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 KP: Surface Tension Effect II |
Hide Abstracts |
Chair: Bill Ristenpart, Harvard University Room: Salt Palace Convention Center 251 D |
Tuesday, November 20, 2007 8:00AM - 8:13AM |
KP.00001: The rebound of small particles impacting a free surface Matthew Hancock, Jeffrey Aristoff, John Bush The impact of small particles on a free surface is a problem of fundamental interest with various applications including biolocomotion, pollination and contaminant transport. We present the results of a combined theoretical and experimental investigation of the normal impact of spherical particles on an air-water surface, and give particular focus to deducing criteria for particle rebound. Computing particle trajectories requires consideration of the particle's inertia and weight, in addition to the forces resisting its motion, specifically, buoyancy, hydrodynamic drag forces and contact or curvature forces associated with the surface tension. Simplified models for these forces yield criteria for particle rebound that are tested against experimental observations. [Preview Abstract] |
Tuesday, November 20, 2007 8:13AM - 8:26AM |
KP.00002: Physics of elastocapillary rise Ho-Young Kim, Wonjin Ahn, L. Mahadevan When a paintbrush is dipped into a pot of paint and pulled out, surface tension forces cause the individual hairs in the brush to coalesce even as the brush becomes impregnated with paint. We study both the statics and dynamics of this elastocapillary interaction in the context of the surface-tension-driven vertical rise of a liquid between two long flexible hydrophilic sheets that are held a small distance apart at one end. We provide an analytic theory for the static shapes of the sheets as well as the liquid rise height which is different from that of the classical law of Jurin. Also we numerically solve the time evolutions of the sheet shapes and the liquid height, obtaining different solutions from that of Washburn. We compare the theoretical results with the experiments to find good agreements between them. [Preview Abstract] |
Tuesday, November 20, 2007 8:26AM - 8:39AM |
KP.00003: Influence of Substrate Conductivity on Circulation Reversal in Evaporating Drops W.D. Ristenpart, P.G. Kim, C. Domingues, J. Wan, H.A. Stone Non-uniform evaporation from sessile droplets induces radial
convection within the drop, which produces the well-known `coffee
ring' effect. The evaporation also induces a gradient in
temperature and consequently a gradient in surface tension,
generating a Marangoni flow. Here we investigate theoretically
and experimentally the thermal Marangoni flow and establish
criteria to gauge its influence. An asymptotic analysis
indicates that the direction of the flow depends on the relative
thermal conductivities of the substrate and liquid, $k_R\equiv
k_S/k_L$,
reversing direction at a critical contact angle over the range
$1.45 |
Tuesday, November 20, 2007 8:39AM - 8:52AM |
KP.00004: ABSTRACT WITHDRAWN |
Tuesday, November 20, 2007 8:52AM - 9:05AM |
KP.00005: Thermocapillary migration of encapsulated bubbles and drops Kaushik Vongole, Asghar Esmaeeli Motion of bubbles/drops as a result of variation of the surface tension with the temperature is called thermocapillary migration and can be of importance in situations where the usually dominant buoyant forces are weak. While the phenomenon has been relatively well studied for simple systems involving a drop or a bubble, there is scant information about the behavior of drops/bubbles in more realistic (complex) systems; primarily due to the difficulties in experimental measurements. One such system is, for example, boiling at the superheat limit where heterogeneous nucleation can be avoided by suspending the fluids that will be boiled off in the form of a drop in another liquid. Here, the vapor nucleation inside the drop leads to formation of a compound drop. The goal of this study is to shed some light on the role of thermocapillarity forces on the dynamics of the above systems and the similar ones. We, however, ignore the evaporation and buoyant convection to make the problem more tractable. We use a front tracking/finite difference method and solve the governing momentum and energy equations for all the phases that are involved. The goal is to correlate the overall behavior of the system, in terms of the bubble and drop motion and deformation as well as induced flow and temperature fields, with the controlling parameters. [Preview Abstract] |
Tuesday, November 20, 2007 9:05AM - 9:18AM |
KP.00006: Size distribution and three-phase interactions in thermocapillarity-driven flows Bhushan Pendse, Asghar Esmaeeli The use of thermo-capillarity forces to manipulate drops and bubbles finds relevance in a good number of micro-fluidics applications. For instance, it has been suggested to use these forces to enhance fluid mixing in the drops, or to move them through a network of channels, or to levitate them. While drop sorting and trafficking is considered a major task in many lab-on-chips applications, however, so far the possibility of using thermo-capillarity forces for this purpose has been widely overlooked. The goal of this study is to explore such a possibility by examination of the motion of droplets of different sizes but of the same fluid, and also to consider interactions of droplets of the same size but of different fluids suspended in a host liquid in a uniform temperature gradient. To this end, we use a front tracking finite/difference scheme and solve the Navier-Stokes and energy equations in all the phase involved. It is expected that the imposition of different forces on the surfaces of the drops (due to the differences in their material properties or sizes) lead to segregation of droplets of different types. [Preview Abstract] |
Tuesday, November 20, 2007 9:18AM - 9:31AM |
KP.00007: Flow of a surfactant-laden thin liquid film down an inclined plane Rachel Levy, Michael Shearer, Thomas Witelski A thin liquid film flowing down an inclined plane can be described by a scalar fourth-order partial differential equation. The addition of insoluble surfactant dramatically alters the free surface of the film. A second equation modeling the transport and diffusion of surfactant is coupled to the height equation. Using numerical simulations and asymptotics, we explore the dependence of traveling wave solutions on capillary, Peclet and Bond numbers. [Preview Abstract] |
Tuesday, November 20, 2007 9:31AM - 9:44AM |
KP.00008: Dynamics of apparent contact lines formed by rapidly moving menisci Roumen Tsekov, Vladimir Ajaev, Olga Vinogradova When a bubble is pressed against a solid wall, an apparent contact line is formed in the region where the meniscus transitions to the equilibrium wetting film. The details of this transition for both stationary and slowly moving menisci have been investigated by many researchers. However, when the bubble is pushed towards the wall sufficiently fast, a different physical picture emerges. Landau-Levich-type trailing films behind the menisci are playing a significant role in the local dynamics of the apparent contact line. Thickness of these films can be significantly larger than that of the wetting films, and is dependent on the capillary number. The dynamics of the local flow then depends on the interactions between the Landau-Levich type film, the ultra-thin wetting film, and the macroscopic meniscus. We propose a model that describes these interactions. Simulation results are discussed with emphasis on the prediction of macroscopically measurable quantities, such as the position of the apparent contact line, as a function of time. [Preview Abstract] |
Tuesday, November 20, 2007 9:44AM - 9:57AM |
KP.00009: Elimination of Parasitic Currents in the Simulation of Contact Line Motion Taehun Lee, Lin Liu Parasitic currents are caused by discretization errors in the computation of the intermolecular forces, in particular, a slight imbalance between the pressure gradient and the surface tension force due to truncation error. They increase as the surface tension force and density gradient of the participating fluids. It was shown that these currents could be eliminated to round-off, if the potential form of the intermolecular forces for non-ideal gases was used with the compact isotropic discretization in the periodic computational domain (Lee and Fischer, Phys. Rev. E v.74, 046709). We propose a formulation of the intermolecular forces for immiscible incompressible fluids in contact with solid in the framework of the lattice Boltzmann equation (LBE) method. The forces between solid and fluids are assumed to be of short range and described by adding linear wall energy (de Gennes, Rev. Mod. Phys. v.57, p.827). The present LBE method eliminates the parasitic currents in the simulation of immiscible fluids even in contact with solid and is able to deal with large density/viscosity difference as a result. The equilibrium contact angle and surface concentration are accurately predicted by prescribing non-dimensional wetting potential. The LBE simulations of spreading and impact of a droplet on a dry solid surface are compared with the previous theoretical and experimental results. [Preview Abstract] |
Tuesday, November 20, 2007 9:57AM - 10:10AM |
KP.00010: Interface mechanics explains cell shapes in the Drosophila retina Sascha Hilgenfeldt, Sinem Erisken, Richard Carthew When biological cells form a functional tissue, their membranes adhere to each other via adhesion molecules such as cadherins. It has long been conjectured that adhesion strength and distribution of cadherins determines cell segregation and overall organization in epithelial and other tissues. For the first time, we combine cadherin adhesion with a rigorous model of cell mechanics to obtain a physical model for a cell membrane energy functional, predicting cell shapes in quantitative detail. This theory is tested using experimental results describing the extraordinarily well-defined geometry of cell clusters in the Drosophila eye [1]. We show that a model using no more than two physically motivated parameters identifies the adhesion strengths of both E- and N-cadherins, reproduces the wild-type geometry to a few percent of accuracy, and is also consistent with the shapes of various mutants. Beyond comparison of membrane lengths and angles, Surface Evolver simulations achieve realistic modeling of the entire shape of the cell clusters. The Drosophila retina is thus identified as a biological system dominated by surface energy terms only, amenable to a surprisingly simple description by thermodynamics and continuum mechanics. [1] T. Hayashi \& R. W. Carthew, Nature {\bf 431}, 647 (2004) [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