Indiana University-Purdue University Indianapolis (IUPUI) / This thesis work aims to make a better knowledge on the insights of physics on microbubble coalescence process, using experimental and numerical approaches. The neck growth and bubble surface wave propagation at the early stage of coalescence, merging preference, as well as a reaction-channel modified microfluidic gas generator are presented in the thesis. Coalescence of unequal-sized microbubbles captive on solid substrate was observed from cross-section view using synchrotron high speed imaging technique and a mi- crofluidic gas generation device. The bridging neck growth and surface wave propaga- tion at the early stage of coalescence were investigated by experimental and numerical methods. The results show that theoretical half power law of neck growth rate is still valid when viscous effect is neglected. However, the inertial-capillary time scale is based on the radius of smaller parent microbubble. The surface wave propagation rate is proportional to the inertial-capillary time scale, which is based on the radius of larger parent microbubble of a coalescence pair. Meanwhile, the relationship of preference distance and size inequality microbub- bles were studied using the same micrfluidic gas generator and observation facilities. The size inequality of parent microbubbles would affect the preference distance of merged bubble in between. The merged bubble gets less closer to the larger parent bubble with an exponent of 1.82 as a reference, which largely affected by shear stress begotten on the solid interface. To express this phenomenon distinguished with free merging bubble pair, we propose the wall shear stress hinders the process of that parent bubbles move towards to each other during coalescence Our hypothesis was confirmed by identical coalescence simulation via ANSYS Fluent. To address the multiple measurement, utilization of Java based photography pro- cessing software ImageJ was applied as a key point to the thesis work. To acquire more microbubble coalescence cases on experiment for study, we enhanced the perfor- mance of microfluidic gas generator with reaction channel optimization. An optimized design on increasing the number of parallel reaction channel from single to triple, was applied to obtain a higher gas generation rate. Also the gas vent shape was modified from triangle to rectangle to provide more information on reaction channel optimiza- tion. The gas generation rate and H2O2 conversion rate were provided to further discuss.

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<p> A theoretical and experimental study is presented of the effect of oil/water system physical properties, surfactant concentration, and drop size on the drop rest-time and lamella behaviour. </p> <p> The work has three distinct parts. The first part is based on the assumption that the dynamic pressure distribution in the lamella can be described by a simple three term polynomial. Equations for the relative lamella thickness profile are derived and are shown to accurately describe experimental lamella thickness profiles measured both in this work and by other investigators. </p> <p> The second part presents and discusses the experimentally measured drop rest-times and simultaneously observed lamella behaviour for the range of variables studied. Five mechanisms are proposed to account for the observed lamella behaviour. </p> <p> The third part derives equations to describe the lamella drainage, the interfacial distribution of adsorbed surfactant for a lamella undergoing drainage, and the dynamic lamella pressure distribution. The solution of the lamella drainage equation is then compared with experimentally determined profiles of the relative lamella thickness for both the complex model and a simple model based on a parallel disc lamella. </p> / Thesis / Doctor of Philosophy (PhD)

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.

Air entraining admixtures (vinsol or non-vinsol) are used in concrete mixes that will be exposed to freeze-thaw cycles or sulfate attack. Entrained air is intended to improve the durability and resistance of hardened concrete to freeze-thaw cycles. However in many instances a significant loss of compressive strength has been observed in concrete mixes containing non-vinsol admixtures. Mixture forensic analysis has determined air void coalescing to be the main factor in observed low compressive strengths. The result of air void coalescing is the over design of compressive strength to account for the possible lower strengths and decreased confidence in the compressive strengths obtained during the quality control/assurance process.

No / Coalescence enhancement of water droplets in oil emulsions is commonly contemplated for the separation of an aqueous phase dispersed in a dielectric oil phase with a considerably lower dielectric constant than that of the dispersed phase. The characteristics and geometry of the electrode system have a large impact on the performance of an electrostatic coalescer and are actually strictly linked to the type of the applied electric field and the emulsion used. Furthermore, addition of chemicals and heating has also been revealed to further enhance the electrocoalescence of water droplets. In this work, the coalescence of two water drops sinking in a dielectric oil phase at an applied high voltage, pulsed dc electric field, in particular with regards to the effects of pressure and temperature on coalescence performance is investigated. The developed model should help to recognise and prove approaches to electrocoalescence mechanisms, the dispersion flow direction with respect to the applied electric field, as well as the electric field configuration.

Thermotropic liquid crystalline polymers (TLCPs) possess a number of physical and mechanical properties such as: excellent chemical resistance, low permeability, low coefficient of thermal expansion, high tensile strength and modulus, and good impact resistance, which make them desirable for use in the storage of cryogenic fluids. Rotational molding was selected as the processing method for these containers because it is convenient for manufacturing large storage vessels from thermoplastics. Unfortunately, there are no reports of successful TLCP rotational molding in the technical literature. The only related work reported involved the static coalescence of two TLCP powders, where three key results were reported that were expected to present problems that preclude the rotational molding process. The first result was that conventional grinding methods produced powders that were composed of high aspect ratio particles. Secondly, coalescence was observed to be either slow or incomplete and speculated that the observed difficulties with coalescence may be due to large values of the shear viscosity at low deformation rates. Finally, complete densification was not observed for the high aspect ratio particles. However, the nature of these problems were not evaluated to determine if they did, in fact, create processing difficulties for rotational molding or if it was possible to develop solutions to the problems to achieve successful rotational molding. This work is concerned with developing a resin selection method to identify viable TLCP candidates and establish processing conditions for successful rotational molding. This was accomplished by individually investigating each of the phenomenological steps of rotational molding to determine the requirements for acceptable performance in, or successful completion of, each step. The fundamental steps were: the characteristics and behavior of the powder in solids flow, the coalescence behavior of isolated particles, and the coalescence behavior of the bulk powder. The conditions identified in each step were then evaluated in a single-axis, laboratory scale, rotational molding unit. Finally, the rotationally molded product was evaluated by measuring several physical and mechanical properties to establish the effectiveness of the selection method. In addition to the development and verification of the proposed TLCP selection method, several significant results that pertain to the storage of cryogenic fluids were identified as the result of this work. The first, and argueably the most significant, was that the selection method led to the successful extension of the rotational molding process to include TLCPs. Also, the established mechanical properties were found to be similar to rotationally molded flexible chain polymers. The biaxial rotationally molded container was capable of performing to the specified requirements for cryogenic storage: withstand pressures up to 34 psi at both cryogenic and room temperatures, retain nitrogen as a gas and as a cryogenic liquid, the mechanical preform retaining nitrogen, as both a gas and as a cryogenic liquid, and resist the development of micro-cracks during thermal cycling to cryogenic conditions. / Ph. D.

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 inertia / Master of Science

Les forces de sélection sont un des moteurs de l’évolution de la diversité phénotypique et de la diversité génétique neutre et des zones codantes du génome. Cette sélection peut s’appliquer sur des caractères transmis génétiquement ou culturellement. Le travail effectué s’intéresse à ces deux processus de sélection. Nous avons étudié dans un premier temps les effets de la transmission intergénérationnelle de la fécondité sur la diversité génétique neutre puis dans un deuxième temps l’impact de la sélection sur des phénotypes codés par des réseaux de gènes sur le polymorphisme de ces gènes.La transmission de la fécondité est un phénomène culturel ou génétique qui se caractérise par une corrélation positive entre la taille de fratrie d’un individu et la taille de fratrie de ses enfants. Il a été observé tant dans des populations humaines qu’animales. Nous montrons, par l’outil de la modélisation, que ses effets et la possibilité de le détecter dépendent autant du type de données étudiées (génétiques ou généalogiques), que des différents types de transmission (uniparentale, biparentale). Nous montrons que d’autres phénomènes, tels que l’hétérogénéité du succès reproducteur des individus, peuvent fortement moduler son impact. Nous développons un certain nombre d’outils permettant de détecter ce phénomène de transmission de la fécondité tant sur des données généalogiques que sur des données génétiques relevant de différents modèles mutationnels (microsatellite, séquences, SNPs) et de différents types de transmission (haploïde ou diploïde, lié au sexe ou non). Nous avons appliqué ces outils notamment à trois populations humaines du Cilento en Italie (généalogies et ADN mitochondrial), des données d’Asie Centrale (chromosome Y) et des données HapMap (autosomes).La seconde partie de la thèse porte sur la modélisation de l’action de la sélection naturelle sur des caractères codés par des réseaux de régulation et décrit l’impact de ce type de sélection sur l’évolution du phénotype et sur la diversité des gènes sous-jacents. Un phénotype est le résultat des interactions entre différents gènes et leurs produits. Nous montrons que la sélection sur ce phénotype va modifier l’organisation du réseau de gènes ainsi que le niveau de polymorphisme des gènes du réseau. Par exemple, lorsque le phénotype optimal correspond à une expression médiane des gènes, les gènes les plus régulateurs vont être soumis à une plus forte perte de diversité. En revanche, si le phénotype optimal correspond à une expression très forte, ce sont les gènes les plus régulés qui vont être les plus contraints. Cette analyse a permis de montrer la complexité des relations entre sélection, réseaux de régulation, phénotypes et environnement. / Selective forces are one of the major determinants of the evolution of phenotypic diversity and genetic diversity, in neutral and coding zones of the genome. Selection can occur on genetically - or culturally - transmitted traits. This thesis considers these two selective processes. First, we studied the effects of intergenerational fertility transmission on neutral genetic diversity. Second, we considered the impact of selection on phenotypes coded by a gene network and on the polymorphism of genes within the network.Fertility transmission is a cultural or genetic phenomenon, which is characterised by a positive correlation between the sibship size of an individual and that of its children. It was observed both in human and animal populations. Using a modelling approach, we show that its effects and the possibility to detect it depend both on the kind of studied data (genetic or genealogical data) and on the different kind of transmission (uniparental, biparental). We show that other phenomena, such as the heterogeneity of reproductive success between individuals, can affect its effects. We develop several tools allowing to infer this phenomenon of fertility transmission on genealogical data, as well as on genetic polymorphism data that follows different mutational models (microsatellites, sequences, SNPs) and different transmission modes (haploid or diploid, sex-linked or not). We applied in particular these tools to three human populations of the Cilento area in Italy (genealogical and mitochondrial DNA data), to Central Asian data (Y chromosome) and to HapMap data (autosomes).The second part of this thesis deals with the modelling of the action of natural selection on traits coded by regulation networks and describes the impact of such selection on the evolution of the phenotype and of the underlying genes. A given phenotype is the result of the interaction between different genes and their products. We show that phenotypic selection will modify the gene network organisation, as well as the level of polymorphism of the genes involved in the network. For example, when the optimal phenotype corresponds to an intermediate level of gene expression, the most regulatory genes will lose much of their diversity. Conversely, if the optimal phenotype corresponds to a very strong expression of the genes, it will be the most regulated genes that will be the most constrained. This analysis allowed us to show the complexity of the relations between selection, regulation networks, phenotypes and the environment.