Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session M3: Bubbles III |
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Chair: Osman Basaran, Purdue University Room: 303 |
Tuesday, November 22, 2011 8:00AM - 8:13AM |
M3.00001: Optical Tomography of Polydisperse Dry Foam Anthony Chieco, Klebert Feitosa, P.T. Korda, A.E. Roth, D.J. Durian Dry foam is a disordered packing of bubbles that distort into familiar polyhedral shapes. We have implemented a method that uses optical axial tomography to reconstruct the internal structure of a dry foam in three dimensions. The technique consists of taking a series of photographs of the dry foam against a uniformly illuminated background at successive angles. By summing the projections we create images of the cross section of the foam and analyze them to locate the Plateau borders and vertices. The vertices are then connected according to Plateau's rules to reconstruct the internal structure of the foam. Using this technique we are able to visualize a large number of bubbles of real 3D foams and obtain statistics of faces and edges. [Preview Abstract] |
Tuesday, November 22, 2011 8:13AM - 8:26AM |
M3.00002: Wall effects in Stokes experiment with a liquid foam Haijing Gao, Hariprasad Subramani, Michael Harris, Osman Basaran Liquid foams are widely used in numerous applications ranging from the oil and gas industry to beauty, healthcare, and household products industries. A fundamental understanding of the relationships between the properties of liquid foams and their flow responses is, however, still in its infancy compared to that involving the fluid dynamics of simple fluids. In this talk, the flow of a dry liquid foam around a spherical bead, i.e. the Stokes problem for liquid foams, is studied experimentally. In contrast to previous work (cf. Cantat 2006), the focus of the present research is to probe the effect of a solid wall that is located a few bubble radii from the bead. The new experimental results show that the elastic modulus of dry liquid foams is directly proportional to the surface tension of the foaming agents and inversely proportional to the average bubble size in the foams, in agreement with previous theoretical and experimental studies. The experiments further show that the close proximity of the solid wall causes profound structural changes to the gas bubbles as the foam flows past the bead. A good understanding of these structural changes and how they can affect the elastic modulus of foams can be indispensable in formulating improved models for accurately describing the dynamical response of foams within the realm of continuum mechanics. [Preview Abstract] |
Tuesday, November 22, 2011 8:26AM - 8:39AM |
M3.00003: Velocimetry of aqueous foam drainage Matthew J. Kennedy, James W. Fleming We study the flow behavior of a freely draining aqueous foam using microparticle image velocimetry. Video shows liquid traveling uphill along the bubble surfaces, counter-directional to the primary flow. Most theoretical models of foam drainage avoid direct calculation of the flow at the gas-liquid interface. Rather, they treat the effect of surface flow empirically due to lack of experimental and theoretical understanding of the forces which cause flow at the surface. This uphill flow represents a significant component of the overall flow. Understanding the surface-driven flow can improve predictions of water-retention time. In the present work, we use a proprietary fire-suppression foam solution comprising hydrocarbon-based non-fluorinated surfactants in water. At the start of drainage, the mean upward flow speed is 0.2 $\pm $ 0.1 mm/s while the mean downward flow speed is 0.8 $\pm $ 0.1 mm/s. The local bubble size at the location-under-imaging is 0.6 mm with a coefficient of variation of 50{\%}. Ongoing efforts concern the effect of the liquid solution constituents on the uphill flow and the effect of bubble size on drainage time. [Preview Abstract] |
Tuesday, November 22, 2011 8:39AM - 8:52AM |
M3.00004: Bubble rearrangements dynamics in foams Marie Le Merrer, Severine Costa, Sylvie Cohen-Addad, Reinhard Hoehler Liquid foams are jammed dispersions of gas bubbles in a surfactant solution. Their structure evolves with time because surface tension drives a diffusive gas exchange between neighboring bubbles. This coarsening leads to a build-up of stresses which are relaxed upon local intermittent bubble rearrangements. These events govern the slow viscoelastic foam response, and similar bubble rearrangements are the elementary processes of plastic flow. Thus, the rearrangement duration is a key parameter describing how the microstructure dynamics control the macroscopic rheological response. We probe the duration of coarsening-induced rearrangements in 3D foams using a multiple light scattering technique (time resolved Diffusing-Wave Spectroscopy) as a function of the surfactant chemistry and the liquid fraction. As the foam becomes wetter, the confinement pressure of the packing goes to zero and the contacts between bubbles vanish. For mobile interfaces, we find that the rearrangements slow down as the jamming point is approached. These findings are compared to scaling laws which reveal an analogy between rearrangements dynamics in foams and granular suspensions. [Preview Abstract] |
Tuesday, November 22, 2011 8:52AM - 9:05AM |
M3.00005: Bubbling regime in planar co-flowing air-water sheets C. Guti\'errez-Montes, R. Bola\~nos-Jim\'enez, A. Sevilla, E. Sanmiguel-Rojas, C. Mart\'Inez-Baz\'an We study by means of experiments and numerical simulations the periodic breakup of an air sheet surrounded by a co-flowing water sheet, for a fixed liquid- to-gas thickness ratio, $h = h_ {w,0}^*/h_{a,0}^*\simeq 5.27$, as a function of their control parameters, namely the Weber number, $We=\rho_w\,u_{w,0}^{*2} \,h_{a,0}^*/\sigma$, and the water-to-air velocity ratio, $\Lambda=u_{w,0}^*/\bar u_{a,0}^*$, where $h_{a,0}^*$ and $h_ {w,0}^*$ are the half-thicknesses of the air and water sheets at the exit. The bubble formation process is divided into two stages governed by different physical phenomena: the formation of an incipient neck, which moves downstream at the water velocity, and the collapse of the neck. Both stages are characterized and a simple theoretical model, which depends on the control parameters, is proposed for each one in order to provide the time scale for the bubbling process, finding a good agreement with the experiments and simulations. Finally, the experimental measurements of the bubbling frequency and bubble size are compared with those obtained numerically within the $We$- $\Lambda$ parameter space studied. [Preview Abstract] |
Tuesday, November 22, 2011 9:05AM - 9:18AM |
M3.00006: Universality of Bubble-Jets in Gravitational Fields Danail Obreschkow, Marc Tinguely, Nicolas Dorsaz, Philippe Kobel, Aurele de Bosset, Mohamed Farhat Gravity matters: for us, as well as for small vapor bubbles in liquids. When cavitation bubbles collapse, they feel the presence of a faint hydrostatic pressure gradient caused by gravity -- an effect, which is widely neglected for the experimental difficulty of uncovering the weak action of gravity. We faced this challenge by designing an experiment able to generate uniquely spherical cavitation bubbles. Captivating high-speed movies showing the collapse of those bubbles manifest beautiful jets caused solely by gravity. These jets were studied systematically by running the experiment aboard an acrobatic aircraft (52nd ESA parabolic flight campaign), able to simulate the gravitational fields of the smallest moons and the largest planets in the solar system. The data reveals a clear connection between the size of the jets and the level of gravity. Further reduction and theoretical developments led to a universal scaling law between the size of jets emitted by cavitation bubbles and a single parameter, which only depends on the pressure field and the bubble volume. [Preview Abstract] |
Tuesday, November 22, 2011 9:18AM - 9:31AM |
M3.00007: Using a polydisperse bubble cloud as a non-invasive pressure probe Ana Medina-Palomo, Javier Rodriguez-Rodriguez Along the last 30 years, several techniques have been developed to measure non-invasively the pressure inside a liquid exploiting different features of the acoustic spectrum scattered by a cloud of bubbles. However, no technique is commercially avalilable nowadays, as all of them encounter technical difficulties that preclude their implementation. One of the common problems is that, in real (mostly medical) applications, bubble populations exhibit a wide range of sizes. We have studied numerically the acoustic behavior of polydisperse bubble clouds with the aim at evaluating the accuracy with which the pressure can be measured using one of these techniques. Namely, the determination of the pressure dependent component of the resonance frequency (Minnaert's frequency). A parametric study has been performed varying the properties of individual bubbles as well as those of the bubble distribution. The accuracy of the pressure measured using different conditions is reported, with suggestions for engineers and scientist working on the design of novel microbubbles (such as Ultrasound Contrast Agents). Finally, we have also developed a simplified expression to calculate the acoustic spectrum of a bubble population. This expression allows us to estimate, without the need of full simulations, the effect of the different parameters explored. Supported by the Spanish Ministry of Science through grant DPI2008-06369. [Preview Abstract] |
Tuesday, November 22, 2011 9:31AM - 9:44AM |
M3.00008: Infrared Measurements of Multiphase Flow Phenomena Jungho Kim, Tae Hoon Kim, Eric Kommer, Serguei Dessiatoun Understanding of phase change heat transfer mechanisms remains elusive due its sensitivity to many variables, but also due to the lack of reliable local information that can enable models to be tested. Although point measurements of variables such as local film thickness and heat transfer have been made, techniques whereby these quantities can be measured over the large areas have been lacking. IR thermometry is an established technology that can be used where optical access to the surface is available in the wavelength of interest. The use of IR measurements is demonstrated in this work to measure the inner and outer wall temperatures of an electrically heated silicon tube during flow boiling of FC-72. The electrical conductivity of silicon can be varied over a broad range by controlling the dopant concentration. Since silicon is largely transparent to IR radiation, the temperature of the inner and outer walls can be measured by coating selected areas with IR opaque thin films. FC-72 is also partially transparent to IR radiation over a broad range of wavelengths, allowing the flow to be visualized. Details of the proposed technique, test apparatus, data reduction, and model development are presented. [Preview Abstract] |
Tuesday, November 22, 2011 9:44AM - 9:57AM |
M3.00009: Flow of Air Bubbles in a Packed Bed Soto Enrique, Zenit Roberto, Aguilar-Corona Alicia The flow of bubbles through a granular media is presented. An index matching technique was used to visualize the permeation of bubble inside the packed bed formed by spheres with diameters from 0.5 mm to 6 mm and specific densities of 1.05 and 2.45. The volume of the bubble is determined by the flow rate and four distinctive modes were found. The first is for small bubbles that percolate without any deformation. The second is for larger bubbles that are deformed but still passed through the bed without break up. For the particles with higher density the third mode is observed and consists in the formation of air paths inside the bed. In the last mode, the air is cumulated till the bubble reaches a critical volume. Above the critical volume the granular media is fluidized and the bubble flows freely inside it. During this process some particles are dragged to the liquid bulk. The pore size and the capillary length were measured. Furthermore, the comparison of the bubbles velocity and shape inside the bed and in the liquid bulk are presented. These results agree with others authors who studied the emergence of bubbles from an immersed granular bed. [Preview Abstract] |
Tuesday, November 22, 2011 9:57AM - 10:10AM |
M3.00010: Anomalous coalescence in sheared two-dimensional foam Hadi Mohammadigoushki, Giovanni Ghigliotti, G.M. Homsy, James Feng We report an experimental study on shearing a monolayer of monodisperse bubbles floating on liquid in a narrow-gap Couette device. The bubbles in such a ``bubble raft'' coalesce only if the shear rate exceeds a threshold value. This is in contrast to the conventional wisdom that bubbles and drops coalesce for gentler collisions, at shear rates below a critical value. Furthermore, the threshold shear rate increases with the bubble size and the viscosity of the suspending liquid, contravening reasoning based on capillary number. Through visualization and scaling arguments, we have advanced an explanation of the anomalous behavior in terms of inertial forces on the bubbles, which compress the bubbles radially inward and accelerate film drainage. The scaling relationship correlates well with experimental data. [Preview Abstract] |
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