This thesis presents the study of air bubble motion in stagnant water and in upward flowing water through a vertical narrow rectangular channel of 2.1X66.5 mm cross section by using image processing and analyzing techniques. The investigated bubble size range is 2 - 70 mm in area equivalent bubble diameter and mean water flow velocity is 0-25 cm/s. This study focuses on the quantitative assessment of bubble size (perimeter, area, volume, width and height), shape, path and rising velocity. The observed bubble shapes consist of circular, ellipse, ellipse wobbling, hat wobbling, cap-hat, cap and cap-bullet types. Ellipse wobbling and hat wobbling type bubble region show transition from ellipsoidal to circular cap region. The results of the ellipse bubble tests were compared with the rise velocity correlation of ellipsoidal bubbles in infinite medium and an empirical correlation for two dimensional ellipse bubbles was obtained. The cap bubble rise velocities measured in this study were compared with the correlations in literature and a new empirical correlation which is different from those given in the literature was obtained from the experimental results of this study. The trends of the cap bubble deformation which is defined as bubble height to bubble width ratio, for various water streams are almost similar in behavior. Therefore, a correlation was obtained from the measured cap bubble deformation values in water stream. The experimental results show that the bubble relative velocity under co-current flow conditions for area equivalent bubble diameter to channel width ratio, &amp / #955 / ae&lt / 0.6 is less than that under stagnant water condition. After bubble shapes reach to the slug type (&amp / #955 / ae &amp / #8805 / 0.6), relative bubble velocities pass over the terminal bubble velocities in stagnant water. If the water velocity is increased further, the bubble relative velocity increases in the slug bubble region. Rising velocities of slug bubbles were analyzed using the experimental data and a new correlation for slug bubble rise velocity was proposed for flowing water condition.

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The particle-bubble interaction is found in industrial applications with the purpose of selective separation of materials especially in the mining industry. The separation is achieved with the use of bubbles that collect particles depending on their hydrophobicity. There are few experimental studies involving a single interaction between a bubble and a particle. The purpose of this work is to understand this interaction by the study of a single bubble interacting with a single particle. Experiments were conducted using ultra-pure water, glass particles and air bubbles. Single interactions of particles with bubbles were observed using two high speed cameras. The cameras were placed perpendicular to each other allowing to reconstruct the three-dimensional position of the particle, the bubble and the particle-bubble aggregate. A single size of particle was used varying the size for the bubbles. It was found that the attachment of a particle to a bubble depends on its degree of hydrophobicity and on the relative position of the particle and the bubble before they encounter.

The presence of bubbles within liquid pools is ubiquitous in many natural and industrial settings. Plants and other living systems can release gas bubbles which detach and rise up through lakes and the ocean. Degassing also forms gas bubbles on solid surfaces inside the liquids, like that from champagne or poured soda drinks. The bubbles eventually rise to the pool surface, where they can bounce or pop into the air. The detailed dynamical interaction of the bubble and the free surface can be greatly affected by any impurities on their surface, which can affect the mobility of the free surface. In this dissertation, we use both experiments and numerical simulations to study these hydrodynamics. First, we study the rise and bouncing of bubbles or water droplets from the free surface inside a perfluorocarbon liquid. From all four different configurations of mobile/immobile interface pairs we show that the mobile interface always induces stronger bouncing but faster coalescence. The bouncing enhancement ratio between mobile and immobile interface is $1.8\pm0.1$ for bubbles and $1.5\pm0.1$ for water droplets, with the size range from $250 \, \mu m - 550 \, \mu m$ for bubble and $600 \, \mu m - 1200 \, \mu m$ for droplet. Then the top phase is replaced with a glass plate to eliminate the influence from other internal properties besides surface mobility. Since our numerical simulations perfectly reproduce the experiments, we extend our simulations to the free frontal collision of two equivalent droplets. The results not only support our previous conclusions but also predict another peculiar second-collision phenomenon under certain conditions. Then we replace the surrounding liquid with more practical ones of water and ethanol. In extra-pure water, we find that a millimeter-sized bubble has a mobile interface. We add arachidic acid on the top surface to further investigate bouncing from an immobile interface without changing the interfacial tension. The bouncing enhancement by mobile vs immobile interfaces is once again verified for the water-air interface. For millimeter-sized bubbles, as we increase the bubble size from $780 \, \mu m - 1550 \, \mu m$ the bouncing enhancement ratio decreases from 1.8 to 1.2. Finally, we look into the bubble shape and evolution of the liquid film profile during the bouncing from a top glass substrate, using interferometry and numerical simulations. We use 640 nm laser interferometry with a maximum thickness resolution of 120 nm. The center-of-mass trajectory and film profiles are measured for the first bounce of bubbles between 0.8 mm to 1.2 mm. Then we compare the 1.48 mm bubble impact on a no-slip top wall with the SRYL model prediction, where they shared the same dimple diameter but have a non-trivial deviation in dimple depth. Lastly, we simulate the frontal collision between two identical 1.45 mm bubbles, which have complex multi-dimple formations during the bouncing process.

This thesis examines firm performance through the dot-com bubble through the lens of executive compensation. Hypotheses based on the theoretical literature of Bolton, Scheinkman and Xiong (2006) as well as Bertrand and Mullainathan (2001) in regards to management compensation in a speculative bubble motivate three regression models with differing market-cap-growth based dependent variables and specific compensation variables. Regression analyses test the models using public compensation and security data from S&P's Execucomp and Compustat databases. Synthesizing regression results show that stock option vesting schedules and executives' status on the board of directors may significantly affect firm performance through the dot-com bubble, but more analysis, using more robust data, is necessary to verify either claim.

This thesis examines stock price bubbles in the Stock Exchange of Thailand (SET) from its establishment in April 1975 until December 2012 using regime-switching bubble models, on the main aggregated market index, called the SET Index, and several disaggregated stock indices by industrial sector. The results suggest some evidence of bubble-like behaviour in these indices, most especially when a structural break is included at July 1997, the date when Thailand switched to adopting a managed floating exchange rate system. Given the limitations of published stock price indices in Thailand a new, consistent index was computed the K-NI. The econometric test results using this new index indicate strong evidence of stock price bubbles in several industrial sectors and at least some evidence of bubbles in all industry groups in the SET. Finally, the standard model is extended to study the transmission of bubbles between industry groups. The results indicate some levels of contagion in the Technology sector, as well as, in several other industry groups, while the Resources sector seems to be relatively isolated.

Studying the interactions of solid particles and deformable gas<br />bubbles in viscous liquids is very important in many applications,<br />especially in mining and chemical industries. These interactions<br />involve liquid-solid-air multiphase flows and an<br />arbitrary-Lagrangian-Eulerican (ALE) approach is used for the direct<br />numerical simulations. In the system of rigid particles and<br />deformable gas bubbles suspended in viscous liquids, the<br />Navier-Stokes equations coupled with the equations of motion of the<br />particles and deformable bubbles are solved in a finite-element<br />framework. A moving, unstructured, triangular mesh tracks the<br />deformation of the bubble and free surface with adaptive refinement.<br />In this dissertation, we study four problems. In the first three<br />problems the flow is assumed to be axisymmetric and two dimensional<br />(2D) in the fourth problem.<br /><br />Firstly, we study the interaction between a rising deformable bubble<br />and a solid wall in highly viscous liquids. The mechanism of the<br />bubble deformation as it interacts with the wall is described in<br />terms of two nondimensional groups, namely the Morton number (Mo)<br />and Bond number (Bo). The film drainage process is also<br />considered. It is found that three modes of bubble-rigid wall<br />interaction exist as Bo changes at a moderate Mo.<br />The first mode prevails at small Bo where the bubble deformation<br />is small. For this mode, the bubble is<br /> hard to break up and will bounce back and eventually attach<br />to the rigid wall. In the second mode, the bubble may break up after<br />it collides with the rigid wall, which is determined by the film<br />drainage. In the third mode, which prevails at high Bo, the bubble<br />breaks up due to the bottom surface catches up the top surface<br />during the interaction.<br /><br />Secondly, we simulate the interaction between a rigid particle and a<br />free surface. In order to isolate the effects of viscous drag and<br />particle inertia, the gravitational force is neglected and the<br />particle gains its impact velocity by an external accelerating<br />force. The process of a rigid particle impacting a free surface and<br />then rebounding is simulated. Simplified theoretical models are<br />provided to illustrate the relationship between the particle<br />velocity and the time variation of film thickness between the<br />particle and free surface. Two film thicknesses are defined. The<br />first is the thickness achieved when the particle reaches its<br />highest position. The second is the thickness when the particle<br />falls to its lowest position. The smaller of these two thicknesses<br />is termed the minimum film thickness and its variation with the<br />impact velocity has been determined. We find that the interactions<br />between the free surface and rigid particle can be divided into<br />three regimes according to the trend of the first film thickness.<br />The three regimes are viscous regime, inertial regime and jetting<br />regime. In viscous regime, the first film thickness decreases as the<br />impact velocity increases. Then it rises slightly in the inertial<br />regime because the effect of liquid inertia becomes larger as the<br />impact velocity increases. Finally, the film thickness decreases<br />again due to Plateau-Rayleigh instability in the jetting regime.<br />We also find that the minimum film thickness corresponds to an<br />impact velocity on the demarcation point between the viscous and<br />inertial regimes. This fact is caused by the balance of viscous<br />drag, surface deformation and liquid inertia.<br /><br />Thirdly, we consider the interaction between a rigid particle and a<br />deformable bubble. Two typical cases are simulated: (1) Collision of<br />a rigid particle with a gas bubble in water in the absence of<br />gravity, and (2) Collision of a buoyancy-driven rising bubble with a<br />falling particle in highly viscous liquids. We also compare our<br />simulation results with available experimental data. Good agreement<br />is obtained for the force on the particle and the shape of the<br />bubble.<br /><br />Finally, we investigated the collisions of groups of bubbles and<br />particles in two dimensions. A preliminary example of the oblique<br />collision between a single particle and a single bubble is conducted<br />by giving the particle a constant acceleration. Then, to investigate<br />the possibility of particles attaching to bubbles, the interactions<br />between a group of 22 particles and rising bubbles are studied. Due<br />to the fluid motion, the particles involved in central collisions<br />with bubbles have higher possibilities to attach to the bubble. / Ph. D.