Dissertations / Theses on the topic 'Coalescence'
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Martula, David Stefan. "Coalescence-induced coalescence in polymeric membrane formation /." Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004333.
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Thompson, Alice B. "Surface-tension-driven coalescence." Thesis, University of Nottingham, 2012. http://eprints.nottingham.ac.uk/12522/.
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When fluid droplets coalesce, the flow is initially controlled by a balance between surface tension and viscosity. For low viscosity fluids such as water, the viscous lengthscale is quickly reached, yielding a new balance between surface tension and inertia. Numerical and asymptotic calculations have shown that there is no simply connected solution for the coalescence of inviscid fluid drops surrounded by a void, as large amplitude capillary waves cause the free surface to pinch off. We analyse in detail a linearised version of this free boundary problem. For zero density surrounding fluid, we find asymptotic solutions to the leading order linear problem for small and large contact point displacement. In both cases, this requires the solution of a mixed type boundary value problem via complex variable methods. For the large displacement solution, we match this to a WKB analysis for capillary waves away from the contact point. The composite solution shows that the interface position becomes self intersecting for sufficiently large contact point displacement. We identify a distinguished density ratio for which flows in the coalescing drops and surrounding fluid are equally important in determining the interface shape. We find a large displacement solution to the leading order two-fluid problem with a multiple-scales analysis, using a spectral method to solve the leading order periodic oscillator problem for capillary waves. This is matched to a single-parameter inner problem, which we solve numerically to obtain the correct boundary conditions for the secularity equations. We find that the composite solution for the two-fluid problem is simply connected for arbitrarily large contact-point displacement, and so zero density surrounding fluid is a singular limit.
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Miller, James Thomas Ph D. Massachusetts Institute of Technology. "Crack coalescence in granite." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/47771.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2008.Includes bibliographical references.
This thesis experimentally investigates crack coalescence in prismatic Barre Granite specimens with two pre-cut, open flaws under uniaxial compression. Using a high-speed video system, crack initiation, propagation, and coalescence are observed. Flaw geometries are chosen to allow one to compare the results with those of studies in other materials as well as to better understand fracturing and coalescence processes. Specifically, the effect of ligament length (L), flaw inclination angle (p3), and bridging angle (a) on coalescence is investigated. The same crack types as in other materials are observed. Coalescence patterns observed fit into a previously developed framework (for molded gypsum and Carrara marble) with the exception of one new coalescence pattern. Crack processes and coalescence patterns suggest a more tensile behavior as grain size increases from gypsum to marble to granite. Similar to previous work in marble and granite, white patches are observed during compression tests. These white patches can be categorized as either diffuse or linear, with linear white patches further subdivided into two more types, namely boundary-following and through-going. The white patches are essentially process zones. The effect of water pressure on coalescence pattern is also investigated. Flaw water pressure is seen to affect coalescence in granite, although further work is needed.
by James Thomas Miller.
S.M.
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Tang, Shanyu. "Bubble charge and coalescence." Thesis, Imperial College London, 1995. http://hdl.handle.net/10044/1/59969.
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This thesis describes an experimental investigation of the interfacial electrical properties of bubbles in aqueous solutions and of their coalescence behaviour, which were studied using laser Doppler anemometry (LDA) and laser light reflection techniques. A double laser Doppler anemometer system was developed to measure the electrophoretic mobilities for single bubbles, generated electrolytically at a Pt microelectrode in aqueous solutions, across which electric fields were subsequently applied using two horizontal electrodes. The effects of solution composition on the interfacial electrical properties of bubbles were then investigated by measurement of the natural rise rates (v) of bubbles and those (v^) in applied electric fields (£). In principle, the derived electrophoretic mobilities, defined by (vg - v)IE, may be related to the effective surface potentials and apparent adsorbed electric charge densities on the bubbles. However, classical theory cannot be used to effect such transformations, nor could it be assumed that the mobilities would correlate with coalescence behaviour of bubbles, as would be the case for solid particles with fixed charge sites. For electrolytes carefully purified of adventitious surfactants by purging with swarms of bubbles over a few hours, bubble electrophoretic mobilities showed a clear pH dependence, with an apparent iso-electric point at about pH 2, indicating that OIT ions were preferentially adsorbed at gas/liquid interfaces. Also, their (negative) mobilities increased with increasing bubble diameter, in the experimentally accessible range of 60 - 100 |im. The behaviour of bubbles in such clean electrolytes did not obey predictions of classical theory, as their gas/liquid interfaces were mobile, unlike that of solid/liquid interfaces, for which the interfacial velocity is zero. However, adsorption of surfactants rigidifies bubble interfaces, so that with a complete monolayer adsorbed, they behave as solid particles. Bubble rise rates and their electrophoretic velocities were sensitive to the adsorption of adventitious surfactants from the laboratory atmosphere. Electrophoretic mobilities of oxygen bubbles in surfactant-free sodium perchlorate aqueous solutions increased with the applied electric field. Experimental results and calculations based on the theory of Brandon et al. indicated that, in surfactant-free electrolyte solutions, the electric field was primarily responsible for polarisation of the adsorbed charge, rather than the hydrodynamic effects resulting from the bubble rise rate. A simple model was presented to describe the polarisation of charge distribution on bubble surfaces in electrolyte solution with the electric field parallel to the bubble rise vector. The initial surface charge density on oxygen bubbles generated in ICT* M surfactant-free NaCl04 solution was estimated to be - 17.4 |xC m'^, which compares favourably with the value of - 9.8 |iC m"^ derived from the diameter dependence of bubble electrophoretic mobilities. The LDA technique was extended to determine the coalescence times of individual bubbles as they approached a planar air/water interface. These results showed no dependence of coalescence times on the pH of surfactant-free electrolytes, as the electrostatic repulsion between the two interfaces as they approached, presumably caused the very small pH-dependent charge to move out of the zone of maximum interaction. However, addition of ionic surfactants caused coalescence times to increase, due to electrostatic repulsion between the partially rigidified surfaces. A laser reflection technique was developed to measure the time dependence of the thickness of the liquid film formed as a bubble approaches a planar gas / aqueous solution interface. Preliminary results indicated that the technique is suitable for studying film thinning, in that the apparent coalescence times were comparable to those derived from the LDA technique, although further refinement of the experiments is needed.
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Wadhwa, Navish. "Non-coalescence of Jets." Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/42636.
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Contrary to common intuition, free jets of fluid can ``bounce'' off each other on collision in mid-air, through the effect of a lubricating air film that separates the jets. While there has been much work on coalescing jets of fluid and non-coalescence in other systems like drop-drop, drop on a bath, jet on a bath, non-coalescence of fluid jets has been little studied. A simple experimental setup was developed to stably demonstrate and study the non-coalescence of jets upon collision. This thesis presents the results of an experimental investigation of oblique collision between two fluid jets. The transition from bouncing to coalescence of jets is examined for various jet sizes and angles. Results indicate that the transition from bouncing to coalescence can be rationalized in terms of critical value of the dimensionless parameter Normal Weber Number, which represents the ratio between inertial and surface tension forces. A parametric study of the characteristic of bouncing jets, conducted by varying the nozzle diameter, jet velocity, angle of inclination and fluid viscosity reveals the scaling laws for the quantities involved such as contact time. These scaling laws help us in elucidating the role of various physical forces at play such as viscous stresses, capillary force and inertiaMaster of Science
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Basdevant, Anne-Laure. "Trois études sur la fragmentation et la coalescence stochastiques." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2006. http://tel.archives-ouvertes.fr/tel-00117403.
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Nous étudions certains processus de fragmentation qui sont liés à des processus de coalescence. Nous nous intéressons en premier lieu au coalescent de Bolthausen et Sznitman qui, retourné dans le temps, devient un processus de fragmentation inhomogène en temps. Nous décrivons alors sa mesure de dislocation instantanée en fonction de lois de Poisson-Dirichlet et en déduisons des asymptotiques sur la taille des blocs en temps grands et petits. Nous étudions aussi une classe de coalescents additifs après retournement de temps en tant que processus de fragmentation. Nous montrons alors que les lois de tous ces coalescents additifs sont absolument continues les unes par rapport aux autres et nous explicitons cette densité. Enfin, nous caractérisons la loi des fragmentations d'intervalle en la mettant en bijection avec les fragmentations de partitions ordonnées.
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Zaborsky, Jiri. "Coalescence dans les écoulements laminaires : étude de drainage et de l'efficacité de coalescence." Grenoble INPG, 1998. http://www.theses.fr/1998INPG0067.
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Le coefficient d'efficacite de coalescence est determine a l'aide d'une methode semi-globale pour plusieurs dispersions liquide/eau. L'ecoulement de taylor d'une dispersion liquide/liquide entre deux cylindres coaxiaux est modelise numeriquement en utilisant l'equation convection - diffusion. L'interet est porte essentiellement sur la solution asymptotique de concentration des gouttes dans l'anneau de taylor. Un modele est aussi developpe pour determiner l'evolution du diametre de sauter moyen d'une dispersion liquide/liquide. Son elaboration a ete achevee experimentalement a l'aide d'une methode d'attenuation lumineuse : la valeur du coefficient de l'efficacite de coalescence a ete determinee par comparaison de l'evolution du diametre de sauter moyen obtenue theoriquement avec celle obtenue experimentalement. Il est montre que le coefficient de l'efficacite de coalescence peut varier dans un large intervalle. Des mesures sur la vitesse limite d'une particule liquide dans l'eau sont egalement effectuees afin d'estimer l'importance des surfactants sur l'evolution du diametre de sauter moyen. L'etude s'acheve par le drainage du film entre une particule de fluide et l'interface libre. L'interet a ete porte sur la determination du profil initial du film. Ceci est resolu de facon tres general pour un nombre de bond et une epaisseur de film quelconque, en respectant la condition de l'ecoulement rampant dans le film. Le temps de drainage d'une particule fluide avec l'interface libre en fonction de son diametre est obtenu experimentalement.
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Galvin, Kevin Patrick. "Growth and coalescence in condensation." Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/46310.
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Shaw, Andrew. "Coalescence of two liquid volumes." Thesis, University of Birmingham, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.422787.
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Munro, James. "Coalescence of bubbles and drops." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/288543.
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When two fluid drops come close enough together to touch, surface tension quickly pulls the drops together into one larger drop. This is an example of a singular fluid flow, as the topology of the interface changes at the moment of contact. Similarly, when a pair of bubbles touch, the surface topology changes and a singular flow begins. Since the stress from surface tension depends on the surface curvature, these singularities are often characterised by divergent fluid velocities. Experimental observation or numerical simulation of these flows is therefore difficult due to the high velocities and small lengthscales. In this thesis, I will find multi-scale theoretical solutions for the singular flows during the initial stages of the coalescence of bubbles and drops, solving for the velocity field in the fluid and the rate of coalescence. Each solution has several lengthscales, and on each lengthscale, we must solve some form of the Navier--Stokes equations. I will employ a variety of analytical and numerical techniques to solve for the flow on each scale. These asymptotic solutions are valid at early times; future numerical simulations of the subsequent flow could be initialised with these solutions, rather than the actual singularity. In the course of solving for these singular flows, I will also describe the solution for the motion of a stretched fluid edge, the retraction of a narrow fluid wedge, the capillary flow around a parabola, and the effect of a time-dependent force on a fluid half-space. These fundamental flows have applications outside of coalescence, which I will outline throughout the thesis.
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Martinez, Ariel R. (Ariel Ruy) 1972. "Fracture coalescence in natural rocks." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/79986.
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DOBLER, FRANCIS. "Mecanismes de coalescence des latex." Université Louis Pasteur (Strasbourg) (1971-2008), 1991. http://www.theses.fr/1991STR13048.
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Les mecanismes de coalescence des latex donnes dans la litterature sont discutes. Cette etude bibliographique identifie les parametres des latex determinant les conditions de coalescence. Ils ont conduit a la definition de latex modeles pour l'etude du mecanisme de coalescence. Ces latex sont de morphologie core-shell. Le cur est un copolymere p(styrene/acrtylate de butyle). L'ecorce est un copolymere de p(st/abu/acide methacrylique). Son taux d'ama determine la tension interfaciale particule/eau. Un mode de synthese par inversion core-shell a ete developpe pour produire ces latex. Les particules de latex sont caracterisees par la repartition de l'ama, leur tension interfaciale avec l'eau, l'adsorption de sds et a partir des proprietes mecaniques des films formes par coalescence. Une methode d'etude de la coalescence en phase aqueuse a ete developpee. Elle permet de suivre les cinetiques de coalescence des particules sous l'action de la seule tension interfaciale particule/eau. La coalescence dans les conditions standards, c'est-a-dire avec evaporation de l'eau a ete caracterisee. On montre qu'aux temperatures (t) et humidites relatives limites (hr) de formation de film, la coalescence est assuree par des forces specifiquement liees a l'evaporation de l'eau. Le mecanisme propose reprend la description proposee par sheetz. Au-dessus des conditions de t et hr limites, la tension interfaciale particule/eau peut devenir une contribution importante. L'influence de la vitesse d'evaporation de l'eau sur la capacite a former un film par coalescence a ete discutee
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Bossa, Benjamin. "Fragmentation et coalescence dans les fluides." Phd thesis, Université de Provence - Aix-Marseille I, 2007. http://tel.archives-ouvertes.fr/tel-00259235.
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La déstabilisation et la fragmentation de systèmes liquides en couches minces se rencontrent fréquemment dans la nature, ainsi que dans des contextes industriels. Cette éude expérimentale entreprend de décrire, comprendre et prévoir les mécanismes des instabilités et de formation des fragments liquides.Une première étude concerne la brisure d'une fine bandelette liquide chutant librement dans une cellule de Hele-Shaw. Les lignes de contact mobiles introduisent des pressions différentes au niveau des interfaces et établissent un gradient de pression dans le fluide, favorisant ainsi sa déstabilisation. Une analyse de stabilité linéaire prédit correctement les taux de croissance et montre l'existence d'un plateau sur la relation de dispersion.
Une seconde étude analyse la déformation et la brisure d'une goutte liquide au sein d'un jet gazeux. Nous montrons que la d´eformation se produit à partir d'un certain nombre de Weber critique et nous proposons un modèle sur la formation et le gonflement du sac qui s'en suit, également appelé bag-breakup.
Une troisième étude concerne l'impact d'une goutte sur un solide de taille comparable. Nous montrons que la goutte se déorme pour former une nappe liquide entouré d'un bourrelet. Nous montrons que l'extension de la nappe déend du nombre de Weber contrairement à sa dynamique. Nous proposons également un modèle qui prédit correctement la taille de la nappe ainsi que la taille des fragments obtenus.
Une quatrième étude est dédiée au phénomène de vieillissement des mousses. Nous exposons un nouveau dispositif expérimental de soufflerie à mousse. Nous donnons une comparaison entre les systèmes expérimentaux classiques et notre dispositif. Nous montrant également une preuve expérimentale de la loi de von Neumann.
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Pagett, Steven. "Fragmentation-coalescence processes : theory and applications." Thesis, University of Bath, 2017. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.715297.
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The main objects of study in this thesis are fragmentation-coalescence processes, where particles are grouped into clusters and evolve by either joining together, to form larger clusters, or splitting apart, to form smaller clusters. The focus is on the number of these clusters and the distribution of their sizes. In particular, we show for a certain class of processes defined on a finite system that there is convergence in the thermodynamic limit to an infinite system. For a second class of processes we show there is a phase transition between regimes where the number of clusters has an entrance law from ∞ or not.
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Vengadasalam, Kirijen. "Computational modelling of coalescence filtration process." Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/17323/.
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The low water-diesel interfacial tensions arising in biodiesels pose a problem for fuel filters designed to separate water contamination from diesel fuel. Such filters operate by passing the fuel through a fibrous non-woven material with the aim of capturing small water droplets on the fibres and holding them while further droplets coalesce with the captured droplets until the droplets are large enough to be carried away from the fibres and subsequently settle out of the fuel by gravity. The coalescence process is however less effective at lower interfacial tensions. The main purpose of this research is to explore the mechanisms at work in a coalescence filter by developing and applying computer simulations of the process, and to understand the effects of fibre properties such as wettability, size and separation on the filtration performance. Following a detailed review of the relevant literature, a macroscopic simulation of the flow within a filter housing is first presented, using finite element analysis via COMSOL Multiphysics to establish the main flow patterns through the filter system. The filter medium itself in this model is treated as a continuous porous medium. The flow at the pore/fibre scale is then analysed by means of a multiphase lattice Boltzmann method based on the multicomponent Shan-Chen model. The wettability of the fibres is incorporated through specification of a fluid density at the solid surfaces, allowing easy control of the local contact angle. The code developed is tested against previously published and validated finite volume/volume-of-fluid simulations of free droplet coalescence, with good agreement seen in the predicted dynamics. The interactions between individual water droplets and fibres is explored, in particular to establish critical conditions (flow speed, fibre contact angle, droplet/fibre size, droplet-fibre separation, fuel viscosity etc.) under which droplets carried by the flow can be captured by fibres, and the conditions under which droplets are released from fibres. The results confirm the difficulties in achieving rapid and effective coalescence when the interfacial tension is low, and reveal the sensitivity of the droplet-fibre dynamics to the contact angle on the fibres and the relative size of the droplets and fibres. In particular larger fibres are not effective for small droplets, so small fibres are essential in the filtration process. Also investigated are the dynamics of multiple droplets with arrays of fibres representing the filtration media. It is found that higher contact angles ( > 120°) lead to lower capture efficiency compared to lower contact angle, while contact angles less than 106° tend to produce a small variation in capture efficiency and capture most of the droplets at a filter porosity of 0.87. It is concluded that the inlet layer of the filter should have fibres with 78° contact angle and the exit layer fibres with contact angle 106°.
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Andan, Saravanan. "Modeling of Drainage in Coalescence Filtration." University of Akron / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=akron1268145371.
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Zhang, Hong Carleton University Dissertation Engineering Mechanical. "Fatigue crack growth and coalescence study." Ottawa, 1993.
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Forel, Emilie. "Mûrissement et coalescence de mousses liquides." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS431/document.
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Les mousses sont des matériaux très largement utilisés dans l'industrie par exemple dans l'agroalimentaire ou la cosmétique. Ce sont des matériaux instables qui vieillissent au cours du temps à cause du mûrissement dû à la diffusion du gaz entre les bulles, de la coalescence qui est la fusion de deux bulles après rupture du film les séparant et du drainage dû à l'écoulement de liquide entre les bulles par gravité. Ces trois processus sont en compétition dans les mousses. Au cours de ma thèse, j'ai réalisé différentes expériences dans le but d'éliminer le drainage et d'étudier le mûrissement, la coalescence et la compétition entre les deux. Après un rappel sur la structure, le vieillissement des mousses et la description du dispositif expérimentale que j'ai mis au point pour contrôler la quantité de liquide dans la mousse, je me suis intéressée au mûrissement et à la coalescence de mousses 2D horizontales. J'ai montré tout d'abord grâce à l'analyse d'image qu'il est possible de différencier les mousses évoluant principalement par mûrissement de celles évoluant par coalescence en introduisant un paramètre de convexité sur les bulles composant la mousse. Les mousses ayant mûri sont alors utilisées pour étudier l'impact de l'humidité des mousses sur la perméabilité des films. La perméabilité est calculée à l'aide d'une nouvelle théorie prenant en compte l'humidité de la mousse. Les mousses qui coalescent, quant à elles, sont utilisées pour étudier l'impact de la fraction liquide, de la pression capillaire et de la taille des bulles sur la coalescence dans les mousses 2D. Cette étude permet de montrer qu'une analyse de ces paramètres à l'échelle de la mousse n'est pas suffisante pour conclure sur leur réel impact sur la coalescence et qu'il est nécessaire d'analyser ces paramètres à l'échelle de la bulle afin de différencier leurs effets. Pour ce faire, j'ai mis au point un programme qui permet d'isoler chaque évènement de coalescence. Ainsi, il existe une fraction liquide critique à partir de laquelle il n'y a plus de coalescence car les films entre les bulles n'existent plus. A 3D, j'ai commencé par établir un lien entre les fractions liquides surface et volumique donnant une nouvelle manière de de mesurer la fraction liquide volumique à partir d'une image de la surface. Ensuite, j'ai étudié le mûrissement de mousses humides 3D. Un des buts était de mettre en évidence la transition entre le régime sec où le rayon moyen croit comme le temps avec un exposant β =1/2 et le régime très humide où β = 1/3. J'ai réalisé des expériences de diffusion multiple de la lumière, sur des mousses confinées et trouvé de valeurs de β voisine de 1/2. Néanmoins, la mesure β dans les mousses très humides n'a pas été possible. Pour parer à cela, le projet "Soft Matter Dynamics" vise à étudier le mûrissement et le réarrangement des bulles dans les mousses humides en microgravité dans la station spatiale internationales (ISS). Mon implication dans ce projet a consisté à réaliser des protocoles de remplissage et de nettoyage de cellules en collaboration avec Airbus, à créer un programme d'automatisation de la mesure de la taille des bulles et à participer à une campagne de test du système de génération des moussesFoams are materials widely used in the industry, like in food industry or cosmetics industry for example. These are unstable materials that age over time by coarsening which is gas diffusion between bubbles, by coalescence which is the fusion of two bubbles after rupture of the film between them or by drainage which is the liquid flow between the bubbles due to gravity. These three processes are in competition in foams. During my thesis, I carried out various experiments in order to eliminate drainage and study coarsening, coalescence and the competition between them. After a quick reminder on foam structure and aging and a description of the experimental set-up that I made allowing to control the liquid content of the foam, I present coarsening and coalescence experiments of horizontal 2D foams. First, I show that it is possible to differentiate foams which evolved mainly by coarsening from those which evolved by coalescence. This is done using a convexity parameter that compares the convexity of the bubbles in the foams. The foams which coarsen are then used to study the impact of foam humidity on the films permeability. The permeability is calculated with the help of a new theory which takes into account the humidity of the foam. The coalescing foams are used to study the impact of the liquid fraction, the capillary pressure and the bubbles' size on coalescence in 2D foams. This study shows that an analysis of these parameters at the scale of the foam does not allow to conclude on their real impact on coalescence and that it is necessary to analyze these parameters at the scale of each bubble in order to differentiate their effects. To this end, I have developed a program that follow-up these bubbles and which isolate each event of coalescence. There is a critical liquid fraction above which there is no more coalescence because the films between the bubbles no longer exist. In 3D, I began by establishing link between surface and volume liquid fractions giving a new method to measure the volume liquid fraction from an image of the surface. Then, I studied coarsening of 3D wet foams. One of the goals was to show the transition between the dry regime where le mean radius increase with time as a power law, with an exponent β in the dry regime β =1/2 and the very wet regime where β = 1/3. I carried out multiple light scattering experiments on confined foams and found the values of $eta$ to be near $1/2. Nevertheless, the measurement of β in very wet foams wasn't possible. To counter this, the "Soft Matter Dynamics" project aims to study the coarsening and bubbles' rearrangement of wet foams in microgravity in the international space station (ISS). My involvement in this project consisted in the realisation of cell filling and cleaning protocols in collaboration with Airbus, the creation of a program for the automatisation of the bubbles' size measurement and the participation in a test campaign on the foam generation system
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Rajaram, Sridhar. "Quantitative image analysis and polymer blend coalescence." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1996. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ45460.pdf.
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Stoyel, Jason Alexander. "Fundamentals of drop coalescence in crude oil." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312176.
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Jayarajah, James Nirmal. "Coalescence and filtration of emulsions using fibres." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343600.
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Wang, Yong-Zhi. "Stress corrosion crack coalescence and lifetime prediction." Thesis, University of Newcastle Upon Tyne, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315623.
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Corral, Manuel Jr. "Controlling drop coalescence using nano-engineered surfaces." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/68830.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 46).
The dynamics of drop coalescence are explored on micro-scale surface features for the first time. Drop coalescence is defined as a process by which two or more droplets, bubbles or particles merge during contact to form a single droplet, bubble or particle. There are two regimes that limit the dynamics of drop coalescence of a liquid. The first is regime is limited by the viscosity of the droplets. The second regime is limited by inertial forces caused by the motion that merges the two droplets. Currently, much work has been done to study drop coalescence in a liquid-liquid environment and the phenomenon has been well defined and modeled. Previous work has been done to understand liquid-liquid drop coalescence using liquids with varying viscosity, but the effects of solid micro-textured surfaces on drop coalescence dynamics of low density liquids, such as water, have not yet been analyzed and quantified. Very little has been studied about drop coalescence in a solid-liquid-air interface. In this thesis, drop coalescence in its inertial regime will be defined in low viscosity liquid, water, on surfaces with varying wettability and micro-scale features. Surfaces include microstructures consisting of a regular array of square posts defined by the aspect ratio of the posts and the spacing between the posts. This work focuses on the development of a fundamental understanding and physical model of micro-scale surface texture effects on drop coalescence to provide aid in future surface design applications. These applications could allow for the controlling of this phenomenon to promote drop-wise condensation in order to increase efficiencies of condensers or to aid in water-oil separation procedures.
by Manuel Corral Jr.
S.B.
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Deminière, Bénédicte. "Destruction des émulsions concentrées par coalescence activée." Bordeaux 1, 1997. http://www.theses.fr/1997BOR10592.
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Les emulsions concentrees sont des systemes metastables qui ont une duree de vie finie. Ces materiaux ont une structure analogue a celle des mousses (on les nomme parfois mousses biliquides). Les applications de ces materiaux sont nombreuses : industrie des peintures, routieres, papetiere, pharmacologique, alimentaire, cosmetique, etc. La metastabilite associee a ces materiaux souleve deux questions fondamentales : i) comment caracteriser la metastabilite des interfaces (probabilite de coalescence d'un film de surface unite) et ii) comment les evenements de coalescence se distribuent dans le materiau pour transformer sa granulometrie jusqu'a la separation de phases macroscopique. Nous etudions la destruction d'emulsions concentrees par coalescence activee. Ces emulsions sont stabilisees par des tensioactifs non ioniques (hlb 10), tels qu'une augmentation de la temperature a pour effet immediat de declencher une transition de phases au sein de la phase continue des emulsions et conduit a l'apparition d'une nouvelle emulsion monodisperse. Nous observons ensuite un scenario de croissance remarquablement homogene, qui s'accelere dans le temps. Nous l'interpretons par un modele champ moyen a un parametre : la frequence de coalescence par unite de surface. Nous en deduisons les parametres associes a la metastabilite des films : l'energie d'activation et la frequence propre de coalescence. Nous etablissons le lien entre ces parametres microscopiques et la duree de vie du materiau. Finalement, nous identifions les variables qui permettent de basculer vers des croissances de type heterogene ou par amas.
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Wang, Ningyu. "Melting, Solidification and Sintering/Coalescence of Nanoparticles." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1284476300.
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Monin, David. "Drainage et coalescence des mousses de savon." Bordeaux 1, 1999. http://www.theses.fr/1999BOR10551.
Full textAbstract:
Les mousses de savon sont des materiaux cellulaires metastables, dont l'evolution est mal comprise. Ce travail aborde les deux aspects du vieillissement des mousses : le drainage du liquide qu'elle contient et la destruction de sa structure. Un dispositif experimental a ete elabore pour mesurer continument la fraction liquide d'une mousse d'une part et sa rupture d'autre part. Le drainage de l'eau contenue dans une mousse qui ne casse pas est controle par deux parametres microscopiques : viscosite de volume et viscosite de surface des monocouches. Il suit une loi universelle. Les ecarts a cette loi universelle caracterisent la rupture de la mousse. Ces ecarts ont ete analyses et modelises. Ils mettent en evidence deux mecanismes de rupture. Dans certains cas, on observe un front de rupture associe a une transition de phase entre deux etats des films qui constituent la mousse. Dans les autres cas, les evenements de rupture sont repartis de facon aleatoire en temps et en espace, amenant une rupture homogene du materiau. Les mecanismes microscopiques de rupture des films demeurent obscurs. Toutefois, l'importance de l'elasticite de surface des monocouches a pu etre demontree. De plus, les parametres physico-chimiques ne suffisent pas a decrire la rupture de la mousse. Des contraintes mecaniques interviennent et laissent au murissement d'ostwald le temps d'intervenir.
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Boucard, Laure. "Déstabilisation des émulsions de bitume et évaluation du comportement à l'interface huile/eau." Thesis, Nantes, 2016. http://www.theses.fr/2016NANT4054/document.
Full textAbstract:
La compréhension des phénomènes physico-chimiques intervenant dans le processus de déstabilisation des émulsions est fondamentale pour prédire le comportement au jeune âge des mélanges à l’émulsion de bitume. Ce travail de thèse vise à identifier les différents mécanismes et à déterminer les paramètres influant sur la stabilité d’émulsions directes concentrées dans des conditions de non séchage. Afin d’étudier la rupture des émulsions, des systèmes modèles et réels ont été formulés avec différentes huiles (bitume, huiles de silicone et d’hexadécane) et différents tensioactifs cationiques (sel d’ammonium quaternaire et diamine). Pour simuler les phénomènes (relargage d’espèces ioniques en solution avec ou sans remontée de pH) intervenant lors de la mise en contact des émulsions avec les granulats, différentes solutions électrolytiques (NaOH, NaCl et KBr) ont été utilisées pour les déstabiliser. Le comportement des systèmes a été étudié en cours de déstabilisation. Des méthodologies et des outils ont été mis en place et ont permis de classer les émulsions selon leur processus et cinétiques de déstabilisation en réalisant des observations macroscopiques, microscopiques et en utilisant la rhéologie (plus particulièrement l’évolution de l’angle de phase du liant). Ces travaux ont permis d’identifier les mécanismes (floculation, coalescence et percolation) intervenant dans le processus de déstabilisation et de déterminer les paramètres influant tels que la concentration en électrolyte, la température et la composition du bitume. Enfin l’action des fractions cristallisables et des acides naphténiques du bitume sur la déstabilisation des émulsions a été établie et discutéeUnderstanding the physical-chemical phenomena occurring in the emulsion breaking process is fundamental to predict the behavior of bitumen emulsion cold mixtures at fresh state. This work aims to identify the different mechanisms involved, and determine the parameters influencing the stability of concentrated oilin- water emulsions without drying. To study the emulsion breaking, models and real systems have been formulated with different oils (bitumen, silicone and hexadecane oils) and different cationic surfactants (quaternary ammonium salt and diamine). In order to simulate the phenomena (release of ionic species in solution with or without pH rising) occurring when the emulsion is put into contact with the aggregates, different electrolyte solutions (NaOH, NaCl and KBr) were used as destabilizing agent. The emulsions behavior was monitored throughout the destabilization using specifically developed methodologies and tools. Emulsions have been ranked in function of their destabilization kinetics and process by performing macroscopic and microscopic observations and by using rheology (especially by following the phase angle evolution of the binder). This work has permitted mechanisms identification (flocculation, coalescence and percolation) involved in the destabilization process and to determine the main factors influencing it such as electrolyte concentration, temperature and bitumen composition. Finally, the impact on the emulsion destabilization of the crystallized fractions and naphthenic acids of bitumen was demonstrated and discussed
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Hagesæther, Lars. "Coalescence and Break-Up of Drops and Bubbles." Doctoral thesis, Norwegian University of Science and Technology, Department of Chemical Engineering, 2002. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-2148.
Full textAbstract:
Fluid particle break-up and coalescence are important phenomena in a number of industrial processes.
A Lagrangian momentum balance model for the collision process between two fluid particles has been developed and tested favorably against experimental data. It is based on an earlier model developed in our department. Oscillations were introduced and the volume balances that are solved avoid earlier approximations. Film drainage was also implemented into the model based on a literature review given. It is believed this approach will lead to a more fundamental modeling of the coalescence process.
An improved break-up model has been developed. It is an extension of earlier work at the department and it introduces an additional criterion for break-up. This criterion gives a lower limit for the daughter fragment sizes in binary break-up, thus also limiting the break-up of smaller fluid particles, and is a more consistent model than the earlier one.
Two break-up models, original model by Luo (1993) and improved model, and a coalescence model have been implemented in a population balance as algebraic sink and source terms. This population balance is in turn included in an in-house CFD-code. The models have been tested against experimental data from a bubble column in our laboratory, and the improved break-up model compares favorably with the experimentally obtained accumulated mass distribution. Too few bubbles are predicted in the lower population classes, but it is shown that this may as well be a result of the coalescence model used as the improved break-up model.
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Vold, Truls Chr. "Droplet breakup and coalescence in compact wellstream seperation." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for kjemisk prosessteknologi, 2000. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-2323.
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Jones, Matthew Kenneth. "Multiscale Analysis of Void Coalescence in Ductile Metals." MSSTATE, 2004. http://sun.library.msstate.edu/ETD-db/theses/available/etd-11112004-165827/.
Full textAbstract:
A mulitscale approach is used to model the coalescence of voids. At the microscale, cylindrical and spherical voids in nickel and the magnesium alloy AM60 are simulated through finite element analyses. The nickel cylindrical void simulations are compared to a set of experiments to validate this micromechanical finite element approach used to study void coalescence. At the macroscale, the coalescence portion of a microstructure-property material model is modified to reflect the behavior of three-dimensional spherical voids using results from the micromechanical simulations. An analysis of an automotive component illustrates the influence of void coalescence at the structural scale.
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Thomson, Ronald D. "Ductile fracture by void nucleation, growth and coalescence." Thesis, University of Glasgow, 1985. http://theses.gla.ac.uk/6487/.
Full textAbstract:
Plastic deformation in ductile metals is limited by a mechanism in which voids, nucleated at second phase particles, grow and coalesce to form a crack. The results of a finite element solution for spherical elastic inclusions in a plastically deforming matrix are discussed. These results have been used in conjunction with experimental work using notched tensile specimens to generate multiaxial states of stress from which the local conditions leading to decohesion of the inclusion/matrix interface were determined. An important feature of these results is the statistical distribution of the interfacial strength. This distribution is bimodal, showing the presence of both weakly and strongly bonded particles. The latter have a modal strength of about 7 times the initial yield stress and the weakly bonded particles are assumed to be pre-existent. Experiments in plane and axisymmetric states of strain indicate that while the stress state is of relevance, the remote strain state is not. The absence of a macroscopic strain state effect is explained in terms of the statistical distribution of the voids nucleated from the population of randomly distributed inclusions. The stress and strain concentrations possible in local patches of high porosity have been investigated by a finite element approach based on the mechanics of a dilating continuum to determine void growth in the porous aggregate and the local conditions at failure. This investigation recognises the importance of the local hardening rate of the aggregate material and leads naturally to the idea of a size scale for failure, in the light of which the concept of a crack-like defect is re-examined.
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Wong, Ngai Yuen. "Crack coalescence in molded gypsum and Carrara marble." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/42927.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2008.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references.
This thesis investigates the fracturing and coalescence behavior in prismatic laboratory molded gypsum and Carrara marble specimens, which consist of either one or two preexisting open flaws, under uniaxial compression. In previous experimental studies, the determination of crack types (shear/tensile) was mainly based on the identification of fractographical features on the crack surfaces. In the present study, a high speed video system was used, which allowed one to precisely observe the cracking mechanisms.Seven crack types, which were characterized by different nature (shear/tensile) and orientations were identified to initiate from the pre-existing flaws in gypsum and marble in the present experimental study. Nine crack coalescence categories with different crack types and trajectories were also identified. The flaw inclination angle (beta), the ligament length (L), i.e. intact rock length between the flaws, and the bridging angle (a), i.e. the inclination of a line linking up the inner flaw tips, between two flaws, have all shown to have different effects on the coalescence patterns. Comparing the fracturing and coalescence behaviors in the two tested materials, tensile fracturing generally occurs more often in marble than in gypsum for the same flaw pair geometries.One of the pronounced differences observed between marble and gypsum during the compression loading test was the development of macroscopic white patches prior to the initiation of macroscopic cracks in marble, but not in gypsum. With the use of the scanning electron microprobe (SEM) and the environmental scanning electron microprobe (ESEM) techniques, the development of white patches and their evolution into macroscopic tensile cracks in marble, and the initiation of hair-line tensile cracks and their evolution into macroscopic cracks in gypsum were studied and compared.
(cont.) The SEM study identified that the white patches in marble were associated withnmicrocracking zones (process zones). The parallel ESEM study on gypsum showed that the extent of process zone development associated with macroscopic tensile cracking wasnless. The different extents of process zone development, related to the inherent material strength and textural properties, are hypothesized to be the key factors in leading to different macroscopic fracturing behavior in gypsum and marble.
by Ngai Yuen Wong.
Ph.D.
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Betton, Eleanor Susanne. "Impact and coalescence of ink-jet printed drops." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610068.
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Segretain, Laurent. "Cristallisation, fonction luminosité et coalescence des naines blanches." Lyon 1, 1994. http://www.theses.fr/1994LYO10355.
Full textAbstract:
L'observation de la fonction luminosite des naines blanches permet d'obtenir l'age du disque galactique a partir de modeles theoriques. Les modeles actuels predisent un age de l'ordre de 9 gyr, alors que d'autres methodes donnent 13 a 15 gyr (amas globulaires par exemple). Le but de la premiere partie de ma these est de prendre en compte le phenomene de sedimentation des elements lors de la cristallisation du cur des naines blanches, ce phenomene n'etant pas pris en compte dans les modeles actuels. Je montre que la prise en compte de ce phenomene conduit a un age du disque galactique de 11 a 12 milliards d'annees, ce qui resoud le paradoxe precedent. Dans la seconde partie de la these j'etudie la coalescence de systemes binaires de naines blanches afin de caracteriser l'objet resultant et de savoir si ce phenomene explique l'origine de certaines naines blanches chaudes, massives et isolees. Pour cela j'ai developpe un code lagrangien (sph: smooth particules hydrodynamic) a trois dimensions incluant la gravitation. Je montre que la coalescence peut expliquer l'origine de ces naines blanches, sous certaines conditions: perte de moment angulaire, source d'energie supplementaire, accretion d'une couche hydrogene apres la coalescence
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Stora, Thierry. "Coalescence des émulsions : phénoménologie et étude de cinétiques." Bordeaux 1, 1995. http://www.theses.fr/1995BOR10639.
Full textAbstract:
La coalescence des emulsions est etudiee d'un point de vue phenomenologique. La coalescence d'emulsions directes, monodisperses, concentrees, stabilisees par des tensio-actifs non-ioniques, est induite par la temperature. A basse temperature, la coalescence procede par la croissance de quelques grosses gouttes. Un seuil de temperature est etabli au-dessus duquel la coalescence est rapide (quelques minutes) et conduit a l'apparition d'une nouvelle population de gouttes monodisperses plus grosses. Le seuil de temperature et la taille de saturation dependent de la taille initiale des gouttes, de la fraction volumique d'huile et de la concentration de tensio-actif. Les cinetiques de coalescence ont ete etudiees par diffusion statique de la lumiere. Au-dessus du seuil, il apparait un anneau de diffusion correspondant a l'apparition de la nouvelle population. L'intensite du pic en fonction du temps suit une loi monoexponentielle. Le temps caracteristique ainsi mesure permet de determiner, moyennant le choix d'un chemin reactionnel, l'energie d'activation controlant la rupture des films de tensio-actifs qui separent les gouttes d'emulsions. L'energie d'activation depend lineairement de la pression dans les films (pression de disjonction). Cette loi conduit a la definition d'une pression de disjonction critique pour laquelle l'energie d'activation est nulle. De plus, les seuils de coalescence definis precedemment correspondent a des seuils de pression de disjonction, qui sont abaisses quand la temperature est augmentee. Enfin, aux temperatures les plus elevees, le tensio-actif devient insoluble dans l'eau, et les microdomaines destabilisent les films separant les gouttes par un mecanisme de pontage
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Hunt, William E. "Breakup and coalescence in turbulent two-phase flows." Thesis, Virginia Tech, 1995. http://hdl.handle.net/10919/40633.
Full textAbstract:
Many engineering processes involve a gas and a liquid or two immiscible liquids in
turbulent flow. The turbulent flows present in two-phase systems will cause the bubbles
or drops of a dispersion to undergo breakup and coalescence, and the resulting changes in
the dispersion may significantly affect the engineering process under consideration. For
this reason, many researchers have studied breakup and coalescence in turbulent two phase
flows. Models that can be used to simulate changes in a dispersion over time have
been proposed, but these models contain constants that change with experimental
conditions and empirical equations that can only be considered valid for certain
experimental setups. The goal of this study was to develop general models that could be
used to predict changes in bubble or drop size distributions over time for turbulent flows
in agitated vessels and pipes.
Computer programs were written to reproduce the results of three agitated vessel
studies. These programs used existing population balance models to approximate the
changes in a dispersion over time measured in previous experiments. A new model for
breakup in agitated vessels was then developed and verified with existing experimental
data. A new model for coalescence in agitated vessels was also developed and verified
with existing experimental data. Both of these models are based on theory and are more
readily extendible than previous breakup and coalescence models. The work for agitated
vessels was then extended to turbulent two-phase pipe flow. Since there was only a
limited amount of experimental data available for breakup and coalescence in pipes, the
model for turbulent pipe flow could not be verified.
Master of Science
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Pangu, Gautam D. "ACOUSTICALLY AIDED COALESCENCE OF DROPLETS IN AQUEOUS EMULSIONS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=case1138379076.
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Pays, Karl. "Les émulsions doubles : coalescence et mûrissement de composition." Bordeaux 1, 2000. http://www.theses.fr/2000BOR10591.
Full textAbstract:
Les emulsions doubles eau/huile/eau sont des dispersions de globules huileux dans lesquels ont ete prealablement dispersees des gouttes d'eau. Ces systemes presentent un interet technologique puisqu'ils offrent la possibilite d'encapsuler des especes hydrophiles dans les gouttes d'eau internes et de controler leur vitesse de liberation. Sur le plan scientifique, ces materiaux sont des modeles pour l'etude de la metastabilite des emulsions. La liberation d'une espece encapsulee resulte de deux mecanismes limites : un mecanisme par coalescence qui implique la rupture d'un film liquide et un mecanisme par murissement de composition resultant de phenomenes de permeation et/ou diffusion. Nous avons trouve des conditions experimentales telles que la liberation est gouvernee uniquement par la coalescence des gouttes internes sur les surfaces des globules. On a pu ainsi etudier ce mecanisme de facon precise et en deduire sans ambiguite les parametres microscopiques impliques dans la rupture des films liquides (energie d'activation et frequence propre de nucleation). Nous avons ensuite etudie la liberation par murissement de composition. Le murissement a ete decrit par un modele phenomenologique simple qui nous a permis d'identifier des leviers pour controler la fuite. Finalement, nous avons fabrique des emulsions doubles, stabilisees par des polymeres amphiphiles, permettant d'encapsuler durablement des especes chimiques.
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Aryafar, Hamarz. "Coalescence of liquid drops at liquid-liquid interfaces." Diss., Restricted to subscribing institutions, 2008. http://proquest.umi.com/pqdweb?did=1666392591&sid=9&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Plouchart, Diane. "Experimental coalescence of microbial communities in anaerobic digesters." Thesis, Montpellier, SupAgro, 2018. http://www.theses.fr/2018NSAM0009/document.
Full textAbstract:
La digestion anaérobie est un procédé biologique effectué par un réseau complexe et synergique de communautés microbiennes permettant la dégradation de matière organiques comme les déchets agricoles ou les effluents de station d’épuration en biogaz, un gaz valorisable en énergie. Les mécanismes influençant les communautés microbiennes au cœur de ce procédé mais aussi dans la nature restent incompris du fait de la faible compréhension de leur dynamique. Les objectifs de ce projet visent à donc développer un système de digestion anaérobie permettant de mieux comprendre la dynamique de l’assemblage des communautés microbiennes. Ainsi un nouveau procédé de réacteurs en continu dont les fonctions d’alimentation de soutirage et de dégazage sont automatisées a été développé. L’automatisation et le multiplexage des réacteurs permettent la manipulation de 30 réacteurs en continu en parallèle. Outre l’automatisation ce système, de nombreux paramètres sont flexibles comme le taux de charge (une fois par minute jusqu’à une condition batch), le volume de réacteur (50 à 200mL), la température (pièce – 55°C), mais aussi l’utilisation du système en aérobie ou l’implémentation d’autres outils comme des LEDs pour les cultures phototrophes. Capable de quantifier précisément la performance d’un écosystème méthanogène, ce système nous a permis de tester la structure et la performance d’écosystèmes méthanogènes mis en mélanges et testés de façon individuelle. En mélangeant des écosystèmes méthanogènes différents, la diversité des Archées a augmenté transitoirement. Une corrélation est d’ailleurs observée entre la diversité de ces communautés mélangées et leur performance méthanogène, seulement à même diversité les communautés individuelles ont un meilleur fonctionnement. L’assemblage de certaines communautés mélangées a pourtant permis une meilleure production de méthane que les communautés individuelles, ce qui suggère le développement d’interactions spécifiques de ces communautés. De façon nouvelle par rapport à la littérature, la majorité des communautés bactériennes individuelles sont retrouvées dans les communautés mélangées. Soit contrairement à l’idée d’une sélection d’une communauté plus adaptée ou plus fonctionnelle, ici la majorité des communautés se sont implantées. Ces expériences suggèrent qu’un paramètre tel que la fonctionnalité d’un bioprocédé peut-être amélioré par bioaugmentationAnaerobic digestion is a biological process carried out by a complex and synergistic network of microbial communities allowing the degradation of organic matter such as agricultural waste or effluents from wastewater treatment plants, into biogas, a gas recoverable into energy. The mechanisms influencing microbial communities at the heart of this process but also in nature remain misunderstood because of a low understanding of their dynamics. The objectives of this project are therefore to develop an anaerobic digestion system to better understand the dynamics of microbial community assembly. Thus, a new continuous reactor process has been developed with automated feeding, biomass wasting and degassing functions. Automation and multiplexing of reactors allows for the continuous parallel manipulation of 30 reactors in parallel. In addition to the automation, many parameters are versatile, such as the substrate loading (once a minute up to batch conditions), the reactor volume (50 to 200 mL), the temperature (room to 55°C), but also the use of the aerobic system or the implementation of other tools such as LEDs for phototrophic cultures. Capable of accurately quantifying the performance of a methanogenic ecosystem, this system has enabled us to test the structure and the performance of five different methanogenic ecosystems that have been mixed and tested individually. By mixing different methanogenic ecosystems the Archaea diversity has increased transiently. Besides, a correlation is observed between the diversity of mixed communities and their methanogenic performance; yet the individual communities have a better functioning at the same level of diversity. Interestingly, the mixture of some communities has allowed for better methane production than individual communities, suggesting the development of specific interactions in these communities. In a novel way compared to the literature and that the majority of individual bacterial communities are found in mixed communities. Contrary to the idea of selecting a more adapted or functional community, here the majority of communities have settled. These experiments suggest that a parameter such as the functionality of a bioprocess can be improved by bioaugmentation
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Gianotti, Daniel. "Fluid Drop Coalescence in a Hele-Shaw Cell." Scholarship @ Claremont, 2003. https://scholarship.claremont.edu/hmc_theses/147.
Full textAbstract:
A fluid drop in a Hele-Shaw cell moves due to surface tension driven potential flow. Using equations for the pressure and the Green’s function for the Laplace Equation, we can formulate an integral equation that determines the motion of the boundary of the drop. By discretizing the boundary contour and following the motion of boundary nodes, the time evolution of the drop can be determined from initial conditions. Results of a numerical simulation show the movement of a drop relaxing from coalescence and the motion of a drop undergoing electrowetting.
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Dib, Jawhar Marie-Claire. "Study of the Coalescence Mechanisms during Silicone Foaming." Thesis, Lyon 1, 2012. http://www.theses.fr/2012LYO10051.
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Le principe d’élaboration des mousses de silicone est basé sur une compétition entre deux réactions mettant en jeu les fonctions hydrogénosilane portées par le polymère précurseur : la première provoque le dégagement d’un gaz (à l’origine de la formation des cellules) et la deuxième, l’hydrosilylation, bien connue et maîtrisée dans les silicones, conduit à la réticulation du milieu réactionnel. De ce fait, le contrôle des propriétés finales de la mousse nécessite la maîtrise de ces deux cinétiques de synthèse du gaz et de réticulation. D’autre part, les propriétés finales des mousses (type de porosité, densité apparente,…) dépendent également de la rhéologie (propriétés élongationnelles adéquates) ainsi que des charges ajoutées à la formulation. L’étude de la nucléation et la croissance cellulaire a été faite sous microscope optique. Les résultats montrent que le phénomène fondamental contrôlant la croissance des bulles est la coalescence. Sous l’influence couplée des effets de surface et viscoélastiques, les bulles se rapprochent et se déforment pour donner naissance à une forme intermédiaire avant d’atteindre leur forme finale. D’autre part, on a montré que l’air initialement dissous dans les formulations ainsi que l’air introduit par agitation permettent de réduire l’effet de peau, d’avoir une distribution de taille homogène et une meilleure structure cellulaire. D'autres facteurs ont également été étudiés dans le but de rendre la distribution de taille plus homogène et améliorer certaines propriétésA foam sample is assumed to be a set of bubbles embedded into a polymeric matrix with an initial gas overpressure. Silicon foams are produced by a competition between two reactions involving the hydrogenosilane functions carried by the polymer precursor: the first reaction generates gas (initiating cell formation) while the other one, hydrosilylation, well known and controlled in silicon, leads to the crosslinking of the rising foam. Thus, obtaining enhanced foam properties requires a good balance between two reactions, crosslinking and gas generation. On the other hand, the final characteristics of the foam (porosity, bulk density…) largely depend on the rheology of the mix (appropriate elongational properties) as well as the added fillers. Nucleation and cell growth were carried out under optical microscopy. The experiments show that the main phenomenon controlling cell growth is bubble coalescence. Due to the surface effects and the viscoelastic properties, bubbles approach from each other and get deformed giving birth to an intermediate shape before reaching their final geometry. Many parameters have direct effect on foam properties. In fact, dissolved gas in formulas as well as the air introduced during manual mixing, reduce the skin effect and guarantee a homogeneous cell size distribution and a better foam structure. Other factors have also been studied in order to render size distribution more homogeneous and improve certain properties
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Ferrari, Chiara. "Analyse multi-longueur d'onde d'amas de galaxies en coalescence." Phd thesis, Université de Nice Sophia-Antipolis, 2003. http://tel.archives-ouvertes.fr/tel-00010416.
Full textAbstract:
Le scénario hiérarchique de formation des structures prévoit que les amas de galaxies se forment par l'accrétion et la coalescence
successives de
sous-structures moins massives.
Je présente notre programme d'observations couplées en optique,
en X et en radio sur un échantillon commun d'amas de galaxies
morphologiquement complexes, susceptibles de receler différents stades du
processus de coalescence ("MUSIC: MUlti-wavelength Sample of Interacting
Clusters"), visant à caractériser la formation et l'évolution de ces
objets. L'analyse multi-longueur d'onde est essentielle pour comprendre ces
systèmes complexes, l'évolution de la distribution de leurs galaxies (via
l'optique), de leur gaz (par l'intermédiaire des observations en X) et de
leur composante non-thermique (i.e. particules relativistes et champs
magnétiques observables aux longueurs d'onde radio).
Dans la première partie de cette thèse, les connaissances
actuelles sur la physique des amas de galaxies en cours de fusion sont
présentées par la comparaison entre les principaux résultats
observationnels et les prévisions des simulations numériques.
\noindent Le programme "MUSIC", les observations effectuées et les
techniques de traitement et analyse des données sont détaillées dans la
deuxième partie. En accord avec les scénario hiérarchique de formation
des structures, les résultats sur les premiers amas de notre échantillon
montrent qu'il s'agit de systèmes en train de se former par un processus de
coalescence entre sous-structures. Ces amas couvrent la séquence de
coalescence à partir de la phase de pré-fusion (A1750), aux phases
centrales de la collision entre sous-structures (A3921 et A521), jusqu'à la
phase de post-fusion avancée (A1413). La structure à grande échelle des
amas en coalescence, et les effets du processus de fusion aussi bien sur la
dynamique de ces systèmes que sur leurs galaxies sont discutés en
détails dans cette deuxième partie et dans les articles inclus.
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Incerti, Véronique. "Coalescence de gouttes dans l'air : du millimètre au nanomètre." Phd thesis, Toulouse, INPT, 2017. http://oatao.univ-toulouse.fr/19664/7/ChireuxIncerti_19664.pdf.
Full textAbstract:
La coalescence intervient dans de nombreuses situations physiques, naturelles ou industrielles, de la microphysique des nuages à la stabilité des émulsions ou l’assèchement des pétroles. Dans toutes ces situations, il est crucial de comprendre les mécanismes physiques en jeu, de manière pouvoir influencer la coalescence, la favoriser ou au contraire l’inhiber, selon les besoins. Dans cette thèse, nous étudions la coalescence dans l’air entre deux gouttes attachées et décomposons le processus global en quatre étapes : l’approche avec drainage du film d’air entre les gouttes, le perçage des interfaces, l’ouverture du pont résultant de ce perçage, les oscillations amorties conduisant à l’équilibre de la goutte résultante. Les théories décrivant les étapes 1, 2 et 4 font intervenir des modèles hydrodynamiques continus, se plaçant à une échelle macroscopique. Cependant, à l’articulation entre les deux premières étapes, intervient le perçage des interfaces, processus gouverné par des forces dont la portée correspond à une échelle de quelques dizaines de nanomètres. Une des difficultés les plus importantes dans l’étude de la coalescence est celle de l’intégration des processus ayant lieu à un niveau moléculaire, dans une théorie du continuum dont l’échelle caractéristique est bien supérieure. L’objectif est de faire le lien entre les différentes échelles : y a-t-il des interactions entre les processus se produisant à ces différentes échelles ? Pour répondre à cette question, nous développons trois axes de travail, engageant chacun une échelle caractéristique. L’un est l’étude, au niveau macroscopique du micromètre, de l’ouverture du pont liquide. Grâce à une caméra rapide, plusieurs régimes d’écoulement sont mis en évidence. Les modèles théoriques existants concernent essentiellement le régime visqueux, et aucun modèle complet ne décrit le régime purement inertiel. Nous explorons expérimentalement ce régime et décrivons la forme et la longueur du pont, à l’aide d’ondes capillaires. Nous mettons en évidence l’existence de deux lignes de très forte courbure, que nous appelons singularités, qui naissent sur le lieu de perçage des interfaces et se propagent presque sans déformation de part et d’autre. Ces singularités, conditionnées par la tension superficielle, moteur de la coalescence, façonnent la forme du pont liquide et donc l’écoulement dans ce dernier. Nous proposons un modèle simple d’écoulement inertiel, basé sur la forme du pont liée à ces singularités. Ce modèle permet de mieux comprendre les rôles des forces hydrodynamiques et de la courbure dans l’évolution temporelle de la largeur du pont. Un autre axe est une étude expérimentale par Microscope à Force Atomique, qui permet de décrire les forces responsables de la coalescence à l’échelle nanométrique, les déformations des gouttes intervenant à cette échelle et leur rôle dans la rupture des interfaces. Les mesures de forces entre goutte et flaque, puis entre deux gouttes sont effectuées avec un AFM principalement en mode dynamique de Modulation de Fréquence. Elles permettent de mettre en évidence une distance seuil de déclenchement de l’instabilité hydrodynamique responsable de la coalescence et de mesurer cette distance en fonction des propriétés physiques du liquide et du rayon des gouttes. Un diagramme de coalescence est proposé, qui permet de prévoir la valeur de la distance de déclenchement de la coalescence et le rôle des déformations d’interfaces à l’échelle nanométrique. Enfin, les oscillations du pont liquide, générées par la coalescence, sont étudiées, les modes et fréquences propres sont calculés numériquement par la méthode des éléments finis, puis comparés aux valeurs expérimentales mesurées à partir des films acquis par caméra rapide.
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Eow, John Son. "Electrostatic enhancement of coalescence of water drops in oil." Thesis, University of Surrey, 2002. http://epubs.surrey.ac.uk/842815/.
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Dispersed water drops in oils can cause detrimental effects. For example in refining and cracking of crude oil, poisoning of catalysts and equipment corrosion can be major problems due to the presence of water. Therefore there is a need to develop more efficient and cost-effective separators. The work in this thesis covers an investigation of the underlying electrostatic phenomena (i.e. drop-drop and drop-interface coalescence and drop deformation and break-up) leading to the development of compact electrocoalescer-separators. Using novel two-dimensional electrode systems, it is shown here that coalescence readily occurs when the electric field is applied in the same direction as the line joining the centres of the two drops, in line with the previous theoretical prediction of the maximum attractive force induced in this way. An adaptive Finite Element Method, incorporating automatic error and mesh generator programmes, has been used to quantify the electric-induced forces of charged spheres in an insulating medium, for short distances that are much smaller than the drop radius, where analytical solutions are no longer reliable. Moreover, drop-drop attraction can also occur when the angle is 125.3° from the electric field direction. Previous work suggests that pulsed d.c. fields are effective for low-aqueous-content systems, and this has been further investigated here. The applied electric field and pulse frequency can be optimised to achieve the highest coalescence rate. High electric fields (> 3.5 kV/cm) are shown to deform and break up aqueous drops when the electric field-induced stresses overcome the interfacial tension. A critical electrostatic Weber number, corresponding to the onset of drop break-up, has been evaluated to be about 0.49 for several aqueous-oil systems. For the separation of dispersed aqueous drops from an oil phase, it is advantageous to incorporate an aqueous layer to induce drop-interface coalescence. A suitably applied electric field is shown to give efficient drop-interface coalescence. The above investigations have led to the design and development of two compact electrocoalescer-separators. The first separator combines the effects of electrocoalescence and gravitational settling. The second separator, which utilises the electrocoalescence and centrifugal effects, can handle larger throughputs with reasonable separation efficiency. Both devices significantly enhance the separation and are good examples of how the fundamental understanding gained in this studies can be applied to realistic practical situations.
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Bayley, Christopher J. "Parametric investigation on the coalescence of coplanar fatigue cracks." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ26986.pdf.
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Wu, Keng-Tung. "Bubble coalescence from multiple entry nozzles in fluidized beds." Thesis, University College London (University of London), 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286488.
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O'Keeffe, Niall. "Fluid-driven fractures in elastic hydrogels : propagation and coalescence." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/287633.
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In this thesis we focus on a novel experimental exploration of fluid-driven fractures in a brittle hydrogel matrix. Fluid-driven fracturing is a procedure by which a fracture is initiated and propagates due to pressure applied by a fluid introduced inside the fracture. We describe how to construct the experimental setup utilised in this research, including how to synthesise polyacrylamide hydrogels to study the processes linked with fluid-driven fracturing. These transparent, linearly elastic and brittle gels permit fracturing at low pressures and speeds allowing accurate measurements to be obtained. The broad range of modulus and fracture energy values attainable from this medium allow the exploration of particular regimes of importance. Fracturing within these hydrogels also creates beautiful spiral patterns on the plastically deformed surfaces. We analyse these patterns and discuss their formation, while also commenting on their fractal-like nature. Initially, we study single fractures that are driven by an incompressible Newtonian fluid, injected at a constant rate into an elastic matrix. The injected fluid creates a radial fracture that propagates along a plane. We investigate this type of fracture theoretically and then verify the scaling predictions experimentally. We examine the rate of radial crack growth, fracture aperture, shape of the crack tip and internal fluid flow field. We exhibit the existence of two distinct fracturing regimes, and the transition between these, in which propagation is either dominated by viscous flow within the fracture or the material toughness. Particle image velocimetry measurements also strikingly show that the flow in the fracture can alter from an expected radial symmetry to circulation cells, dependent on the regime of propagation. We then expand our research to the problem of two coplanar fluid-driven radial fractures. This was chosen to focus on the physical mechanisms that are key to fracture network formation, related to many geophysical and industrial practices. Initially, the two fractures propagate independently of each other. At a critical separation they begin to interact, with non-uniform growth occurring along the fracture edges due to the evolving stress state in the gel matrix. When the radial extents of the fractures become sufficiently large, they coalesce and form a bridge between them. Following initial contact, a large increase in flow is seen into the newly created bridge and most of the growth is localised along this, perpendicular to the line connecting the injection sources. From experimental measurements, we observe a universal dynamic behaviour for the growth of this bridge. We model this universal behaviour theoretically and construct scalings related to the growth after coalescence, which again identifies both a viscous and toughness regime. The toughness regime is verified experimentally for the bridge growth and the universal shape of the thickness profile along the bridge. The coalesced fractures then transition into a single fracture at late times. Finally, we discuss a number of other interesting scenarios that may occur such as, non-coalescing fractures, asymmetric coalescence and ridge formation.
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Gonçalves, da Silva Bruno Miguel. "Modeling of crack initiation, propagation and coalescence in rocks." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/55156.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2009.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 254-260).
Natural or artificial fracturing of rock plays a very important role in geologic processes and for engineered structures in and on rock. Fracturing is associated with crack initiation, propagation and coalescence, which have been studied experimentally and analytically by many researchers. The analytical models developed to describe the initiation and propagation of cracks in brittle materials can be incorporated in Finite Element (FE) and Displacement Discontinuity (DD) codes. Corresponding research has been going on at MIT and has led to the development of a DDM code - FROCK - which currently uses a stress-based criterion proposed by Bobet (1997) to model crack initiation and propagation. Even though the predictions obtained with this criterion generally correspond to the experimental results, there are cases, in which the results obtained with FROCK are not satisfactory. This thesis proposes and implements new crack initiation and propagation criteria in the DDM code FROCK, namely a strain-based criterion and two stress-dependent criteria. It also studies the crack initiation and propagation processes numerically, using the FEM code ABAQUS. Existing crack initiation and propagation criteria (stress, strain and energy based) are also investigated with ABAQUS. The crack development processes are studied by modeling pairs of pre-existing flaws (double-flaw geometries) embedded in specimens subjected to vertical compressive loads in both ABAQUS and FROCK. For the different flaw arrangements studied, the difference between the stress and strain fields around the flaw tip gradually increases as the horizontal distance between the inner flaw tips increases. In terms of crack initiation, the results obtained with the stress and strain-based criteria studied were more consistent with the experimental observations than the results obtained with the energy-based criterion. The proposed strain-based criterion implemented in FROCK yielded better results than Bobet's stress-based criterion currently used in FROCK, for the five flaw arrangements studied. The results obtained with the two proposed stress-dependent criteria indicate that the critical shear stress at which a crack propagates in rock does not depend upon the normal stress applied, since the best crack propagation results were obtained for very low or zero friction angles.
by Bruno Miguel Gonçalves da Silva.
S.M.
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Kapur, Arnav. "Human-machine cognitive coalescence through an internal duplex interface." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/120883.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 59-62).
In this thesis, we present a non-invasive and non-intrusive system that enables silent duplex human-machine communication and enables an interface that is internal to the user. We present a peripheral nerve-computer interface, AlterEgo, that allows a user to silently converse with a computing device without any voice or any discernible movements - thereby enabling the user to communicate with devices, AI assistants, applications or other people in a silent, concealed and seamless manner. A user's volitional internally articulated speech is characterized by efferent signal signatures in internal speech articulators that are captured and recognized by the proposed system. The hope is to facilitate a natural language user interface, where users can silently communicate in natural language and receive information and sensory input aurally through bone conduction. This enables a discreet, closed-loop interface with a computing device, and thus providing a seamless form of cognitive augmentation. The goal of the thesis is to describe the architecture, design, implementation and operation of the entire system along with demonstrating the utility of the platform as a personal computing system.
by Arnav Kapur.
S.M.