Дисертації: "Marangoni Flow in Droplets"

1

Alhendal, Yousuf A. "Computational two phase Marangoni flow in a microgravity environment." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/computational-two-phase-marangoni-flow-in-a-microgravity-environment(a3ba6f7f-f619-4bae-a355-e7b007d97e13).html.

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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.

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Schmitt, Maximilian [Verfasser], Holger [Akademischer Betreuer] Stark, and Uwe [Gutachter] Thiele. "Active emulsion droplets driven by Marangoni flow / Maximilian Schmitt ; Gutachter: Uwe Thiele ; Betreuer: Holger Stark." Berlin : Technische Universität Berlin, 2017. http://d-nb.info/1156010268/34.

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3

Li, Menglin [Verfasser]. "Self-propelled droplet driven by Marangoni flow and its applications / Menglin Li." Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2019. http://d-nb.info/1224474856/34.

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4

Jehannin, Marie. "About the role of physico-chemical properties and hydrodynamics on the progress of a precipitation reaction : the case of cerium oxalate particles produced during coalescence of drops." Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS265/document.

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Réussir à contrôler la morphologie et la taille de particules solides obtenues par précipitation est un enjeu industriel majeur. C’est notamment le cas dans l’industrie nucléaire pour le recyclage du combustible usé. Les caractéristiques des précipités sont liées aux conditions de mélange des phases liquides dans les procédés. Les corrélations entre les paramètres physiques des particules obtenues et les conditions hydrodynamiques n’ont pas été examinées jusqu’à présent. Dans cette étude, des systèmes expérimentaux originaux, basés sur la coalescence de deux gouttes, sont utilisés afin de mieux comprendre les liens entre hydrodynamique et réaction de précipitation. Deux configurations de gouttes aqueuses ont été investiguées, la première consiste en deux gouttes posées à fort angle de contact (>90°) dans l’huile, il s’agit d’un système modèle pour les gouttes en émulsion, la second configuration correspond à deux gouttes posées à faible angle de contact (>25°) dans l’air. Dans chaque cas, une espèce réactive est dissoute dans chaque goutte, à savoir de l’acide oxalique ou du nitrate de cérium dans la seconde. Lorsque les deux gouttes se touchent, elles peuvent éventuellement coalescer, alors les espèces chimiques se mélangent et réagissent pour produire un précipité d’oxalate de cérium. Les caractéristiques de ce précipité et ses effets sur l’hydrodynamique sont examinés en fonction du solvant utilisé. De plus, dans le cas des gouttes posées sur une surface de silice dans l’air, une différence de tension de surface entre deux gouttes crée un gradient qui génère un flux de Marangoni dirigé de la goutte de faible tension de surface au-dessus de la goutte de forte tension de surface. En jouant sur la différence de tension de surface entre les deux gouttes, et ainsi sur le flux de Marangoni, il est possible de modifier les conditions hydrodynamiques lors de la coalescence des gouttes. Des mélanges eau/diols ont été utilisés comme solvant afin de pouvoir modifier la différence de tension de surface entre les liquides des deux gouttes indépendamment de leur concentration en réactif. Les diols utilisés, le 1,2-propanediol et le 1,3-propanediol sont des isomères, ils sont la même densité, des viscosités semblables mais des tensions de surface différentes. En fixant la fraction volumique d’eau dans le solvant, et en jouant sur les fractions volumiques de chaque diols, il est possible de contrôler la tension de surface des mélanges sur une gamme de 10 mN/m pour une concentration en réactifs donnée, et en conservant la densité et viscosité des solvants. Trois régimes de précipitation ont été identifiés dans le cas de la coalescence de gouttes d’eau/diols/réactifs en fonction de l’excès oxalique. Les motifs de précipitation en découlant ont été imagés par microscopie optique et les différents précipités ont été caractérisés à l’aide de microscopie confocale, MEB, DRX et SAXS. Le régime intermédiaire présente des motifs périodiques surprenants. Ces motifs correspondent à des domaines nettement délimités d’oxalate de cérium de différentes morphologies, à savoir des aiguilles et des « microflowers ». L’obtention de tels motifs peut s’expliquer par un mécanisme de rétroaction entre convection, réaction et diffusion
The size and morphology control of precipitated solid particles is a major economic issue for numerous industries. For instance, it is interesting for the nuclear industry, concerning the recovery of radioactive species from used nuclear fuel. The precipitates features, which are a key parameter from the post-precipitate processing, depend on the process local mixing conditions. So far, the relationship between precipitation features and hydrodynamic conditions have not been investigated. In this study, a new experimental configuration consisting of coalescing drops is set to investigate the link between reactive crystallization and hydrodynamics. Two configurations of aqueous drops are examined. The first one corresponds to high contact angle drops (>90°) in oil, as a model system for flowing drops, the second one correspond to sessile drops in air with low contact angle (<25°). In both cases, one reactive is dissolved in each drop, namely oxalic acid and cerium nitrate. When both drops get into contact, they may coalesce; the dissolved species mix and react to produce insoluble cerium oxalate. The precipitates features and effect on hydrodynamics are investigated depending on the solvent. In the case of sessile drops in air, the surface tension difference between the drops generates a gradient which induces a Marangoni flow from the low surface tension drop over the high surface tension drop. By setting the surface tension difference between the two drops and thus the Marangoni flow, the hydrodynamics conditions during the drop coalescence could be modified. Diols/water mixtures are used as solvent, in order to fix the surface tension difference between the liquids of both drops regardless from the reactant concentration. More precisely, the used diols, 1,2-propanediol and 1,3-propanediol, are isomer with identical density and close viscosity. By keeping the water volume fraction constant and playing with the 1,2-propanediol and 1,3-propanediol volume fractions of the solvents, the mixtures surface tensions differ up to 10 mN/m for identical/constant reactant concentration, density and viscosity.Three precipitation behaviors were identified for the coalescence of water/diols/recatants drops depending on the oxalic excess. The corresponding precipitates patterns are visualized by optical microscopy and the precipitates are characterized by confocal microscopy SEM, XRD and SAXS measurements. In the intermediate oxalic excess regime, formation of periodic patterns can be observed. These patterns consist in alternating cerium oxalate precipitates with distinct morphologies, namely needles and “microflowers”. Such periodic fringes can be explained by a feedback mechanism between convection, reaction and the diffusion

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Tsoumpas, Ioannis. "Experimental study of the evaporation of sessile droplets of perfectly-wetting pure liquids." Doctoral thesis, Universite Libre de Bruxelles, 2014. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209196.

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The study presented in this dissertation concerns the evaporation, in normal ambient conditions, of sessile droplets (pinned and freely receding) of various HFE liquids (instead of the widely used water), which are considered so far as environmentally friendly and are often used as heat-transfer fluids in thermal management applications. They are pure perfectly-wetting and volatile liquids with low thermal conductivity and high vapor density. These properties affect in their own way many aspects concerning droplet evaporation such as the evaporation-induced contact angles, evaporation rate of a droplet, contact line pinning and Marangoni flow, all of which are treated in the present dissertation.

In general, the thesis starts with a general introduction including but not limited to sessile droplets (Chapter 1). In Chapter 2 we provide a general overview of capillarity-related concepts. Then, in Chapter 3 we present the interferometric setup, along with the liquids and the substrate that is used in the experiments, and also explain the reasons why this particular method is chosen. In Chapter 4 we address, among others, the issue of evaporation-induced contact angles under complete wetting conditions. The behavior of the global evaporation rate is also examined here, whereas in Chapter 5 we discuss the influence of thermocapillary stresses on the shape of strongly evaporating droplets. Finally, before concluding in Chapter 7, we address in Chapter 6 the still open question of the influence of non-equilibrium effects, such as evaporation, on the contact-line pinning at a sharp edge, a phenomenon usually described in the framework of equilibrium thermodynamics. The experimental results obtained are also compared with the predictions of existing theoretical models giving rise to interesting conclusions and promising perspectives for future research.

Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

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6

Burge, Wayne. "Marangoni Instabilities in Two-Layer Fluid Flow." Thesis, University of East Anglia, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.518388.

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7

Weiss, Michael. "Surfactant adsorption and Marangoni flow in liquid jets." Thesis, University of Oxford, 2004. http://ora.ox.ac.uk/objects/uuid:7e313dbf-30b6-4ad7-8607-c75e89b084eb.

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8

Khaw, Mei Kum. "Studies on Magnetically Actuated Droplets for Digital Microfluidic." Thesis, Griffith University, 2017. http://hdl.handle.net/10072/365947.

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Digital microfluidic is an emerging liquid handling technique where discrete droplets are manipulated on a substrate. For the past decades, conventional microfluidic applications are based on continuous flow concept. They require complicated networks of channels, pumps and valves to manage the flow of droplets in microchannels. In digital microfluidics, droplets are moved individually on an open surface. The droplets have the flexibility to move in various directions, making a single device flexible for diverse reaction designs and applications. The manipulation of discrete droplets allows reduction in sample size, faster heat transfer and reaction rates and easier collection of samples. The droplets can be manipulated via electrostatic force, magnetic force, gravitational force, pressure gradient, pH change, surfactant concentration, temperature change, Marangoni propulsion and light-induced surface tension gradient. Magnetic actuation is an excellent candidate for digital microfluidic applications because of the simplicity of using external magnetic field for a non-contact and non-invasive control over magnetised droplets. The magnetic field can penetrate through substrates and biological materials. There is also a wide variety of available magnetic particles and it is easy to control the amount of magnetic particles loaded into the carrier liquid. Some magnetic particles can absorb nucleic acids and other biomolecules making it possible for biomolecular separation. Magnetic manipulation is not affected by factors such as surface charges, pH and ion concentration. In most cases, magnetic manipulation does not induce heating.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Engineering
Science, Environment, Engineering and Technology
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9

Semenov, Sergey. "Computer simulations of evaporation of sessile liquid droplets on solid substrates." Thesis, Loughborough University, 2012. https://dspace.lboro.ac.uk/2134/10277.

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Present work is focused on the numerical study of evaporation of sessile liquid droplets on top of smooth solid substrates. The process of evaporation of a sessile liquid droplet has lots of different applications both in industry and research area. This process has been under study for many years, and still it is an actual problem, solution of which can give answers on some fundamental and practical questions. Instantaneous distribution of mass and heat fluxes inside and outside of an evaporating sessile droplet is studied in this research using computer simulations. The deduced dependences of instantaneous fluxes are applied for self-consistent calculations of time evolution of evaporating sessile droplets. The proposed theory of evaporating sessile droplets of liquid has been validated against available experimental data, and has shown a good agreement. Evaporation of surfactant solution droplets is studied experimentally. The theory, proposed for two stages of evaporation, fits experimental data well. An additional evaporation stage, specific for surfactant solutions, is observed and described. Mathematical modelling of this stage requires further research on surfactant adsorption and its influence on the value of receding contact angle. Numerical study of the evaporation of microdroplets is conducted in order to evaluate the significance of different evaporation mechanisms (diffusive and kinetic models of evaporation) and different physical phenomena (Kelvin s equation, latent heat of vaporization, thermal Marangoni convection, Stefan flow).

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10

Chatterjee, Aniruddha. "Physical and computational models of Marangoni and buoyancy flow during dissolution." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/43172.

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During the production of titanium products, the presence of aluminum-rich regions can cause Type II alpha stabilized defects which are deleterious to down-stream performance. Al-rich material can enter the melt via ballistic transfer from the melting hearth at various stages during electron beam cold hearth re-melting (EBCHR) of Ti-6Al-4V (Ti-6wt%Al-4wt%V) alloy. If this material is not fully dissolved and homogenized when solidification occurs, the ingot will contain Al-rich regions. Thus, in order to produce high-performance components for aerospace applications, titanium producers must understand the dissolution process for alloying elements entering the melt. To study and characterize the phenomena associated with the dissolution and homogenization of alloying elements during EBCHR processing of Ti-6Al-4V, a water-ethanol physical analogue model has been developed to simulate the thermal, compositional and fluid flow behavior that are active in the dissolution process. The physical model consists of a hot water solvent contained in a transparent cell (beaker) in which solidified ethanol or ice solute is dipped. The data generated from the physical model was used to validate a coupled thermal- fluid flow-composition model (developed in the commercial CFD code ANSYS CFX). The analogue model focuses on characterizing the effects of thermal and compositional variations on surface tension driven fluid flow (Marangoni flow) and buoyancy driven flow during the dissolution of a low density, low surface tension and low melting point solid material (frozen ethanol) in a high density, high surface tension and high melting point liquid (water), which was found to be analogous to the dissolution of solid Al in liquid Ti. In addition, the analogue model was also capable to predict the dissolution behavior when there was no compositional difference between the solute and the solvent. Based on a comparison of fluid flow pattern and interface shape, and temperature data obtained at discrete locations in the experimental and computational results, the numerical model has been shown to quantitatively and qualitatively predict the dissolution behavior observed in the physical process.

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Huber, Michael R. "An investigation of low Marangoni number fluid flow in a cold corner." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from the National Technical Information Service, 1993. http://handle.dtic.mil/100.2/ADA271317.

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12

Carle, Florian. "Flow motion in sessile droplets : evaporation and nanoparticles assembly." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4726/document.

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L'évaporation d'une goutte reposant sur un support plat semble être un système relativement simple à étudier et a fait l'objet d'études scientifiques depuis plus d'un siècle. Cependant, l'étude de l'évaporation de gouttes sessiles est toujours d'actualité aujourd'hui avec l'essor de nouvelles techniques de visualisation ou de l'apparition de nouveaux types de fluides complexes.Cette étude expérimentale sera focalisée sur deux aspects distincts :- L'étude sur l'évaporation de fluides purs permettra d'étudier la dynamique d'évaporation et les ondes hydrothermales qui apparaissent dans les gouttes de fluides volatils lors du changement de phase. L'influence du type de fluide (différents alcools et alcanes) et du niveau de gravité (terrestre, lunaire et martienne) seront étudiés. De plus, l'utilisation de différents niveaux de gravité permet de développer un modèle empirique afin de prendre en compte dans le modèle quasi-stationnaire limité par diffusion de la vapeur la convection naturelle qui augmente fortement le débit d'évaporation.- Si les fluides complexes présentent une dynamique de séchage similaire à celle des fluides purs, d'autres mécanismes entrent en jeux, comme la gélification, l'organisation des particules et l'apparition de craquelures (voir Figure 2). Le mouillage et les différents groupes fonctionnels graphés sur les particules seront étudiés en regard du motif final de craquelures
Sessile droplets are widely found in day to day life: it might be a coffee spilt, rain onto a waterproof raincoat or again, water falling onto a cooking plate. However, despite the vast number of studies devoted to droplets for almost half a century, the fundamental phenomenon of the evaporation of sessile droplets is still a field that attracts a high level of interest due to its wide applicability and the development of new visualisation techniques or new types of complex fluids. This experimental study is focused two distinct aspects:- The evaporation of pure fluids has allow to study hydrothermal waves that appear in the droplets of volatile fluids during phase change. The influence of the type of fluid ---different alcohols and alkanes--- and the gravity levels ---Terrestrial, Lunar and Martian--- is investigated to have a better understanding of the flow motion inside droplet. Moreover, the use of different gravity levels allows to experimentally evidence the contribution of the atmospheric convective transport to sessile droplet evaporation. This investigation has allowed to develop an empirical model to take account of natural convection which greatly increases the evaporation rate in the quasi-steady diffusion-controlled evaporation model.- If complex fluids exhibit an evaporation dynamic similar to pure fluid, other mechanisms come into play, such as gelation, particles organisation and cracks formation. Wetting and different functional groups on the particles graphs will be studied in relation to the final pattern of cracks

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13

Petkovic, Bojan. "Deposition of droplets onto solid objects in aerosol flow." Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/20891.

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In this work, the effect of velocity on deposition coefficients and capture efficiencies on a circular disk, placed normal to an aerosol flow was investigated. The superficial gas velocity was varied in the range of 0.1 m/s to 1.5 m/s, while the volume median diameter of the droplet size distribution varied between 3.9 and 7.5 microns. The morphology and distribution of deposits on the upstream and downstream surface of the disk were observed and measured. The effect of contact angles (20°, 51°, 94°) on deposition, and dry vs. wet surface effects were also investigated. It was found that in the range of velocity and droplet sizes investigated, deposition on the upstream side was dominated by the inertial impaction mechanism. Capture efficiencies increased with velocity and droplet size, and could be explained by the inertial impaction mechanism from the upward flow, using the potential flow approximation. For the downstream side, capture efficiencies increased with droplet size and showed a minimum with velocity. It is postulated that the governing deposition mechanism for the downstream side is the inertial impaction mechanism with gravity in the flow direction. On the upstream side, it was found that deposits were concentrated closer to the coupon edge, while on the downstream side, the distribution of deposits on the surface was uniform. In the range of investigated contact angles, there was no significant difference observed between the deposition rates. The same can be said for the effect of dry vs. wet coupon surface.

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14

Gomes, Zoby Maria Regina. "Liquid Droplets and Gas Interactions in Two-phase Flow." Thesis, Imperial College London, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526366.

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15

Koleski, Goce. "Flower-like azimuthal instability of a divergent flow at the water/air interface." Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0244.

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Un écoulement axisymétrique à une interface eau-air s’avère instable azimutalement. Durant cette thèse,nous avons mené deux expériences afin d’étudier ce point : (1) une petite fontaine subaquatique propulse un jet contre l’interface eau-air créant ainsi en surface un écoulement centrifuge radial; (2) une microbille chauffée par laser, en mouillage partiel à la surface de l’eau, engendre un écoulement thermocapillaire divergent. Lorsque la vitesse du jet ou la puissance du laser est suffisamment forte, il se produit une brisure de symétrie de l’écoulement torique initial en paires de vortex contrarotatifs entourant la source.Nous précisons les caractères morphologiques du tore ainsi que du dipôle par le biais d’expériences de tomographie laser et d’injection de colorant. Dans l’expérience du jet d’eau, nous montrons que la taille du tore est essentiellement déterminée par la distance séparant l’injecteur de la surface. Dans les deux expériences, un état "bloqué" de l’interface en régime toroïdal mais "débloqué" en régime dipolaire est mis en évidence par suivi de traceurs. Ce type de phénomène est piloté par l’élasticité de surface. Une preuve convaincante est la réponse élastique, à l’extinction du laser, de la couche de surfactants adsorbés à l’interface. Le principal intérêt de ce travail est de mettre en avant le rôle – clé que joue l’élasticité interfaciale dans le scénario de l’instabilité. D’un point de vue théorique, nous étudions la convection thermocapillaire induite par une source fixe ponctuelle à l’interface eau-air. Nous résolvons l’équation de Stokes incompressible au sein du demi – espace contenant le liquide et déterminons la solution exacte du problème advectif, non-linéaire, dans le régime axisymétrique en limite de champ lointain. Enfin, nous posons les bases sur lesquelles élaborer une théorie de l’instabilité. Ce travail de thèse devrait permettre de comprendre comment une petite sphère chaude à la surface de l’eau déclenche le type d’instabilité étudié ici, devenant de ce fait une "particule active" capable de s’autopropulser à grande vitesse
Axisymmetric flows on a water-air interface prove to be azimuthally unstable. In this thesis work, we design two setups to explore this fact : (1) a small subaquatic fountain propelling a jet against the water-air interface where it creates a centrifugal radial flow, (2) a laser – heated microbead in partial wetting at the surface of water that induces a divergent thermocapillary flow. At sufficiently high jet speeds or laser powers appears a symmetry – breaking of the toroidal base flow in the form of counter – rotating vortex pairs surrounding the source. Morphological traits of the torus and the dipole are uncovered through a wealth of laser tomography and dye injection experiments. In the water jet experiment, we show that the torus size is primarily fixed by the distance between the injector and the surface. In both experiments,the tracking of tracer particles evidences a ‘locked’ interface in the toroidal regime, whereas it ‘unlocks’ when a dipole sets in. Such a phenomenon is conditioned by surface elasticity. Cogent evidence is brought by the elastic response to laser shutdown of a surfactant layer adsorbed at the water surface. Unveiling the key role of surface elasticity in the scenario of the instability is the main achievement of this work.On a theoretical level, we focus on thermocapillary convection induced by a fixed point source of heat sitting across the water-air interface. We solve the incompressible Stokes equation within the water – filled half – space and derive an exact solution to the advective nonlinear regime in the far – field axisymmetric limit. We then lay the groundwork on which to build a model of the instability. This thesis work paves the way for understanding how a hot microsphere found on the water surface triggers such an instability, thereby becoming an ‘active particle’ able to achieve self – propulsion at large speeds

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Kufås, Eirik. "Mathematical Modeling of Coalescence of Oil Droplets in Water Flow." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2008. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-12879.

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Liquid-liquid coalescers are devices used for increasing the droplet size of the dispersed phase in continuous phase flow, such as oil droplets in water flow. The efficiency of separation technologies is strongly dependent on the droplet size, which is desirable to shift into larger droplet diameters. Theory behind coalescence and its modeling is studied in this Masers thesis. Aker Process Systems AS, Division of Advanced Separation Technology, provided the assignment proposal.The scope of this work is a literature study on the coalescence phenomenon and the closely related break-up phenomenon and CFD modeling in general. Further a mathematical model for simulating coalescence of oil droplets in continuous water flow is developed by the use of the commercial CFD-code FLUENT. The basis for the model is a swirl-based coalescer called Compact Tubular Coalescer (CTC), developed by Aker Process Systems AS.The validity of the model is evaluated before different aspects of the performance of the coalescer are studied. Several validation criteria were tested and were acceptable, but some weaknesses regarding lack of test cases were detected. The performance testing showed good performance of the CTC, it was able to increase the Sauter Mean Diameter (SMD) of the droplet with up to 250% for the smallest droplets (20 μm) and highest volume fractions (7%). Remarkable differences of the performance were observed as the physical properties were changed. Higher viscosity and droplet surface tension lead to increased coalescence rate and decreased break-up rate.Future work is recommended to concentrate on improving the present model and to investigate more aspects of the model. An effort should also be made to use a Eulerian approach to model the dispersed phase with the use of population balances, in order to be able to simulate flows with larger dispersed phase volume fractions.

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17

Li, Yaofa. "Experimental studies of Marangoni convection with buoyancy in simple and binary fluids." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53893.

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The flow in a layer of volatile fluid driven by a horizontal temperature gradient is a fundamental transport model for numerous evaporative passive cooling applications. When a thin film of a volatile liquid is subject to a horizontal temperature gradient, changes in the surface tension at the free surface lead to Marangoni stresses that drive the flow. In a thicker liquid layer, the flow is also affected by buoyancy. This thesis describes experimental studies of convection driven by a combined action of Marangoni stresses and buoyancy in simple and binary volatile liquid layers confined in a sealed rectangular cavity heated at one end and cooled at the other. Experiments with varying concentrations of noncondensables (i.e., air) ca were performed to investigate their effect on the phase change and heat and mass transport. In the simple liquid, thermocapillary stresses drive the liquid near the free surface away from the heated end. Varying ca is shown to strongly affect the stability of this buoyancy-thermocapillary flow for Marangoni numbers Ma = 290 - 3600 and dynamic Bond numbers BoD = 0.56 - 0.82: removing air suppresses transition to multicellular and unsteady flow. The results are compared with numerical simulations and linear stability analysis. In the binary liquid considered here, a methanol-water (MeOH-H2O) mixture, solutocapillary stresses drive the flow near the free surface towards the heated end. Four distinct flow regimes are identified for this complex flow driven by thermocapillarity, solutocapillarity, and buoyancy, and are summarized in a flow regime map as a function of ca and the liquid composition (MeOH concentration). At low ca, solutocapillary effects are strong enough to drive the liquid near the free surface towards the heated end over the entire liquid layer, suggesting that binary-fluid coolants could significantly reduce film dryout.

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18

Zhang, Zhongkui. "Modeling of Al evaporation and Marangoni flow in Electron Beam Button Melting of Ti-6Al-4V." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/43996.

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The Electron Beam Cold Hearth Remelting (EBCHR) process has emerged as a key process in producing high quality Ti-6Al-4V ingot and electrode as it is able to effectively consolidate both sponge and scrap material while removing undesired impurities and inclusions, such as Low Density Inclusions (LDIs) and High Density Inclusions (HDIs). However, the challenge of composition control arises in processing alloys such as Ti-6Al-4V where evaporative loss of elements with higher vapor pressure (Al in this case) cannot be ignored. Therefore, in order to cast a product of specified composition, a thorough understanding of the evaporation mechanism and melt flow conditions becomes crucial in process control and optimization. This research presents a comprehensive model of the melt pool produced during Electron Beam Button Melting (EBBM) which has been developed to serve as an intermediate step in the development of a comprehensive tool for analysis and optimization of the industrial EBCHR process. With proper geometry and boundary conditions, the EBBM model can be readily applied to an industrial EBCHR furnace to minimize costly experiments in optimizing process parameters. A thermal-fluid-compositional model has been developed that includes Al evaporation, thermal and compositional buoyancy, thermal and compositional Marangoni flow and flow attenuation in the mushy regime. Experiments on Ti-6Al-4V and CP titanium with a circular electron beam pattern were conducted in a laboratory scale EBBM furnace in order to study the evaporation process and fluid flow in the liquid pool. The data obtained from the experimental work was used to tune the thermal boundary conditions and validate the model predictions. The temperature, surface velocity, pool profile and concentration profile have been experimentally quantified and used for validation of the mathematical model.

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19

Tadrous, Ebram. "Experimental investigation of the transition of Marangoni convection around a stationary gas bubble towards turbulent flow." Universitätsverlag Chemnitz, 2020. https://monarch.qucosa.de/id/qucosa%3A74993.

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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

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20

McCallum, Marcus Anthony. "The simulation of wet steam flow in a turbine." Thesis, University of Strathclyde, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366697.

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21

Cao, Yang. "STUDY ON BUBBLE BEHAVIORS IN SUBCOOLED FLOW BOILING." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215532.

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22

Cowling, Neil Peter. "Thin film flow over a topography and non-isothermal droplets : a numerical study." Thesis, University of Leeds, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.551241.

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Research towards understanding continuous thin film flows and droplet spreading is as relevant today as it ever was. Theoretically, lubrication theory has played a pivotal role with the equations involved requiring numerical solution. The most commonly employed solvers are based upon either a time-splitting or multigrid strategy; no consensus has been reached as to which is the most accurate and efficient. With modern engineering applications demanding solutions at smaller and smaller scales, in turn requiring the use of finer grids to ensure mesh independent solutions, efficiency is a necessary consideration. The work of this thesis divides into two strands. First, a three-dimensional continuous film problem is modelled and formulated in two equivalent ways: as two coupled second-order equations, or as a single fourth-order equation. These are solved numerically by multigrid and time-splitting solvers, finding that, due to the larger time-steps which are possible, the multigrid scheme, when solving the coupled equations, offers the fastest route to converged solutions; the accuracy of solution for each solver is comparable. Following the use of static mesh adaptivity, the conclusions drawn for uniform meshes concerning the solvers are found to be equally valid on non-uniform meshes. Following that, a new model is proposed to investigate unpinned droplets evaporating from a thick, heated substrate into the surrounding atmosphere. A study of accuracy and efficiency is also conducted for a droplet spreading problem; it isfound that the multigrid scheme, when solving the coupled system of equations, is again the most efficient solver. This scheme is adapted for the evaporation model, leading to excellent qualitative and some quantitative agreement with previous studies of both the pinned and unpinned stages of evaporation. To the' author's knowledge, this is the first model to successfully capture the behaviour in both stages of evaporation and also the change in this behaviour depending upon the properties of the substrate and liquid considered.

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23

Beussman, Kevin Michael. "The Dynamics of Viscous Droplets near Micro-Patterned Solid Surfaces in Creeping Flow." Thesis, North Dakota State University, 2014. https://hdl.handle.net/10365/27322.

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The interaction between droplets and solid surfaces is of great importance in industrial applications, biochemical processes, and fundamental materials research on surface wettability. In this work, a three-dimensional spectral boundary element method has been employed to investigate the dynamics of a viscous droplet moving under gravity influence normal and parallel to a micro-patterned solid surface. The dynamics of the droplet moving perpendicular to the substrate are investigated under the influence of Bond number, droplet size, and topological features of the substrate. We find that the droplet dynamics can be controlled by varying Bond number, droplet size, and pattern height and width; however, the pattern length has little effect. For a droplet moving parallel to the surface, the Bond number and pattern projection direction greatly change the droplet dynamics. However, after moving past the pattern, the droplet position, velocity, and deformation return to that of a flat-plate solution.

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24

Drumright-Clarke, Mary Ann. "Numerical simulations that characterize the effects of surfactant on droplets in shear flow." Diss., Virginia Tech, 2002. http://hdl.handle.net/10919/26895.

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Numerical simulations utilizing the code SURFER++ with the incorporation of an insoluble surfactant in the VOF scheme were conducted to characterize the effects of surfactant on a drop in shear flow. The drop is suspended in a matrix liquid. A parameter called reduction, which specifically relates to a percentage decrease in effective surface tension, is used to measure the surfactant amount on the interface. In a model system where reduction = 0.1, viscosity ratio = 1 and density ratio = 1, it was found that stable drops tend to be more elongated and less inclined to the primary flow direction than drops unexposed to surfactant. This can be explained by the location of surfactant at the interface as the drop evolves. Breaking drops also show a flattened angle, but exhibit shorter necks and faster time to break than similar drops without surfactant. As reduction increases, various physical characteristics of the drops change across Reynolds number.
Ph. D.

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25

Zhao, Sicheng. "Interactive dynamics of fluid flow and metallic alloys solidification." Thesis, Aix-Marseille 3, 2011. http://www.theses.fr/2011AIX30010.

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Nous avons étudié les phénomènes convectifs et leur interaction dynamique avec la formation des microstructures pendant la solidification dirigée d’alliages étalliquesbinaires.La méthode post-mortem a été utilisée d’abord pour étudier la Transition olonnaire-Equiaxe pendant la solidification dirigée d’échantillons cylindriques d’Al-3,5wt%Ni non affiné sous la Technique de Rotation Accélérée de Creuset. La simulation numérique a été éffectuée et acquérie les résultats en concordance avec les manipulations.La technique in-situ a été appliquée pour comprendre l’évolution en fonction de temps des grains pendant solidification d’Al-4wt%Cu. La caractéstiques tatistiques des grains ont été discutées.La convection d’instabilité déclenchée par la poussée ou la tension superfaciale sous les gradients thermiques verticale et horizontale dans un système de double couches liquide-zone poreuse ont réspectivement étudié par analysis d’instabilité linéaire.L’inhomogénéité de la perméabilité de zone pateuse dendritique a été tenue en compte afin de comprendre son influence sur le début de convection pendant la solidification dirigée d’Al-3,5wt%Li
We studied the convective phenomena and their dynamical interaction with the formation of the microstructurs during directional solidification of binary metallic alloys.The post-mortem method was used first to study the Columnar-Equiaxed-Transition during the directional solidification of unrefined Al-3.5wt%Ni in cylindric samples under the Accelerated Crucible Rotation Technique. The numerical imulation was carried out and achieved the results in agreement with experiments.The in-situ technique was applied to understand the evolution of equiaxed grains during solidification of Al-4wt%Cu in function of time. The statistical characteristics of equiaxed grains were discussed.The buoyancy-driven and surface-tension-driven instability convection under vertical and horizontal thermal gradients in a liquid-porous double-layered system were respectively investigated through linear instability analysis.The inhomogeneity of the dendritic mush permeability was taken into account in order to understand its influence on the triggering of convection during the directional solidification of Al-3.5wt%Li

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26

Faletra, Melissa Kathleen. "Segregation of Particles of Variable Size and Density in Falling Suspension Droplets." ScholarWorks @ UVM, 2014. http://scholarworks.uvm.edu/graddis/265.

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The problem of the falling under gravity suspension droplet was examined for cases where the droplet contains particles with different densities and different sizes. Cases examined include droplets composed of uniform-size particles with two different densities, of uniform-density particles of two different sizes, and of a distribution of particles of different densities. The study was conducted using both simulations based on Oseenlet particle interactions and laboratory experiments. It is observed that when the particles in the suspension droplet have different sizes and densities, an interesting segregation phenomenon occurs in which lighter/smaller particles are transported downward with the droplet and preferentially leave the droplet by entering into the droplet tail, whereas heavier/larger particles remain for longer periods of time in the droplet. When computations are performed with two particle densities or two particle sizes, a point is eventually reached where all of the lighter/smaller particles have been ejected from the droplet, and the droplet continues to fall with only the heavier/larger particles. A simple model explaining three stages of this segregation process is presented.

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27

Mikkelsen, Alexander. "Experimental Studies of Flow- and Electric Properties of Oil Droplets Including Suspended Clay Particles." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-16798.

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Experiments on oil droplets made of silicone oil and sodium-fluorohectorite (Na-Fh) clay particles suspended in castor oil were performed. The electric field (E-field)-induced structuring of clay particles placed inside the droplet was studied using two optical microscopes with optical paths normal to one another. This configuration allowed for simultaneous observation of the droplet behavior from both a front view (optical path perpendicular to E-field lines) and a side view (optical path parallel to E-field lines). Prior to the application of the electric field, the Na-Fh particles were randomly dispersed inside and on the surface of the silicone oil droplet. The isotropic distribution in zero field was confirmed by adjusting the focus on the microscope and examining the intersection between the clay particles and focus plane. The application of direct current (DC) electric fields initiated clay particle movement inside the drop and the formation of a ribbon pattern consisting of short particle chains oriented parallel to the E-field direction. The ribbon formation rate displayed a linear E-field dependence and viscous flow inside the droplet seemed to govern the particle structuring. The viscous flow inside the drop was briefly studied together with the phenomenon of droplet rotation appearing at strong DC E-fields. The clay particles behaved differently when an alternating current (AC) E-field was applied. AC E-fields (with frequency equal to 200 Hz) produced chain patterns throughout the drop and parallel to the E-field direction. In both the AC and DC E-field, the particle alignment was time-dependent, and after the application of the E-fields, clay particles slowly spread out and clustered in the bottom of the drop. Settling experiments were also performed and revealed that the stress exerted by the surrounding castor oil on the settling silicone oil droplet was reduced by a factor approximately equal to 1.8 when 1 % Na-Fh clay particles were added. The stability and length of oil-water droplets with smectite clay particles formed in an oval microfuidic T-junction and by using the cross-flow shear method have also been studied. Clay particles were found to affect the length of the formed droplets when the flow rate ratio (dispersed phase flow rate/ continuous flow rate} were larger than 1, but large variations in droplet length and measurement errors make it difficult to conclude whether the effect is systematic or not. The variation in droplet length was generally observed to increase when clay particles were added to the continuous phase (dist. water) and when the flow rate ratio was increased. Surface tension measurements performed with the Du Noüy ring method revealed that the distilled water had some impurities that may have interacted with the clay particles. The pendant drop method was later used to perform surface tension measurement of pure dist. water with or without clays exposed to air or oil. Adding clay particles to the water did not change the surface tension considerably. However, droplet lengths measured at the end of the microfluidic chip showed that clay particles might need more time to affect droplet properties.

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28

WANG, AIHUA. "EFFECTS OF FREE SURFACE HEAT TRANSFER AND SHAPE ON THERMOCAPILLARY FLOW OF HIGH PANDTL NUMBER FLUIDS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=case1094682055.

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29

Ulrichs, Enno Sebastian. "Experimental investigations into the behavior and influence of water droplets in a compressor cascade flow." [S.l.] : [s.n.], 2007. http://deposit.ddb.de/cgi-bin/dokserv?idn=985090871.

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30

Selvi, İlker Doymaz Fuat. "Modeling of collection of non-spherical particle assemblies by liquid droplets under potential flow conditions/." [s.l.]: [s.n.], 2006. http://library.iyte.edu.tr/tezler/master/kimyamuh/T000553.pdf.

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31

Huo, Yunlong. "Finite element modeling of internal flow and stability of droplets levitated in electric and magnetic fields." Online access for everyone, 2005. http://www.dissertations.wsu.edu/Dissertations/Summer2005/y%5Fhuo%5F083005.pdf.

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32

Lim, Bryan Neo Beng. "Computational simulations of fuel/air mixture flow in the intake port of a SI engine." Thesis, University of Sheffield, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310769.

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33

Vantzos, Orestis. "Mathematical Modeling of Charged Liquid Droplets: Numerical Simulation and Stability Analysis." Thesis, University of North Texas, 2006. https://digital.library.unt.edu/ark:/67531/metadc5240/.

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The goal of this thesis is to study of the evolution of 3D electrically charged liquid droplets of fluid evolving under the influence of surface tension and electrostatic forces. In the first part of the thesis, an appropriate mathematical model of the problem is introduced and the linear stability analysis is developed by perturbing a sphere with spherical harmonics. In the second part, the numerical solution of the problem is described with the use of the boundary elements method (BEM) on an adaptive mesh of triangular elements. The numerical method is validated by comparison with exact solutions. Finally, various numerical results are presented. These include neck formation in droplets, the evolution of surfaces with holes, singularity formation on droplets with various symmetries and numerical evidence that oblate spheroids are unstable.

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34

Wan, Man Pun. "Indoor transport of human expiratory droplets in association with airborne infectious disease transmission using a multiphase-flow approach /." View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?MECH%202006%20WAN.

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35

Malik, Jennifer E. "Using Computational Modeling Techniques to Identify and Target Viable Drug Delivery Protocols to Treat Chronic Otitis Media." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1534780839820268.

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36

Mullins, Benjamin James, and n/a. "Study of Capture, Fibre Wetting and Flow Processes in Wet Filtration and Liquid Aerosol Filtration." Griffith University. School of Environmental Engineering, 2004. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20040919.124658.

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This thesis examines the particle capture, fibre wetting and droplet flow processes within wet filters collecting solid and liquid aerosols and within filters collecting only liquid aerosols. The processes involved in this type of filtration were examined through a series of experiments and models developed to describe the behaviour of fibre/liquid systems. This work can be summarized in 4 categories: (1) The bounce and immediate re-entrainment of liquid and solid monodisperse aerosols under a stable filtration regime (pre cake formation) by wet and dry fibrous filters. In this work it was found that the solid particles generally exhibited a lower fractional filtration efficiency than liquid particles (of the same size), although this difference decreased in the smaller size fractions. However, for the wet filtration regime (each fibre of the filter was coated by a film of water), no significant difference in filtration efficiency was detectable between solid and liquid aerosols. Either the bounce effect of the particles is inhibited by the liquid film, or the filtration conditions in the wet filter are so different that the aerosol properties are less significant with respect to capture. (2) A microscopic study of the effect of fibre orientation on the fibre wetting process and flow of liquid droplets along filter fibres when subjected to airflow and gravity forces was conducted. The flow of the liquid collected by the fibres was observed and measured using a specially developed micro-cell, detailed in the thesis. The experimental results were compared to a theoretical model developed to describe the flow of droplets on fibres. The theory and experimental results showed a good agreement. A sensitivity analysis of the model was performed which showed the droplet radius to be the most significant parameter. The model has the potential to improve filter self-cleaning and minimise water use. (3) An experimental study of the capture of solid and liquid (oil) aerosols on fibrous filters wetted with water. Variable quantities of liquid irrigation were used, and the possibility for subsequent fibre regeneration after clogging or drying was also studied. It was found that self-cleaning (removal of solid aerosols by water) occurred even under heavily dust-laden conditions, and post evaporation of water. With the collection of oil aerosols on fibres wetted with water, a predominance of the barrel shaped droplet on the fibre was observed, with oil droplets displacing water droplets (if the oil and fibre combination created a barrel shaped droplet), creating various compound droplets of oil and water not previously reported in literature. (4) An extensive experimental investigation of the wetting processes of fibre/liquid systems during air filtration (when drag and gravitational forces are acting) has shown many important features, including droplet extension, oscillatory motion, and detachment from fibres as airflow velocity increases. The droplet oscillation is believed to be induced by the onset of the transition from laminar to turbulent flow as droplet size increases. To model such oscillation it was necessary to create a new conceptual model to account for the forces both inducing and preventing such oscillation. The agreement between the model and experimental results is satisfactory for both the radial and transverse oscillations.

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37

Mullins, Benjamin James. "Study of Capture, Fibre Wetting and Flow Processes in Wet Filtration and Liquid Aerosol Filtration." Thesis, Griffith University, 2004. http://hdl.handle.net/10072/365591.

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This thesis examines the particle capture, fibre wetting and droplet flow processes within wet filters collecting solid and liquid aerosols and within filters collecting only liquid aerosols. The processes involved in this type of filtration were examined through a series of experiments and models developed to describe the behaviour of fibre/liquid systems. This work can be summarized in 4 categories: (1) The bounce and immediate re-entrainment of liquid and solid monodisperse aerosols under a stable filtration regime (pre cake formation) by wet and dry fibrous filters. In this work it was found that the solid particles generally exhibited a lower fractional filtration efficiency than liquid particles (of the same size), although this difference decreased in the smaller size fractions. However, for the wet filtration regime (each fibre of the filter was coated by a film of water), no significant difference in filtration efficiency was detectable between solid and liquid aerosols. Either the bounce effect of the particles is inhibited by the liquid film, or the filtration conditions in the wet filter are so different that the aerosol properties are less significant with respect to capture. (2) A microscopic study of the effect of fibre orientation on the fibre wetting process and flow of liquid droplets along filter fibres when subjected to airflow and gravity forces was conducted. The flow of the liquid collected by the fibres was observed and measured using a specially developed micro-cell, detailed in the thesis. The experimental results were compared to a theoretical model developed to describe the flow of droplets on fibres. The theory and experimental results showed a good agreement. A sensitivity analysis of the model was performed which showed the droplet radius to be the most significant parameter. The model has the potential to improve filter self-cleaning and minimise water use. (3) An experimental study of the capture of solid and liquid (oil) aerosols on fibrous filters wetted with water. Variable quantities of liquid irrigation were used, and the possibility for subsequent fibre regeneration after clogging or drying was also studied. It was found that self-cleaning (removal of solid aerosols by water) occurred even under heavily dust-laden conditions, and post evaporation of water. With the collection of oil aerosols on fibres wetted with water, a predominance of the barrel shaped droplet on the fibre was observed, with oil droplets displacing water droplets (if the oil and fibre combination created a barrel shaped droplet), creating various compound droplets of oil and water not previously reported in literature. (4) An extensive experimental investigation of the wetting processes of fibre/liquid systems during air filtration (when drag and gravitational forces are acting) has shown many important features, including droplet extension, oscillatory motion, and detachment from fibres as airflow velocity increases. The droplet oscillation is believed to be induced by the onset of the transition from laminar to turbulent flow as droplet size increases. To model such oscillation it was necessary to create a new conceptual model to account for the forces both inducing and preventing such oscillation. The agreement between the model and experimental results is satisfactory for both the radial and transverse oscillations.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environmental Engineering
Faculty of Environmental Sciences
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38

Cai, Yangjun. "Simple Alternative Patterning Techniques for Selective Protein Adsorption." University of Akron / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1257386752.

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39

Malý, Milan. "Internal Flow of Spill-Return Pressure-Swirl Atomizers." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-437981.

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Tlakové vířivé trysky (TVT) jsou používané v mnoha aplikacích, kde je potřebná velká plocha kapek nebo kde povrch musí být nanesen kapalinou, např. spalování, sprejové chlazení nebo nanášení barev. Parametry spreje z TVT jsou úzce spojené s jejich vnitřním prouděním. Obtokové trysky vylepšují koncepci klasických TVT přítomností otvoru, skrz který může kapalina odtékat zpět do nádrže. Díky této koncepci je možné regulovat vstřikovací množství kapaliny změnou průtoku tímto otvorem, zatímco se ve vířivé komůrce udržuje vysoký tlak, který zaručí dobrou kvalitu spreje. Obtokové trysky byly historicky málo prozkoumány a jejich vnitřní proudění nebylo studováno téměř vůbec. V této práci je popsáno vnitřní proudění několika obtokových trysek jak experimentálně, tak numericky. Tato data jsou následně korelována s měřenými vlastnostmi spreje. Výsledky ukazují, že přidání obtokového otvoru silně ovlivní vnitřní proudění i v případech, kdy obtokem neproudí žádná kapalina. V některých případech se vůbec nezformuje vzdušné jádro a tím se destabilizuje výtok z trysky, čímž vznikne nestabilní sprej. Mimoosé obtokové otvory generují a stabilizují vzdušné jádro, což pomáhá formovat kapalinovou stěnu a vysoce kvalitní sprej. Nicméně některé konfigurace změnily charakter rozpadu kapalinové stěny, což se projevilo i na kvalitě spreje. Navíc regulační schopnost a stabilita spreje závisí na vzdálenosti obtokových otvorů od osy vířivé komůrky. Na závěr byla upravena neviskózní teorie, která analyticky popisuje vnitřní proudění v TVT, tak aby byla aplikovatelná i na obtokové trysky. Pomocí tohoto přístupu byla odvozena teoretická predikce výtokového součinitele a velikosti vzdušného jádra v závislosti na obtokovém poměru (SFR). Zároveň byly pro obtokové trysky upraveny empirické korelace původně odvozené pro TVT. Tato práce přináší nový vhled k porozumění vnitřního proudění obtokových trysek a její výsledky najdou uplatnění při jejich návrhu.

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40

Tadrous, Ebram [Verfasser], Günter [Akademischer Betreuer] Wozniak, Günter [Gutachter] Wozniak, and Janusz A. [Gutachter] Szymczyk. "Experimental investigation of the transition of Marangoni convection around a stationary gas bubble towards turbulent flow / Ebram Tadrous ; Gutachter: Günter Wozniak, Janusz A. Szymczyk ; Betreuer: Günter Wozniak." Chemnitz : Universitätsverlag Chemnitz, 2021. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa2-749938.

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41

Jauseau, Nicolas. "Multiphase Flow Effects on Naphthenic Acid Corrosion of Carbon Steel." Ohio University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1354149810.

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42

Shen, Huanhuan. "Interferometric out-of-focus imaging and digital holography for the characterization of droplets or bubbles : theory, optical design, characterization of a flow, synchronized experiments." Rouen, 2014. http://www.theses.fr/2014ROUES015.

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Un simulateur original d'imagerie interférométrique en défaut de mise au point (ILIDS), permettant de modéliser n'importe quel système optique, est développé. Le formalisme de ce simulateur repose sur l'intégrale de Huygens-Fresnel généralisée. Le champ initial diffusé par des gouttes est simplifié par deux glare points. Un système original d'ILIDS, utilisant une configuration cylindrique, est conçu grâce au simulateur. Cette nouvelle configuration permet d'obtenir simultanément la position en trois dimensions et la taille des gouttelettes ou des bulles. Elle comprend une lentille cylindrique supplémentaire ayant un angle de rotation approprié autour de l'axe optique. Cette configuration anamorphique permet de lier l'orientation des franges d'interférence d'une part, et la forme de l'image en défaut de mise au point d'autre part, à la position axiale de la particule. Trois expériences sont réalisées successivement : l'observation de gouttes d'eau dans l'air, de bulles dans l'eau au sein d'un aquarium cubique et de bulles dans la glycérine située dans un canal cylindrique. Les comparaisons entre simulations et expériences montrent des résultats cohérents. Les précisions des positions axiales et des talles obtenus par la configuration cylindrique d'ILILDS sont évaluées expérimentalement. Les positions axiales sont validées par une comparaison avec leurs valeurs calibrées, tandis que les diamètres sont vérifiés grâce à une configuration couplée deux techniques: holographie numérique sur l'axe et configuration cylindrique d'ILIDS
An original simulator of Interferometric Laser Imaging for Droplet Sizing (ILIDS), allowing predicting the image patterns obtained by any imaging system, is developed. The formalism of the simulator relies on the generalized Huygens-Fresnel integral. The initial field scattered by the droplet is simplified by two glare points. An original ILIDS system is designed due to the simulator. The advantage of this configuration is that the three dimensional locations and sizes of droplets can be obtained simultaneously. The cylindrical ILIDS configuration includes a supplemental cylindrical lens rotated in a proper angle with respect to the axis of imaging system. The anamorphic configuration allows to change the orientation of the fringes and the form of the out-of-focus image with respect to the axial location of the particle. Three experiments are successively conducted: water droplets in air, bubbles in water at cubic aquarium and bubbles in glycerin at cylindrical channel. The comparisons of the simulations and experiments show good consistence. The precisions of the axial location and diameter obtained by cylindrical ILIDS technique are evaluated experimentally. The axial locations obtained by cylindrical ILIDS configuration are validated by comparing them with calibrated values, while the diameters are validated due a synchronized experiment coupling Digital In-Line Holography technique and cylindrical ILIDS technique

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43

Lee, Yousub. "Simulation of Laser Additive Manufacturing and its Applications." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1440360229.

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44

Qin, Tongran. "Buoyancy-thermocapillary convection of volatile fluids in confined and sealed geometries." Diss., Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/54939.

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Convection in a layer of fluid with a free surface due to a combination of thermocapillary stresses and buoyancy is a classic problem of fluid mechanics. It has attracted increasing attentions recently due to its relevance for two-phase cooling. Many of the modern thermal management technologies exploit the large latent heats associated with phase change at the interface of volatile liquids, allowing compact devices to handle very high heat fluxes. To enhance phase change, such cooling devices usually employ a sealed cavity from which almost all noncondensable gases, such as air, have been evacuated. Heating one end of the cavity, and cooling the other, establishes a horizontal temperature gradient that drives the flow of the coolant. Although such flows have been studied extensively at atmospheric conditions, our fundamental understanding of the heat and mass transport for volatile fluids at reduced pressures remains limited. A comprehensive and quantitative numerical model of two-phase buoyancy-thermocapillary convection of confined volatile fluids subject to a horizontal temperature gradient has been developed, implemented, and validated against experiments as a part of this thesis research. Unlike previous simplified models used in the field, this new model incorporates a complete description of the momentum, mass, and heat transport in both the liquid and the gas phase, as well as phase change across the entire liquid-gas interface. Numerical simulations were used to improve our fundamental understanding of the importance of various physical effects (buoyancy, thermocapillary stresses, wetting properties of the liquid, etc.) on confined two-phase flows. In particular, the effect of noncondensables (air) was investigated by varying their average concentration from that corresponding to ambient conditions to zero, in which case the gas phase becomes a pure vapor. It was found that the composition of the gas phase has a crucial impact on heat and mass transport as well as on the flow stability. A simplified theoretical description of the flow and its stability was developed and used to explain many features of the numerical solutions and experimental observations that were not well understood previously. In particular, an analytical solution for the base return flow in the liquid layer was extended to the gas phase, justifying the previous ad-hoc assumption of the linear interfacial temperature profile. Linear stability analysis of this two-layer solution was also performed. It was found that as the concentration of noncondensables decreases, the instability responsible for the emergence of a convective pattern is delayed, which is mainly due to the enhancement of phase change. Finally, a simplified transport model was developed for heat pipes with wicks or microchannels that gives a closed-form analytical prediction for the heat transfer coefficient and the optimal size of the pores of the wick (or the width of the microchannels).

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45

Maquet, Jean. "Contribution à l'étude des mécanismes de surstabilité d'une surface libre chauffée par un laser ou un fil chaud." Rouen, 1987. http://www.theses.fr/1987ROUES047.

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Simulation numérique de l'écoulement laminaire bidimensionnel créé par un fil chaud placé sous une surface libre. Le code de calcul inclut les convections naturelle et de Marangoni, les transferts de chaleur à l’interface ainsi que la viscosité interfaciale. Analyse linéaire de stabilité dans le cas d'une couche liquide horizontale d'extension infinie, limitée par une paroi rigide et une surface libre. Modélisation

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46

Hennessy, Matthew Gregory. "Mathematical problems relating to the fabrication of organic photovoltaic devices." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:7753abec-bb6e-4d8a-aa5b-b527c5beb49b.

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The photoactive component of a polymeric organic solar cell can be produced by drying a mixture consisting of a volatile solvent and non-volatile polymers. As the solvent evaporates, the polymers demix and self-assemble into microscale structures, the morphology of which plays a pivotal role in determining the efficiency of the resulting device. Thus, a detailed understanding of the physical mechanisms that drive and influence structure formation in evaporating solvent-polymer mixtures is of high scientific and industrial value. This thesis explores several problems that aim to produce novel insights into the dynamics of evaporating solvent-polymer mixtures. First, the role of compositional Marangoni instabilities in slowly evaporating binary mixtures is studied using the framework of linear stability theory. The analysis is non-trivial because evaporative mass loss naturally leads to a time-dependent base state. In the limit of slow evaporation compared to diffusion, a separation of time scales emerges in the linear stability problem, allowing asymptotic methods to be applied. In particular, an asymptotic solution to linear stability problems that have slowly evolving base states is derived. Using this solution, regions of parameter space where an oscillatory instability occurs are identified and used to formulate appropriate conditions for observing this phenomenon in future experiments. The second topic of this thesis is the use of multiphase fluid models to study the dynamics of evaporating solvent-polymer mixtures. A two-phase model is used to assess the role of compositional buoyancy and to examine the formation of a polymer-rich skin at the free surface. Then, a three-phase model is used to conduct a preliminary investigation of the link between evaporation and phase separation. Finally, this thesis explores the dynamics of a binary mixture that is confined between two horizontal walls using a diffusive phase-field model and its sharp-interface and thin-film approximations. We first determine the conditions under which a homogeneous mixture undergoes phase separation to form a metastable bilayer. We then present a novel mechanism for generating a repeating lateral sequence of alternating A-rich and B-rich domains from this bilayer.

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47

Belkhelfa, Yazid. "Etude du comportement dynamique et du transfert de matière et de chaleur entre des particules sphériques et un écoulement laminaire ou turbulent." Phd thesis, INSA de Rouen, 2008. http://tel.archives-ouvertes.fr/tel-00560879.

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A caractérisation de l'écoulement, du transfert de chaleur et de masse lors du déplacement de gouttelettes de diamètre inferieur au millimètre dans un milieu extérieur font l'objet de notre étude. La première partie présente l'état de l'art des connaissances théoriques et expérimentales des comportements aérodynamiques ainsi que les mécanismes de transfert thermiques et massiques intervenant entre une phase dispersée et une phase continue. La deuxième partie est consacrée à l'étude du phénomène d'évaporation d'une gouttelette mono-dispersée en chute libre dans l'air. Pour cela, nous avons réalisé un dispositif expérimental. Les mesures, nous permettent de prédire l'évaporation de la gouttelette en fonction des caractéristiques physico-chimiques et de l'hygrométrie du milieu extérieur. Pour la modélisation du transfert de chaleur et de masse nous avons utilisé un modèle simple qui tient en compte du couplage entre le mouvement et les phénomènes de transferts, validé dans une précédente étude au sein du laboratoire. Un bon accord est observé. La troisième partie traite de la simulation numérique de l'interaction entre les particules sphériques dans un régime laminaire. Tout d'abord, nous avons proposé et validé un modèle simple qui ne tient pas en compte des phénomènes d'interaction. Les résultats obtenus sont en concordance avec la littérature. Par la suite, nous avons étudié l'interaction entre trois particules identiques et co-alignées. Ce modèle tient compte de la nature de la particule, du nombre du Reynolds et de la distance de séparation. Nous avons validé ce travail par une comparaison avec une étude précédente que nous avons généralisé. La dernière partie est cernée sur l'étude de la dispersion des gouttelettes dans un écoulement turbulent homogène et isotrope. Pour cela, nous avons proposé un modèle Lagrangien de suivi des trajectoires. La production de la turbulence est assurée par une condition de turbulence de grille. Nous avons considéré que les caractéristiques moyennes de l'écoulement fluide sont connues. La sélection des fluctuations de vitesse turbulente est assurée par une méthode probabiliste gaussienne que nous avons développée. La fluctuation est conservée durant un certain temps lié à turbulence, elle est renouvelée au cours du calcul. Ce renouvellement est donné par le temps caractéristique de turbulence.

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48

Degonville, Maximilien. "Etude numérique de la dynamique sous écoulement de gouttes et vésicules avec viscosités de surface." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0751/document.

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De nombreux systèmes fluides dans les domaines de la biologie ou encore de la cosmétique sont limités par une interface dont les propriétés mécaniques régissent la stabilité. En particulier, les objets tels que des gouttes, vésicules ou polymersomes se déforment dans un écoulement simple et mènent à une grande richesse de dynamiques spatio-temporelles contrôlées par la nature des matériaux qui composent l'interface. Les travaux présentés concernent l'étude numérique de la déformation de ces objets dans un écoulement de Stokes, en particulier dans des situations où les viscosités de l'interface jouent un rôle important. Un code de calcul couplant intégrales de frontières et éléments finis a été utilisé afin de décrire la physique interfaciale et étudier leur comportement une fois plongés dans un écoulement. Ces travaux ont permis d'étudier l'influence des viscosités interfaciales sur la dynamique d'une goutte dans un écoulement extensionnel plan, leur influence sur sa dynamique de déformation et sur les conditions de rupture de celle-ci. Les études réalisées sur une vésicule fortement dégonflée et plongée dans un écoulement cisaillé ont caractérisé la bifurcation entre les deux familles de forme existantes dans ces conditions. Ces formes ayant une influence sur la dynamique de la vésicule dans l'écoulement, celle-ci a été étudiée dans le cadre d'un écoulement infini puis proche d'une paroi parallèle à l'écoulement. Enfin, de premiers résultats sur la dynamique d'un polymersome dans un écoulement cisaillé permettent de construire un diagramme de phase illustrant les différents comportement de cet objet en fonction de la viscosité de la membrane et du taux de cisaillement
There are many fluid systems in the biology, food industry, pharmacology or cosmestics fields that are bound by an interface which mechanical properties rule the system stability. Objects like droplets, vesicles or polymersomes change their shape in a simple flow which lead to a wealth of space and time dynamics. These properties are controlled by the nature of the interface material. The aim of this work is the numerical study of the deformation of droplets, vesicles and polymersomes in a Stokes flow, especially when the interfacial viscosities play an important role. A numerical computation code coupling boundary integrals and finite elements was used to describe the interfacial physics of these objects and study their behaviour when immerged in a flow. Multiple resolution strategies where developped to this end in order to optimize the numerical computation in the cas of an interface with viscosities.Using this work, the influence of interfacial viscosities on the dynamics of a droplet in an extensional flow is studied : in particular, their influence on the stretching dynamics of a droplet and its break up conditions was characterized. The study of a vesicle, droplet bounded by a lipid bilayer, strongly deflated and immerged in a shear flow detailed the bifurcation between two shape types existing for this system. These shapes have an influence on the vesicle dynamics under flow, which is studied for an unbounded flow and a near-wall flow. Finally, we show first results about the dynamics of a polymersome in a shear flow. We used them to build a phase diagram for the behaviour of this object depending on the membrane viscosity and the shear rate

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49

Bruyat, Anne. "Influence de l'évaporation de gouttes multicomposant sur la combustion et des effets diphasiques sur l'allumage d'un foyer aéronautique." Thesis, Toulouse, ISAE, 2012. http://www.theses.fr/2012ESAE0041/document.

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La conception de nouveaux moteurs impose de respecter des normes de sécurité concernant les performances d'allumage et de ré-allumage en conditions critiques. Des campagnes d'essais étant onéreuses, les industriels cherchent donc à disposer d'outils numériques ﬁables. Afin d'améliorer la simulation des écoulements, le caractère multicomposant du carburant doit être pris en compte. L'objectif de cette thèse est d'étudier l'influence de l'évaporation d'un brouillard de gouttes sur un écoulement réactif. Pour cela, une étude de la propagation d'une flamme laminaire 1D est réalisée à l'aide d'un code de calcul multiphysique (CEDRE). Un train continu de gouttes monodisperse est injecté, les gouttes étant mono ou bicomposant. L'influence de la dynamique d'évaporation sur la combustion est étudiée. Deux cinétiques chimiques réduites multicomposant sont comparées. La composition, le diamètre et la richesse initiale des gouttes ont un impact sur la structure de flamme, la vitesse de flamme et la composition des gaz brûlés. Ensuite, l'effet de l'évaporation est étudié en phase d'allumage pour un brouillard de gouttes polydisperses monocomposant avec un modèle de noyau d'allumage local. L’écoulement instationnaire non-réactif dans un secteur de chambre industriel (MERCATO) est calculé avec une approche LES. Le caractère instationnaire, voire périodique, de la phase dispersée est mis en évidence en certains points de l'écoulement. Les résultats, associés au modèle d'allumage et à des critères, sont utilisées pour réaliser une carte de probabilité d'allumage. Des essais de calcul d'allumage complet de la chambre sont réalisés. Les résultats indiquent une surestimation des termes sources liés à l'évaporation de la phase dispersée et à la combustion
The design of new aircraft engines needs in particular to comply with safety standards for the performance of stabilized combustion and ignition or re-ignition under critical conditions. Experimental campaigns are expensive, so numerical tools are needed. To improve the accuracy of the models used to simulate ﬂow, the multicomponent nature of the fuel must be taken into account, whether it is kerosene or alternative fuel. The objective of this thesis is to study the inﬂuence of a droplet mist vaporization on a reactive ﬂow. For this, an academic study of the propagation of a 1D laminar ﬂame is performed using a CFD code {CEDRE). A continuous stream of monodisperse droplets is injected, the droplets being mono or bicomponent. The influence of the dynamics of evaporation on combustion is particularly studied. Two reduced multicomponent chemical kinetics are compared. The composition, the diameter and the initial equivalent ratio of droplets have an impact on the structure of the ﬂame, the flame speed and composition of the burnt gases. A local ignition kernel model is applied to study the inﬂuence ofvaporization on ignition in the case of monocomponent, polydisperse droplets. Experimental data are available for a monosector combustion chamber (MERCATO) so the non-reactive unsteady flow is simulated with a LES approach. The unsteady, sometimes periodic, nature of the dispersed phase is highlighted in some points of the ﬂow. A ignition model is applied to instantaneous ﬂow ﬁelds and criteria are analysed to realise an ignition probability map which validates the approach. Finally, ignition of a combustion chamber is tested. The results point out an overestimation of source terms related to the evaporation of the dispersed phase and combustion

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50

Neiss, Coraline. "Modélisation et simulation de la dispersion turbulente et du dépôt de gouttes dans un canal horizontal." Thesis, Grenoble, 2013. http://www.theses.fr/2013GRENI093/document.

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Ce travail de thèse est consacré à l'étude des écoulements diphasiques dispersés turbulents gaz/gouttes et plus particulièrement à la modélisation du phénomène de dépôt de gouttes en canal horizontal, dont la compréhension et la prédiction sont essentielles pour de nombreuses applications industrielles. Les gouttes sont supposées de taille plus petite que les échelles de longueur caractéristiques de l'écoulement de gaz turbulent, avec une masse volumique grande devant celle de la phase continue, les forces qui agissent sur les gouttes se limitent ainsi à la traînée, à la poussée d'Archimède et à la gravité. Le taux de présence de la phase dispersée est suffisamment important pour tenir compte de l'influence des gouttes sur la turbulence du gaz (couplage à deux sens), mais suffisamment faible pour pouvoir négliger les collisions entre les gouttes. En écoulement horizontal, le dépôt des gouttes en paroi est piloté par deux mécanismes principaux qui agissent en parallèle : la gravité et la diffusion turbulente/vol libre. Cette physique du dépôt est déclinée en deux volets, avec une première étude à l'échelle 3D locale et une seconde étude à l'échelle système 1D. Dans chacune de ces approches, un modèle pour la vitesse de dépôt de gouttes en paroi est développé, puis validé par comparaison à des données expérimentales. Le modèle de dépôt local, établi sous l'hypothèse d'un film liquide infiniment mince et absorbant, est implanté dans le code de simulation numérique NEPTUNE_CFD, puis validé par comparaison aux données expérimentales de Namie & Ueda, qui étudient le dépôt des gouttes en canal horizontal. Une analyse des équations de transport des principales grandeurs moyennes de l'écoulement, ainsi que des transferts d'énergies entre phases, est menée afin de mettre en évidence les phénomènes de couplage et leurs influences sur la turbulence de la phase continue. Le modèle unidimensionnel, développé dans le cadre d'un besoin industriel, est implanté dans le code CATHARE-3 et est confronté aux données de l'expérience REGARD du CEA Grenoble
Droplets dispersion and deposition in turbulent duct flows are important processes, occurring in numerous environmental and industrial applications. This work is devoted to the study of gas-droplets flows and, more particularly, the objective is to improve the droplets deposition modeling in horizontal flows. Droplets are supposed to be smaller than the Kolmogorov scale, with a density large compared to the density of the gas phase. Under these assumptions, the motion of a droplet is considered to be governed by the drag force, the buoyancy force, and the gravity. Dilute incompressible and isothermal gas-droplets flows are studied, so inter-particle collisions are neglected but two-way coupling is retained, which means that modulation of turbulence by the particles is accounted for. In horizontal flow, droplets reach the wall under the actions of the gravitational settling and the turbulent diffusion. Two approaches will be used in developing this deposition physics with a first study at the 3D local scale and a second one at the 1D scale, realized for an industrial need. For each case, a model is developed for the mean deposition velocity of the droplets, with is implemented in a numerical simulation tool and then validated by comparison to experimental data. The local deposition model is established under the assumptions that the liquid film is extremely thin and perfectly absorbing and is implemented in the Neptune_CFD code. The experience carried out by Namie & Ueda, which consist in small droplets deposition from a turbulent dispersed flow in a horizontal rectangular duct, is simulated. An analysis of the interphase transfer terms in the kinetic energy equations shows the interactions between the dispersed phase and the continuous one and the impact of these phenomena on the turbulence of the gas phase is pointed out. The 1D deposition model is developed for the CATHARE-3 code and experimental data from the REGARD facility of the CEA Grenoble are used for validation

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Дисертації з теми "Marangoni Flow in Droplets"

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