<p>A battery assembly experiences both mechanical and thermal loadings during its operation. It is critical to perform the thermomechanical analysis to propose a novel design for the highest efficiency.In this study,two main goals include mechanical characterization and deformation responses for a battery cell and assembly, as well as air-cooled concepts design and analysis.Initially, the cell dimensions were measured by cell-sectioning method, and then the mechanical properties were empirically measured by both 3-point flexural, and nanoindentation experiments. Moreover, three pairs of experiments and simulations were conducted to study mechanical behaviors on both a single cell and a battery assembly. They include (1) point-force loading for single, open cell; (2) internal pressurization for single, sealed cell; and (3) internal pressurization for battery assembly.Additionally, both parametric and experimental studies were executed to design, analyze,and validate air-cooled concepts based on the idea of microchannel heatsink. The proposed concepts have the features, which are integrated into the battery cell for generating the cooling channels. A series of thermomechanical simulations and a forced convection testbed were built for computationally and empirically analyzing the performances of the concepts. The results from the mechanical characterization showed a significant difference between the actual and nominal values of both cell dimensions and mechanical properties. Therefore, the effect of the manufacturing process to such values must be considered before inputting for analyzing the deformation responses. From the thermomechanical analyses, it was found that the mechanical loading might negatively influence the thermal performance if there were not enough mechanical supports from the air-cooling structure. The impact was minimal in the tapered-channel battery assembly. This configuration also significantly reduced the temperature difference on the cell compared with other concepts and the reference design.<br></p>

Climate change is a critical global issue that continues to shape the way we understand and interact with the world around us. It is discussed more than ever before, especially in politics. To slow down the temperature rise of our planet, decreasing the amount of green house gas emissions produced by our way of living, industries, and the production of energy is necessary. Ocean Harvesting Technologies (OHT), a company from Sweden based in Blekinge, is currently developing a new iteration of renewable, wave energy converters (WEC) that they claim to be ecient from both an energy and cost perspective. A new prototype is in development where thermal and fluid characteristics inside the WEC during operation, are important aspects that need to be evaluated. This project is aimed to develop a computational simulation model of the WEC and perform simulations in order to evaluate the cooling and heating performance of the current model that is under development. The methodology used for this project was divided into three stages to streamline the work: steady-state stationary conjugate heat transfer(CHT) simulations, and transient airflow simulations with motion and compressible air, that are combined into a full-system transient CHT model for operational conditions. CAD models and delimi- tations were provided by OHT and the model was broken down, simplified and assessed to begin the work. The computational software used for the simulations in this project was STAR-CCM+ and the complete process of pre-processing, simulation setup/run and post-processing was executed using the same software. To simulate the fluid and the oper- ational motion of the WEC, the Overset mesh methodology was used, and to resolve the turbulent flow, URANS k! SST was used in the solver. The thermodynamic simulations were initially set up and simulated in two sub-models in order to speed up the method development and to get an early indication of the performance of the WEC. The first sub-simulation handled the compressible air together with the Overset mesh motion while the second simulation aimed to model the thermodynamics of the generator components, ball screw, and other solids. Since OHT is in a relatively early development phase, no experimental data could be used for validation, however, data sheets for generator com- ponents and simple handbook calculations were used to validate the simulation models performance. The sub-simulations resulted in an ecient simulation strategy and a lot of knowledge and understanding of the system performance was gained to implement in the full-system model The final outcome of this thesis work was a complete CHT model that showed the ca- pability of running several hundreds of seconds of operational time while producing a significant amount of performance data such as temperature profiles of critical parts, air pressure/temperature fluctuations, and drag losses of the complete WEC. Furthermore, the sub-simulation models can be used individually as stand-alone models in order to op- timize the system on a component level, e.g., drag losses from the generator components during motion.

Wave power has been increasing the interest of many researchers looking for alternative sustainable energy sources since the reserves have proved to be capable of satisfying a considerable percentage of the world´s energy demands. This option has not been adopted as a sustainable source since there are some challenges in the process of designing a low cost device that converts the kinetic energy of the waves into electric energy and that could still be efficient enough to be competitive against other options. A new proposal from Anders Hagnestål looks like a very promising way of moving forward in this field. The structure of this newly proposed generator includes neodymium magnets that at temperatures over 60°C might suffer irreversible demagnetization, compromising the normal functioning of the machine. Because of the electrical losses in iron components, overheating is a possibility that must be studied. The aim of this study is to find the temperature distribution of the components that are subject to changing magnetic fields (where the losses will occur). This will be done for a variety of cases regarding environmental and working conditions with the purpose of determining if the generator will need a cooling technique to avoid damage to the magnets. The studied structure consists of a stator and a translator conformed by iron, FR4, glass fiber and, of course, the magnets. The task at hand was carried out first through a one-dimensional analytical model, then through a two-dimensional analytical model and finally by means of simulations on Comsol Multiphysics (Computer-Aided-Engineering software). All of the aforementioned methods implicate assumptions that deviate from reality, but are still useful for the task at hand. Results from the 1D calculation turned out to be unreliable due to the numerous approximations but helped to prove and understand the effect of each of the environmental conditions on the temperature distribution. On the other hand, the 2D calculations and the simulations had a very good agreement which provides some reliability. Furthermore, said results showed that the components might even reach temperatures as high as 380°C under certain conditions. As this number is clearly over the safe limit of the magnets, it was concluded that cooling techniques are needed to ensure the safety of the generator. After some discussion with Hagnestål, cooling methods were proposed. In addition to this, the seemingly most appropriate option was pointed out with the intention of achieving a low-enough temperature and keeping the costs as low as possible. This alternative was a combination of modifying geometric parameters (which would ultimately reduce heat generation) and inducing a low velocity air flow. / Vågkraft är en hittills outnyttjad förnybar energikälla som i framtiden kan tillgodose i storleksordningen 10 % av världens energibehov, om de tekniska utmaningarna kan lösas så att vågkraft kan levereras till konkurrenskraftiga priser. Därmed finns också ett starkt intresse från både akademi och näringsliv att lösa dessa utmaningar. Anders Hagnestål håller på att utveckla en ny linjär generatortyp som enligt beräkningar slår alla befintliga lösningar för effektomvandling för vågkraft med bred marginal. Maskinen har dock komplex geometri, och det är svårt att beräkna dess prestanda. Maskinen innehåller neodymmagneter, vilka kan avmagnetiseras om de blir för varma där 60°C kan ses som en gräns då magneterna börjar påverkas. Om magneterna avmagnetiseras blir maskinen svagare. Eftersom magneterna upphettas av virvelströmmar i magneterna och förluster i omgivande elektroplåt, är det av intresse att göra en termisk analys av maskinen vilket är syftet med detta examensarbete. Målet är att beräkna temperaturutbredningen i maskinens olika delar vid olika driftsfall, och se om man behöver tillföra extern kylning av maskinen för att skydda magneterna. Maskinen består av en translator som omsluter den inre statorn där magneterna är lokaliserade, vilka är byggda av fiberkompositer, elektroplåt, rostfritt stål och neodymmagneter. Beräkningar gjordes först med en endimensionell analytisk modell, därefter med en tvådimensionell analytisk modell och slutligen med numeriska beräkningar i 2D med det kommersiella finita elementmetodberäkningsprogrammet Comsol Multiphysics. Samtliga dessa modeller har avvikelser från det verkliga fallet, men är ändå användbara och ger en fingervisning om hur den termiska situationen för maskinen kan se ut. 1D-beräkningarna visade sig innehålla lite för grova approximationer för att ge pålitliga resultat, men gav en del intuitiv insikt om problemet. Den analytiska 2D-beräkningen stämde bra överens med Comsol-beräkningen, vilket indikerar att beräkningarna är korrekta. Resultaten visade på mycket höga temperaturer i vissa driftsfall utan kylsystem, 380 °C, vilket är en indikator på att antingen någon form av kylning förmodligen behövs, i.a.f. i en del driftsfall, eller att värmeförlusterna i den delen av generatorn behöver minskas genom t.ex. att pollängden ökas. En kombination av luftflöden med låg hastighet och förändrad geometri har föreslagits i examensarbetet för att minska temperaturen.

Switches and crossings are vital components of the railway network. Obstacles to the smooth functioning of these components could result in delays and network traffic. Given the geographical location of Sweden, snow is one of the major obstacles for the switches. The presence and hardening of snow act as an obstacle to the movement of the switch rail, thus hindering its function. Electrically heated switches melt and clear the snow for movement of the switch rail. They typically operate at a power level of 10 kW–30 kW. With 6800 switches operational in Sweden, the potential for energy savings is huge. This master thesis intends to investigate the possibility of reducing energy consumption through insulating a side of the rail. To achieve that, a comprehensive transient conjugate heat transfer analysis is carried out using CFD simulations. The initial refinement of the measured data highlighted the uncertainties in them, and which shaped the course of the thesis. The analysis of these uncertainties gave critical insights and led to useful recommendations for future work. The fluid-solid interactions between the rail and flow of air and their impact on transient heat loss have been analyzed to gain critical insights regarding the choice of side of implementation of insulation. The validation of the model at lower electrical power levels threw light on the dire requirement of numerical modeling of snow melting, which happens at the higher power levels of the heating element. One of the critical observations made after the implementation of the insulation is the reduction in the temperature of the heating element, which leads us to conclude that the insulation not only saves energy but also prolongs the life of the heating element by reducing thermal fatigue. / Växlar och korsningar är viktiga komponenter i järnvägsnätet. Om dessa komponenter inte fungerar smidigt kan det resultera i förseningar och avbruten nätverkstrafik. Med tanke på Sveriges geografiska läge är snö ett av de största hindren för växlarna. Snö och hårt packad snö kan hindra spårväxelns rörelse och funktion. Elektriskt uppvärmda spårväxlar smälter bort snön så att spårväxeln kan fungera. Spårväxlarna har vanligtvis en effektnivå på 10 kW - 30 kW. Med 6 800 växlar i drift i Sverige är potentialen för energibesparingar är enorm. Denna masteruppsats syftar till att undersöka möjligheten att minska energiförbrukningen genom att isolera en sida av rälsen. För att uppnå detta utförs en omfattande transient konjugerad värmeöverföringsanalys med hjälp av CFD-simuleringar. Den inledande dataförädlingen av mätdata belyste osäkerheterna i datan vilket formade det fortsatta arbetet med avhandlingen. Analysen av dessa osäkerheter gav kritiska insikter och användbara rekommendationer för framtida arbete. Fluid - solid-interaktionerna mellan skenan och luftflödet och deras inverkan på den transienta värmeförlusten har analyserats för att få kritiska insikter om valet av sida för isolering. Valideringen av modellen vid lägre effektnivåer kastade ljus över det akuta behovet av numerisk modellering av snösmältningen som sker vid värmeelementets högre effektnivåer. En av de kritiska observationerna som gjordes efter implementeringen av isoleringen är minskningen av värmeelementets temperatur, vilket drar slutsatsen att isoleringen inte bara sparar energiförbrukningen utan också förlänger elementets livslängd genom att minska den termiska utmattningen.

Le présent travail de recherche concerne l'étude de la convection de Rayleigh-Bénard-Marangoni dans un récipient cylindrique doté d'un fond en substrat solide. Le substrat solide est chauffé sur sa face inférieure par un flux de chaleur localisé. L'étude comporte deux parties : La première partie du travail consiste en une modélisation physique du problème associée à des simulations numériques. Les équations de Navier-Stokes et de l'énergie sont résolues en 3D par une méthode de volumes finis. Un transfert de chaleur conjugué solide-liquide est considéré. Des morphologies originales de cellules (type et nombre) sont observées, elles dépendent des conditions géométriques, des nombres adimensionnels qui régissent la physique de l'écoulement (nombre de Prandtl, de Rayleigh et de Marangoni ainsi que du rapport des conductivités thermiques du substrat solide et du fluide). Les transferts de chaleur sont aussi évalués pour chaque cas d'étude. Dans la deuxième partie, nous allons détaillons une étude expérimentale de la convection de Rayleigh-Bénard-Marangoni dans la même configuration que celle étudiée numériquement. Les structures convectives et leurs évolutions sont étudiées à partir d’images relevées par thermographie infra-rouge. Différents modes d'organisation des cellules convectives ont pu être mis en évidence pour ce type de chauffage à flux thermique imposé non uniforme. / The present research work concerns the study of Rayleigh-Bénard-Marangoni convection in a cylindrical container with a solid substrate base. This solid substrate is heated by a localized heat flux on its underside. The study is divided into two parts : The first part of the work consists of a physical modelling of the problem associated with numerical simulations. The Navier-Stokes and energy equations are solved by using a 3D finite volume method. A conjugate solid-liquid heat transfer is considered. Original morphology of cells (type and number) are observed, they are linked to the geometrical conditions, the dimensionless numbers which govern the physical problem (Prandtl, Rayleigh and Marangoni numbers and the ratio of solid substrate to liquid thermal conductivities). The heat transfers are also evaluated in each case. In the second part of the work, we present an experimental study of Rayleigh-Bénard-Marangoni convection in the same configuration as that studied numerically. Convective structures and their evolutions are studied from images recorded by infrared thermography. Different modes of organization of convective cells have been highlighted for this type of heating with imposed non-uniform heat flux.

Ce travail de thèse concerne l’étude des écoulements de fluides gazeux compressibles laminaires subsonique-supersonique dans une tuyère de type convergent-divergent. Les écoulements étudiés sont à nombres de Reynolds modérés et s’affranchissent de l’hypothèse de condition adiabatique de paroi couramment utilisée afin de mieux prendre en compte les phénomènes de transfert de chaleur par convection et rayonnement avec le milieu extérieur. Cette étude des phénomènes de transferts conjugués a permis de déterminer le comportement dynamique simultané du fluide et de la paroi de la tuyère. Enfin, compte tenu des niveaux élevés de températures mis en jeu dans ces systèmes, une analyse concernant le comportement thermomécanique de l’ensemble de la structure de paroi avec des matériaux monocouches et multicouches a été réalisé. De nombreuses configurations géométriques, propriétés physiques et conditions aux limites sur le fluide et la paroi ont été analysées. Les résultats présentés montrent, la structure des écoulements à travers les iso-contours de vitesses, des nombres de Mach, des pressions dans le fluide, des températures dans le fluide et dans la paroi ainsi que les déformations et les contraintes de la paroi qui résultent des couplages thermomécaniques. Une analyse des performances de la tuyère, en termes de force de poussée et de coefficient de débit spécifique, est largement discutée dans ce travail. / This work concerns the study of flows of compressible gaseous laminar subsonic-supersonic nozzle in a convergent-divergent type. The flows are studied to moderate Reynolds numbers and free themselves from the assumption of adiabatic wall conditions commonly used to better take into account the phenomena of heat transfer by convection and radiation with the external environment. This study combined transfer phenomena was determined simultaneously the dynamic behavior of the fluid and the wall of the nozzle. Finally, given high levels of temperatures at stake in these systems, an analysis of the thermomechanical behavior of the entire wall structure with monolayer and multilayer materials was performed. Many geometric configurations, physical properties and boundary conditions on the fluid and the wall were analyzed. The results presented show the structure of the flow through the iso-contours of speed, Mach numbers, pressures in the fluid, temperatures in the fluid and in the wall as well as the deformations and stresses resulting from the wall thermomechanical couplings. A performance analysis of the nozzle, in terms of thrust coefficient and specific yield, is widely discussed in this work.

Cette thèse consiste à mettre en place un couplage externe aéro-thermo-mécanique, sur la base d'un schéma partitionné, entre les codes de recherche CEDRE (mécanique des fluides, volumes finis) et Z-set (modules indépendants pour la mécanique des structures et la thermique du solide, éléments finis). Les résultats numériques sont confrontés à ceux de l'expérience (une campagne de mesures a été menée dans le cadre de cette étude), dans le cas d'un problème complexe lié au domaine de l'aérospatial : l'interaction flamme-paroi. Ce phénomène est piloté par la thermique, à travers le flux de chaleur pariétal généré par la flamme. A cause de la disparité des temps caractéristiques thermiques entre les milieux fluide et solide, la partie aéro-thermique du couplage est traitée de façon simplifiée, en considérant le fluide comme une suite d'états stationnaires. L'échauffement de la plaque métallique provoque sa déformation (la loi de comportement mécanique du matériau est de type élasto-visco-plastique). Le déplacement de l'interface fluide-structure est propagé sur le maillage fluide. En se basant sur les similitudes entre jets non réactifs et réactifs (de type flamme) dans le cas de l'impact, des calculs couplés sont menés dans des configurations 2D et 3D de l'impact d'un jet chaud non réactif. / This thesis consists in setting up an external fluid-thermal-structural coupling, based on a partitionned scheme, between the research codes CEDRE (fluid mechanics, finite volumes) and Z-set (independent solvers for structural mechanics and heat transfer through the solid). The numerical results are compared with experimental data, to study a complex problem related to the aerospace certification process: the flame-wall interaction. This phenomenon is is driven by the heat flux generated by the flame close to the wall. Because of the disparity of thermal characteristic times between the fluid and the solid, the aero-thermal part of the coupling is simplified by considering the fluid as a sequence of steady states. The heating of the metallic plate causes its deformation (the material has a viscoplastic behavior). The displacement of the fluid-structure interface is propagated through the fluid mesh. Based on similitudes between impinging reacting jets (flames) and non-reacting jets, coupled computations are performed in 2D and 3D configurations with an equivalent non-reacting hot jet.

In this doctoral work, we adress various problems arising when dealing with multi-physical simulations using a segregated (non-monolithic) approach. We concentrate on a few specific problems and focus on the solution of aeroelastic <p>flutter for linear elastic structures in compressible fl<p>ows, conjugate heat transfer for re-entry vehicles including thermo-chemical reactions and finally, industrial electro-chemical plating processes which often include<p>stiff source terms. These problems are often solved using specifically developed<p>solvers, but these cannot easily be reused for different purposes. We have therefore considered the development of a <p>flexible and reusable software platform for the simulation of multi-physics problems. We have based this<p>development on the COOLFluiD framework developed at the von Karman Institute in collaboration with a group of partner institutions.<p>For the solution of fl<p>uid fl<p>ow problems involving compressible <p>flows, we have used the Finite Volume method and we have focused on the application of the method to moving and deforming computational domains using the Arbitrary Lagrangian Eulerian formulation. Validation on a series of testcases (including turbulent flows) is shown. In parallel, novel time integration<p>methods have been derived from two popular time discretization methods.<p>They allow to reduce the computational effort needed for unsteady fl<p>ow computations.<p>Good numerical properties have been obtained for both methods.<p>For the computations on deforming domains, a series of mesh deformation techniques are described and compared. In particular, the effect of the stiffness definition is analyzed for the Solid material analogy technique. Using<p>the techniques developed, large movements can be obtained while preserving a good mesh quality. In order to account for very large movements for which mesh deformation techniques lead to badly behaved meshes, remeshing is also considered.<p>We also focus on the numerical discretization of a class of physical models that are often associated with <p>fluid fl<p>ows in coupled problems. For the elliptic problems considered here (elasticity, heat conduction and electrochemical<p>potential problems), the implementation of a Finite Element solver is presented. Standard techniques are described and applied for a variety of problems, both steady and unsteady.<p>Finally, we discuss the coupling of the <p>fluid flow solver with the finite element solver for a series of applications. We concentrate only on loosely and strongly coupled algorithms and the issues associated with their use and implementation. The treatment of non-conformal meshes at the interface between two coupled computational domains is discussed and the problem<p>of the conservation of global quantities is analyzed. The software development of a <p>flexible multi-physics framework is also detailed. Then, several coupling algorithms are described and assessed for testcases in aeroelasticity and conjugate heat transfer showing the integration of the <p>fluid and solid solvers within a multi-physics framework. A novel strongly coupled algorithm, based on a Jacobian-Free Newton-Krylov method is also presented and applied to stiff coupled electrochemical potential problems. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

The performance evaluation and parametric studies of an Inertance Tube Pulse Tube Refrigerator (IPTR) are performed for different length-to-diameter ratios, with the Computational Fluid Dynamics (CFD) package FLUENT. The integrated model consists of individual models of the components, namely, the compressor, compressor cooler, regenerator, cold heat exchanger, pulse tube, warm heat exchanger, inertance tube and the reservoir. The formulation consists of the governing equations expressing the conservation of mass, momentum and energy with axi-symmetry assumption and relations for the variable thermophysical properties of the working medium and the regenerator matrix, and friction factor and heat transfer coefficients in oscillatory flows. The local thermal non-equilibrium of the gas and the matrix is taken into account for the modeling of heat exchangers and the regenerator which are treated as porous zones. In addition, the wall thickness of the components is also accounted for. Dynamic meshing is used to model the compressor zone. The heat interaction between pulse tube wall and the oscillating gas, leading to surface heat pumping, is quantified. The axial heat conduction is found to reduce the overall performance. The thermal non-equilibrium results in a higher cold heat exchanger temperature due to inefficiencies. The dynamic characteristics of pulse tube are analyzed by introducing a time constant. The study is extended to other types of PTRs, namely, the Orifice type Pulse Tube Refrigerator (OPTR), Double Inlet type Pulse Tube Refrigerator (DIPTR) and a PTR with parallel combination of inertance tube and orifice (OIPTR). The focus of the second phase of analysis is the pulse tube region. The oscillatory flow and temperature fields in an open-ended pipe driven by a time-wise sinusoidally varying pressure at one end and subjected to an ambient-to-cryogenic temperature difference across the ends, is numerically studied both with and without the inclusion of buoyancy effects. Conjugate effects arising out of the interaction of oscillatory flow with heat conduction in the pipe wall are taken into account by considering a finite thickness wall with an insulated exterior surface. Parametric studies are conducted with frequencies in the range 5-15 Hz for an end-to-end temperature difference of 200 K. As the pressure amplitude increases, the temperature difference between the wall and the fluid decreases due to mixing at the cold end. The pressure amplitude and the frequency have negligible effect on the time averaged Nusselt number. The effect of buoyancy is studied for hot side up and cold side up configurations. It is found that the time averaged Nusselt number does not change significantly with orientation or Rayleigh number. Sharp changes in Nusselt number and velocity profiles and an increase in energy transfer through solid and gas were observed when natural convection comes into play with hot end placed down. Cooldown experiments are conducted on a preliminary experimental setup. Comparison of the numerical and experimental cooldown curves disclosed a number of areas where improvement is required, primarily the leakage past the piston and the design of the heat exchangers. The setup is being improved to bring out a second and improved version for attaining the lower cold heat exchanger temperature.

Tato diplomová práce se zabývá posouzením tepelně-mechanické únavy výfukového potrubí. Nejprve byla provedena rešeršní studie, ve které je rozebrán fenomén tepelně-mechanické únavy. Byly prezentovány hlavní mechanismy poškození a přístupy k jejich modelování. Diskutována byla i specifická chování materiálu vystavenému tepelně-mechanickému zatěžování. Byl vypracován přehled vhodných modelů materiálu a modelů únavové životnosti společně s algoritmem predikce tepelně-mechanické únavy komponenty. Poté byl tento teoretický základ aplikován na praktický případ výfukového potrubí podléhajícího tepelně-mechanickému zatěžování. Dva tepelně závislé elasto-plastické modely materiálu byly nakalibrovány a validovány na základě experimentálních dat. Byl vytvořen diskretizovaný konečnoprvkový model sestavy výfukového potrubí. Model tepelných okrajových podmínek byl předepsán na základě výpočtů ustáleného sdruženého přestupu tepla. Slabě sdružená tepelně-deformační úloha byla vyřešena metodou konečných prvků pro oba modely materiálů. Bylo použito paradigma nesvázaného modelu únavy, které je vhodné pro nízkocyklovou únavu. Životnost byla tedy vyhodnocena jako součást post-procesoru. Použity byly dva modely únavové životnosti – energeticky založený model a deformačně založený model. Získané hodnoty životnosti byly porovnány vzhledem k použitým modelům materiálu a modelům únavové životnosti. Nakonec jsou diskutovány závěry této práce, oblasti dalšího výzkumu a navrženy možnosti na zlepšení použitých přístupů.