Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session G25: Bubbles: General |
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Chair: Henri-Louis Girard, MIT Room: 607 |
Sunday, November 24, 2019 3:48PM - 4:01PM |
G25.00001: Reducing ice adhesion via in-situ electrolysis Henri-Louis Girard, Srinivas Subramanyan, Ha Eun David Khang, Yang Shao-Horn, Kripa Varanasi The formation of ice on solid substrate is the cause of numerous problems such as loss of shape of airfoils, weight increase of structures, heat transfer through roofs, slipperiness of surfaces, and more. Current de-icing technologies such as resistive heating, mechanical fracturing, or chemical spraying are either energy intensive or environmentally problematic. The use of super-hydrophobic surfaces to mitigate ice adhesion has been explored and shown to lead to significant reductions in the adhesion strength of ice as long as the texture was not penetrated by the ice. Unfortunately, cold surfaces exposed to humid environments are subject to frost formation which fills the defects and reduces the performance of these substrates. Here, we demonstrate the use of water electrolysis as a means to create stress-concentrators within the ice-solid interface \textit{in situ}. This study investigates the capture of bubbles at the ice-solid interface and the effect of these bubbles on the adhesion of ice on the surface. [Preview Abstract] |
Sunday, November 24, 2019 4:01PM - 4:14PM |
G25.00002: Bubble Breathing during Dissolution in Confined Geometries under Partial Wetting Ke Xu, Amir Pahlavan, Ruben Juanes One expects that, during the dissolution of a gas bubble into surrounding liquid, the bubble volume will decrease monotonically as a result of continuous mass loss. This intuitive picture, however, changes in a surprising way when the dissolving bubble is confined in a geometry under partial wetting to the gas and the liquid. We show that the bubble then experiences cycles of volume expansion (``inhaling'') and shrinkage (``exhaling''), until it fully dissolves. This bubble ``breathing'' is the result of condensation, growth and merging of liquid droplets on the gas-solid surface, and their eventual expulsion from the gas bubble. Theoretical analysis shows that these counter-intuitive dissolution dynamics are driven by a reduction in the system's free energy. We provide a scaling argument that identifies the transition from this intermittent expansion-shrinkage ``breathing'' regime and the classical shrinkage-dominated regime. This behavior could play a major role in determining the macroscopic mass-transfer dynamics in partially wetting systems under confinement, such as oxygen transfer in low-temperature fuel cells and enhanced hydrocarbon recovery in porous rocks. [Preview Abstract] |
Sunday, November 24, 2019 4:14PM - 4:27PM |
G25.00003: ABSTRACT WITHDRAWN |
Sunday, November 24, 2019 4:27PM - 4:40PM |
G25.00004: ABSTRACT WITHDRAWN |
Sunday, November 24, 2019 4:40PM - 4:53PM |
G25.00005: Bubble under field : similarities and differences Sebastien Mawet, Stephane Dorbolo, Herve Caps, Cyprien Gay, Florence Elias Deformations undergone by a droplet submitted to an electrical force have been recently studied by Beroz et al. They propose a law based on the equilibrium between capilarity and electrical force. On the other hand, Ikkala et al. focus on the dynamics of a ferrofluids droplet resting on a superhydrophobic surfaces under a a magnetic field. They observe the division of a droplet in two smaller ones. Both works show the current interest for the manipulation and the deformation of droplet. Here, we propose to compare with bubbles. We propose to characterize the shape of the bubble submitted to a electric and a magnetic field. Both applied fields lead to similar deformations of the bubble. In particular, we characterize the shape variations of the surface of the hemispherical bubble immersed in the uniform electric field of a plan capacitor. We also observe those variations for a ferrofluids hemispherical bubble under a uniform magnetic field. [Preview Abstract] |
Sunday, November 24, 2019 4:53PM - 5:06PM |
G25.00006: Numerical Simulations of Gas-Liquid Dispersion in Millichannels Through Parallel Contacting Sections Xiaojin Tang, Thomas Abadie, Omar Matar The generation of a regular train of bubbles or droplets in microchannels has been a challenge for the past decade for optimising microreactor design and operation. Although many contacting methods (e.g. T-junctions, cross-junctions) have been studied for single channels, the effects of operating conditions for generating well-controlled bubble dispersions with multiple contacting sections still requires further understanding. For industrial applications, millichannels can be more useful than microchannels to avoid blockage and for higher throughput. However, few research results in millichannels could be found in the literature. We study the gas dispersion in a liquid flowing in a rectangular millichannel through three parallel contacting sections. A finite-volume solver with a Volume-Of-Fluid method to capture the interface is used. The effects of geometry and operating conditions on the gas flow through the contacting sections are analysed along with the breakup frequencies. The effects of contacting section geometry on bubble size distributions and velocities under which stable bubble trains can be formed are discussed as a step towards developing an optimal structure of millichannels where uniform and highly dispersed bubble swarms can be achieved. [Preview Abstract] |
Sunday, November 24, 2019 5:06PM - 5:19PM |
G25.00007: Estimation of the Refractive Index inside Laser-Induced Cavitation Bubble: An Experiment Ariana Sabzeghabae, Luis Flipe, Enoch Gutierrez Herrera, Guillermo Aguilar ~An experimental procedure was used to estimate the refractive index changes inside a cavitation bubble. An Nd:YAG laser of 6 ns was used to induce cavitation bubbles inside ethanol. A HeNe continuous laser beam was aimed perpendicular to the pump beam for ray tracing purposes and estimating the refractive index changes inside the cavitation bubble. High-speed photography was used to measure the diameter of the bubbles and monitor the deflection of the HeNe beam. To confirm this analysis, a series of static bubbles with known refractive indices inside PDMS molds were designed. Knowledge about the trend of refractive index changes inside the bubble could give researchers insightful information about the temperature and pressure gradients inside the cavitation bubbles by assuming the ideal gas law. [Preview Abstract] |
Sunday, November 24, 2019 5:19PM - 5:32PM |
G25.00008: Bubble pinch-off in turbulence: shape oscillations and escaping self-similarity Daniel Ruth, Wouter Mostert, Stéphane Perrard, Luc Deike Though bubble pinch-off is an archetype of a dynamical system evolving towards a singularity, it has always been described in idealized theoretical and experimental conditions. Using experiments, simulations, and analytical modeling, we consider bubble pinch-off in a turbulent flow, representative of natural conditions in the presence of strong and random perturbations. We show that the turbulence sets the initial conditions for pinch-off, but once the pinch-off starts, the turbulent time at the neck scale becomes much slower than the pinching dynamics: the turbulence freezes. We show that the average neck size, $\overline{d}$, can be described by $\overline{d} \sim (t-t_0)^{\alpha}$, where $t_0$ is the pinch-off, or singularity time, and $\alpha\approx 0.5$, in close agreement with the axisymmetric theory with zero initial flow. Neck shape oscillations set by the initial conditions are described by a quasi-two-dimensional linear perturbation model, and persistent asymmetries in the neck are related to the complex flow field induced by the deformed bubble shape. In many cases, a three-dimensional kink-like structure forms on part of the neck just before pinch-off, causing $\overline{d}$ to escape its self-similar decrease. [Preview Abstract] |
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