Formation of gas bubbles in complex fluids and their subsequent rise due to buoyancy is a very important fundamental phenomenon both in nature and industry. Bubble size and bubble velocity are critical parameters which govern the interfacial transport phenomena and play an important role in gas-solid contact. These characteristics affect the operating parameters as well as the design of equipment in industrial applications. Non-Newtonian, Shear-thickening fluids have been studied extensively due to their immense potential for commercial use in shock absorbing and force damping applications, such as liquid body armor, sports and personal protection. Furthermore, a better understanding of shear-thickening fluid is pertinent to industrial processing for enhancing flow, preventing the breakage or clogging of mixing equipment, and preventing clogging in narrow orifices. Despite their significance, many aspects of the flow of these non-Newtonian fluids remain poorly understood. In the first part of this dissertation, we study the dynamics of rising bubbles in three dimensional fluidized beds using computational fluid dynamics-discrete element method (CFD-DEM) to shed light on the physics underpinning phenomena uncovered previously using magnetic resonance imaging (MRI). We were able to understand the underlying mechanism behind the anomalous collapse of a bubble in side-by-side injection as well as an alternating asynchronous pinch-off pattern due to jet interaction in a fluidized bed by looking into the gas streamlines and the drag force on the particles. In the second part of this dissertation, we study dynamics of rising bubbles in Newtonian fluids and non-Newtonian cornstarch-water suspensions experimentally using optical imaging. We were able to identify that Capillary number (Ca) is a key dimensionless parameter governing the regimes of interacting jets in water. We also observed a periodic coalescence of bubbles at the same points in space in cornstarch-water suspensions and attributed this behavior to leading bubbles entering a shear thickening regime. Further, we identified the key dimensionless parameters for wobbling behavior of single bubbles in cornstarch suspensions to be Bond (Bo), and Reynolds (Re) number, regardless of the bubble being in a Newtonian or a shear-thinning regime. We believe our findings can be applied in industry to optimize the mass transport and liquid mixing for a range of applications.

In this thesis, we develop a physical understanding of the effects of viscosity and geometry on the dynamics of interfacial flows in drops and bubbles. We first consider the coalescence of pairs of conical water droplets surrounded by air. Droplet pairs can form cones under the influence of an electric field and have been observed to coalesce or recoil depending on the angle of this cone. With high resolution numerical simulations we show the coalescence and non-coalescence of these drop pairs is negligibly affected by the electric field and can be understood through a purely hydrodynamic process. The coalescence and recoil dynamics are shown to be self similar, demonstrating that for these conical droplet pairs viscosity has a negligible effect on the observed behavior. We generalize this result to the coalescence and recoil of droplets with different cone angles, and focus on droplets coalescing with a liquid bath and flat substrate. From the simulations of these droplets with different cone angles, an equivalent angle is found that describes the coalescence and recoil behavior for all water cones of any cone angle. While viscosity is found to negligibly affect the coalescence of conical water drops, it plays a key role in regulating the coalescence process of bursting gas bubbles. When these gas bubbles burst, a narrow liquid jet is formed that can break up into tiny liquid jet drops. Through consideration of the effects of viscosity, we show that these jet drops can be over an order of magnitude smaller than previously thought. Here, viscosity plays a key role in balancing surface tension and inertial forces and determining the size of the jet drops. Finally, we investigate the drainage of surfactant free, ultra-viscous bubbles where surface tension serves only to set the initial shape of the bubble. We use interferometry to find the thickness profiles of draining bubble films up to the point the of rupture. A theoretical film drainage model considering the balance of viscous and gravitational stresses is developed and numerically computed. The numerical results are found to be consistent with the experimentally obtained thickness profiles. In this work we provide insight into the role of viscosity in the outlined interfacial flows. The results of this thesis will advance the understanding of drop production in clouds, the marine climate, and the degassing of glass melts.

The rise of soft robots poses a promising revolution across a variety of fields, such as invasive surgical procedures or aquatic animal monitoring and sampling, by providing a softer solution to delicate problems. However, with their youth comes a need for growth, particularly in regard to increasing mobility in aquatic environments seeing as motion is often slow and belabored. Additionally, exit strategies in breaking the air-water interface are not thoroughly explored to date. To address these challenges, this study looks to bioinspiration for the answer in the form of Emperor Penguins. By utilizing microbubbles in their plumage to decrease drag forces on their bodies, Emperor Penguins are able to propel themselves out of the water to heights not theoretically achievable through buoyancy alone. Not only is the strategy highly effective, it lends well to the soft robotic field as pneumatic actuation is a commonly used mechanism of locomotion. To explore this behavior and simulate its effects, this study tests a hollow silicone ellipsoid with hole punctures applied to its surface for microbubble release. Bubble characteristics such as separation point, bubble diameter, and downstream bubble expansion were monitored when subjected to a fluid flow to determine ideal air pressure through the ellipsoid body. Drag reduction is tested by measuring the robot’s leap height out of the water.

The way of the Jedovnice creek: connection with the spring Falling into the underground halls and back to the light. The Water Way is an intermedial poem that is concerned to the element of water, character of its way through the landscape and its presence in the landscape. Since the type of work I most prefer is the work in the landscape, I am returning back to the natural landscape, strong places in Moravian karst near Brno. The audiovisual poem is primarily focused on the moment of melting. Sublimation of ice from the ice shelter, ephemeral phenomena on the surface, such as miniature whirls, waves, rays of sunlight and especially moonlight. The poem focuses on the possibilities of transferring the experience with a specific place, and the events in a unique, unrepeatable time and space into the theatrical scene and possibilities of the musical and audiovisual interpretation of such experience. I work with digital media (video mix and audiostop) to transfer the artist's physical experience in a unique time and unique natural setting into the scenic form of the work. Considering the physical and symbolic qualities of the water element, I have abandoned the composition of the event in the classical sense.

[pt] O presente estudo se refere ao campo de partículas deformáveis, em particular às bolhas de ar em líquidos de diferentes propriedades físicas. Estudando a passagem de bolhas de ar em interfaces líquido-líquido, constatou-se que as bolhas formadas na água e passando para os líquidos superiores (de densidade inferior), são envolvidas por uma película de água de espessura não uniforma, para diâmetros equivalentes na faixa de 2,5 a 5,7mm. Os fluidos superiores possuem viscosidade cinemática na faixa 1,2 e 55,0 cs e tensão interfacial com a água entre 13,0 e 32,0 din/cm. A influência dessa película no comportamento das bolhas de ar é acentuada quanto a: forma, pulsação de forma, trajetória, velocidade terminal. Constatou-se que a espessura média dessa película aumenta com o diâmetro equivalente e varia com as propriedades físicas dos fluídos superiores. Particular importância da película se nota quando o fluido superior tem pequena viscosidade cinemática: as bolhas de forma irregular são arredondadas pela película, de maneira que, para as bolhas maiores, apesar do peso da película a velocidade é maior em comparação com a de uma bolha sem película. Com o aumento da dimensão das bolhas, um diâmetro é atingido, para o qual há o rompimento da película com o consequente desprendimento da água em forma de gota; esse diâmetro parece variar pouco com as propriedades dos fluidos superiores. O campo de pesquisa do presente estudo apresenta inúmeras sugestões, e algumas estão sendo estudadas presentemente. / [en] The present study refers to the case of deformable particles, in particular to air bubbles in liquids of different physical properties. On studying the passage of air bubbles through liquid-liquid interfaces, it was verified that bubbles, formed in water and rising in the upper liquid (low density), were surrounded by non-uniform water film when the bubbles had na equivalent diameter between 2,5 and 5,7mm. The kinematic viscosity of the upper liquids ranged from 1,2 to 55,0 centistokes, and the interfacial tension from 13,0 to 32,0 din/cm. The presence of that film affects the form, trajectory and terminal velocity of the air bubbles. It was verified that the average film thickness increases with the equivalent bubble diameter and changes with the physical properties of the upper liquids. Interesting phenomena were noted when the upper liquid viscosity was low – the film caused the irregular air bubbles to be changed to a spherical form, in such a way that the larger bubbles, depite film weight, had a greater terminal velocity than non filmed bubbles. As the bubble dimension was increased, a limit was found, at which the water film broke, and a drop was formed. The critical diameter seems not to be affected by the properties of the upper liquids. Research in this Field presents several possibilities, which are now under study.

No description available.

While sea spray aerosols (SSAs) generation by oceanic breaking waves continues to be an active research area, lake spray aerosols (LSAs) production by freshwater breaking waves is an emerging research field. Recent studies have linked LSAs to regional cloud processes and the aerosolization of freshwater pathogens and pollutants. Yet, differences in spray aerosol ejection between freshwater and saltwater and their impact on the water-to-air dispersal of microorganisms and pollutants are poorly understood. The goals of this dissertation work were to understand mechanistic differences between spray aerosol generation in freshwater and saltwater, develop a representation of LSA emissions in atmospheric models and evaluate their impact on regional aerosol loading, and compare the aerosolization of bacteria and microplastics by SSAs and LSAs. Experiments in a breaking-waves analogue tank revealed that the subsurface bubble plume in saltwater is characterized by more submillimeter bubbles than that in freshwater, and hence, saltwater surface foams were more persistent and were comprised of more submillimeter surface bubbles. Consequently, the average number concentration of generated SSAs was eight times higher than that of LSAs. Using these measurements, the developed LSA emission parametrization revealed that freshwater emissions were, at least, an order of magnitude lower than saltwater emissions for the same wave-breaking conditions. When implementing this emission parameterization to simulate LSA emissions from the Laurentian Great Lakes, LSAs did not contribute significantly to regional aerosol loading (< 2%), yet their impact on coarse-mode aerosols was more significant with up to a 19-fold increase in some areas. Furthermore, modeled LSAs reached up to 1000 km inland and were incorporated in the lakes' cloud layer. Despite the generation of more spray aerosols in saltier waters, cumulative salt additions in the freshwater–saltwater continuum (0-35 g/kg) led to a nonmonotonic increase in freshwater bacterial aerosolization abundance, which exhibited a peak at lower oligohaline conditions (0.5-1 g/kg). However, the aerosolization of microplastics by SSAs was one order of magnitude higher than that by LSAs. Overall, this dissertation work showed that LSA emissions are intrinsically different from SSA emissions, which influences their role in transferring microorganisms and pollutants at the air-water interface. / Doctor of Philosophy / When waves break, they entrain large volumes of air in the form of subsurface bubbles. These bubbles rise to the surface and pop ejecting small droplets into the air, also known as spray aerosols. The droplets ejected from saltwater breaking waves are referred to as sea spray aerosols (SSAs) and are extensively studied due to their important role in Earth's atmosphere. However, the ejection of lake spray aerosols (LSAs) from freshwater breaking waves is far less understood. With recent studies linking freshwater breaking waves to regional cloud processes and the transfer of aquatic pathogens to the air, a better understanding of LSAs formation and how it compares to SSAs production was needed. The goals of this dissertation work were to understand the differences between spray aerosol generation in freshwater and saltwater, develop a representation of LSA emissions in atmospheric models and assess their contribution to atmospheric aerosols, and contrast the role of LSAs and SSAs in transferring bacteria and microplastics to the air. Experiments in a spray aerosol generation tank revealed that saltwater breaking waves generate more submillimeter bubbles at the subsurface level than freshwater breaking waves and that the generated surface foam is more persistent and is comprised of smaller bubbles in saltwater. Consequently, SSA generation in the experimental tank was eight times higher than LSA generation. When implementing these results in an atmospheric model to simulate LSA emission from the surface of the Laurentian Great Lakes, it was found that the regional aerosol population was not significantly affected. However, LSA particles were transported inland up to 1000 km and reached cloud level which hints at possible implications on public health and regional climate. Despite a higher generation of aerosols by breaking waves in saltier waters, the abundance of freshwater bacteria that was dispersed to the air by spray aerosols did not increase monotonically in response to a gradual increase in freshwater salinity. Yet, microplastics transfer to the air by SSAs was an order of magnitude higher than that by LSAs. The results of this dissertation work highlight the important differences between the generation of spray aerosols by breaking waves in freshwater and saltwater and their corresponding roles in the water-to-air dispersal of microorganisms and pollutants.

A method in which the transport and evolution of the bubble population in a surface ship wake is numerically simulated is presented. The simulation is accomplished by constructing an advective-diffusive transport model for the scalar bubble field and solving this model for late times after ship passage. The bubble population model requires convection velocities and turbulent diffusion information that is supplied by solving the Reynolds-averaged parabolized Navier-Stokes equations with a <i>k</i> - ∊ turbulence model. The mean flow equations are solved by approximating the differential equations with a second order accurate finite difference scheme. The resulting large, sparse, banded matrix is solved by applying a version of the conjugate gradient method. The method has proven to be efficient and robust for the free shear flow problems of interest here. The simulation is initiated with given information in a plane at some point downstream of the ship from which the solution is propagated. The model is executed for a single and a twin propeller ship at 15 knots. The simulation shows that the development of the hydrodynamic and bubble near wake is dominated by ship geometry via strong advective transport. The far wake is dominated by diffusion and bubble rise and dissolution. Thus relatively large changes in geometry have a limited influence on the far wake. / Ph. D.

Matter on earth exists mostly in three different phases of solid, liquid, and gas. With extreme amounts of energy, temperature, or pressure, a matter can be changed between the phases. Six different types of phase-change phenomena are possible: freezing (the substance changes from a liquid to a solid), melting (solid to liquid), condensation (gas to liquid), vaporization (liquid to gas), sublimation (solid to gas), and desublimation (gas to solid). Another form of phase change which will be discussed here is the wetting or dewetting transitions of a superhydrophobic surface, in which the phase residing within the surface structure switches between vapor and liquid. Phase transition phenomena frequently occur in our daily life; examples include: a ``liquid'' to ``solid'' transition when cars decrease their distance at a traffic light, solidification of liquids droplets during winter months, and the dancing of droplets on a non-sticking pan. In this dissertation we will address seven different phase-change problems occurring in nature. We unveil completely new forms of phase-change phenomena that exhibit rich physical behavior. For example, during traffic flow, drivers keep a large distance from the vehicle in front of them to ensure safe driving. When vehicles come to a stop, for example at a red light, drivers voluntarily induce a ``phase transition'' from this ``liquid phase'' to a close-packed ``solid phase''. This phase transition is motivated by the intuition that traveling as far as possible before stopping will minimize the overall travel time. However, we are going to investigate this phase-change process and show that this long standing intuition is wrong. Phase-change of solidification will be discussed for different problems. Moreover, the complex physics of oil as it wicks up sheets of frost and freezing of bubble unveil completely new forms of multiphase flows that exhibit rich physical behavior. Finally, the ``Cassie'' to ``Wenzel'' transition will be investigated for layered nano-textured surfaces. These phenomena will be modeled using thermodynamics and fluid mechanics equations. / Doctor of Philosophy / The main focus of this dissertation is on the dynamical phase change phenomena occurring in nature. First, we study the solid to liquid phase change of group of people moving from rest. We show that increasing the packing density of vehicles at a stop-and-go motion (e.g., vehicles at a traffic light) would not increase the efficiency of the flow once it is resumed. Second, we present a passive anti-frosting surfaces just by using the chemistry of ice. We show how the in-plane frost growth can be passively suppressed by patterning arrays of microscopic ice stripes across a surface. Third, we elucidate how bubbles deposited on a chilled and icy substrate freeze in different ambient conditions. We reveal the various phenomena that govern how soap bubbles freeze and produce a variety of beautiful effects. Fourth, we will study oil-ice interactions which are important for the emerging science of using oil-impregnated surfaces for anti-icing and anti-frosting applications, where oil drainage from the surface due to wicking onto ice is a pressing issue. We observe oil as it wicks up sheets of frost grown on aluminum surfaces of varying wettability: superhydrophilic, hydrophilic, hydrophobic, and superhydrophobic. Fifth, we study the effect of topography of the nanopillars on dynamics of jumping droplets. The critical diameter for jumping to occur was observed to be highly dependent on the height and diameter of the nanopillars, with droplets as small as 2 µm jumping on the surface with the tallest and most slender pillars. Sixth, we show that micrometric condensate spontaneously launches several millimeters from a wheat leaf’s surface, taking adhered pathogenic spores with it. We quantify spore liberation rates of order 10 cm⁻² hr⁻¹ during a dew cycle. Finally, inspired by duck feathers, two-tier porous superhydrophobic surfaces were fabricated to serve as synthetic mimics with a controlled surface structure. We show the effect of layers of feathers on energy barrier for the wetting transition.

Yes / Purpose: We develop new quantitative methods to estimate the level of speculation and long-term sustainability of Bitcoin and Blockchain. Design/Methodology/Approach: We explore the practical application of speculative bubble models to cryptocurrencies. We then show how the approach can be extended to provide estimated brand values using data from Google Trends. Findings: We confirm previous findings of speculative bubbles in cryptocurrency markets. Relatedly, Google searches for cryptocurrencies seem to be primarily driven by recent price rises. Overall results are sufficient to question the long-term sustainability of Bitcoin with the suggestion that Ethereum, Bitcoin Cash and Ripple may all enjoy technical advantages relative to Bitcoin. Our results also demonstrate that Blockchain has a distinct value and identity beyond cryptocurrencies - providing foundational support for the second generation of academic work on Blockchain. However, a relatively low estimated long-term growth rate suggests that the benefi ts of Blockchain may take a long time to be fully realised. Originality/value: We contribute to an emerging academic literature on Blockchain and to a more established literature exploring the use of Google data within business analytics. Our original contribution is to quantify the business value of Blockchain and related technologies using Google Trends.