompanied by a change in crystallographic structure VO2(M), while a rutile-like structure VO2(R) is obtained at high temperature. This structural change induces a drastic modification of the optical properties. The synthesis of vanadium-based films is performed using magnetron sputtering. We proceed to a subsequent annealing in air to form crystalline films of about 400 nm thickness. In order to increase the thermochromic effect of our thin film (Δε) we study the temperature and duration of the annealing. In a second time we try to increase the emissivity switch between the low and high temperature phase by adding an aluminum doping. After optimization, scale up have been successfully done and the optimized parameters have been used to build a prototype of thermochromic selective layer that has been compared to the standard industrial solar absorber

Au cours de ce travail, nous avons préparé des clips moléculaires efficaces à partir de dimères de cuivre(I) ou d'or(I) portant des ligands organophosphorés en tirant parti des interactions métallophiles. Dans un premier temps, un complexe de cuivre(I) portant des ligands bis(2-pyridyl)phospholes a été utilisé comme clip moléculaire pour organiser des systèmes pi monotopiques à fonction cyano et portant divers fragments pi-conjugués. Ces dimères formés par assemblage pis'auto-organisent à l'état solide en colonnes pi infinies. Dans un deuxième temps, un complexe d'or(I) portant un ligand biphosphole a été utilisé comme clip moléculaire pour organiser des unités éthynyl[6]helicenes en dimères. Ces dimères ont montré une augmentation des propriétés chiroptiques par rapport au ligand éthynyl[6]helicene libre. Dans un troisième temps, un complexe bimétallique de cuivre(I) portant des ligands 1,1-bis(diphénylphosphino)méthane (dppm) s'est révélé être un clip moléculaire efficace pour la conception d'architectures supramoléculaires auto-assemblées par réaction avec des cyanométallates. Ces dérivés supramoléculaires ont des topologies différentes et sont émissifs dans le domaine visible après excitation dans l'UV. Dans certains cas, ils ont montré des propriétés de luminescence thermochromique intéressantes. / In this work, we have prepared organophosphorated ligands based copper(I) or gold(I) dimers that act as efficient molecular clips thanks to metallophilic interactions. Firstly, a bimetallic copper(I) complex bearing bis(2-pyridyl)phosphole ligands was used as a molecular clip to organize monotopic cyano-capped pi-systems carrying various pi-conjugated fragments into self-assembled pi-stacked dimers. These dimers organized in the solid state within infinite columnar pi-stacks. Secondly, a bimetallic gold(I) complex bearing a biphosphole ligand was used as a molecular clip to organize ethynyl-capped [6]helicene moieties into self-assembled dimers. These dimers showed an enhancement of the chiroptical properties as compared to the free ethynyl[6]helicene ligand. Thirdly, a bimetallic copper(I) complex bearing 1,1-bis(diphenylphosphino)methane (dppm) ligands has revealed a powerful molecular clip to design self-assembled supramolecular architectures by reaction with different cyanometallates. These supramolecular derivatives have different topologies and are emissive in the visible spectrum upon UV excitation and in some cases they showed intriguing thermochromic luminescence properties.

<p>Smart windows that modulate solar radiation by changing their optical state in response to temperature stimulus are developing as promising solutions towards reducing the energy consumption of buildings. The market adoption of such systems has been slow due to the barriers in scalability, cost, as well as complexity in their integration into existing systems. Aiming these features, we have proposed a retrofit smart window design based on the temperature-responsive polymer Methyl Cellulose (MC). The system utilizes a sustainable, earth abundant and cost-effective cellulose based thermo-responsive material to transform existing windows to a thermally dynamic smart window system. The observed optical change of MC from transparent to opaque state is dependent on temperature and is triggered by the thermodynamic mechanism of reversible coil-globule transition, which results in a stable performance of the proposed device. Its solar modulation ability was studied using ultraviolet-visible- spectroscopy. Effect of MC concentration and various salts on the optical performance were investigated. It was found that the transition temperature the polymer can be tuned by varying MC concentration and by adding salts to the system. The tunability of transition temperature is a function of the concentration of salt and the type of anion in the salt. It was observed that the transition temperature of the window can be tuned between to , allowing a wide range of control over switching temperature. Controllable LCST, low freezing point, sustainable base material, scalable production, low cost, retrofit system makes them ideal candidates for smart window applications. </p>

No description available.