Detailed understanding of bubbles growing on a solid surface is a fundamental requirement in many technological domains, with particular application to water electrolysis in relation to the present-day socio-economic significance of clean energy transition. Evolution of bubbles at the electrode surface greatly determines the overall efficiency and throughput of an electrolysis cell. Bubbles residing on the electrode surface creates resistance to the flow of electric current and reduces the active electro-catalytic area. Therefore, fast removal of the bubbles is desirable for efficient operation. With this motivation, this dissertation aims to build deeper understanding of the bubble dynamics during the pre-detachment and detachment stage. To this end, single hydrogen bubbles grown on microelectrodes are chosen as the object of study. Thermocapillary and electric forces acting on an electrolytic bubble are introduced and a thorough account of the forces acting on the bubble is taken. A dynamical model of the bubble motion is developed. By means mathematical and physical modeling of the forces, working mechanism is provided for a novel mode of bubble detachment, namely oscillatory bubble detachment. The model predictions of oscillation parameters are in good correlation with experimental observations. Furthermore, the equation of motion of the bubble is shown to undergo bifurcation thus providing mathematical reasoning behind the existence of different detachment modes. A deeper look is taken specifically at the oscillatory mode. The electrolyte flow velocity is computed and compared with PTV based measurements. Force variation during one oscillation cycle is characterized and correlated with relevant geometric and operational parameters. Based on dynamical conditions of the bubble motion, the surface charge at the bubble interface is quantified. The calculated values match with literature values from bubble electrophoresis experiments. A detailed look is also taken at the effect of electrode size on the thermocapillary effect. The temperature and flow velocity field in the electrolyte is computed for various electrode size. Additional details regarding the flow structure were found. The location of the interfacial temperature hotspot was quantified. The current density distribution along the electrode surface was found to be strongly non-uniform. The Marangoni and the hydrodynamic force acting on the bubble was quantified at various electrode sizes. Further a model was developed to approximate the thermocapillary effect of a bubble on a large electrode. The location of temperature hotspot was found to be different when compared to bubbles on a microelectrode. This influences the Marangoni flow structure and also the Marangoni force on the bubble. Overall, this dissertation provides a systematic framework for characterizing forces acting on the bubble and investigating the dynamics of the bubble motion, which adds to our current understanding of bubble evolution and, takes one step towards predictive detachment models.

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Plusieurs études tant numériques qu’expérimentales font état de la présence d’instabilités thermiques dans des films liquides chauffés uniformément par le bas pour des conditions aux limites et d’écoulements particuliers. La présence de ces instabilités modifiera les transferts thermiques associés. Le sujet de ce travail de thèse consiste à étudier numériquement les instabilités thermoconvectives d’un écoulement laminaire tridimensionnel de convection mixte dans un canal horizontal à surface libre. Les variations de la tension de surface avec la température (effet Marangoni ou effet thermocapillaire) sont prises en compte. Bien que d’un intérêt certain pour de nombreuses applications industrielles, cette situation a été très peu étudiée d’un point de vue académique dans la configuration considérée ici. Dans cette de configuration plusieurs types de structures thermoconvectives sont susceptibles d’apparaître. Lorsque les forces induites par les courants de convection naturelle, forcée et thermocapillaire sont du même ordre de grandeur, les premiers résultats montrent un développement des instabilités sous forme de rouleaux convectifs longitudinaux stationnaires semblables à ceux rencontrés pour des écoulements de type Poiseuille-Rayleigh-Bénard. A notre connaissance, c’est la première fois que l’écoulement de convection de type Poiseuille-Rayleigh-Bénard associé aux effets Marangoni est étudié. Le nombre et la distribution spatiale des rouleaux convectifs le long du canal dépendent des conditions de l’écoulement. Nous proposons une étude numérique pour ces conditions particulières d’écoulement pouvant conduire à des instabilités avec une évaluation de leur effet sur les transferts de chaleur. Les équations de Navier-Stokes et de l’énergie sont résolues numériquement par la méthode de volumes finis en prenant en compte les effets thermocapillaires. Les résultats présentés concernent l’influence des paramètres contrôlant l’écoulement (nombres de Reynolds, de Rayleigh, de Biot, de Marangoni et le rapport de forme) sur les motifs de l’écoulement et les échanges thermiques. Dans une seconde partie du travail, complémentaire à la première, une analyse de stabilité linéaire de l’écoulement dans un canal ouvert à surface libre d’extension latérale infinie est réalisée en utilisant la méthode spectrale de type collocation Chebyshev pour résoudre un système aux valeurs propres. Les diagrammes de stabilité déterminant les seuils des paramètres conduisant à l’instabilité thermoconvective ont été obtenus et analysés, ainsi que les structures spatiales associées. / Several studies both numerical and experimental have reported the presence of thermal instabilities in liquid films uniformly heated from below for specific boundary conditions and flows. The presence of these instabilities modifies the associated heat transfer. The subject of this PhD thesis is to study numerically the instability of three-dimensional laminar mixed convection within a liquid flowing on a horizontal channel heated uniformly from below. The upper surface is free and assumed to be flat. The variations of the surface tension with the temperature (Marangoni effect or thermocapillary effect) are taken into account. Although of great interest for many industrial applications, this problem has received little attention from an academic point of view. In this configuration, several types of thermoconvective structures may appear. When the strength of the buoyancy, thermocapillary effects and forced convective currents are comparable, the results show the development of instabilities in the form of steady longitudinal convective rolls similar to those encountered in the Poiseuille-Rayleigh-Bénard flow. To our knowledge, this is the first time that the Poiseuille-Rayleigh-Bénard flow associated to the Marangoni effects has been investigated. The number and spatial distribution of the convective rolls along the channel depend on the flow conditions. We propose a numerical study on the flow conditions that could lead to thermal instabilities with an evaluation of their effect on the heat transfer. The coupled Navier-Stokes and energy equations are solved numerically by the finite volume method taking into account the thermocapillary effects. The results presented concern the influence of several control parameters (the Reynolds, Rayleigh, Biot and Marangoni numbers and the aspect ratio of the channel) on the flow patterns and heat transfer characteristics. In the second part of this work, complimentary to the first, a linear stability analysis of a horizontal liquid film flowing in an open channel, with infinite lateral extension and uniform heating from below, is carried out. An eigenvalue problem is obtained in the course of this analysis which is solved numerically using the Chebyshev collocation spectral method. The stability diagrams determining the threshold parameters leading to thermoconvective instabilities were obtained and analyzed as well as the associated spatial patterns.

Motivated by the existence of complex behaviors arising from interactions between chemistry and fluid dynamics in numerous research problems and every-day life situations, we theoretically investigate the dynamics resulting from the interplay between chemistry, diffusion, and fluid motions in a reactive aqueous solution. As a chemical reaction induces changes in the temperature and in the composition of the reactive medium, such a reaction can modify the properties of the solution (density, viscosity, surface tension,…) and thereby trigger convective motions, which in turn affect the reaction. Two classes of convective flows are commonly occurring in solutions open to air, namely Marangoni flows arising from surface tension gradients and buoyancy flows driven by density gradients. As both flows can be induced by compositional changes as well as thermal changes and in turn modify them, the resulting experimental dynamics are often complex. The purpose of our thesis is to gain insight into these intricate dynamics thanks to the theoretical analysis of model systems where only one type of convective flow is present. In particular, we numerically study the spatio-temporal evolution of model chemical fronts resulting from the coupling between reactions, diffusion, and convection. Such fronts correspond to self-organized interfaces between the products and the reactants, which typically have different density and surface tension. Fluid motions are therefore spontaneously induced due to these differences across the front. In this context, we first address the propagation of a model autocatalytic front in a horizontal solution layer, in the presence of pure Marangoni convection on the one hand and of pure buoyancy convection on the other hand. We evidence that, in both cases, the system attains an asymptotic dynamics characterized by a steady fluid vortex traveling with the front at a constant speed. The presence of convection results in a deformation and acceleration of the chemical front compared to the reaction-diffusion situation. However we note important differences between the Marangoni and buoyancy cases that could help differentiate experimentally between the influence of each hydrodynamic effect arising in solutions open to the air. We also consider how the kinetics and the exothermicity of the reaction influence the dynamics of the system. The propagation of an isothermal front occurring when two diffusive reactants are initially separated and react according to a simple bimolecular reaction is next studied in the presence of chemically-induced buoyancy convection. We show that the reaction-diffusion predictions established for convection-free systems are modified in the presence of fluid motions and propose a new way to classify the various possible reaction-diffusion-convection dynamics./En induisant des changements de composition et de température, une réaction chimique peut modifier les propriétés physiques (densité, viscosité, tension superficielle,…) de la solution dans laquelle elle se déroule et ainsi générer des mouvements de convection qui, à leur tour, peuvent affecter la réaction. Les deux sources de convection les plus courantes en solution ouverte à l’air sont les gradients de tension superficielle, ou effets Marangoni, et les gradients de densité. Comme ces deux sources sont en compétition et peuvent toutes deux résulter de différences de concentration ou de température, les dynamiques observées expérimentalement sont souvent complexes. Le but de notre thèse est de contribuer à la compréhension de telles dynamiques par une étude théorique analysant des modèles réaction-diffusion-convection simples. En particulier, nous étudions numériquement l’évolution spatio-temporelle de fronts chimiques résultant du couplage entre chimie non-linéaire, diffusion et hydrodynamique. Ces fronts constituent l’interface auto-organisée entre les produits et les réactifs qui typiquement ont des densités et tensions superficielles différentes. Des mouvements du fluide peuvent dès lors être spontanément initiés dus à ces différences au travers du front. Dans ce contexte, nous étudions la propagation d’un front chimique autocatalytique se propageant dans une solution aqueuse horizontale, d’une part en la seule présence d’effets Marangoni, et d’autre part en présence uniquement d’effets de densité. Nous avons montré que dans les deux cas, le système atteint une dynamique asymptotique caractérisée par la présence d’un rouleau de convection stationnaire se propageant à vitesse constante avec le front. Ce front est à la fois déformé et accéléré par les mouvements convectifs par rapport à la situation réaction-diffusion. Nous avons mis en évidence d’importantes différences entre les deux régimes hydrodynamiques qui pourraient aider les expérimentateurs à différencier les effets de tension superficielle de ceux de densité générés par la propagation de fronts chimiques en solution. Nous avons également considéré l’influence de la cinétique de réaction ainsi que de l’exothermicité sur la dynamique de ces fronts. Enfin, nous avons étudié la propagation en présence de convection d’un front de réaction impliquant deux espèces de densités différentes, initialement séparées et réagissant selon une cinétique bimoléculaire. Nous avons montré que la convection modifie les propriétés réaction-diffusion du système et nous proposons de nouveaux critères pour classifier les dynamiques réaction-diffusion-convection.

A numerical code for solving the time-dependent incompressible 3D Navier-Stokes equations with finite volumes on overlapping staggered grids in cylindrical and rectangular geometry is developed. In the code, written in FORTRAN, the momentum equation for the velocity is solved by projection method and Poisson equation for the pressure is solved by ADI implicit method in two directions combined with discrete fast Fourier transform in the third direction. A special technique for overcoming the singularity on the cylinder's axis is developed. This code, taking into account dependence upon temperature of the viscosity, density and surface tension of the liquid, is used to study the fluid motion in a cylinder with free cylindrical surface (under normal and zero-gravity conditions); and in a rectangular closed cell with a source of thermocapillary convection (bubble inside attached to one of the cell's faces). They are significant problems in crystal growth and in general experiments in fluid dynamics respectively. Nevertheless, the main study is dedicated to the liquid bridge problem.<p><p>The development of thermocapillary convection inside a cylindrical liquid bridge is investigated by using a direct numerical simulation of the 3D, time-dependent problem for a wide range of Prandtl numbers, Pr = 0.01 - 108. For Pr > 0.08 (e.g. silicon oils), above the critical value of temperature difference between the supporting disks, two counter propagating hydrothermal waves bifurcate from the 2D steady state. The existence of standing and traveling waves is discussed. The dependence of viscosity upon temperature is taken into account. For Pr = 4, 0-g conditions, and for Pr = 18.8, 1-g case with unit aspect ratio an investigation of the onset of chaos was numerically carried out. <p><p>For a Pr = 108 liquid bridge under terrestrial conditions ,the appearance and the development of thermoconvective oscillatory flows were investigated for different ambient conditions around the free surface.<p><p>Transition from 2D thermoconvective steady flow to a 3D flow is considered for low-Prandtl fluids (Pr = 0.01) in a liquid bridge with a non-cylindrical free surface. For Pr < 0.08 (e.g. liquid metals), in supercritical region of parameters 3D but non-oscillatory convective flow is observed. The computer program developed for this simulation transforms the original non-rectangular physical domain into a rectangular computational domain.<p><p>A study of how presence of a bubble in experimental rectangular cell influences the convective flow when carrying out microgravity experiments. As a model, a real experiment called TRAMP is numerically simulated. The obtained results were very different from what was expected. First, because of residual gravity taking place on board any spacecraft; second, due to presence of a bubble having appeared on the experimental cell's wall. Real data obtained from experimental observations were taken for the calculations.<p> / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished

L’effet thermocapillaire (ou Marangoni) est la résultante mécanique d’un gradient de tensioninterfaciale induit par la présence d’un gradient de température sur une interface fluide. Il semanifeste par (i) la migration d’un objet fini (goutte, bulle) immergé, et (ii) une déflexion del’interface. Sa nature interfaciale le rend particulièrement pertinent à petite échelle, notammenten microfluidique diphasique. Ce travail de thèse montre comment un effet thermocapillaireinduit localement par chauffage laser peut être utilisé pour produire des composants optofluidiquesélémentaires (vanne, aiguillage, échantillonneur), et en présente une étude quantitative.La déstabilisation d’un jet microfluidique forcée par laser, conduisant à sa rupture, est égalementprésentée et caractérisée. Cette « boîte à outils » optique fournit ainsi une approche sans contact,pour produire et manipuler des gouttes en microfluidique digitale sans nécessité d’une microfabricationdédiée. Par ailleurs, afin de caractériser sur des temps longs les gouttes produites,et ainsi considérer des populations statistiquement significatives, un dispositif optoélectroniquesimple pour mesurer les gouttes et leur vitesse en temps réel a également été développé. / The thermocapillary (or Marangoni) effect is the mechanical result of an interfacial tension gradientinduced by a temperature gradient on a fluid interface. This effect manifests itself byinducing (i) the migration of an immersed finite-size object (droplet, bubble), and (ii) a deflexionof the interface. Due to its interfacial nature, the Marangoni effect is particularly relevantat small length scales, especially in the context of two-phase microfluidics. This thesis aims atapplying the thermocapillary effect locally induced by laser heating, in order to create some basicoptofluidic actuators (valve, switch, sampler). A quantitative study of these actuators is presented.The laser-forced destabilization of a co-flowing microfluidic jet, leading to its breakup,is also investigated. This “optical toolbox” represents a non-contacting, and microfabricationfreeapproach for the production and handling of droplets in digital microfluidics. Moreover, tocharacterize these droplet over long times, thus considering statistically significant populations,a simple optoelectronic device has been developed for measuring the size and velocity of thedroplets in real time.

Dans ce document, nous présentons nos travaux sur les décharges dans l'heptane. L'une des conditions retenue pour ces études est le choix d'un gap micrométrique. Nous avons travaillé avec des gaps compris entre 10 et 150 µm qui correspondent à des tensions de claquage comprises entre 1 et 15 kV. Du claquage jusqu'à 1 µs, la décharge a été caractérisée par ombroscopie et par spectroscopie d'émission optique (SEO). L'ombroscopie a montré que la vitesse de propagation de l'onde de choc et de la bulle est de l'ordre de 1200 m s-1 et 100 m s-1, respectivement. Au-delà de 1 µs, la dynamique de la bulle a été étudiée. Une nouvelle méthode est proposée pour estimer la pression à l'initiation de la décharge. La technique est basée sur la réponse d'une "bulle test" qui se trouve dans le champ acoustique d'une nouvelle décharge dont on veut connaître la pression. Elle est aux environs 80 bar. La SEO a montré une dominance des rayonnements continus pendant les premières 200 ns qui ont été attribués à la recombinaison électron-ion. Au-delà de 200 ns, les rayonnements continus s'effondrent et les raies d'émission deviennent dominantes. L'étude de l'élargissement de la raie H[alpha] de l'hydrogène a montré que la densité électronique peut atteindre 1019 cm-3. En ce qui concerne l'interaction plasma-surface, nous avons pu démontrer que l'impact créé est gouverné par la quantité de charges déposée. Sa morphologie est une résultante d'un équilibre entre la force due à la pression et la force de Marangoni. Nous avons étudié dans une dernière partie la synthèse des nanoparticules de platine (diamètre 5 nm) insérées dans une matrice de carbone hydrogéné présentant un ordre à courte distance / In this document, we report our work on discharges in heptane. One of the specific conditions selected is the choice of a micrometric gap distance. Typically, gaps were between 10 and 150 µm, corresponding to breakdown voltages between 1 and 15 kV. From breakdown up to 1 µs, the plasma discharge was characterized by shadowgraphy and optical emission spectroscopy (OES). Shadowgraphy results showed that the velocities of shock wave and bubble interface are about 1200 m s-1 and 100 m s-1, respectively. Beyond 1 µs, experimental and theoretical studies of the oscillatory dynamics of the bubble are made. Then, we proposed a new method to estimate the pressure at discharge breakdown. The technique is based on the response of a 'test bubble' present in the acoustic field of a new discharge whose pressure is to be known. It is estimated to be about 80 bar. OES, between 300 and 800 nm, showed a dominance of continuous radiations during the first 200 ns which were attributed to electron-ion recombination processes. Beyond 200 nm, continuous radiations collapse and then, the emission lines dominate the spectrum. The study of the H? line broadening showed that the electron density can reach 1019 cm-3. Regarding the interaction of the discharge with the electrode surfaces, we demonstrated that the diameter of the impact is governed by the quantity of charges deposited by the discharge. However, the impact morphology is determined by a balance between the force exerted by the plasma pressure and the Marangoni's force. Finally, we studied the possibility to synthesize platinum nanoparticles (5 nm in diameter) embedded in a matrix of hydrogenated carbon exhibiting a short range order

In this study, thermocapillary-driven convection around a gas bubble under a horizontal heated wall is experimentally investigated under gravitational conditions. The thermocapillary convective flow under conditions beyond the laminar steady state towards turbulent flow is explored in detail. Generally, Marangoni convection is more critical and important under microgravity conditions rather than on earth. Under low gravity, this surface tension induced flow can dictate both heat and mass transfer processes. Thus, thermocapillary convection should be considered by manufacturers during material production processes in space. Moreover, temperature gradients can be purposefully used to eliminate or move bubbles or drops suspended in liquid materials. In addition to that, thermocapillary convective flow appears in many other applications like manufacturing of single-walled carbon nanotubes and mono crystal production, to mention only few examples. Researchers have always seen Marangoni convection as an interesting topic for both numerical and experimental studies. Regarding the configuration of the injected gas bubble under a horizontal heated wall, this physical problem is mainly characterized by a dimensionless number that represents the ratio of convective heat flow induced by capillary convection to the heat transfer due to conduction which is termed Marangoni number (Mg). The past decade has seen different approaches to describe the flow behaviour at high Marangoni numbers. The thermocapillary flow has been mainly investigated and categorized regarding a stable laminar behaviour and a non-laminar one, which is characterized by periodic or non-periodic oscillations. Through previous studies, the point of the transition of the thermocapillary flow from the periodic oscillatory zone to the non-periodic one has been well investigated. However, there is a lack of information about this non-periodic behaviour at very high temperature gradients. Therefore, in the current study, our experimental investigations focus mainly on exploring different factors affecting the non-periodicity of the Marangoni convection and on explaining how this flow behaves under conditions above the transitional Marangoni number (Mg tran ). The experimental work was launched using a PIV technique and shadowgraphy. In addition to that, temperature measurements at different locations in the matrix fluid around the air bubble were conducted to determine the undisturbed temperature gradients at different boundary conditions. The transient observation of both velocity and temperature measurements at locations near the bubble allowed deeper insight in the behaviour of the thermocapillary bubbleconvection. Moreover, through shadowgraphy, a qualitative evaluation of the fluid flow periodicity around the gas bubble was achieved. The implementation of experiments inside a pressure chamber under gauge pressure conditions formed a novel methodology to enable us conducting experiments under higher temperature gradients in order to reach high Marangoni numbers. The thermocapillary bubble convection was categorized into laminar, periodic oscillatory, and non-periodic oscillatory flow. The periodic fluid flow oscillations were categorized in symmetric and asymmetric ones depending on the different applied boundary conditions. The non-periodic fluid flow oscillations around the gas bubble were also achieved at high temperature gradients for different bubble aspect ratios. We proved that for every bubble size, the non-periodic oscillatory state of the fluid flow around the gas bubble undergoes four different modes (A-D). The last one (phase D) is a developed turbulent state starting at Mg- numbers of 75000 for the smallest bubble aspect ratio of 1.2 up to the maximal measured Mg- number of 140000 for a bubble aspect ratio of 2.3. Hence, turbulent thermocapillary bubble convection was realized and studied in our experimental configuration. Moreover, the thermocapillary flow driving velocities at the bubble periphery were measured at different boundary conditions. This study clearly demonstrates that it is the high magnitude of the driving velocity that initiates the interactions between thermocapillary flow vortices leading finally to a highly developed oscillation mode (turbulent state) and that buoyancy plays a secondary role in the described flow configuration.:1 INTRODUCTION 2 LITERATURE REVIEW 3 EXPERIMENTAL SETUP AND METHODOLOGY 4 RESULTS AND DISCUSSION 5 CONCLUSIONS AND RECOMMENDATIONS / In dieser Arbeit wird die thermokapillare Konvektion um eine Gasblase unter einer horizontal beheizten Wand unter Gravitationsbedingungen experimentell untersucht. Diese thermokapillare konvektive Strömung jenseits des laminaren stationären Zustands in Richtung turbulenter Strömung steht in dieser Arbeit im Fokus. Im Allgemeinen ist die Marangoni-Konvektion unter Schwerelosigkeitsbedingungen kritischer und wichtiger als auf der Erde. Unter geringen Schwerkraftkräften kann diese durch Oberflächenspannung induzierte Strömung sowohl Wärme- als auch Stoffübergangsprozesse maßgeblich bestimmen. Daher sollte die thermokapillare Konvektion bei Materialproduktionsprozessen im Weltraum berücksichtigt werden. Darüber hinaus können Temperaturgradienten gezielt angewendet werden, um in flüssigen Materialien suspendierte Blasen oder Tropfen zu entfernen oder zu bewegen. Außerdem tritt thermokapillare Strömung in vielen anderen Anwendungen auf, beispielsweise bei der Herstellung von einwandigen Kohlenstoffnanoröhren oder der Herstellung von Einkristallen, um nur einige Beispiele zu nennen. Forscher haben die Marangoni-Konvektion immer als ein wichtiges und interessantes Thema für numerische und experimentelle Studien betrachtet. In Bezug auf die Konfiguration der injizierten Blase unter einer horizontal beheizten Wand wird dieses physikalische Problem hauptsächlich durch eine dimensionslose Kennzahl, die das Verhältnis des durch Kapillarkonvektion induzierten konvektiven Wärmeübertragungs zur Wärmeübertragung durch Leitung darstellt und als Marangoni-Zahl (Mg) bezeichnet wird, definiert. In den letzten Jahrzehnten wurden verschiedene Ansätze zur Beschreibung des Strömungs-Verhaltens bei höheren Marangoni-Zahlen verfolgt. Dabei wurde die Thermokapillarströmung grundsätzlich in ein stabiles laminares und ein nicht laminares (oszillierendes) Verhalten, das durch periodische oder nicht periodische Geschwindigkeit- und Temperatur-Fluktuationen gekennzeichnet ist, eingeteilt. Durch frühere Studien wurde das Regime des Übergangs des thermokapillaren Verhaltens von der periodischen Schwingungszone zur nichtperiodischen gut untersucht. Es fehlen jedoch immer noch detaillierte Informationen über das nichtperiodische Verhalten bei sehr hohen Temperaturgradienten. Daher konzentrieren sich unsere experimentellen Untersuchungen in der vorliegenden Studie hauptsächlich auf die Untersuchung verschiedener Faktoren, die die Nichtperiodizität der konvektiven Thermokapillarströmung beeinflussen, und auf eine Klärung, wie sich diese Strömung unter verschiedenen Randbedingungen über der kritischen Marangoni-Zahl (Mg c ) verhält.Die experimentelle Arbeit wurde sowohl mit einer PIV-Technik als auch mit der Shadowgraph- Technik durchgeführt. Darüber hinaus waren Temperaturmessungen auf Sensorbasis an verschiedenen Stellen in der verwendeten Flüssigkeit um die Luftblase geeignet, um die ungestörten Temperaturgradienten bei verschiedenen Randbedingungen zu bestimmen. Die zeitabhängige Messung sowohl von Geschwindigkeiten als auch von Temperaturen an Orten in der Nähe der Blase lieferte Informationen über das Verhalten der Konvektion der thermokapillaren Strömung. Darüber hinaus wurde durch die Shadowgraph-Technik eine qualitative Bewertung der Fluidströmungsperiodizität um die Blase ermöglicht. Die Durchführung von Experimenten in einer Druckkammer unter Überdruck-Bedingungen bildet eine neuartige Methode, um solche Experimente unter höheren Temperaturgradienten durchzuführen und höhere Marangoni-Zahlen zu erreichen. Die thermokapillare Blasenkonvektion wurde in dieser Arbeit in laminaren stetigen Flüssigkeitsströmungen, periodischen und nichtperiodischen oszillierenden Flüssigkeitsströmungen eingeteilt. Die periodischen Fluidströmungsschwingungen wurden in Abhängigkeit von unterschiedlichen Randbedingungen in symmetrische und asymmetrische eingeteilt. Die nichtperiodischen Strömungsoszillationen um die Gasblase wurden auch bei hohen Temperaturgradienten für verschiedene Blasenaspektverhältnisse erreicht. Wir konnten zeigen, dass für jede Blasengröße der nichtperiodische Schwingungszustand der Strömung um die Gasblase vier verschiedene Modi (A-D) besitzen kann. Die letzte (Phase D) ist ein hoch entwickelter turbulenter Zustand, der bei Mg-Zahlen von 75000 für das kleinste Blasenaspektverhältnis von 1,2 bis zur maximal gemessenen Mg-Zahl von 140000 für das Blasenaspektverhältnis von 2,3 beginnt. Der ausgebildete turbulente Zustand der thermokapillaren Strömung konnte mit unserer experimentellen Konfiguration erstmalig erreicht werden. Darüber hinaus konnten die Antriebsgeschwindigkeiten der thermokapillaren Strömung an der Peripherie der Blase bei verschiedenen Randbedingungen gemessen werden. Diese Studie zeigt deutlich, dass es die Höhe der Antriebsgeschwindigkeit ist, welche die Wechselwirkungen zwischen thermokapillaren Strömungswirbeln unterschiedlicher Größe antreibt, die schließlich zu chaotischen Schwingungen der im Folgenden beschriebenen Grenzlinie führen. Diese Studie zeigt auch, dass die Auftriebskonvektion in der beschriebenen Strömungskonfiguration eine untergeordnete Rolle spielt.:1 INTRODUCTION 2 LITERATURE REVIEW 3 EXPERIMENTAL SETUP AND METHODOLOGY 4 RESULTS AND DISCUSSION 5 CONCLUSIONS AND RECOMMENDATIONS