Omniphobic surfaces, which repel polar and non-polar liquids alike, have proven of value in a myriad of applications ranging from piping networks, textiles, food and electronics packaging, and underwater drag reduction. A limitation of currently employed omniphobic surfaces is their reliance on perfluorinated coatings/chemicals, increasing cost and environmental impact and preventing applications in harsh environments. Thus, there is a keen interest in rendering conventional materials, such as hydrocarbon-based plastics, omniphobic by micro/ nanotexturing rather than via chemical makeup, with notable success having been achieved for silica surfaces with doubly reentrant pillars (DRPs). We discovered a critical limitation of DRPs – they catastrophically lose superomniphobicity in the presence of localized physical damages/defects or on immersion in wetting liquids. In response, we pioneered bio-inspired gas-entrapping microtextured surfaces (GEMS) architecture composed of doubly reentrant cavities (DRCs). DRCs are capable of robustly entrapping air when brought into contact with liquid droplets or on immersion, which prevents catastrophic wetting transitions even in the presence of localized structural damage/defects. This dissertation presents our multifaceted research on DRCs via custom-built pressure cells, confocal laser scanning microscopy, environmental scanning electron microscopy, contact angle goniometry, high-speed imaging, and upright optical microscopy. Specific accomplishments detailed in this thesis include: (i) the microfabrication protocols for silica GEMS developed at KAUST; (ii) the characterization of GEMS’ omniphobicity via apparent contact angles and immersion; (iii) the demonstration of ~ 1000,000,000% delays in wetting transitions in DRCs compared to those in simple cavities (SCs) under hexadecane; (iv) a proposal for immersion of surfaces as a criterion for assessing their omniphobicity in addition to apparent contact angles; (v) effects of surface chemistry, hydrostatic pressure, and cavity dimensions on Cassie-to-Wenzel transitions in DRCs and SCs; (vi) the demonstration of “breathing” (liquid-vapor) interfaces in GEMS under fluctuating hydrostatic pressures; and (vii) the demonstration of directional wetting transitions in DRCs (or cavities in general) arranged in one- and two-dimensional lattices. The last chapter in the thesis presents future research directions such as breathing surfaces capable of preempting vapor condensation and gas replenishment.

L’objectif est d’améliorer la connaissance des écoulements de films minces se développant au sein des colonnes servant à distiller les gaz de l’air sous conditions cryogéniques. Ce travail porte sur la caractérisation expérimentale de l’épaisseur du film liquide dans des conditions hydrodynamiques proches de celles rencontrées dans l’industrie. Tout d’abord, ce travail a permis de déterminer les conditions opératoires permettant la réalisation d’écoulement en similitude hydrodynamique avec les écoulements cryogéniques mais à température et pression proches de l’ambiant. Ensuite, un dispositif expérimental a ensuite été développé afin de permettre la réalisation d’écoulement de film liquide avec et sans contre-courant gaz sur plan incliné. Une métrologie optique utilisant un procédé de fluorescence a été développée et calibrée afin de mesurer des épaisseurs de films minces inférieures à 2 mm. Pour finir, l’étude expérimentale a permis de caractériser l’écoulement du film mince par l’étude statistique de son épaisseur, l’étude des régimes d’ondes de surface ainsi que son aire interfaciale. / The aim of this study is to get a better knowledge of thin film flow inside column used to distil the gases of air under cryogenic conditions. Experimental characterisation of the liquid film thickness submitted to hydrodynamic conditions similar to those found in real processes is investigated in this work. First, operating conditions were defined that allow thin film flow in hydrodynamic similitude with cryogenic flows but under conditions close to standard temperature and pression. Then, an experimental setup was designed in order to realize liquid film flows down an inclined plate with and without counter-current air flow. An optical technique using fluorescence was built and calibrated in order to measure the thickness of liquid film up to 2 mm. Finally, thin liquid film flow characteristics were experimentally studied with special attention given to the statistical variation of film thickness, interfacial wave patterns and interfacial area.

This thesis is dedicated to the study of the interaction between a gas jet and a liquid film on a moving surface. This flow configuration corresponds to the gas-jet wiping technique, which is widely used in the coating industry to reduce and control the thickness of a liquid film dragged by a moving substrate. For that purpose, a turbulent slot jet impinges on the liquid surface, involving a runback flow and consequently a lower coating thickness downstream wiping. The different process parameters (nozzle pressure, nozzle to substrate standoff distance, slot width, substrate speed) allow controlling the final film thickness. This metering technique is very common in coating processes, such as the application of gelatin layers on photographic films.<p><p>The first part of this thesis deals with the prediction of the mean jet wiping flow, i.e. the film thickness distribution in the wiping region. A lubrication model is developed for that purpose, which is simplified to a zero-dimensional model giving directly the final thickness<p><p>In the second part, the prediction of splashing occurrence in jet wiping is addressed. The splashing phenomenon in jet wiping is featured by the ejection of droplets from the runback flow, and it constitutes a physical limit to the process. An experimental investigation is conducted on a water model facility, and based on a phenomenological description, a dimensionless correlation in terms of film Reynolds number and jet Weber number is derived for splashing occurrence. The latter is perfectly well validated with observations on industrial lines.<p><p>The last part of this thesis is dedicated to the study of the unsteady phenomena occurring on the free surface of the liquid film downstream wiping. This phenomenon has never been understood nor characterized up to now. In the present research, undulation is investigated both theoretically and experimentally. Two model test facilities with dedicated measurement techniques have been designed and constructed. They allow performing parametric studies of the undulation characteristics (amplitude, wavelength, wave velocity), and analyzing the jet/film interaction.<p> / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished

Les propriétés des mousses liquides sont majoritairement gouvernées par les caractéristiques de leurs interfaces liquide/gaz. Nous illustrons ces effets à l'échelle locale par différents exemples : – Les réarrangements topologiques, pendant lesquels les bulles changent de voisines, sont les événements élémentaires à l'origine de propriétés rhéologiques et de stabilité des mousses. En réalisant des expériences sur une assemblée de films dans un cadre cubique, nous avons étudié les mécanismes de formation du nouveau film pour différentes solutions de tensioactifs modifiant les propriétés interfaciales. – L'observation de l'éclatement d'un film de savon unique montre que cette dynamique est ralentie à cause de l'élasticité des interfaces, jusqu'à l'apparition de rides ou de fractures pour une compression critique. – Par des mesures force/déplacement, nous avons montré qu'un radeau de particules se comporte comme un granulaire 2D, qui peut se déformer en-dehors du plan de l'interface, et dans lequel la contrainte peut dépendre de la friction à la paroi. De plus, l'ajout de ponts capillaires entre les particules procure au radeau une meilleure résistance à la traction et à la compression. – En injectant de l'air dans une pâte, nous avons créé des bulles stables dans des conditions permettant l'adsorption des tensioactifs à la surface des particules pour les rendre partiellement mouillantes. En utilisant ce mécanisme dans un système cimentaire, des bulles solides sont alors fabriquées / Properties of liquid foams are mainly governed by the features of liquid/gas interfaces. We illustrate this phenomenon at the local scale through different examples : – Topological rearrangements, i.e. switching of neighboring bubbles, are the elementary process of liquid foams stability and dynamics. Experiments are performed in a cubic assembly of films, in order to investigate the mechanism of creation of the new film for different surfactants solutions and therefore different interfacial properties. – Observation of soap film bursting shows that the dynamics is slowed down because of interfacial elasticity, until wrinkles or cracks appear for a critical compression. – Through strength/displacement measurements, we show that a particle raft behaves as a 2D granular material, which can buckle, and whose stress can depend on wall friction. Moreover, the addition of liquid bridges between particles provides higher compressive and tensile strengths to the raft. – Blowing air into a paste allows creating stable bubbles, when surfactants adsorb at particles surface, modifying their wetting properties. We demonstrate that this method can lead to solid bubbles with a cementitious system

In order to enhance accessibility to microgravity research, the design process for experiments on the ISS must be streamlined and accessible to all scientific disciplines, not just aerospace engineers. Thus, a general design and analysis toolbox with accompanying best practices manual for microgravity liquid containment is proposed. The work presented in this thesis improves the design process by introducing a modular liquid tank design which can be filled, drained, or act as a passive liquid-gas separation device. It can also be pressurized, and used for aerosol spray. This tank can be modified to meet the design requirements of various experimental setups and liquids. Furthermore, rough simulations of this tank are presented and available to the user for modification. The simulation and design methodology for other general cases is discussed as well. After reading this thesis, the user should have a basic understanding of how liquids behave in microgravity. She will be able to run simple simulations, design, build, test, and fly a liquid management device which has been modified to suit the requirements of her specific experiment. The general tank design can be manufactured using 3-D printing, traditional CNC milling, or a combination thereof. The design methodology and best practices presented here have been used to design tanks used in experiments on the International Space Station for Budweiser and Lambda Vision. Both tanks functioned nominally on orbit. While the specific data from these experiments cannot be presented due to proprietary restrictions, using this thesis as a design guide for new experiments should yield favorable results when applied to new tank designs. If the reader has any questions or would like an updated design process, the author’s preferred contact information can be found using the Orcid iD: 0000-0002-2617-2957 .

Cette thèse présente la Simulation des Grandes Echelles (LES) de l’injection, de la pulvérisation et de la cavitation dans un injecteur pour les applications liées aux moteurs à combustion interne. Pour la modélisation de l’atomisation, on utilise le modèle ELSA (Eulerian Lagrangian Spray Atomization). Le modèle résout la fraction volumique du combustible liquide ainsi que la densité de surface d’interface liquide-gaz pour décrire le processus complet d’atomisation. Dans cette thèse, l’écoulement à l’intérieur de l’injecteur est également pris en compte pour une étude ultérieure de l’atomisation. L’étude présente l’application du modèle ELSA à un injecteur Diesel typique, à la fois dans le contexte de RANS et de LES.Le modèle est validé à l’aide de données expérimentales disponibles dans Engine Combustion Network (ECN). Le modèle ELSA, qui est normalement conçu pour les interfaces diffuses (non résolues), lorsque l’emplacement exact de l’interface liquide-gaz n’est pas pris en compte, est étendu pour fonctionner avec une formulation de type Volume of Fluid (VOF) de flux à deux phases, où l’interface est explicitement résolu. Le couplage est réalisé à l’aide de critères IRQ (Interface Resolution Quality), qui prennent en compte à la fois la courbure de l’interface et la quantité modélisée de la surface de l’interface. Le modèle ELSA est développé en premier lieu en considérant les deux phases comme incompressibles. L’extension à la phase compressible est également brièvement étudiée dans cette thèse. Il en résulte une formulation ELSA compressible qui prend en compte la densité variable de chaque phase. En collaboration avec l’Imperial College de Londres, la formulation de la fonction de densité de probabilité (PDF) avec les champs stochastiques est également explorée afin d’étudier l’atomisation. Dans les systèmes d’injection de carburant modernes, la pression locale à l’intérieur de l’injecteur tombe souvent en dessous de la pression de saturation en vapeur du carburant, ce qui entraîne une cavitation. La cavitation affecte le flux externe et la formulation du spray. Ainsi, une procédure est nécessaire pour étudier le changement de phase ainsi que la formulation du jet en utilisant une configuration numérique unique et cohérente. Une méthode qui couple le changement de phase à l’intérieur de l’injecteur à la pulvérisation externe du jet est développée dans cette thèse. Ceci est réalisé en utilisant le volume de formulation de fluide où l’interface est considérée entre le liquide et le gaz; le gaz est composé à la fois de vapeur et d’airambiant non condensable. / This thesis presents Large Eddy Simulation (LES) of fuel injection, atomization and cavitation inside the fuel injector for applications related to internal combustion engines. For atomization modeling, Eulerian Lagrangian Spray Atomization (ELSA) model is used. The model solves for volume fraction of liquid fuel as well as liquid-gas interface surface density to describe the complete atomization process. In this thesis, flow inside the injector is also considered for subsequent study of atomization. The study presents the application of ELSA model to a typical diesel injector, both in the context of RANS and LES. The model is validated with the help of experimental data available from Engine Combustion Network (ECN). The ELSA model which is normally designed for diffused (unresolved) interfaces, where the exact location of the liquid-gas interface is not considered, is extended to work with Volume of Fluid (VOF) type formulation of two phase flow, where interface is explicitly resolved. The coupling is achieved with the help of Interface Resolution Quality (IRQ) criteria, that takes into account both the interface curvature and modeled amount of interface surface. ELSA model is developed first considering both phases as incompressible, the extension to compressible phase is also briefly studied in this thesis, resulting in compressible ELSA formulation that takes into account varying density in each phase. In collaboration with Imperial College London, the Probability Density Function (PDF) formulation with Stochastic Fields is also explored to study atomization. In modern fuel injection systems, quite oftenthe local pressure inside the injector falls below the vapor saturation pressure of the fuel, resulting in cavitation. Cavitation effects the external flow and spray formulation. Thus, a procedure is required to study the phase change as well as jet formulation using a single and consistent numerical setup. A method is developed in this thesis that couples the phase change inside the injector to the external jet atomization. This is achieved using the volume of fluid formulation where the interface is considered between liquid and gas; gas consists of both the vapor and non condensible ambient air.

Two and three-phase flow processes involving gas, liquid and solid, are common in nature and industry, and include some of the most complex and poorly-understood transport problems. In this research hydrodynamics, heat and mass transfer processes in complex two and three-phase flows were investigated. The interfacial surface area concentration in a short vertical column subject to the through flow of fiber-liquid-gas slurry was experimentally measured using the gas absorption technique. The experimental data were statistically analyzed for parametric effects, and were empirically correlated. The absorption of a gaseous species by a slurry droplet with internal circulation and containing reactive micro-particles was simulated, and parametrically studied. The micro-particles were found to enhance the absorption rate. The absorption rate was sensitive to droplet recirculation, and shrinkage of particles with time resulted in declining absorption rates. The transport of soot particles, suspended in laminar hot gas flowing in a tube, was modeled and parametrically studied. Due to coupled thermal radiation and thermophoresis, a radially-nonuniform temperature profile develops, leading to sharp, non-uniform radial soot-concentration profiles. The assumption of monodisperse particles leads to over-prediction of thermophoresis. The transport and removal of particles suspended in bubbles rising in a stagnant liquid pool were modeled based on a Eulerian – Monte Carlo method. The bubble hydrodynamics were treated in Eulerian frame, using the Volume-of-Fluid (VOF) technique, while particle equations of motion were numerically solved in Lagrangian frame. The bubbles undergo shape change, and have complex internal circulation, all of which influence the particle removal. Model predictions were also compared with experimental data. Using a resemblance between two-phase flow in microchannels, and in large channels at microgravity, a simple Weber number-based two-phase flow regime map was developed for microchannels. Based on the available air-water experimental data, a criterion for the prediction of conditions that lead to flow regime transition out of the stratified-wavy flow pattern in horizontal annular channels was proposed. The thermocapillary effects on liquid-vapor interface shape during heterogeneous bubble ebullition in microchannels were analytically studied.