Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session R5: Bubbles: General |
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Chair: Sigurdur Thoroddsen, King Abdullah University of Science and Technology Room: 3008 |
Tuesday, November 25, 2014 1:05PM - 1:18PM |
R5.00001: Particle induced air bubble break-up in a Hele-Shaw cell Peng Zhang, John Mines, Sungyon Lee, Sunghwan Jung Hydrodynamic interactions of drops and bubbles with particles in viscous fluids are important in the multiphase separation and reaction processes. In the present work, we explore the fundamental mechanism of such complex processes by studying the collision of a single bubble with a fixed solid particle inside a Hele-Shaw cell. Physical experiments show that an air bubble either splits or slides around the particle depending on the initial transverse offset between the bubble and particle centroids. A bubble slides around the particle until the offset is decreased below a critical value, in which case the bubble splits into two daughter bubbles. We are able to predict this slide-split transition using a theoretical model that compares the relative change in surface energy, gravitational potential and viscous dissipation in the two regimes. [Preview Abstract] |
Tuesday, November 25, 2014 1:18PM - 1:31PM |
R5.00002: Determination of the diffusion coefficient in a bubble suspension for large but finite Reynolds numbers Rodolfo Alcala, Alicia Aguilar, Roberto Zenit, Bernardo Figueroa, Jesus Correa This paper presents experimental results concerning the study of a bubble suspension confined in a thin channel for different volume fractions of gas, in a regime characterized by Reynolds numbers of order 10$^{2}$ - 10$^{3}$. The experimental set-up consists in a Hele-Shaw cell thin channel, a high speed camera, a diffused backlight system and a rotameter to control the flow of Nitrogen into the system. A trajectography technique is used to obtain the flow properties from series of digital images captured by the high speed camera. The trajectories and velocities of the bubbles were calculated from the instantaneous bubbles positions. With these measurements, the diffusion coefficients for different gas fractions were determined using the method of the autocorrelation function. [Preview Abstract] |
Tuesday, November 25, 2014 1:31PM - 1:44PM |
R5.00003: Dissolution of spherical cap CO$_2$ bubbles attached to flat surfaces in air-saturated water Pablo Pe\~nas, Miguel A. Parrales, Javier Rodriguez-Rodriguez Bubbles attached to flat surfaces immersed in quiescent liquid environments often display a spherical cap (SC) shape. Their dissolution is a phenomenon commonly observed experimentally. Modelling these bubbles as fully spherical may lead to an inaccurate estimate of the bubble dissolution rate. We develop a theoretical model for the diffusion-driven dissolution or growth of such multi-component SC gas bubbles under constant pressure and temperature conditions. Provided the contact angle of the bubble with the surface is large, the concentration gradients in the liquid may be approximated as spherically symmetric. The area available for mass transfer depends on the instantaneous bubble contact angle, whose dynamics is computed from the adhesion hysteresis model [Hong et al., Langmuir, vol. 27, 6890-6896 (2011)]. Numerical simulations and experimental measurements on the dissolution of SC CO$_2$ bubbles immersed in air-saturated water support the validity of our model. We verify that contact line pinning slows down the dissolution rate, and the fact that any bubble immersed in a saturated gas-liquid solution eventually attains a final equilibrium size. [Preview Abstract] |
Tuesday, November 25, 2014 1:44PM - 1:57PM |
R5.00004: Gas dissolution in antibubble dynamics Benoit Scheid, Jan Zawala, St\'ephane Dorbolo Antibubbles are ephemeral objects. Their lifetime is driven by the slow drainage of the air shell from the bottom to the top of the antibubble under the action of the hydrostatic pressure. We show in this work that this argument is only valid if the water used to make the surfactant mixture is saturated in air. Otherwise, two paths are used by the air that conducts to the thinning and the eventual collapse of the air shell: the drainage from the bottom to the top of the antibubble and the dissolution of the air by the liquid. Using degassed water dramatically shortens the lifetime of the antibubbles, as observed experimentally and rationalised by time-dependent simulations. Consequently, the antibubble lifetime is not only correlated to physical and chemical properties of the air-liquid interface but also to the gas content of the liquid. We also show that pure gas dissolution does not depend on the antibubble radius, a behaviour that allows to rationalise unexplained experimental data found in the literature. [Preview Abstract] |
Tuesday, November 25, 2014 1:57PM - 2:10PM |
R5.00005: History effects on the diffusion-driven growth and dissolution of a gas bubble Javier Rodriguez-Rodriguez, Miguel A. Parrales, Pablo Pe\~nas, Oscar Enriquez, Elena Igualada-Villodre, Devaraj van der Meer A bubble of a gas that is soluble in the surrounding liquid may grow or dissolve depending on whether the saturation concentration at the bubble's pressure is lower or higher than the gas concentration in the bulk liquid. In the limit of small Peclet, the (slow) diffusion-driven bubble growth or dissolution rates are commonly calculated using the Epstein-Plesset theory, despite the fact that it is only valid when the gas concentration field in the liquid is initially uniform. Here we show how to modify this theory to account for non-uniformities in the initial concentration field resulting from the past history of variations of the ambient pressure. In particular, we obtain a history term that closely resembles the Basset memory integral found in the unsteady translation of a sphere through a viscous fluid. The new formulation is applied to the particular example of a bubble, initially in diffusive equilibrium with the ambient, that is subjected to a depression and a later compression. The results are compared to numerical simulations as well as experiments. Funded by the Spanish Ministry of Economy and Competitiveness through grant DPI2011-28356-C03-02. [Preview Abstract] |
Tuesday, November 25, 2014 2:10PM - 2:23PM |
R5.00006: Thermocapillary motion of bubble under the action of gravity in a self-rewetting fluid Omar Matar, Manoj Tripathi, Kirti Sahu, George Karapetsas, Khellil Sefiane The motion of a bubble driven under the action of buoyancy and thermocapillarity inside a tube with a non-uniformly-heated walls, containing a so-called ``self-rewetting fluid" is investigated. The surface tension of the ``self-rewetting fluid" exhibits a parabolic dependence on temperature with a well-defined minimum. We perform direct numerical simulation of axisymmetric bubble motion in a fluid whose temperature increases linearly with vertical distance from the bottom of the tube for a range of Bond and Gallileo numbers, and for various parameters that govern the functional dependence of surface tension on temperature. We demonstrate that bubble motion can be reversed and then arrested in self-rewetting fluids for sufficiently small Bond numbers; this in contrast with the linear fluid (surface tension linearly decreases with increasing temperature). We also demonstrate that considerable bubble elongation is possible under significant wall confinement, and for strongly self-rewetting fluids and large Bond numbers. In the Stokes flow limit, we derive the conditions under which a spherical bubble can come to rest in a self-rewetting fluid whose temperature varies linearly in the vertical direction, and demonstrate that this is possible for both positive and negative temperature. [Preview Abstract] |
Tuesday, November 25, 2014 2:23PM - 2:36PM |
R5.00007: The effect of gravity-induced pressure gradient on bubble luminescence Outi Supponen, Danail Obreschkow, Philippe Kobel, Nicolas Dorsaz, Marc Tinguely, Mohamed Farhat The violent collapse of a bubble can heat up its gaseous contents to temperatures exceeding those on the sun's surface, resulting in a short luminescence flash. Occurring at the very moment of the collapse, luminescence must be highly sensitive to the bubble geometry at the preceding final stage. This represents an important feature as any pressure anisotropy in the surrounding liquid will result in a deformation of an initially spherical bubble, inducing a micro-jet that pierces the bubble and makes it experience a toroidal collapse. We therefore present these as complementary phenomena by investigating the link between jets and luminescence of laser-generated single bubbles. Through ultra-high-speed imaging, the micro-jet formation and evolution of a single bubble are observed with unprecedented detail, whilst the bubble light emission is analyzed by means of a spectrometer. The bubble energy and the micro-jet size are controlled by adjusting the laser-pulse and by varying the gravity level aboard ESA parabolic flights, respectively. We here provide systematic evidence on how bubble-jets suppress luminescence in a considerable manner, even in normal gravity where the jet is barely observable. We conclude that gravity must be accounted for in accurate models of luminescence. [Preview Abstract] |
Tuesday, November 25, 2014 2:36PM - 2:49PM |
R5.00008: Enhanced Condensation of Vapor Bubbles by Acoustic Actuation Thomas Boziuk, Marc Smith, Ari Glezer The effects of acoustic actuation on enhancement of the condensation rate of vapor bubbles in a liquid pool are investigated experimentally. Vapor bubbles are formed by direct injection into quiescent liquid in a sealed tank under controlled ambient pressure that varies from atmospheric to partial vacuum. The bubbles are injected vertically from a pressurized steam reservoir through nozzles of varying characteristic diameters, and the actuation is applied during different stages of the bubbles formation and advection. It is shown that kHz range acoustic actuation leads to excitation of high-amplitude surface capillary (Faraday) waves at the vapor-liquid interface that significantly increases the condensation rate. The concomitant controlled changes in bubble volume and in the structure of the vapor interface strongly affect bubble advection in the liquid pool. The increase in condensation rate is affected by the surface waves that increase the mixing in the thermal boundary layer surrounding the bubble, and on the advection of the bubble within the pool. High-speed image processing is used to quantitatively measure the scale of the capillary waves and their effect on vapor bubble dynamics at several ambient pressures that affect the global condensation rate. [Preview Abstract] |
Tuesday, November 25, 2014 2:49PM - 3:02PM |
R5.00009: Investigation of a relationship between Spherical-shape particle flocculation and acoustic-cavitation-oriented bubbles (ACOBs) under kHz-band ultrasonic irradiation Sayuri Yanai, Yuki Mizushima, Takayuki Saito We investigated unprecedented spherical-shape particle flocculation with an effect of acoustic-cavitation-oriented bubbles (ACOBs) that were generated in water under kHz-band ultrasonic irradiation. In past studies, particle concentrations forming stripes under MHz-band ultrasonic irradiation have been investigated and reported by many previous researchers. However, the spherical-shape particle flocculation is very anomalous. Further, it is able to flocculate mm-order particles that are principally impossible to manipulate using of MHz-band ultrasonic. We focused on the mechanism of the spherical-shape particle flocculation under 20-kHz-ultrasonic irradiation in water. From our experimental results of spherical-shape particle flocculation, we found out that the flocculation factors were not only acoustic radiation force but also behavior of the ACOBs. The ACOBs adhering to the particle surface moved to a certain position with the particle, depending on acoustic pressure distribution in the water. In the present study, we report and discuss the results of the visualized relationship among the ACOB motion, the particle motion and acoustic pressure distribution in water. [Preview Abstract] |
Tuesday, November 25, 2014 3:02PM - 3:15PM |
R5.00010: Theoretical and Experimental Investigation of Particle Trapping via Acoustic Bubbles Yun Chen, Zecong Fang, Brett Merritt, Darius Saadat-Moghaddam, Dillon Strack, Jie Xu, Sungyon Lee One important application of lab-on-a-chip devices is the trapping and sorting of micro-objects, with acoustic bubbles emerging as an effective, non-contact method. Acoustically actuated bubbles are known to exert a secondary radiation force on micro-particles and trap them, when this radiation force exceeds the drag force that acts to keep the particles in motion. In this study, we theoretically evaluate the magnitudes of these two forces for varying actuation frequencies and voltages. In particular, the secondary radiation force is calculated directly from bubble oscillation shapes that have been experimentally measured for varying acoustic parameters. Finally, based on the force estimates, we predict the threshold voltage and frequency for trapping and compare them to the experimental results. [Preview Abstract] |
Tuesday, November 25, 2014 3:15PM - 3:28PM |
R5.00011: Microscopic engine driven by laser-induced cavitation bubbles Pedro Quinto-Su In this work an analogue to a microscopic intermittent internal combustion engine is realized with a single microparticle periodically driven by cavitation bubbles at rates of up to 500 Hz. [Preview Abstract] |
Tuesday, November 25, 2014 3:28PM - 3:41PM |
R5.00012: Satellite formation during bubble transition through an interface between immiscible liquids Erqiang Li, Shabbab Al-Otaibi, Ivan Vakarelski, Sigurdur Thoroddsen A bubble can pass through the interface between two immiscible liquids if it is energetically favourable. Once the intermediate film has drained sufficiently, the bubble makes contact with the interface, forming a triple-line and producing strong capillary waves which travel around the bubble and can pinch off a satellite on the opposite side, akin to the coalescence cascade dynamics. We identify the critical Ohnesorge number where such satellites are produced and characterize their sizes. The total transition time scales with the bubble size and differential surface tension, while the satellite pinch-off time scales with the capillary-inertial time of the pool liquid which originally surrounds the bubble. We also use high-speed video imaging to study the contact neck motion. For low viscosity it grows in time with a power-law exponent between 0.44 and 0.50, with a prefactor modified by the net sum of the three interfacial tensions. Increasing the receiving drop viscosity drastically slows down the triple-line motion, when the Ohnesorge number exceeds around 0.08. This differs qualitatively from the coalescence of two miscible drops of different viscosities, where the lower viscosity sets the coalescence speed. We thereby propose a strong resistance from the triple-line. [Preview Abstract] |
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