Bulletin of the American Physical Society
2006 59th Annual Meeting of the APS Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2006; Tampa Bay, Florida
Session HF: Drops and Bubbles VI: Foams |
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Chair: Emmanuel Villermaux, IRPHE Marseille, France Room: Tampa Marriott Waterside Hotel and Marina Florida Salon 4 |
Monday, November 20, 2006 2:00PM - 2:13PM |
HF.00001: Lamella Thinning Laws - Fundamental Building Blocks in Foam Dynamics Anthony Anderson, Stephen Davis Capillary pressure drives the liquid in foam films (lamellae) into the adjacent film junctions (Plateau borders), resulting in the thinning and eventual rupture of the films. These thinning processes obey scaling laws, which are found using asymptotic methods and boundary integral simulations. Three idealized arrangements are considered: a Plateau border joining (1) two free films, (2) a free film and a bounded film, (3) two bounded films. [Preview Abstract] |
Monday, November 20, 2006 2:13PM - 2:26PM |
HF.00002: Nanoscale patterns on micron-sized bubbles in foams Emilie Dressaire, David Bell, Rodney Bee, Alex Lips, Howard Stone The rheology and coarsening of foams is closely related to the microstructural characteristics of the small gas bubbles and their surface properties. We present experimental results of a foam formed upon shearing a mixture composed of glucose syrup and sucrose ester. Transmission Electron Microscopy reveals micron-size bubbles whose surfaces are fully covered with regular nanodimension, generally hexagonal, patterns. The influence of the shear rate during foam generation and the setting time on the development of the nanoscale patterns on the gas microcells are described. Plausible routes, driven by disproportionation of the gas from the small bubbles, for the formation of the nanoscale patterns are considered including a nucleation/crystallization pathway (Kim et al. 2003 Langmuir {\bf 19}, p. 8455) and the buckling of an elastic insoluble surface film. [Preview Abstract] |
Monday, November 20, 2006 2:26PM - 2:39PM |
HF.00003: On the coarsening of two-dimensional foams Benjamin Bossa, J\'er\^ome Duplat, Emmanuel Villermaux Besides its common and esthetic character, foam coarsening is a paradigm for aging in a broad class of complex systems. Among the natural questions to characterize the process are that of the shape of the cell size distribution, its rate of deformation, the effect of initial conditions, the possible existence of an attractive self-similar regime, and the link with the microscopic rate of change of a cell area prescribed by von Neuman's law. We address these questions using a foam ``wind tunnel'' consisting in a long Hele-Shaw cell where we inject continuously $CO_{2}$ bubbles at one extremity and follow the resulting 2D foam as it progresses towards the other end of the cell. Averaging on time at fixed locations along the cell, we thereby have access to several aspects of the foam structure at different successive instants of its life. We will focus on the cell size distribution and number of neighbors conditioned to cell size and will show in particular that these quantities are progressively insensitive to the way the foam has been initially prepared. These observations legitimate a mean-field representation of the aging process which successfully represents the overall foam evolution. [Preview Abstract] |
Monday, November 20, 2006 2:39PM - 2:52PM |
HF.00004: Linear shear of quasi-2D foams Gijs Katgert, Matthias Moebius, Martin van Hecke We study foam rheology in a quasi-2-dimensional geometry in which a singly layer of foam bubbles is confined between the surface of a soapy solution and a glass plate. In this geometry the foam flow exhibits shear banding down to very low driving rates. In our experiment the foam is sheared linearly and the influence of packing fraction, bubble size and bubble size dispersity on the shape of the shearbanded flow profiles is investigated. Individual bubble motions are also tracked in order to investigate the fluctuations in the flow. [Preview Abstract] |
Monday, November 20, 2006 2:52PM - 3:05PM |
HF.00005: An experimental study of a quasi-two dimensional rising foam Nora Bennani, Akiko Fujiwara, Shu Takagi, Yoichiro Matsumoto Motivated by the use of the flotation process to clean a non-homogeneous liquid, we here report on an experimental study of quasi-two dimensional flowing foam. Conditions are free-drainage which is driven by gravity and capillarity. The coarsening process, which is due to the aging of the foam, is also occurring, changing the general shape of this polydispersed foam cells. Tea seed saponin was used as surfactant, and Rhodamine-B fluorescent particles were tracked using the Particle Tracking Velocimetry technique. Experiments were performed in an acrylic tank filled with tap water (height H= 1m, width W= 0.15 m and Depth D= 8mm). The air was injected from its bottom part with a fixed flow rate, and went through a porous plate (size of the pores was 10$\mu $m), and created 3mm diameter non-spherical bubbles. The void fraction, in the liquid phase, was estimated to be around 1{\%}. Fluorescent particles were beforehand added in the liquid phase in order to trace wastewater particle motion. The generated foam gas cells sizes were in the range of 0.5 to 5 cm, depending on the surfactant concentration and the coarsening process. The behaviours of these particle tracers and of the liquid, with these herein foaming conditions, are here presented and are compared to available data and theories. [Preview Abstract] |
Monday, November 20, 2006 3:05PM - 3:18PM |
HF.00006: Simulation of bubble growth in polymer foaming Pengtao Yue, James Feng, Christopher Bertelo, Howard Hu Bubble growth plays an important role in determining the cell size distribution in thermoplastic foams. In this work, the diffusion-driven bubble growth in a polymer melt is computed by direct numerical simulation. The pressure and mass inside each bubble follow the equation of state for an ideal gas. A finite element method is used to calculate the gas concentration and flow variables in the polymer melt. Henry's law is employed to relate the bubble pressure and the gas concentration at the bubble surface. An Arbitrary Lagrangian-Eulerian (ALE) technique is used to handle the moving boundary. Within each time step, the whole system is solved iteratively. By modeling the polymer melts as Oldroyd-B fluids, we will study the influence of rheology on single bubble growth and interactions between multiple bubbles. [Preview Abstract] |
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