Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session A21: Bubbles: Dynamics |
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Chair: Randy Ewoldt, University of Illinois at Urbana Champaign Room: D139-140 |
Sunday, November 20, 2016 8:00AM - 8:13AM |
A21.00001: Arrested bubble 'rise' in a narrow tube Catherine Lamstaes, Jens Eggers A long air bubble placed inside a vertical tube closed at the top rises by displacing the fluid above it. Bretherton, however, found that if the tube radius, $R$, is smaller than a critical value $R_{c}=0.918 \; \ell_c$, where $\ell_c=\sqrt{\gamma/\rho g}$ is the capillary length, there is no solution corresponding to steady rise. We explain this finding by studying the unsteady bubble motion for $R |
Sunday, November 20, 2016 8:13AM - 8:26AM |
A21.00002: Sinking Bubbles Jeremy Koch, Randy Ewoldt Intuition tells us that bubbles will rise and steel objects will sink in liquids, though here we describe the opposite. With experimental demonstration and theoretical rationale, we describe how the motion of containers of liquid with immersed solid objects and air bubbles can cause curious behaviors: sinking bubbles and rising high-density particles. Bubbles and solid spheres of diameter on the order of a few millimeters are introduced into fluids with different rheological constitutive behaviors. Imposed motion of the rigid container allows for control of the trajectories of the immersed particles -- without the container imparting direct shearing motion on the fluid. Results demonstrate the necessary conditions to prevent or produce net motion of the bubbles and heavy particles, both with and against gravitational expectations. [Preview Abstract] |
Sunday, November 20, 2016 8:26AM - 8:39AM |
A21.00003: Numerical simulations of the rise and stability of Taylor bubbles in vertical tubes using the diffuse-interface method Habib Abubakar, Arnoldo Badillo, Omar Matar Taylor bubbles are characteristic features of the slug flow regime in gas-liquid flows in vertical pipes. Experimental observations have shown that at sufficiently large pipe diameters ($>$0.1 m), the slug flow regime, and hence Taylor bubbles, are no longer observed. Numerical simulations of a Taylor bubble rising in a quiescent liquid have also shown that the turbulent bubble wake in such ‘large-diameter’ tubes has great impact on the stability of the subsequent trailing bubbles. In view of these observations, large-scale numerical simulations of Taylor bubbles are carried out using the diffuse-interface method over a range of experimentally relevant conditions. The results of these simulations (including benchmark cases) are discussed with a view to providing insight into the mechanisms underlying Taylor bubble instability. [Preview Abstract] |
Sunday, November 20, 2016 8:39AM - 8:52AM |
A21.00004: Armoring confined bubbles in concentrated colloidal suspensions Yingxian Yu, Sepideh Khodaparast, Howard Stone Encapsulation of a bubble with microparticles is known to significantly improve the stability of the bubble. This phenomenon has recently gained increasing attention due to its application in a variety of technologies such as foam stabilization, drug encapsulation and colloidosomes. Nevertheless, the production of such colloidal armored bubble with controlled size and particle coverage ratio is still a great challenge industrially. We study the coating process of a long air bubble by microparticles in a circular tube filled with a concentrated microparticles colloidal suspension. As the bubble proceeds in the suspension of particles, a monolayer of micro-particles forms on the interface of the bubble, which eventually results in a fully armored bubble. We investigate the phenomenon that triggers and controls the evolution of the particle accumulation on the bubble interface. Moreover, we examine the effects of the mean flow velocity, the size of the colloids and concentration of the suspension on the dynamics of the armored bubble. The results of this study can potentially be applied to production of particle-encapsulated bubbles, surface-cleaning techniques, and gas-assisted injection molding. [Preview Abstract] |
Sunday, November 20, 2016 8:52AM - 9:05AM |
A21.00005: Tightrope walking bubbles Helene De Maleprade, Christophe Clanet, David Quere A fiber can hold a certain amount of liquid, which allows us to capture flying drops and control their motion. Immersed in water, a fiber can efficiently capture air bubbles only if it is hydrophobic. Using a superhydrophobic coating on an inclined wire, we experimentally control the rising velocity of air bubbles walking along the tightrope.~ We discuss the nature of the friction around the walker, and the resulting speed of bubbles. [Preview Abstract] |
Sunday, November 20, 2016 9:05AM - 9:18AM |
A21.00006: Effect of gravity on the liquid film surrounding a bubble translating in a tube. Omer Atasi, Sepideh Khodaparast, Benoit Scheid, Howard A. Stone The motion of confined elongated bubbles in small diameter tubes filled with viscous liquid is a ubiquitous problem relevant to many industrial and medical applications such as lubrication, oil extraction and the treatment of pulmonary disorders. As a confined bubble proceeds into a liquid-filled tube a thin film of liquid is formed on the tube wall. For negligible inertia and buoyancy (\textit{Bo}, \textit{Re} $\simeq $ 0), the thickness of this film depends only on the capillary number \textit{Ca}. However, gravitational effects are not negligible for horizontal tubes of millimeter-scale diameter, corresponding to a finite Bond number \textit{Bo}. We perform experiments and theoretical analysis to investigate the effect of \textit{Bo} on the thin film thickness. Several values of \textit{Bo }are tested experimentally by changing the tube diameter. Due to gravity, the film deposited on the upper wall of the channel is thinner than the film at the bottom wall, and the bubble is inclined toward the bottom of the tube as it translates along the tube. The inclination angle increases with increasing \textit{Bo} and \textit{Ca}. Our theoretical analysis shows that this effect is caused by the bubble being off-center in the tube at finite values of \textit{Bo}. [Preview Abstract] |
Sunday, November 20, 2016 9:18AM - 9:31AM |
A21.00007: Mixing of a passive scalar in a turbulent bubbly flow Elise Alméras, Varghese Mathai, Detlef Lohse, Chao Sun In this work, we investigate the mixing of a passive scalar at high Schmidt number by a homogenous bubble swarm in the presence of external turbulence. The experiments are conducted in the Twente Water Tunnel, in which nearly homogeneous and isotropic turbulence is produced using an active grid. The level of the external turbulence is varied for Taylor-Reynolds number ranging from 180 to 360 and the global gas volume fraction is varied from 0 to 3$\%$. We continuously inject a passive fluorescent dye at a fixed position, and measure the horizontal concentration profile of the dye at different heights by recording the fluorescence levels and applying an image processing. A horizontal effective diffusivity is then calculated from the spatial evolution of the variance of the horizontal concentration profile. The diffusion coefficient is found to increase with the strength of the external turbulence and the gas volume fraction, indicating an enhancement of mixing. Finally, we connect the effective diffusion coefficient to the hydrodynamic properties of the flow in order to have a better understanding on the underlying mixing mechanisms. [Preview Abstract] |
Sunday, November 20, 2016 9:31AM - 9:44AM |
A21.00008: Bubble Size Distribution in a Vibrating Bubble Column Shahrouz Mohagheghian, Trevor Wilson, Bret Valenzuela, Tyler Hinds, Kevin Moseni, Brian Elbing While vibrating bubble columns have increased the mass transfer between phases, a universal scaling law remains elusive. Attempts to predict mass transfer rates in large industrial scale applications by extrapolating laboratory scale models have failed. In a stationary bubble column, mass transfer is a function of phase interfacial area (PIA), while PIA is determined based on the bubble size distribution (BSD). On the other hand, BSD is influenced by the injection characteristics and liquid phase dynamics and properties. Vibration modifies the BSD by impacting the gas and gas-liquid dynamics. This work uses a vibrating cylindrical bubble column to investigate the effect of gas injection and vibration characteristics on the BSD. The bubble column has a 10 cm diameter and was filled with water to a depth of 90 cm above the tip of the orifice tube injector. BSD was measured using high-speed imaging to determine the projected area of individual bubbles, which the nominal bubble diameter was then calculated assuming spherical bubbles. The BSD dependence on the distance from the injector, injector design (1.6 and 0.8 mm ID), air flow rates (0.5 to 5 lit/min), and vibration conditions (stationary and vibration conditions varying amplitude and frequency) will be presented. In addition to mean data, higher order statistics will also be provided. [Preview Abstract] |
Sunday, November 20, 2016 9:44AM - 9:57AM |
A21.00009: Modeling the initial contact line dynamics of dewetting bubbles Mark Menesses, Matthieu Laurent, James Bird When a rising bubble comes to rest beneath a solid horizontal surface, the resulting liquid film dewets to minimize the total free energy of the three phase system. For partially wetting surfaces, the presence of the contact angle yields dynamics which are assumed to be governed by viscous effects. In contrast, the early-time dynamics for drops spreading on partially wetting surfaces are dominated by inertial effects. Motivated by the discrepancy between these two systems, we conduct experiments on dewetting bubbles and find that the short-time dynamics fail to obey purely viscous or inertial scalings. We draw from previously proposed dewetting and spreading models to develop a new model that can rationalize the anomalous scalings that we observe. Our results suggest that the speed that a bubble adheres to a partially wetting surface is set by an interplay of capillary waves and contact line motion. [Preview Abstract] |
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