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<p>Thin liquid films are often studied by reducing the Navier-Stokes equations</p><p>using Reynolds lubrication theory, which leverages a small aspect ratio</p><p>to yield simplified governing equations. In this dissertation a plate</p><p>coating application, in which polydimethylsiloxane coats a silicon substrate,</p><p>is studied using this approach. Thermal Marangoni stress</p><p>drives fluid motion against the resistance of gravity, with the parameter</p><p>regime being chosen such that these stresses lead to a stable advancing front.</p><p>Additional localized thermal Marangoni stress is used to control the thin film;</p><p>in particular, coating thickness is modulated through the intensity of such</p><p>localized forcing. As thermal effects are central to film dynamics, the dissertation</p><p>focuses specifically on the effect that incorporating temperature dependence</p><p>into viscosity, surface tension, and density has on film dynamics and control.</p><p>Incorporating temperature dependence into viscosity, in particular,</p><p>leads to qualitative changes in film dynamics.</p><p>A mathematical model is developed in which the temperature dependence</p><p>of viscosity and surface tension is carefully taken into account.</p><p>This model is then</p><p>studied through numerical computation of solutions, qualitative analysis,</p><p>and asymptotic analysis. A thorough comparison is made between the</p><p>behavior of solutions to the temperature-independent and</p><p>temperature-dependent models. It is shown that using</p><p>localized thermal Marangoni stress as a control mechanism is feasible</p><p>in both models. Among constant steady-state solutions</p><p>there is a unique such solution in the temperature-dependent model,</p><p>but not in the temperature-independent model, a feature that</p><p>better reflects the known dynamics of the physical system.</p><p>The interaction of boundary conditions with finite domain size is shown</p><p>to generate both periodic and finite-time blow-up solutions, with</p><p>qualitative differences in solution behavior between models.</p><p>This interaction also accounts for the fact that locally perturbed solutions,</p><p>which arise when localized thermal Marangoni forcing is too weak</p><p>to effectively control thin film thickness, exist only for a discrete</p><p>set of boundary heights.</p><p>Modulating the intensity of localized thermal Marangoni forcing is</p><p>an effective means of modulating the thickness of a thin film</p><p>for a plate coating application; however, such control must be initiated before</p><p>the film reaches the full thickness it would reach in the absence of</p><p>such localized forcing. This conclusion holds for both the temperature-independent</p><p>and temperature-dependent mathematical models; furthermore, incorporating</p><p>temperature dependence into viscosity causes qualitative changes in solution</p><p>behavior that better align with known features of the underlying physical system.</p> / Dissertation

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.<p><p>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.<p> <p>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.<p><p><p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

<b>Structure of the thesis</b><p><p>The present work has been organized in two main parts: in the first one, the focus will be on the scientific and theoretical aspects of the evaporation process in presence of an inert gas flow while in the second all the technical aspects and more practical tests related to the real implementation of the micro-gravity experiment CIMEX-1 will be detailed. In any cases, the discussion will always start from the phenomenology observed considering that ” Nature is far more reach of any speculations.”<p><p><b>Part I: Evaporation in presence of inert gas</b> <p><p>In chapter 1, a detailed presentation of the experimental setups for the on-ground tests is given together with the presentation of the qualitative and quantitative results obtained. Actually, the main parameters that regulate such kind of experiments are the mass flow rate of inert gas, the total pressure of the cell and the geometrical shape and dimensions of the evaporating regions.<p>Consequently, the experiments aimed at covering the maximal possible combination of these three parameters with special attention to the variation of the inert gas flow and of the thickness of the evaporating liquid layer. More precisely, the liquid layer thickness was in the range 1.2 to 3.8 mm while the inert gas flow was set in the range 50 to 2500 ml/min. The pressure has been partially neglected as control parameter because its control was discovered not to be very reliable.<p>The visualization system used in all the experiments consisted in a opportunely calibrated infrared camera. It allowed for having a quantitative analysis of the temperature distribution at the interface of the evaporating liquid.<p>The infrared images also helped to follow the thermal history of the interface. In many cases, it has been possible to clearly observe the evolution of instability patterns at the interface that represent an original contribution to the understanding of such a kind of phenomena.<p>The physical and mathematical modeling of the observed phenomenology will be the subject of the chapter 2. One of the peculiar issue of the problem under consideration is that the thermal gradient normal to the interface is not directly imposed like in the usual Marangoni-Bénard experience, but is a result of the cooling of the interface due to the evaporation.<p>Moreover,the interface is subject to the shear stress of the inert gas flow and to the one due to the thermo-capillarity. Finally, the gas phase is to be considered as a mixture; this oblige to solve a diffusion problem in the gas phase. A physical model that takes into account the different aspects mentioned above is presented together with the governing equations and the appropriate boundary conditions.<p>Numerical issues involved in solving the model are also analyzed. Numerical results obtained are finally discussed and compared when possible with experimental results.<p><p><b>Part II: Preparation of the CIMEX-1 experiment on-board the International Space Station.</b><p><p>In chapter 3, we will describe the main platforms used to perform low-gravity experiments. They will be classified according to the low-gravity level and to the low-gravity interval duration that could be ensured for experiments. According to these criteria, the list of the low-gravity platforms will be as follows: Drop Towers with ≈ 4 sec. of micro-gravity, Parabolic Flights that can assure not more than ≈ 25 sec. Sounding Rockets with a low-gravity time of the order of several minutes depending on the rockets, Foton Capsules that assure for many days of high quality - i.e. without perturbations - low-gravity level and ,last but not least, the International Space Station where the low-gravity duration could be even of several weeks which is a sufficient time duration for the most part of the experiments.<p>The chapter 4 will be entirely devoted to the ITEL experiment that is the precursor and the core of the CIMEX-1. After a brief overview of the experiment that has been performed twice on-board sounding rockets of the MASER class, the experimental setups used both on-ground and in micro-gravity will be detailed.<p>The focus will be on the experimental results obtained on-ground during the preparatory tests and during the two sounding rocket flights with special attention to the first one. The analysis will be supported by the presentation of many results obtained in numerical simulations.<p>The two parabolic flight campaigns performed to test one of the key sub-systems of the CIMEX-1 setup are the subject of the chapter 5. The separating-condensing unit is mandatory for performing the experiment on-board the International Space Station because the limitations on the crew intervention oblige to have a closed loop experiment.<p>The goal of the two parabolic flights will be detailed together with the setup and the experimental scenario. The main results will be also shown and some considerations on the efficiency of the system will be presented.<p>It is worthy to stress that the results obtained during these parabolic flights have been determinant at the European Space Agency level to fly the CIMEX-1 experiment on-board the International Space Station.<p>Finally, in the section conclusions and perspectives the main results obtained will be summarized together with the new scenarios opened by the present work and some guidelines for further development in the experimental, theoretical and technical analysis. / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished

The lack of significant buoyancy effects in zero-gravity conditions poses an issue with fluid transfer in a stagnant liquid. In this thesis, the movement of a bubble or droplet in both stagnant and rotating liquids is analysed and presented numerically using computational fluid dynamics (CFD). The governing continuum conservation equations for two-phase flow are solved using the commercial software package (2011). The Volume of Fluid (VOF) method is used to track the liquid/gas interface in 2D and 3D domains. User-Defined Functions (UDFs) are employed in order to include the effect of surface tension gradient and fluid properties as a function of temperature, with a view to efficiently investigating temperature effects on the properties of the two phases. The flow is driven via Marangoni influence induced by the surface tension gradient, which in turn drives the bubble/droplet from the cold to the hot region. For stationary liquid, the results indicate that the scaled velocity of the bubble decreases with an increase in the Marangoni number, which agrees with the results of previous space experiments. An expression for predicting the scaled velocity of a bubble has been regressed based on the obtained data from the present numerical study for thermal Marangoni numbers up to 10,721. An expression for predicting the scaled velocity of a Fluorinert droplet migrating in oil has also been presented for an MaT range from 24.05 to 2771. The interactions of two droplets in thermocapillary motion have also been studied and compared with the results obtained for the isolated droplet. The results have shown that the leading droplet will not move faster than if it were isolated, as the trailing droplet has no influence on the velocity of the leading droplet. Three-dimensional results show that no bubbles broke in any of the cases observed and agglomeration could occur during thermocapillary migration for bubbles placed side by side. The results of the motion of a singular and multiple bubbles incorporating thermocapillary forces in a rotating liquid in a zero-gravity environment have been presented for the first time. When the Rossby number is 1, the effects of rotation are important. Furthermore, the deflection of the gas bubble motion increases towards the axis of rotation with a decrease in the Rossby number (Ro). Bubble population balance modelling has been investigated in normal gravity using Luo kernels for breakage and agglomeration and two different laminar kernels for zero-gravity conditions. The simulations covered a wide range of scenarios and results are presented as a bell and histogram shapes for number density and particle percentage distribution, respectively.

The effect of activating flux PATIG on welding arc was investigate in master thesis, A-TIG welding with flux PATIG. The test was performed on six materials with different chemical and mechanical properties. TIG and A-TIG welding was carried out after application flux. Performed require layer of PATIG flux was quite difficult. Result was compared between conventional TIG and experimental A-TIG method of welding. The best reached goals were for high-alloy steels. Typical and 3times deeper penetration was reached for A-TIG compared to conventional TIG welding.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19706号 / 工博第4161号 / 新制||工||1642(附属図書館) / 32742 / 京都大学大学院工学研究科原子核工学専攻 / (主査)教授 功刀 資彰, 教授 杉本 純, 教授 福山 淳 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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This study investigates the factors that affect the lifetime and popping location of surface bubbles. The experiment was conducted using three different liquids (water, Sodium Dodecyl Sulfate, and Decane) with varying bubble sizes, using three different needle sizes. Each setup was tested 50 times. For pure water bubbles, the foot of the bubble is the most critical location because it typically has the highest temperature gradient, which creates a localized Marangoni flow that thins the film and eventually leads to the bubble bursting at the foot. When SDS was added to water, the bubble lifetime increased significantly. This is because the Marangoni stresses were reduced, and the bubble film thinned mainly due to curvature-driven drainage flow. The lifetime of the SDS bubble had a positive correlation with increasing bubble size. For Decane bubbles, the volatility of the liquid plays a significant role in the lifetime and popping location of the bubble. When the Decane was heated to 40°C, the lifetime of the bubbles increased significantly from 0-20 seconds to 8-12 minutes. This is because the high volatility of the Decane caused rapid evaporation of the bubble cap at the interface, which cooled the surface of the liquid. This temperature difference creates a difference in surface tension, which causes the liquid to flow from the bulk liquid into the apex of the bubble, thickening the cap film until it cools down. Then, it pops from the top due to the curvature-driven drainage.