Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session G09: Bubbles: Micro-/Nano-bubbles |
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Chair: Claus-Dieter Ohl, Otto von Guericke University Magdeburg, Institute of Physics, Universitätsplatz 2, 39106 Magdeburg Room: 136 |
Sunday, November 20, 2022 3:00PM - 3:13PM |
G09.00001: On Demand Bulk Nanobubble Generation Juan Manual Rosselló, Claus-Dieter Ohl A critiical feature of bulk nanobubbles that distingusihes them from droplets and particles is their ability to expand under the action of a rarefaction wave. This feature has been probed in experiments with two kinds of waves. 1) a short bi-polar pressure wave with sub-microsecond duration created with a laser-induced breakdown near a free interface and 2) a typical lithotripter shock wave trailed by a rarfaction wave. Both waves cause the expansion vapor bubbles only if the same volume of water is illumiated by a short and intense laser beam. We argue that the laser beam by some means nucleate nanobubbles that are then expanded into visible bubbles. By applying a suitable timing between rarefaction wave and laser beam and assume that classical diffusion holds we can measure the population of nanobubbles generated. |
Sunday, November 20, 2022 3:13PM - 3:26PM |
G09.00002: Investigation of cavitation bulk nanobubbles in various pH and surfactant concentrations Jinseok Lee, Ritesh Prakash, Jinkee Lee Nowadays, nanobubbles (NBs) are attracting interest from many researchers because of their various applications and high stability. However, since it is very challenging to investigate the NBs quantitatively or qualitatively, few studies have been conducted to observe the characteristics of the NBs in various media. In this study, we generated the cavitation bulk NBs by varying the pH and surfactant concentration of the solutions in which NBs were generated. The generated NBs were analyzed in terms of zeta potential, average diameter, and concentration. The zeta potential of the NBs was analyzed by the electrophoretic light scattering (ELS) method and the average diameter and concentration of the NBs were observed by the nanoparticle tracking analysis (NTA) method. The zeta potential of the NBs was directly affected by the properties of the additive which are added to the solution such as HCl, NaOH, a cationic surfactant, and an anionic surfactant. The average diameter of the NBs was highly related to the zeta potential and surfactant concentration. The concentration of the NBs had the highest value nearby the CMC (critical micelle concentration). Moreover, by applying the DLVO theory, the theoretical investigation of the stability of NB was conducted. |
Sunday, November 20, 2022 3:26PM - 3:39PM Author not Attending |
G09.00003: Steady Streaming generated by an acoustically oscillating slug Shambhu Anil, Pushpavanam Subramaniam A sessile micro bubble oscillating under the influence of an ultrasound field creates strong microstreaming vortices. These induced vortices have been exploited by researchers in particle trapping, micro-pumping, micro-mixing, and particle separation. Analytical studies in the past have been conducted assuming the sessile bubble to be semi-cylindrical. However, experiments with applications in micro-mixing and micro-pumping often encounter an oscillating bubble interface that is comparatively flat at a steady state. Our focus in this study is to obtain a semi–analytical solution to the steady two-dimensional flow field induced by an oscillating trapped interface of a slug in a microchannel using perturbation techniques in cartesian coordinates. We consider three different boundary layers i.e., two close to the enclosing walls and one close to the oscillating gas-liquid interface separately, as Reynolds stresses are high in these regions. We obtain a composite solution to the zeroth order flow using matched asymptotics. Mixed mode streaming is observed in first order non – oscillatory flow. The simplified first-order problem is solved numerically to obtain the flow field generated by the bubble. |
Sunday, November 20, 2022 3:39PM - 3:52PM |
G09.00004: Mechanistic insights into nanobubbles dynamics through in-situ liquid phase electron microscopy Sarthak Nag, Yoko Tomo, Hideaki Teshima, Koji Takahashi, Masamichi Kohno The observation of surface nanobubbles at real-time scales is essential to understand the interactions between their adjacencies. Therefore, to gain insights into their dynamic behavior, we used in-situ liquid-phase electron microscopy technique to observe surface nanobubbles with high spatial and temporal resolutions. A water film, having thickness of hundreds of nanometers, was encapsulated between two silicon nitride membranes and was observed using a 200 kV transmission electron microscope. The gas nanobubbles were nucleated by radiolysis phenomenon, which creates the locally gas oversaturated environment in the liquid. Our study focuses on the pinning-depinning characteristics of nanobubbles' contact line and the coalescence following contact line depinning. The differential gas oversaturation around a strongly pinned gas nanobubble leads to the asymmetric and directional depinning of its contact line. Further, we found that the two nanobubble coalescence is initiated by the formation of an adsorbed gas layer between the nanobubbles' adjacent contact line, which also acts as a bridge for gas exchange. Overall, our experimental investigation shows that the gas oversaturation is dominant in governing the studied nanobubble dynamics. |
Sunday, November 20, 2022 3:52PM - 4:05PM |
G09.00005: Transition in the growth mode of plasmonic bubbles in binary liquids Marvin Detert, Yibo Chen, Harold Zandvliet, Detlef Lohse Metal nanoparticles under laser irradiation can produce enormous heat due to surface plasmon resonance. When submerged in a liquid, this can lead to the nucleation and growth of plasmonic bubbles. We study the growth of plasmonic microbubbles in binary liquids via high-speed imaging. By mixing fluids with a large difference in refractive index, we can additionally visualize instantaneous, local changes in the concentration. Surprisingly, for a certain concentration range, the bubble undergoes a spontaneous transition from slow, evaporative to fast, convective growth. The transition occurs as the three-phase contact line reaches the spinodal temperature of the more volatile component of the binary liquid. This leads to massive, selective evaporation and creates a strong solutal Marangoni flow along the bubble, which marks the beginning of convective growth. After the transition the bubble starts to oscillate in position and in shape. Though different in magnitude, the frequencies of both oscillations follow the same power law f ~ (ρ/σ R3 )-1/2, which is characteristic for bubble shape oscillations. The transitions and the oscillations both induce a strong motion in the surrounding liquid, opening doors for various applications where local mixing is beneficial. |
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