This thesis deal with design and implementation of innovative cooling method, intended primarily for medium-power synchronous generators. The main objective of this proposal is to remove the large heat exchanger connected to generator. This heat exchanger unduly increases the space requirements for the machine location. The proposed solution is to use a direct water-cooled stator. It is assumed that the rotor winding will be still cooled by air. Unlike current cooling system, the hot air from the rotor can be cooled in smaller cooler inside the generator. In this work are described methods which can be used for design of water cooling basic parameters, taking required temperatures into account. A small induction motor was selected for practical verification of the proposed cooling concept. This motor was modified into two variants - related to the old cooling of synchronous generators and related to the proposed solution. Both of these variants were measured and compared with each other. Subsequently, CFD models of these two variants were set up. Measured temperatures were used for debugging of models and identification of material properties of components of these machines. The final model of water-cooled variant also makes it possible to simulate the work of motor for higher performance and to determine the overload compared with the old cooling variant. Some knowledge and experience obtained from the small water-cooled induction machine were used in the design of water-cooling for large synchronous generator. In a similar way, CFD models of the old variant of cooling and proposed variant of water- cooling were created. Although these models were not verified by actual measurements on the generators, the results indicated that the application of water-cooling in this type of machine is appropriate and provides many benefits.

Masters degree thesis with name “Air flow in closed space” in teoretical part describes air flow. Defined here basic types of flow including the flow in a closed space and the methods for the description of the air flow. The practical part deals with project eva-luation distribution of air conditioning system using CFD model. Next solves a second variant of air distribution and compare the changes that have occurred. The end of the practical part approaching the possibility of using CFD model for creating the quality environment maps and the possibility to create variants of calculating with changing levels of the supply air.

Abstact: In order to address the wind-industry's need for a new generation of more advanced wake models, which accurately quantify the mean flow characteristics within a reasonably CPU-time, the two-dimensional analytical approach by Belcher et al. (2003) has been extended to a three-dimensional wake model. Hereby, the boundary-layer approximation of the Navier-Stokes equations has been linearized around an undisturbed baseflow, assuming that the wind turbines provoke a small perturbation of the velocity field. The conducted linearization of the well established actuator-disc theory brought valuable additional insights that could be used to understand the behavior (as well as the limitations) of a model based on linear methods. Hereby, one of the results was that an adjustment of the thrust coecient is necessary in order to get the same wake-velocity field within the used linear framework. In this thesis, two different datasets from experiments conducted in two different wind-tunnel facilities were used in order to validate the proposed model against wind-farm and single-turbine cases. The developed model is, in contrary to current engineering wake models, able to account for effects occurring in the upstream flow region. The measurement, as well as the simulations, show that the presence of a wind farm affects the approaching flow even far upstream of the first turbine row, which is not considered in current industrial guidelines. Despite the model assumptions, several velocity statistics above wind farms have been properly estimated, providing insight about the transfer of momentum inside the turbine rows. Overall, a promising preliminary version of a wake model is introduced, which can be extended arbitrarily depending on the regarded purpose.

This thesis deal with design and implementation of innovative cooling method, intended primarily for medium-power synchronous generators. The main objective of this proposal is to remove the large heat exchanger connected to generator. This heat exchanger unduly increases the space requirements for the machine location. The proposed solution is to use a direct water-cooled stator. It is assumed that the rotor winding will be still cooled by air. Unlike current cooling system, the hot air from the rotor can be cooled in smaller cooler inside the generator. In this work are described methods which can be used for design of water cooling basic parameters, taking required temperatures into account. A small induction motor was selected for practical verification of the proposed cooling concept. This motor was modified into two variants - related to the old cooling of synchronous generators and related to the proposed solution. Both of these variants were measured and compared with each other. Subsequently, CFD models of these two variants were set up. Measured temperatures were used for debugging of models and identification of material properties of components of these machines. The final model of water-cooled variant also makes it possible to simulate the work of motor for higher performance and to determine the overload compared with the old cooling variant. Some knowledge and experience obtained from the small water-cooled induction machine were used in the design of water-cooling for large synchronous generator. In a similar way, CFD models of the old variant of cooling and proposed variant of water- cooling were created. Although these models were not verified by actual measurements on the generators, the results indicated that the application of water-cooling in this type of machine is appropriate and provides many benefits.

L’évaluation du débit en réseaux hydrauliques à surface libre est une problématique actuelle sur le plan scientifique, à forts enjeux technologiques, économiques et écologiques. Dans cette thèse, de nouvelles méthodologies d’instrumentation, basées sur une synergie entre mesures non intrusives de hauteur d’eau et modélisation numérique ont été développées. Celles-ci s’appliquent d’une part à des collecteurs dont le fonctionnement hydraulique est complexe et, d’autre part, à des ouvrages non-standard (Venturi, déversoirs d’orage). Ce travail de thèse multidisciplinaire vise une meilleure compréhension de l’écoulement pour en déduire des relations Q=f(hi) plus robustes, spécifiques à chaque site et associées à leurs incertitudes; mais également l’identification de possibles modifications du site de mesure afin d’améliorer l’estimation du débit. Au final, l’applicabilité des méthodologies développées a été éprouvée au travers de plusieurs études sur sites réels. / The evaluation of the flow rate in free surface water systems is a current scientific problem, related to high technological, economical and ecological issues. In this study, new methods of instrumentation based on a synergy between non-intrusive water level measurements and numerical modeling have been developed. These methods are applied first to sewer pipes with complex hydraulic conditions then to non-standard hydraulic structures (Venturi flumes, Combined Sewer Overflows). This multidisciplinary work aims at a better understanding of the flow to identify more robust site-specific Q=f(hi) relationships related to their uncertainties. It also aims at the identification of possible modification of the measurement site in order to improve the flow rate evaluation. Finally, the applicability of the developed methodologies has been tested through several real site studies.

No description available.

Les principaux objectifs de cette étude est de fournir les informations essentielles sur le comportement thermique des cellules de batterie pour une application automobile, en particulier pour les véhicules électriques et hybrides. Cette application est notre cadre de travail expérimental afin de développer un modèle électro-thermique 3D efficace pour les cellules lithium-ion et du pack batterie. L'étude expérimentale se concentre sur la distribution de température en différents points de la surface de la cellule, de l'impact de différents débits constants, et également l'importance du système de refroidissement sur le comportement en température de la batterie. Cette thèse met en évidence le comportement de température de la cellule dans des conditions de décharge agressive et de l'impact de l'empilement de plusieurs cellules à l'intérieur de la batterie. Une étude de cas sur le comportement thermique de la cellule dans une application véhicule électrique hybride série est proposée pour compléter les cycles de conduite en utilisant différentes stratégies de refroidissement. En outre, l'étude expérimentale est étendue à la caractéristique du comportement de refroidissement par flux d'air à l'intérieur de la batterie, en utilisant le système d'image de particules (PIV). Le modèle électro-thermique CFD 3D est développé sous un logiciel Open Source OpenFOAM. L'objectif principal est d'obtenir un modèle relativement simple mais précis avec un temps de calcul raisonnable. Le modèle proposé, estime la production de chaleur, à partir du courant de la batterie et la résistance interne en fonction de la température, le transfert de chaleur par conduction, convection forcée et rayonnement. / The main objectives of this study are to provide the essential information on the thermal behaviour of the battery cells for automotive purpose especially for EVs and HEVs through experimental work in order to develop an effective 3D electro-thermal model for lithium ion battery cells and pack. The experimental study is focusing on the distribution of temperature at various points of the battery cell surface, impact of different constant discharge rates, and also the importance of cooling system on the battery temperature behaviour. This thesis highlights the battery cell temperature under abuse discharge condition and the impact of stacking the battery cells inside the battery pack. Impact of different temperature and SOC on the battery cell internal resistance and a case study on the battery cell thermal behaviour used in a series HEV to complete driving cycles using different cooling strategies are also studied. Furthermore, the experimental study is extended to the characteristic of the cooling air flow behaviour inside the battery pack, using particulate image velocimetry (PIV) system. The 3D electro-thermal CFD model is implemented in a free, open source CFD software package called OpenFOAM. The target is to have a relatively simple but accurate model with reasonable computation time. This proposed model considers the heat generation from battery current and internal resistance as a function of temperature, heat transfer through conduction, forced convection and radiation.

L'utilisation des meubles frigorifiques de vente fermés a augmenté régulièrement dans les supermarchés en raison des économies d'énergie réalisées par rapport aux meubles ouverts. D’où la nécessité d'élargir les connaissances scientifiques à ce type de meuble. Pour l’instant la plupart des études de la littérature ont porté sur l'amélioration de l'efficacité énergétique après l'installation de portes, tandis que les études sur les mécanismes de transfert de chaleur dans les meubles frigorifiques fermés sont rares. De plus, il convient d’étudier également les circulations d’air car ils influencent les échanges de chaleur entre l’air et les produits, donc leur température. Cette thèse a pour objectif de mieux comprendre les phénomènes d’écoulement d’air et de transfert de chaleur dans les meubles frigorifiques fermés par la mise en œuvre d'approches expérimentales et numériques.Des investigations expérimentales ont été menées sur un meuble frigorifique fermé placé dans une cellule d’essai à température contrôlée. Quatre-vingts thermocouples calibrés répartis dans le meuble ont permis d’observer les évolutions spatio-temporelles des températures de l’air et du produit dans différentes conditions de fonctionnement. Nous avons fait varier la température de l'air ambiant (15, 19, 24 et 29 ° C), le volume occupé par le produit (meuble vide ou plus ou moins chargé de blocs de méthylcellulose) et la fréquence d'ouverture des portes (0 : fermé en permanence, 10, 20, 40, 60 Ouvertures Par Heure - OPH). Des expériences ont également été réalisées dans une configuration ouverte du meuble frigorifique (portes complètement retirées) afin de déterminer les avantages des portes sur les performances thermiques.Les résultats ont montré que lorsque les portes étaient fermées en permanence, les champs de température étaient similaires quels que soient la température ambiante et le pourcentage de volume occupé : la température la plus élevée se situe à l’avant de l'étagère supérieure alors que la température la plus basse est observée à l’arrière de l'étagère inférieure. Cette répartition change lorsque les portes sont périodiquement ou définitivement ouvertes : la position où la température est la plus élevée migre vers l’avant de l'étagère du milieu. Même pour une fréquence très élevée d’ouverture des portes (60 OPH), les températures de l’air et des produits dans le meuble fermé sont restées plus basses d’au moins 1,0 ° C par rapport au meuble sans portes.Des mesures de vitesse d'air par anémométrie à fil chaud au niveau du rideau d’air ont permis d'observer son allure générale tandis que les mesures effectuées dans le conduit arrière ont permis de quantifier la répartition du flux d'air à travers le plaque arrière perforée. L’utilisation d’une technique de vélocimétrie par image de particules (PIV) a permis de caractériser le rideau d’air avec une résolution et une précision spatiale supérieures. Les résultats ont notamment montré l’existence d’une zone de recirculation de l'air dans la partie supérieure du meuble où l’on observe également une infiltration d'air ambiant chaud par les fentes présentes autour des portes. Ceci induit une augmentation de la température du rideau d'air. Des simulations numériques bidimensionnelles d’écoulement (CFD) avec le modèle de turbulence k-ε ont permis de reproduire les principaux phénomènes d'écoulement observés par PIV et de voir leur influence sur la distribution de température dans le meuble.Enfin, un modèle simplifié des transferts de chaleur a été développé par une approche zonale en régime permanent et en régime transitoire ce qui permet respectivement de prévoir les températures moyennes de l’air et du produit et les fluctuations de température en fonction des cycles marche / arrêt du compresseur. Le modèle transitoire a été résolu avec une approche spectrale. L'influence de différents paramètres sur les niveaux de température et l'amortissement des fluctuations peut ainsi être identifiée. / The use of closed refrigerated display cabinets in supermarkets has been increased steadily because of the potential energy savings compared to open ones. This growing trend has contributed to the necessity to expand research in the field of retail refrigeration. Most studies in literature, however, focused on the improvements of energy efficiency after door installation while studies on the mechanism of heat transfer and airflow within closed display cabinets are still limited. In fact, the airflow pattern influences the heat exchange between air and products, thus, product temperature. This PhD thesis aims to gain an insight into the mechanism of airflow and heat transfer in closed refrigerated display cabinets by the implementation of experimental and numerical approaches.Experimental investigations were conducted in a closed refrigerated display cabinet (an integral type with a single band air curtain and two double-glazing doors) located in a controlled-temperature test room. Air/product temperatures and air velocity are the main parameters taken into investigations. Eighty calibrated thermocouples distributed throughout the cabinet made it possible to observe the spatial and temporal evolutions of the air and product temperatures under different operating conditions. These conditions were ambient air temperature (15, 19, 24 and 29 °C), product-occupied volume (unloaded, half-loaded and full-loaded with test packages made of methylcellulose), door-opening frequency (0 - permanently closed, 10, 20, 40, 60 Openings Per Hour - OPH) and opening duration (15s and 30s). An automatic door opening system was developed and allowed to apply the opening regime as prescribed in the standard test (EN ISO 23953-2, 2015). The experiment was also conducted in an open configuration of the cabinet (doors were completely removed) to determine the benefits of the doors on the temperature performance. The results showed that when the doors were permanently closed, the temperature distribution in the cabinet was similar whatever the ambient temperatures and occupied-volume percentages – the highest temperature position at the front-top shelf and the lowest temperature position at the rear-bottom shelf. The temperature distribution changed when the doors were periodically or permanently open – the front of the middle shelf became the highest temperature position while the lowest temperature position remained at the rear-bottom shelf. However, the air and product temperatures in the cabinet with doors remained lower despite a very high door-opening frequency (i.e. 60 OPH, product temperatures at least 1.0 °C lower), compared to the case without doors.Air velocity measurement using a hot-wire anemometer at the front of the cabinet from the discharge to the return air grilles allowed to observe the shape of the air curtain, while the measurement in the rear duct allowed to quantify the air flow distribution over the perforated back panel of different shelves. The use of a Particle Image Velocimetry (PIV) technique allowed the characterization of the air curtain with higher spatial resolution and accuracy. The result showed a zone of air recirculation at the upper part of the cabinet where warm ambient air infiltration through the door gaps was also observed, leading to an increase in the air curtain temperature. A 2D-CFD k-ε turbulence model was developed to reproduce the main flow phenomena observed by PIV so that its influence on the internal temperature distribution can be examined.Finally, a simplified heat transfer model was developed based on a zonal approach in both static and dynamic regimes which permits, respectively, the predictions of time-averaged air and product temperatures and temperature fluctuations according to the on/off cycle of the compressor regulation. The dynamic model was solved with a spectral approach, thus the influence of different parameters on the damping of the temperature fluctuations can be identified.

This thesis presents a modelling approach of laser welding process of aluminium alloy from the thermo-mechanical point of view to evaluate the occurrence of hot cracking based on simulation results and relevant criteria. The model was created stepwise in COMSOL Multiphysics, starting with the thermal model where heat conduction of solid and liquid phase was computed. Then the CFD model was created by involving the driving forces of liquid motion in the weld pool, i.e. natural convection and Marangoni effect. Lastly, the temperature profile calculated by the CFD model was loaded into the mechanical model for computation of thermal stress and strain. The mechanical results were required in  criteria for measuring the  susceptibility of hot cracking. The main findings include that Marangoni effect plays a dominant role in generating the fluid flow and convective heat flux in the weld pool, thus enhancing the heat dissipation and lowering temperature in the workpiece. By contrast, such temperature reduction caused by the air convection, radiation and natural convection is negligible. The welding track further from the clamped side experiences smaller transversal residual stress, but it does not necessarily suggest higher susceptibility to hot cracking according to the applied criteria. It can be concluded judging from current results that these first models of laser welding process work satisfactorily. There is still a work to do to obtain the full maturity of this model due to its limitation and some assumptions made for simplicity. / Denna avhandling presenterar en modelleringsmetod för lasersvetsningsprocessen av aluminiumlegering ur termomekanisk synvinkel för att utvärdera förekomsten av het sprickbildning baserat på simuleringsresultat och relevanta kriterier. Modellen skapades stegvis i COMSOL Multiphysics, med början med den termiska modellen där värmeledning av fast och flytande fas beräknades. Sedan skapades CFD-modellen genom att involvera drivkrafterna för flytande rörelse i svetsbassängen, dvs. naturlig konvektion och Marangoni-effekt. Slutligen laddades temperaturprofilen beräknad av CFD-modellen in i den mekaniska modellen för beräkning av termisk stress och töjning. De mekaniska resultaten krävdes i kriterier för att mäta känsligheten för het sprickbildning. De viktigaste resultaten inkluderar att Marangoni-effekten spelar en dominerande roll när det gäller att generera vätskeflödet och konvektivt värmeflöde i svetsbassängen, vilket förbättrar värmeavledningen och sänker temperaturen i arbetsstycket. Däremot är sådan temperaturreduktion orsakad av luftkonvektion, strålning och naturlig konvektion försumbar. Svetsbanan längre från den fastspända sidan upplever mindre tvärgående restspänning, men det föreslår inte nödvändigtvis högre känslighet för hetsprickning enligt de tillämpade kriterierna. Man kan dra slutsatsen utifrån aktuella resultat att dessa första modeller av lasersvetsningsprocesser fungerar tillfredsställande. Det finns fortfarande ett arbete att göra för att få full mognad för denna modell på grund av dess begränsning och vissa antaganden för enkelhetens skull.

This work seeks to illustrate the potential benefits afforded by implementing aspects of fluid dynamics, especially the latest computational fluid dynamics (CFD) modeling approach, through numerical experimentation and the traditional discipline of physical experimentation to improve the calibration of the severe reactor accident analysis code, MELCOR, in one of several spent fuel pool (SFP) complete loss-of-coolant accident (LOCA) scenarios. While the scope of experimental work performed by Sandia National Laboratories (SNL) extends well beyond that which is reasonably addressed by our allotted resources and computational time in accordance with initial project allocations to complete the report, these simulated case trials produced a significant array of supplementary high-fidelity solutions and hydraulic flow-field data in support of SNL research objectives. Results contained herein show FLUENT CFD model representations of a 9x9 BWR fuel assembly in conditions corresponding to a complete loss-of-coolant accident scenario. In addition to the CFD model developments, a MATLAB based control-volume model was constructed to independently assess the 9x9 BWR fuel assembly under similar accident scenarios. The data produced from this work show that FLUENT CFD models are capable of resolving complex flow fields within a BWR fuel assembly in the realm of buoyancy-induced mass flow rates and that characteristic hydraulic parameters from such CFD simulations (or physical experiments) are reasonably employed in corresponding constitutive correlations for developing simplified numerical models of comparable solution accuracy. / text