Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session HJ: Bubbles V: General Experiments |
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Chair: Ellen Longmire, University of Minnesota Room: 101I |
Monday, November 23, 2009 10:30AM - 10:43AM |
HJ.00001: Superheated water drops in hot oil Enrique Soto, Roberto Zenit, Andrew Belmonte Drops of water at room temperature were released in hot oil, which had a temperature higher than that of the boiling point of water. Initially, the drop temperature increases slowly mainly due to heat transfer diffusion; convective heat transfer is small because the motion takes place at a small Reynolds number. Once the drop reaches the bottom of the container, it sticks to the surface with a certain contact angle. Then, a part of the drop vaporizes: the nucleation point may appear at the wall, the interface or the bulk of the drop. The vapor expands inside the drop and deforms its interface. The way in which the vapor expands, either smooth or violent, depends on the location of the nucleation point and oil temperature. Furthermore, for temperatures close to the boiling point of water, the drops are stable (overheated); the vaporization does not occur spontaneously but it may be triggered with an external perturbation. In this case the growth of the vapor bubble is rather violent. Many visualization for different conditions will be shown and predictions of the growth rate will be discussed. [Preview Abstract] |
Monday, November 23, 2009 10:43AM - 10:56AM |
HJ.00002: Numerical Analysis of Optical Fiber Probing by Ray Tracing Method. Akihiro Sakamoto, Takayuki Saito Ray tracing numerical analysis of optical fiber probing, which is one of practical measurement techniques of bubbles and droplets dynamics, has been developed as a reliable instrument of bursting gas-liquid surface. The analysis is constructed by bounded surfaces of flat planes, cylinders, and ellipsoids and constant refractive index objects in three dimensions. The rays' energy of reflection and refraction are calculated repeatedly on the surfaces considered with polarization. The rays' source is assumed as linear polarized light with random fluctuations simulating laser source. The numerical results of the ray trajectories agree with the visualization results. In addition, the signal of returned ray energy forms sharpen peak just before the sensing edge bursting gas-liquid surface, same as experiment. [Preview Abstract] |
Monday, November 23, 2009 10:56AM - 11:09AM |
HJ.00003: Deformation and Magnetophoresis of Bubbles in Magnetic Fluids (Ferrofluids) Philip Yecko, Wah-Keat Lee, Ruben Scardovelli, A. David Trubatch The deformation and coalescence of small bubbles in magnetic fluid (ferrofluid) are directly observed and measured using a novel X-ray phase contrast imaging technique. High resolution X-ray images and videos of water-based ferrofluid (EMG-607/707) reveal: (i) vapor bubbles having diameters in the range 50 to 1000 microns form readily, (ii) neighboring bubbles chain together readily, but do not merge, and (iii) the dynamics of interfaces (bubbles) in ferrofluids are modified by the presence of long chain-like aggregates of the constituent magnetic nanoparticles. Isolated bubbles larger than a few hundred microns become visibly prolate in an applied field, elongating along the field direction. The observed deformations compare favorably with theoretical estimates and the results of direct numerical simulations (DNS). Coalescence is driven by attractive magnetophoretic force induced by non-uniform fields associated with individual bubbles, as was verified by comparing coalescence dynamics to theoretical prediction and to detailed results from DNS. Chain like aggregates of magnetic nanoparticles aligned with the applied field were ubiquitous and led to anisotropic field dependent drag effects. A multiple color function Volume of Fluid (VOF) technique was used to suppress bubble merger in DNS. [Preview Abstract] |
Monday, November 23, 2009 11:09AM - 11:22AM |
HJ.00004: Dynamics of Bubble Rising in Vertical and Inclined Square Channel Luz Amaya-Bower, Taehun Lee A stable Lattice Boltzmann Equation (LBE) Model based on the Cahn-Hilliard diffuse interface approach is used to investigate the dynamics of a bubble rising in a vertical and inclined square channel with large density and viscosity ratios. Deformation parameter ($\Delta )$ and terminal velocity (U$_{t})$ of the bubble are interrelated quantities which depend on non-dimensional numbers such as Bond Number (Bo), Morton Number (Mo) and ratio between bubble diameter and channel width ($\kappa )$. This study confirms the relationship between $\kappa $ and $\Delta $ and film thickness ($\delta )$, as it was reported by previous experimental studies. As $\kappa $ is increased, higher $\Delta $ and smaller $\delta $ are exhibited. This finding is independent of the value of Bo and Mo. In addition, an evaluation was performed for inclined channel to relate the non-dimensional value Froude Number (Fr) and the inclination angle ($\theta )$ as function of Bo and Mo. For each set of values of Bo and Mo, there is a critical value of $\theta $ which corresponds to the highest value of Fr, consequently highest U$_{t}$. This finding is consistent previous simulation and experimental results. This study was performed using a range of Bo and Mo, (10$^{-5} \quad <$ Mo $<$ 10$^{2})$ and (1 $<$ Bo $<$ 30), and the inclination of the channel is varied from 0\r{ } to 75\r{ }. [Preview Abstract] |
Monday, November 23, 2009 11:22AM - 11:35AM |
HJ.00005: Microcantilevers with strain gauges as active and passive bubble sensors Matthew Stegmeir, Ellen Longmire, Susan Mantell, Mubassar Ali In the current study, we investigate the sensitivity of microfabricated cantilevers with integrated strain gauge sensing to collisions of air bubbles in confined water channel flow. The vertical channel used is 585mm long with a 10mmx2mm cross-section. Flow is upward. Bubbles of diameter 400-2000$\mu $m are examined. Flow Reynolds numbers based on mean fluid velocity and hydraulic diameter of 1000-2500 are considered. Cantilevers extend from the center of the 2mm wall and are oscillated perpendicular to the flow direction. Bubbles are introduced upstream of cantilever mounting location and travel in the direction of the flow. Cantilever sizes of 6mmx2mm and 3mmx0.5mm with thickness $\sim $125$\mu $m and resonance frequencies of 340Hz and 2670Hz in water are considered. Bubble impacts are recorded using a high frame-rate camera. Strain gauge data are correlated with images. Active and passive results are considered for each beam. Changes in the instantaneous sinusoidal amplitude of the strain gauge signal are used to detect impacts. The effects of impacts on the signal from the strain gauge will be discussed. Results indicate that active sensing using the shorter, stiffer beam is most effective at detecting bubble impacts. Supported by the National Science Foundation (CMS-0300125). [Preview Abstract] |
Monday, November 23, 2009 11:35AM - 11:48AM |
HJ.00006: Transient Pressure Measurements in Microscale Bubble Flows Siavash Aslanbeigi, Michael McNeil, Lian Leng, Axel Guenther Microscale bubble flows have found a wide range of applications in lab-on-a-chip systems and for microchemical synthesis. Most previous studies of these flows have relied on optical micrographs of the fluid phase distribution. We present time-resolved measurements of the fluid pressure during steady flow along the channel that provide for a very sensitive tool to discriminate between flow regimes, to determine bubble/droplet velocities and -- in multichannel arrangements - to achieve flow synchronization. We integrated piezoresistive pressure transducers in soft lithographically patterned microfluidic devices. On-chip integration significantly reduced the available dead volume and removed any unwanted bubbles in the sensing channel. The integrated pressure sensors were calibrated and electrically amplified. Dynamic pressure measurements at millisecond time resolution and a sensitivity exceeding the capillary pressure by at least one order of magnitude were obtained. The presented results were obtained at different wetting conditions and for segmented gas-liquid flows at Capillary numbers of 0.001-0.05. [Preview Abstract] |
Monday, November 23, 2009 11:48AM - 12:01PM |
HJ.00007: An Experimental Investigation of the Implosion of Cylindrical Shell Structures C.M. Ikeda, J. Wilkerling, J.H. Duncan An experimental study of the physics of the implosion of cylindrical shell structures in a high-pressure water environment was performed. The shell structures are filled with air at atmospheric pressure and the implosions occur when the water pressure is raised above the shell buckling stability limit. High-speed photography (27,000 fps) was used to observe and measure the motion of the structure during its implosion. High-frequency underwater blast sensors recorded dynamic pressure waves at 13 positions in the tank. The cylindrical models are made from various aluminum alloys (diameter D = 39.1 mm, wall thickness t = 0.89 mm) and brass (D = 16.7 to 25.4 mm, t = 0.33 to 0.36 mm). The ends of the tubes were sealed with Aluminum caps. The pressure records are interpreted in light of the high-speed movies. Cylinder length-to-diameter (L/D) ratios between 6 and 10 were examined; in this range the cylinders implode in a mode 2 cross-sectional shape at pressures between 6.9 and 28.7 bar. It is found that the pressure versus time records from sensors placed at the same dimensionless radial position (r/D) from the cylinder surface scale well with time and pressure scales from cavitation bubble collapse theory. [Preview Abstract] |
Monday, November 23, 2009 12:01PM - 12:14PM |
HJ.00008: Bubble bursting mediated aerosols Henri Lhuissier, Emmanuel Villermaux Wave breaking over the ocean in the surf zone is responsible for a substantial amount of atmospheric aerosols production. The objects mediating their formation are bubbles entrained below breaking waves, and bursting at the sea surface. We describe the mechanisms by which the liquid shell constitutive of a bubble ultimately results into small drops, also called {\it film drops}. A bubble bursts when a hole nucleates through the liquid shell. The hole grows at the Culick velocity balancing inertia with surface tension and is bordered by a rim collecting the shell liquid. This initially smooth toroidal rim corrugates when the centripetal acceleration caused by the recession motion is strong enough to trigger a Rayleigh-Taylor destabilization. Ligaments then emerge from corrugations crests and resolve by a Plateau-Rayleigh mechanism into droplets. The final myst properties are thus solely determined by the shell geometry at the bursting onset. It depends on the ratio of the bubble radius to the capillary length, and on the slow gravity drainage of the liquid on which are superimposed rearrangements due to the marginal regeneration at the bubble foot. Our findings will be discussed in connexion with know facts in that context. [Preview Abstract] |
Monday, November 23, 2009 12:14PM - 12:27PM |
HJ.00009: Faraday waves at foam/liquid interface Herve Caps, Giles Delon Monodisperse foams are produced in Hele-Shaw cells and submited to vertical oscillations. This leads to a destabilization of the interface bewteen the foam and the liquid bath. Faraday instability has been identified and characterized in terms of wavelength and destabilization threshold. The control parameters which are considered are: the frequencies of the oscillations, varying between $10$~Hz and $100$~Hz, the amplitudes of the oscillations, ranging from $1$~mm to $15$~mm and the bubble size, which is millimetric. Considering the foam as a continuous media, the waves at the interface can be linked to an effective surface tension of the interface, wich depends on the bubble size and the oscillation parameters. Results are interpreted with help of fast-cam recording and energy considerations. This study paves the way to a new continuous approach of liquid/foam interfaces. [Preview Abstract] |
Monday, November 23, 2009 12:27PM - 12:40PM |
HJ.00010: Forced Aspiration of bubbles into a capillary tube Melanie Durth, Christophe Clanet, Juan Fernandez One way to remove lodged bubbles in small vena is to force the bubble to be completely aspirated into a fine needle. We study the aspiration of a bubble into a vertical capillary tube, for different bubble size relative to the capillary diameter (i.e. bubble confinement) and low Bond numbers (pipette diameter $<<$ capillary length). In this case, there is a critical condition of flow rate depending on the bubble confinement and the capillary number Ca beyond which the bubble is aspirated completely into the capillary. Below this value, the bubble breaks-up forming a liquid slug at the entrance of the tube. A simple model which takes into account the draining time of the annular liquid thin film and the characteristic time of the capillary instability, explains the observed experimental results and establish the characteristic time to aspirate completely the bubble. [Preview Abstract] |
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