Le travail de thèse présenté ici apporte des éléments de compréhension sur l'influence de la gestion de l'eau et de la gestion thermique d'une PEMFC sur ses performances électriques. Un modèle bidimensionnel représentant les transferts de matière et de chaleur dans l'épaisseur d'une cellule élémentaire et le long des canaux d'alimentation est mis en place. Une partie spécifique de l'étude concerne la modélisation microscopique des agglomérats réactionnels et l'influence de l'eau présente dans ces zones actives sur les performances électriques locales et globales de la pile. Dans l'optique de réaliser un modèle pouvant s'intégrer à un système de contrôle, les transports couplés de l'eau liquide et vapeur, de la chaleur et des charges sont résolus analytiquement. Quelles que soient les conditions de fonctionnement, le modèle permet de calculer quel est l'état interne de la pile en terme d'hydratation, de production de courant et de chaleur. Le diagnostic de l'état interne de la pile en fonction des conditions opératoires permet de connaître précisément comment adapter les paramètres d'alimentation de la pile pour obtenir des performances électriques optimales. Les distributions locales d'eau, de courant et de température sont présentées en fonction de la stratégie d'alimentation en gaz de la pile et de l'orientation du circuit de régulation thermique. Une partie consacrée au diagnostic de fonctionnement d'une pile illustre en quoi l'utilisation du modèle et la connaissance de l'état interne de la pile apporte des informations primordiales lors de l'utilisation d'une pile à combustible / The present work contributes to the understanding of water management and thermal management of a PEM fuel cell influences on the electrical performances. A bidimensional model representing mass and heat transfer in the cell thickness and along distribution channels is done. A specific part of the study concerns a microscopic representation of reactive agglomerates. This part presents the impact of the liquid water presence on local and global current densities. In te vein of integrating this model in a total fuel cell control system, simplifications have been done and coupled mass, heat and charge transfers are solved analytically. For any operating condition, the model gives a complete view of the hydric, thermal and electric inner situation of the cell. This diagnosis of the inner state of the cell leads to find the operating conditions giving to the optimal electric performances. Water, current and temperature distributions are presenting for different gas feeding strategies and different thermal management configurations. A specific part is dedicated to illustrate how this local diagnosis of the cell state can be used to estimate its global electric performances

This diploma thesis deals with the problems of heat transfer on printed circuit boards. The first part consists of a theoretical analysis of the principles of conduction of heat in different environments, comparing the properties of common type’s base materials for PCBs in terms of thermal properties and focuses on heat transfer from the chip. In the following part they are general information about the program ANSYS ® Workbench ™. Next part consists of the basic designs of PCBs and their improving. PCBs thermal properties for different configurations are verified with calculations, simulations and practical measurements. In the last part there are created design recommendations for PCBs design based on the comparison of the results of initial proposals and proposals to improvements.

Thermal management is a major bottleneck for the next-but-one generation of semiconductor devices, especially the performance of SiC and GaN devices is limited by heat dissipation. This thesis evaluates four new packaging concepts with regards to thermal management: Diamond based substrates, phase change materials, Cu-Graphene composite films and anisotropic heat dissipation. Anisotropic heat dissipation is shown to be the most auspicious concept. A metal-matrix composite baseplate for a high performance power module using annealed pyrolytic graphite is created and evaluated. The baseplate shows a locally increased heat dissipation compared to a plain metal baseplate by 30 %. Furthermore, the thermal contact between device (baseplate) and cooler is of high importance. A study of different characterization methods for thermal interface materials is performed and a new method for the quantification of the thermal contact conductance is presented. The study shows that a combination of several methods is necessary so that the complete picture of heat dissipation performance of thermal interface materials becomes apparent. The new developed method allows to select the perfect thermal grease for a given combination of device and cooler. / Wärmemanagement ist eine große Herausforderung sowohl für aktuelle als auch für zukünftige Halbleiterprodukte. Speziell die nächste Produktgeneration mit SiC oder GaN Chips benötigen neue Entwärmungskonzepte, um ihr volles Potential bezüglich höherer Stromstärken zu entfalten. In dieser Arbeit wurden vier neuartige Konzepte erforscht: Diamant basierte Substrate, Phasen-Wechsel-Materialien, Cu-Graphene Kompositschichten und anisotrope Entwärmung. Es zeigte sich, dass anisotrope Entwärmung das vielversprechendste Konzept ist. Als Demonstrator wurde eine Bodenplatte mit thermisch pyrolytischen Graphiteinleger für ein Leistungsmodul gefertigt. Sie zeigt eine lokale Erhöhung der Entwärmung von 30 %. Weiter ist der thermische Kontakt zwischen Bauteil und Kühler sehr wichtig. Verschiedene Charakterisierungsmethoden für thermische Schnittstellen-Materialien wurden verglichen. Dieser Vergleich zeigt, dass eine Kombination verschiedener Methoden notwendig ist, um ein vollständiges Bild über die Leistungsfähigkeit solcher Materialien zu gewinnen. Eine neue Messmethode wurde entwickelt, um die thermische Kontakt-Leitfähigkeit zu messen. Diese neue Methode ermöglicht es, die beste Wärmeleitpaste für eine vorgegebene Kombination aus Produkt und Kühleroberfläche zu identifizieren.

Batteries are promising sources of green and sustainable energy that have been widely used in various applications. Lithium-ion batteries (LIBs) have an important role in the energy storage sector due to its high specific energy and energy density relative to other rechargeable batteries. The main challenges for keeping the LIBs to work under safe conditions, and at high performance are strongly related to the battery thermal management. In this study, a critical literature review is first carried out to present the technology development status of the battery thermal management system (BTMS) based on air and liquid cooling for the application of battery energy storage systems (BESS). It was found that more attention has paid to the BTMS for electrical vehicle (EV) applications than for stationary BESS. Even though the active forced air cooling is the most commonly used method for stationary BESS, limited technical information is available. Liquid cooling has widely been used in EV applications with different system configurations and cooling patterns; nevertheless, the application for BESS is hard to find in literature.To ensure and analyze the performance of air and liquid cooling system, a battery and thermal model developed to be used for modeling of BTMS. The models are based on the car company BMW EV battery pack, which using Nickel Manganese Cobalt Oxide (NMC) prismatic lithium-ion cell. Both air and liquid cooling have been studied to evaluate the thermal performance of LIBs under the two cooling systems.According to the result, the air and liquid cooling are capable of maintaining BESS under safe operation conditions, but with considering some limits. The air-cooling is more suitable for low surrounding temperature or at low charging/discharge rate (C-rate), while liquid cooling enables BESS to operate at higher C-rates and higher surrounding temperatures. However, the requirement on the maximum temperature difference within a cell will limits the application of liquid cooling in some discharge cases at high C-rate. Finally, this work suggests that specific attention should be paid to the pack design. The design of the BMW pack is compact, which makes the air-cooling performance less efficient because of the air circulation inside the pack is low and liquid cooling is more suitable for this type of compact battery pack.

Batteries play an important role in a sustainable future. As the development for better andsmarter batteries continues, new areas of use emerge boosting its demand. Controlling thetemperature of a battery cell is a vital objective to ensure its longevity and performance. Bothcooling and heating methods can be applied to keep the temperature within a certain rangedepending on its need. This study will review the technical aspects of lithium-ion batteries,observe the different thermal management systems and cooling methods, and lastly examinethe required cooling flow needed for a battery cell to prevent its temperature from rising tocritical levels during its discharge. Using CFD ANSYS Fluent as a simulation tool, the resultsshow that different charging rates, in terms of C-rate, require different rates of mass flow tocontrol the temperature. Simulating the cell with natural convection, the cell peaks at hightemperatures even at lower C-rates, reaching up to 36,4°C and 48,8°C for 1C and 2C,respectively. Applying the cooling method with a flow rate of 0,0077kg/s reduces thetemperature significantly, resulting in temperatures of 26,95°C and 31,27°C for 1C and 2C,respectively.

<p> With new technologies taking advantages of the rapid miniaturization of devices to microscale across emerging industries, there is an unprecedented increase in the heat fluxes generated. The relatively low phase-change thermal resistance associated with boiling is beneficial for dissipating high heat flux densities in compact spaces. However, for boiling heat transfer, a high degree of geometrical confinement significantly alters two-phase interface dynamics which affects the flow pattern, wetting dynamics, and moreover, the heat transfer rate of the boiling processes. Hence, it is crucial to have a deeper understanding of the mechanistic effects of confinement on two-phase heat dissipation and carefully examine the applicability of boiling correlations developed for unconfined pool boiling to predict and optimize design of extremely compact two-phase thermal management solutions. This dissertation develops and demonstrate a fundamental understanding of the impact of confinement on pool boiling. To elucidate the mechanisms that impact confined boiling, this study experimentally evaluates boiling characteristics through the quantification of boiling curves and high-speed visualization across a range of gap spacing smaller than the capillary length of the working fluid. </p> <p><br></p> <p> This work reveals the existence of two distinct boiling regime uniquely observed in boiling in confined configurations (namely, intermittent boiling and partial dryout). In contrast to pool boiling where the maximum heat transfer coefficient occurs below the critical heat flux limit, the intermittent boiling regime demonstrates the highest heat transfer coefficient in confined boiling. Then, this study provides a mechanistic explanation for the enhanced heat transfer rate due to geometrical confinement. Mainly, small residual pockets of vapor, termed ‘stem bubbles’ herein, remain on the boiling surface through a pinch-off process. These stems bubbles act as seeds for vapor growth in the next phase of the boiling process without the need for active nucleation sites. Furthermore, this dissertation develops a more accurate, mechanistic-based model for the phenomena that occur at CHF in confined configurations. The newly developed mechanistic understanding and model provides guidance on new directions for designing extremely compact two-phase thermal solutions.</p>

La maîtrise de la gestion thermique du moteur à combustion interne permet de répondre à des problématiques telles que la réduction de la consommation de carburant et des émissions de polluants. Cette gestion peut être réalisée par des systèmes mécatroniques, plus précisément grâce à une vanne électromécanique multivoie, appelée ACT valve (Active Cooling thermo-management valve), permettant de mettre en œuvre une stratégie de gestion thermique lors du contrôle des températures dans différentes branches du circuit de refroidissement du moteur thermique.L’objectif du travail est d’améliorer la robustesse du processus de conception de cette vanne en tenant compte des contraintes fonctionnelles multi-physiques telles que la déformation, l’usure, mais aussi de contraintes de fabrication et de tolérancement géométrique liées au processus d’injection des pièces thermoplastiques. Ces incertitudes doivent être prises en compte dès la phase de la conception pour assurer l'efficacité et la fiabilité de ces vannes jusqu'à la fin de leurs vies.Ces travaux de thèses proposent tout d’abord une nouvelle méthode de conception de ces vannes qui se base sur des modèles numériques multi-physiques permettant à tous les métiers d’avoir une base de données commune. Validés expérimentalement, Ces modèles ont permis de mettre en évidence la sensibilité de certains paramètres géométriques sur le couple développé par l’actionneur de la vanne et de s’assurer de la fiabilité du système par la prédiction de l’usure sur un des éléments clés de l’ACT valve.Bien que l’analyse de sensibilité nous ait permis de comprendre l’influence de certains paramètres sur le système, nous avons proposé une nouvelle technique d’identification des configurations optimales du design de cette vanne en utilisant une méthode d’optimisation méta-heuristique multi-objectifs. Les suggestions de conception offertes par cette méthode permettent de réduire le couple résistant sur l’actionneur de la vanne ainsi que l’encombrement global du système. / The thermal management of the internal combustion engine can solve issues related to fuel consumption reduction and pollutant emissions. This management can be applied using mechatronic systems, more precisely thanks to a multi-way electromechanical valve, called ACT valve (Active Cooling thermo-management valve), that presents a thermal management strategy when controlling temperatures in different branches of the engine cooling circuit.The aim of this work is to improve the robustness of the design process of this valve taking into account the multi-physical functional constraints such as deformation, wear, but also geometrical tolerances constraints related to the thermoplastic parts manufacturing process. These uncertainties must be taken into account in the first steps of the design phase to ensure the effectiveness and reliability of this valve over its lifetime.This work first proposes a new method of designing these valves, which is based on multi-physical modeling, allowing the product designers to have a common database. Experimentally validated, these models made it possible to highlight the sensitivity of certain geometrical parameters on the torque developed by the actuator of the valve and to make sure of the reliability of the system with wear prediction on one of the key elements of ACT valve.Although the sensitivity analysis allowed us to understand the influence of certain parameters on the system, we proposed a new technique for identifying optimal configuration configurations of this valve using a metaheuristic, multi-objective optimization method. The design suggestions offered by this method can reduce the resistive torque on the valve DC-actuator as well as the overall packaging.

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The electronic market is continually moving towards higher power densities. As a result, the demand on the cooling is increasing. Focus has to be put on the whole thermal management chain, from the component to be cooled to the ambient. Thermal interface materials are used to efficiently transfer heat between two mating surfaces or in some cases across larger gaps. There are several different thermal interface materials with various application areas, advantages and disadvantages. This study aimed to evaluate thermal and mechanical properties of graphite sheets and graphite gap pads. The work was done in cooperation with Ericsson AB. A test rig based on the ASTM D5470 standard was used to measure the thermal resistance and thermal conductivity of the materials at different pressures. It was found that several graphite sheets and gap pads performed better than the materials used in Ericsson’s products today. According to the tests, the thermal resistance could be reduced by about 50 % for the graphite sheets and 90 % for the graphite gap pads. That was also verified by placing the materials in a radio unit and comparing the results with a reference test. Both thermal values and mechanical values were better than for the reference materials. However, the long term reliability of graphite gap pads could be an issue and needs to be examined further. / Elektronikbranschen rör sig mot högre elektriska effektertätheter, det vill säga högre effekt per volymenhet. Som en följd av detta ökar också efterfrågan på god kylning. Kylningen måste hanteras på alla nivåer, från komponenten som ska kylas, ända ut till omgivningen. Termiska interface material (TIM) används för att förbättra värmeöverföringen mellan två ytor i kontakt med varandra eller för att leda värmen över större gap. Det finns flera olika TIM med olika tillämpningsområden, fördelar och nackdelar. Denna studie gick ut på att utvärdera termiska och mekaniska egenskaper hos grafitfilmer och så kallade ”graphite gap pads” då de används som TIM. Projektet gjordes i sammarbete med Ericsson AB. En testuppställning baserat på ASTM D5470-standarden användes för att utvärdera värmeledningsförmågan och den termiska resistansen hos de olika materialen vid olika trycknivåer. Resultaten visade att flera grafitfilmer och ”gap pads” presterade bättre än materialen som används Ericssons produkter idag. Enligt testerna skulle den termiska resistansen kunna minskas med 50 % för grafitfilmerna och 90 % för ”gap padsen”. Materialens fördelaktiga egenskaper verifierades i en radioenhet där temperaturerna kunde sänkas i jämförelse med ett referenstest med standard-TIM. De nya materialen var mjukare än referensmaterialen och skulle därför inte orsaka några mekaniska problem vid användning.  Den långsiktiga tillförlitligheten för grafitbaserade ”gap pads” måste dock undersökas vidare eftersom de elektriskt ledande materialen skulle kunna skapa kortslutningar på kretskorten.

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