Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session L07: Bubbles: General |
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Chair: Pedro Saenz, University of North Carolina at Chapel Hill Room: Ballroom G |
Monday, November 25, 2024 8:00AM - 8:13AM |
L07.00001: Effective and Environment-Friendly Oil Removal with Microbubble Jet Jung Jae Woo, Yewon Kim, Hyungmin Park, Hyejeong Kim This study investigates the fundamental physics underlying the use of microbubble jets to enhance oil-cleaning processes, providing an eco-friendly alternative to conventional chemical methods that pose significant environmental and health risks. Microbubbles, particularly those under 50 µm, offer prolonged suspension in water and effective pollutant adsorption, beneficial in surface cleaning applications. Previous research has focused on underwater applications, yet the detailed mechanisms of microbubble-enhanced cleaning remain unclear, especially in diverse fluidic environments. |
Monday, November 25, 2024 8:13AM - 8:26AM |
L07.00002: Cleaning Surfaces with Bubbles with Sub-Resonance Acoustic Waves Yan Jun Lin, Zhengyang Liu, Sunghwan Jung The use of bubbles in an aqueous medium to clean biological surfaces holds promising potential for developing sustainable methods to clean agricultural produce. Bubbles with a diameter of 1.2 mm exhibit a resonant frequency of approximately 5300 Hz. However, one of the low sub-resonant frequencies near 90 Hz induces a distinctive swaying motion when suspended underwater. This swaying motion at sub-resonance facilitates a unique sliding behavior as bubbles ascend inclined surfaces, presumably enhancing shear stress and cleaning efficacy. Additionally, the sub-resonant frequency causes bubbles to deviate from a linear path, curving away from the sound source and colliding with surfaces with a greater perpendicular component of speed, increasing shear force and bounce height, further improving the cleaning process. The observed sub-resonance effects are confirmed to be independent of the boundary effect, as demonstrated by replicating the same sub-resonance in both large and small tanks. This research sheds light on the potential of acoustically manipulated bubbles as an effective, non-chemical cleaning technique for agricultural produce and other surfaces. |
Monday, November 25, 2024 8:26AM - 8:39AM |
L07.00003: Polymer-Dispersed Nanoparticles for Catalytic Carbon Capture in Natural Seawater Myeongsub Kim, Joshua Donjuan, Abhishek Ratanpara Rapid technological advancement continuously increases energy consumption and demand, primarily satisfied by fossil fuel consumption. The reliance on fossil fuels results in substantial greenhouse gas emissions, with CO₂ being the most prominent contributor to global warming. This study investigates the catalytic performance of nickel nanoparticles (NiNPs) in natural seawater with carboxymethyl cellulose (CMC) polymers as an environmentally sustainable carbon capture solution. The catalytic characteristics of NiNPs were investigated by analyzing the change in diameter of CO2 microbubble generated in specially designed flow-focusing geometry-based microchannel. We utilized NiNPs with diameters of 100 nm and 300 nm CMC concentrations of 100mg/L,200mg/L, and 300mg/L. Additionally, eight NiNP concentrations ranging from 6mg/L to 150mg/L were tested for CO2 dissolution in seawater. The results show that, in different CMC and NiNP concentrations, a bell-shaped curve was formed when increasing the concentration, indicating the existence of optimized CMC and NiNP pair concentrations. The results also suggested that a concentration of 10mg/L NiNPs in 100mg/L CMC provided a maximum CO2 dissolution of 57% under the test conditions. At CMC concentrations of 200mg/Land 300mg/L, the nine concentrations of 70mg/l and 90mg/l, CO2 dissolution was found to be 58.8% and 67.2%, respectively. The study discusses practical solutions of the proposed solution in commercial carbon capture plants. |
Monday, November 25, 2024 8:39AM - 8:52AM |
L07.00004: Galloping bubbles Jian Hui Guan, Saiful I Tamim, Connor W Magoon, Howard A Stone, Pedro J Saenz Despite centuries of investigation, bubbles continue to unveil intriguing dynamics relevant to a multitude of practical applications. Here we introduce bubbles that spontaneously start to `gallop' along horizontal surfaces inside a vertically vibrated fluid chamber, self-propelled by a resonant interaction between their shape oscillation modes. These active bubbles exhibit distinct trajectory regimes, including rectilinear, orbital, and run-and-tumble motions, which can be tuned dynamically via the external forcing. Through periodic body deformations, galloping bubbles swim leveraging inertial forces rather than vortex shedding, enabling them to maneuver even when viscous traction is not viable. Integrating experiments, simulations, and theory, we demonstrate that the galloping symmetry breaking provides a robust self-propulsion mechanism, arising in bubbles whether separated from the wall by a liquid film or directly attached to it, and is captured by a minimal oscillator model, highlighting its universality. Through proof-of-concept demonstrations, we showcase the technological potential of galloping locomotion for applications involving bubble generation and removal, transport and sorting, navigating complex fluid networks, surface cleaning, and directing bubble motions in low gravity environments. The rich dynamics of galloping bubbles suggest exciting opportunities in heat transfer, microfluidics, soft robotics, and active matter. |
Monday, November 25, 2024 8:52AM - 9:05AM |
L07.00005: Collective Dynamics of Galloping Bubbles Connor W Magoon, Xinyun Liu, Jian Hui Guan, Saiful I Tamim, Pedro J Saenz Recent work has shown that a capillary-size bubble, held by buoyancy against the top wall of a vertically vibrated fluid chamber, may spontaneously break symmetry and self-propel in a direction perpendicular to the driving, exhibiting motion reminiscent of galloping. Depending on the combination of parameters, a single bubble may exhibit straight-line, orbital, or chaotic motion through the interaction of axisymmetric and non-axisymmetric shape modes excited by the external driving. Here, we investigate the collective dynamics of galloping bubbles through experiments and simulations, focusing on characterizing pair dynamics as a step towards understanding their many-bubble behaviors. Our experiments reveal rich collective dynamics, including the formation of orbiting pairs, leapfrogging along vertical walls, and self-assemblies. Using simulations, we characterize the fluid-mediated interactions between two bubbles and between a bubble and a vertical wall as a function of external driving, bubble volume, separation, and orientation. We perform a spectral decomposition of the bubble shape oscillations and the induced far-field flow, paving the way for the development of a reduced model for interactions and collective dynamics. |
Monday, November 25, 2024 9:05AM - 9:18AM |
L07.00006: Contact Angles of Surface Nanobubbles: How Far Can MD Simulations Explain? Hideaki Teshima, Hiroki Kusudo, Carlos Bistafa, Yasutaka Yamaguchi Despite a quarter-century of scientific endeavor, the properties of nanobubbles on solid surfaces remain elusive. In particular, the mechanisms behind the significantly larger contact angles (i.e., the flat shape) than those predicted by Young's equation are still under debate because the interfacial tensions cannot be precisely measured in experiments. In this study, for the first time, we calculated the solid-liquid, solid-gas, and liquid-gas interfacial tensions of surface nanobubbles using molecular dynamics (MD) simulations. It was found that Young's equation still holds for nanobubbles with diameters of less than 10 nm. We also found that the gas molecules adsorbed onto the solid surface just under the bubbles significantly decrease the solid-gas interfacial tensions, thus increasing the contact angles. However, this is still insufficient to rationalize the experimentally observed values (>150°). Our results clarify that factors not usually considered in MD analysis, such as surface charge, contact line pinning, and whether systems are open or closed, are crucial in explaining the unusual contact angles of surface nanobubbles and related characteristics. |
Monday, November 25, 2024 9:18AM - 9:31AM |
L07.00007: On the flow phenomena generated by liquid plunging jets: effect of jet velocity Aynur Atalay, Omar K Matar, Klaus Hellgardt, Julia Hofinger, Sebastian Meinicke Plunging liquid jets have proven to be an effective means of entraining and dispersing gas into a liquid pool. They are preferred in industrial applications due to their ability to mix fluids and distribute gas without the need for an agitator, making them suitable for a range of products and processes. The effect of jet velocity on bubble velocity and bubble size distribution of a plunging liquid jet is studied. A range of jet velocities is investigated while keeping other parameters constant. The research focuses on investigating the impact of jet velocity on three key aspects: the total amount of entrained gas; the size of gas bubbles affected and dispersed by the jet; and the depth of penetration of the jet, with particular emphasis on understanding the distribution of bubble sizes. To achieve these objectives, a three-dimensional simulation approach employing a full Eulerian method coupled with a Large-Scale Interface capturing method and Population Balance modelling is applied. Modelling aspects, including meshing, turbulence model etc., will be discussed. The obtained results will be validated through experimental data of plunging jet experiments from literature. |
Monday, November 25, 2024 9:31AM - 9:44AM |
L07.00008: The formation of bubble emulsions in microgravity: experimental design Madeline Elizabeth Federle, Roberto Zenit
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Monday, November 25, 2024 9:44AM - 9:57AM |
L07.00009: Degassing-dominated bubble populations in air-entraining free-surface turbulence Declan B. Gaylo, Kelli L Hendrickson, Dick K P Yue The size distribution of bubbles created by air entrainment at a free surface is important to a variety of natural and engineering applications. In addition to entrainment, fragmentation and degassing of bubbles are relevant physical mechanisms. When fragmentation is dominant, Garret et al. (J. Phys. Oceanogr., vol. 30, 2000) predict a -10/3 power law for the bubble size distribution of large Weber number, We, bubbles. This power law is ubiquitous in breaking waves. Here, we study entrainment by free surface turbulence (FST) where, unlike breaking waves, the energy to entrain bubbles comes directly from turbulence beneath the free surface. We perform direct numerical simulation (DNS) of a canonical FST flow at a range of Froude number, Fr, to study the relative effects of fragmentation versus degassing during active air entrainment. Even at We>>1 when we expect fragmentation to be strongest, we find the effect of degassing is dominate over fragmentation. We develop a theory to predict the power law of the bubble size distribution under degassing dominance, which agrees with DNS results. This distribution is distinct from the fragmentation-dominated distribution in two ways. First, two regimes of bubble degassing in turbulence lead to a split power law, with a critical bubble radius scaling with Fr and Reynolds number Re. Second, in both regimes the power law is more negative (fewer large bubbles) than -10/3. We discuss what measures, in addition to the power-law of the bubble size distribution, can be used to determine if a given air entraining flow is fragmentation or degassing dominated. |
Monday, November 25, 2024 9:57AM - 10:10AM |
L07.00010: Unsteady dynamics of long gas bubbles travelling in a liquid-filled capillary tube Mirco Magnini, Miguel A Herrada, Jens Eggers, Howard A Stone The steady propagation of a long gas bubble through a viscous liquid within a circular tube is a classical problem in fluid mechanics since the seminal studies of Bretherton and Taylor. This problem has been extensively studied for small capillary and Reynolds numbers, where a steady flow is achieved. However, recent experimental and computational studies revealed that if the Weber number of the flow is sufficiently larger than unity, the rear meniscus of the bubble becomes unstable and time-dependent patterns arise. In this work, we employ linear global stability analysis and direct numerical simulations to study the occurrence and origin of this instability. For capillary numbers in the range Ca=0.005-0.04, we show that the flow becomes unstable when the Weber number grows above values in the range We=9-16. The instability is due to a non-monotonic pressure profile established along the rear meniscus of the bubble, which surface tension is unable to oppose beyond a certain threshold in the Weber number. The linear global stability analysis and DNS predict bubble shapes, stability boundaries and time-dependent patterns in good agreement with each other. The stability boundary is identified well by a modified Weber number which describes the competition of pressure and capillary forces acting on the rear meniscus of the bubble. |
Monday, November 25, 2024 10:10AM - 10:23AM |
L07.00011: Electrostatic interaction induced bubble coalescence in saturated electrolytes Fleur Avontuur, Luis M Portela, Bijoy Bera Coalescence of (produced) gas bubbles in an electrolyzer plays a crucial role in the subsequent dynamics and removal of these bubbles, leading to a specific efficiency of the electrolyzer. One of the parameters influencing this bubble coalescence is the restructuring of interfacial charge due the the electrolyte being saturated with the produced gas. In this work, we investigate the coalescence of two simultaneously growing gas bubbles, positioned next to each other, in a saturated electrolyte. We particularly focus on the effect of the approach velocity (towards each other) of these bubbles, resulting in an atypical film (between the two gas bubbles) thinning dynamics prior to the coalescence. The thin film dynamics is observed to be dependent on the redistribution of charges on either interface (of the thin film) due to reactions occurring in presence of the saturating gas in the surrounding. The resulting electrostatic interaction governs the timescale of gas bubble coalescence below a threshold approach velocity. Above this approach velocity, the coalescence dynamics is governed by the capillary timescale of the drainage of the thin film. The observation is further supported by the coalescence behavior at various pH values of the electrolyte, since these pH values contribute to different degrees of electrostatic charge redistribution at the interface. |
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