Bulletin of the American Physical Society
60th Annual Meeting of the Divison of Fluid Dynamics
Volume 52, Number 12
Sunday–Tuesday, November 18–20, 2007; Salt Lake City, Utah
Session AC: Drops and Bubbles I |
Hide Abstracts |
Chair: Gary Leal, University of California, Santa Barbara Room: Salt Palace Convention Center 150 G |
Sunday, November 18, 2007 8:30AM - 8:43AM |
AC.00001: 3-D Stability of a Draining Film Between Two Drops Sukhvinder Kaur, L. Gary Leal The drainage of a thin film between two drops in a flow has usually been treated as an axisymmetric deterministic problem. In this paper, we carry out a quasi-static 3-D linear stability analysis to determine the stability of the draining film to non-axisymmetric perturbations. The linear stability calculation is interfaced with the full axisymmetric calculation of two drops approaching in an external flow field in order to obtain the correct film shape at each time interval. We find that the first non-axisymmetric mode is the most unstable. Calculations show that while the critical thickness for rupture remains mostly unchanged, the growth rates change significantly when the interface is tangentially mobile. Finally, a comparison of the critical thickness for film rupture from the linear stability calculation with that from the axisymmetric full drop problem reveals the relative importance of non-axisymmetric rupture on the drainage time and conditions for coalescence. [Preview Abstract] |
Sunday, November 18, 2007 8:43AM - 8:56AM |
AC.00002: The Dueling Bubble Experiment Anshuman Roy, Marcos Borrell, John Felts, Gary Leal, Amir Hirsa When two drops or bubbles are brought into close proximity to each other, the thin film of the fluid between them drains as they are squeezed together. If the film becomes thin enough that intermolecular forces of attraction overwhelm capillary forces, the drops/bubbles coalesce and the time it takes for this to happen, starting from the point of apparent contact is referred to as the drainage time. One practical version of this scenario occurs during the formation of foams, when the thin film forms between gas bubbles that are growing in volume with time. We performed an experimental study that is intended to mimic this process in which the two drops (or bubbles) in the size range of 50-100 microns diameter are created by oozing a liquid/gas out of two capillaries of diameter less than 100 microns directly facing each other and immersed in a second fluid. We present measurements of drainage times for the cases of very low viscosity ratios PDMS drops in Castor oil (less than 0.05) and bubbles of air in PDMS, and highlight the differences that arise in part due to the different boundary conditions for thin film drainage for liquid-liquid versus gas-liquid systems, and in part due to the different Hamaker constants for the two systems. [Preview Abstract] |
Sunday, November 18, 2007 8:56AM - 9:09AM |
AC.00003: Effects of matrix viscoelasticity on drop deformation in steady shear Kausik Sarkar, Nishith Aggarwal We investigate a viscous/Oldroyd-B drop in an Oldroyd-B matrix. We compare simulated drop deformation and inclination with experimental observations by other groups. A non-monotonic change in the steady state drop deformation is observed with increasing Deborah number (\textit{De}) and explained in terms of the competition between increased localized polymer stretching at the drop tips and the decreasing effects due to change in drop orientation angle. The transient drop orientation angle is found to evolve on the polymer relaxation time scale for high . The breakup of a viscous drop in a viscoelastic matrix is inhibited for small \textit{De}, and promoted at higher \textit{De}. The effect of polymeric to total viscosity ratio $\beta $ was seen to affect through the parameter $\beta $ \textit{De} indicating a dominant role of the first normal stress difference. A viscoelastic drop in a viscoelastic matrix with matched relaxation time experiences less deformation compared to the case when one of the phases is viscous. But the inclination angle assumes an intermediate value between two extreme cases. Increased drop phase viscoelasticity compared to matrix phase leads to decreased deformation. [Preview Abstract] |
Sunday, November 18, 2007 9:09AM - 9:22AM |
AC.00004: Shape and stability of levitated viscous drops John Lister, Alice Thompson, Antoine Perriot, Laurent Duchemin A drop of molten glass can be levitated above a porous spherical mould by air injection. Owing to the viscosity contrast, the float height for a given shape is established on a much shorter time scale than the subsequent deformation of the drop under gravity, surface tension and the lubrication pressure. The set of solution branches for equilibrium, non-deforming shapes is surprisingly complicated and shows a rich bifurcation structure in $(Bo, Ca)$ space (drop volume, injection velocity). The stability of equilibria is determined using a novel boundary- integral representation that factors out the rapid adjustment of the float height. [Preview Abstract] |
Sunday, November 18, 2007 9:22AM - 9:35AM |
AC.00005: Supergravity effects on the geometry of a sessile drop Minerva Vargas, Guillermo Hernandez-Cruz, Raymundo Najera, Eduardo Ramos We have made experimental observations of the geometry of a drop of a Newtonian fluid sitting on a horizontal surface, subjected to constant vertical accelerations in the range from 1g to 13g. The shape of the drop was observed from plan and side views using a set-up composed by a cube beam splitter and a camera. Supergravity conditions were achieved using a centrifuge with 1.7 arm length and operated at a maximum angular speed of 86 rpm. We used water and ethanol as working fluids, and the Bond number range explored was from 1.3 to 16 for water and 3.7 to 49 for ethanol. Quantitative information on the shape of the surface of the drop was obtained by image processing. Preliminary observations with water indicate that $h \sim a^{-1/6}$ ($h$ is the height of the drop and $a$ is the vertical acceleration), in contrast to $h\sim a^{-1/2}$ predicted by a simplified theory. Possible sources for the discrepancy will be discussed. [Preview Abstract] |
Sunday, November 18, 2007 9:35AM - 9:48AM |
AC.00006: Effect of liquid transparency on laser-induced-motion of drops Rohit Shukla, Khaled Sallam An Experimental investigation of the role of liquid transparency in controlling laser-induced-motion of liquid drops is carried out. Droplets with diameters of 1-- 4 mm were propelled on a hydrophobic substrate using pulsed-laser beam (532 nm, 10 Hz, 5-10 mJ/pulse) with 1 mm diameter fired parallel to the substrate. The test liquid was distilled water whose transparency was varied by adding different concentrations of Rhodamine 6G dye. High speed imaging was used to observe the motion of the drops. Measurements include direction of motion, distance traveled before the drops come to rest, and drop acceleration at the start of the motion. The motion of both transparent and opaque drops was dominated by thermal Marangoni effect. The present results show that direction of motion depends on the drop transparency; opaque drops moved away from the laser beam, whereas transparent drops moved at small angles toward the laser beam. This is plausible because the laser beam was absorbed near the front face of opaque drops, whereas the laser beam was focused near the rear face of transparent drops. [Preview Abstract] |
Sunday, November 18, 2007 9:48AM - 10:01AM |
AC.00007: How do drops evaporate? Nebojsa Murisic, Lou Kondic The problem of evaporating drops with non-pinned contact line, although seemingly trivial, so far lacks satisfactory theoretical description. In particular, there has been much discussion regarding appropriate evaporative mass flux model. We make an attempt to resolve this issue by comparing our experimental data with the results of several mathematical models for evaporating drops. After describing experimental procedure, we propose several models for mass flux and develop a governing equation for evolution of drop's thickness. Two-dimensional numerical results are then compared to the experimental results, and the most appropriate mass flux model is identified. Finally, we propose the governing equation for the full 3D system and present some new numerical results related to curious phenomena, where so-called ``octopus-shaped'' instabilities appear ahead of the contact line of volatile drops\footnote{Y. Gotkis, I. Ivanov, N. Murisic, L. Kondic, \textsl{Phys. Rev. Lett.} \textbf{97}, 186101 (2006).}. [Preview Abstract] |
Sunday, November 18, 2007 10:01AM - 10:14AM |
AC.00008: Microgravity Experiment: The Fate of Confined Shock Waves P. Kobel, D. Obreschkow, N. Dorsaz, A. de Bosset, M. Farhat \textit{Shockwave induced cavitation} is a form of hydrodynamic cavitation generated by the interaction of shock waves with vapor nuclei and microscopic impurities. Both the shock waves and the induced cavitation are known as sources of erosion damage in hydraulic industrial systems and hence represent an important research topic in fluid dynamics. Here we present the first investigation of shock wave induced cavitation inside \textit{closed and isolated} liquid volumes, which confine the shock wave by reflections and thereby promise a particularly strong coupling with cavitation. A microgravity platform (ESA, 42$^{nd}$ parabolic flight campaign) was used to produce stable water drops with centimetric diameters. Inside these drops, a fast electrical discharge was generated to release a strong shock wave. This setting results in an amplified form of shockwave induced cavitation, visible in high-speed images as a transient haze of sub-millimetric bubbles synchronized with the shockwave radiation. A comparison between high-speed visualizations and 3D simulations of a shock front inside a liquid sphere reveals that focus zones within the drop lead to a significantly increased density of induced cavitation. Considering shock wave crossing and focusing may hence prove crucially useful to understand the important process of cavitation erosion. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700