Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session Q9: Fluid Dynamics at Interfaces |
Hide Abstracts |
Sponsoring Units: DFD Chair: Takeru Yano Osaka University, and Angbo Fang, Hong King University of Science and Technology Room: D220 |
Wednesday, March 23, 2011 11:15AM - 11:27AM |
Q9.00001: Slosh dynamics and rebound suppression of a partially filled sphere Taylor Killian, Robert Klaus, Tadd Truscott We introduce a study on the slosh dynamics of a partially filled elastic sphere. Currently the physical design of fluid-filled containers utilizes clever construction and machinery to mitigate sloshing motions. There are numerous cases that have been observed but we focus on the impact of a sphere under free fall with an initially undisturbed free surface. The study focuses on measurement and simulation of the force distribution between the fluid and the sphere through the use of high-speed imaging and finite element analysis. Using the cavity shape data, a potential flow numerical model is developed that predicts the unsteady forces. Our hypothesis is that the sphere's movements can be counteracted or cancelled by the exchange of energy between the sphere and the fluid. Forces are modulated by the formation of a parabolic cavity in the fluid, formed after the first impact. The second impact results in a collapse of this cavity forming a powerful jet which effectively dampens the motion of the sphere. [Preview Abstract] |
Wednesday, March 23, 2011 11:27AM - 11:39AM |
Q9.00002: Shrinking Instabilities of Toroidal Liquid Droplets in The Stokes Flow Regime Zhenwei Yao, Mark Bowick We analyze the stability and dynamics of toroidal liquid droplets. In addition to the Rayleigh instabilities akin to those of a cylindrical droplet there is a shrinking instability that is unique to the topology of the torus and dominates in the limit that the aspect ratio is near one (fat tori). We first find an analytic expression for the pressure distribution inside the droplet. We then determine the velocity field in the bulk fluid, in the Stokes flow regime, by solving the biharmonic equation for the stream function. The flow pattern in the external fluid is analyzed qualitatively by exploiting symmetries. This elucidates the detailed nature of the shrinking mode and the swelling of the cross-section following from incompressibility. Finally the shrinking rate of fat toroidal droplets is derived by energy conservation. [Preview Abstract] |
Wednesday, March 23, 2011 11:39AM - 11:51AM |
Q9.00003: Normal elasticity of liquid bridge by atomic force microscope Bongsu Kim, Wonho Jhe The quartz tuning-fork based atomic force microscope (QTF-AFM) has previousely been established as a suitable measurement technique for investigating liquid bridges. By operating a QTF-AFM in the non-contact tapping mode, we are able to measure the normal elasticity of liquid bridges that are formed via capillary condensation or that result from an adsorbed liquid layer. Elasticity, a property typically associated with solids, is studied here for the case of the nano-scale water bridge. We present results that add to our understanding of the origin of the elasticity in nano liquid bridges. [Preview Abstract] |
Wednesday, March 23, 2011 11:51AM - 12:03PM |
Q9.00004: Droplet impact and the dynamics of rapidly moving contact lines Shmuel M. Rubinstein, John M. Kolinski, Shreyas Mandre, Lakshminarayanan Mahadevan, David A. Weitz When a~liquid drop approaches a flat solid surface, the air~beneath it is compressed,~flattening the bottom of the drop and~forcing initial contact to occur in a~ring-shape, trapping a pocket~of air in its center as two wetting fronts~rapidly expand both~outward and inwards to completely wet the surface. We combine total internal~reflection (TIR) microscopy with a~novel virtual frame technique~(VFT) to directly observe the sub-micron length~scales above a~solid surface as the drop approaches, impacts and then spreads~over it. [Preview Abstract] |
Wednesday, March 23, 2011 12:03PM - 12:15PM |
Q9.00005: Interfacial Effects on Droplet Dynamics in Poiseuille Flow Jonathan Schwalbe, Kendra Erk, Jeffrey Martin, Petia Vlahovska, Steven Hudson Interfacial rheology governs many properties of emulsions, and here we report theory and experiments that account for and measure surface viscous and elastic forces. For the theoretical portion, Stokes flow is assumed in bulk phases and a jump in hydrodynamic stress at the interface is balanced by Marangoni and surface viscous forces according to the Boussinesq-Scriven constitutive law. Our model employs linear equation of state for the surfactant. Our analysis predicts slip, cross-stream migration and droplet-circulation velocities for a spherical drop in plane Poiseuille flow. These results and the corresponding interfacial parameters are separable: e.g., cross- stream migration occurs only if surfactant is present; slip velocity depends on viscosity contrast and dilatational Boussinesq number, but not shear Boussinesq number. Drop dynamics in plan Poiseuille flow are measured experimentally using microfluidics, particle velocimetry, and shape analysis. Several types of surfactant-stabilized aqueous drops in oil are examined and the interfacial properties depend on interfacial composition. [Preview Abstract] |
Wednesday, March 23, 2011 12:15PM - 12:27PM |
Q9.00006: ABSTRACT WITHDRAWN |
Wednesday, March 23, 2011 12:27PM - 12:39PM |
Q9.00007: Nonequilibrium molecular dynamics of vapor--liquid interface Takeru Yano Evaporation and condensation at a vapor--liquid interface are studied by moderately large-scale nonequilibrium molecular dynamics simulations for a vapor--liquid two phase system composed of about 0.3 million Lennard-Jones molecules. Constant evaporation and condensation are realized by driving two vapor regions on the either side of a planar liquid film, and thereby the simulation is free from artificial controls of molecular motions in the liquid film and in the neighborhood of the interfaces. This enables us to evaluate the mass, momentum, and energy fluxes across the system, which are relevant to the velocity distribution of molecules leaving the interface at the vapor--liquid nonequilibrium states. [Preview Abstract] |
Wednesday, March 23, 2011 12:39PM - 12:51PM |
Q9.00008: Evaporation out of a 2D model soil Bertrand Selva, Remi Dreyfus Our goal is to improve our understanding of water transport in the soil-plant-atmosphere continuum. For this purpose, we focus on water losses due to evaporation at the soil surface. Such losses are known to be important at places where plants do not entirely cover the surface. Our model soil is a 2D porous medium with controlled wettability and humidity. It has been reported that evaporation is characterized by three stages: a first stage with a strong and constant evaporation flux, a second stage where mass transfer is dominated by diffusion mechanisms, and a third stage that occurs when the medium is almost empty. Here we focus on the first two stages and the transition between them which occurs when an intermediate unsaturated zone has reached its maximum width. This width strongly depends on the wettability distribution of the porous medium. In our experiments, we have explored a regime where gravity effects and capillary forces have similar contributions. In this particular regime we found that the first stage is characterized by a continuously decreasing evaporation flux and the second stage by usual diffusion transfer mechanisms. In order to understand this behavior, we have developed a model which allows us to predict the transition between the two stages and which is in agreement with the decreasing values of the first stage evaporation flux. [Preview Abstract] |
Wednesday, March 23, 2011 12:51PM - 1:03PM |
Q9.00009: Effects of Sub-Phase Thickness on Interfacial Microrheology Paul Christophel Martin, Kenneth W. Desmond, Eric R. Weeks The interface between two fluids is known to have a rheological response. In our work, we study human serum albumin protein molecules (HSA) at an air-water interface. Prior experimental work showed that the ratio of the surface viscosity to the sub-phase ``bulk'' viscosity influences the rheology of the HSA interface. Recent theoretical work has shown that the thickness of the sub-phase h can also influence the rheology of the interface. The finite thickness of the sub-phase only becomes important once h is on the order of the ratio of the surface viscosity to the sub-phase ``bulk'' viscosity, which is on the order of 100 microns for an HSA-air-water interface. To characterize the interfacial rheology, we suspend tracer particles at the interface, measure their correlated motions, and investigate how the results depend on h for water layers O(100 microns) thick. [Preview Abstract] |
Wednesday, March 23, 2011 1:03PM - 1:15PM |
Q9.00010: Probing single- and multi-phase flow at the pore level Sujit Datta, Amber Krummel, David Weitz We use a new experimental technique to study 3D flow behavior in a porous medium in situ with high spatiotemporal resolution. At the multi-pore level, we probe the fluid configurations resulting from two-phase flow conditions imposed upon the system and correlate these to bulk flow measurements. [Preview Abstract] |
Wednesday, March 23, 2011 1:15PM - 1:27PM |
Q9.00011: Viscous flow and heat transfer in channels with structured walls Vladimir Ajaev, Steffen Hardt, Peter Stephan We develop a mathematical model of pressure-driven flow in channels with walls structured by arrays of parallel grooves filled with air or gas. Motivated by cooling applications, we study heat transfer from a heater embedded in the wall to the liquid. The flow in the liquid is described using a Stokes flow model, and thermocapillary effects due to presence of the liquid-gas interface segments in the grooves are also taken into account. The rate of heat transfer is determined by a competition of two physical effects: the insulating effect of the gas in the grooves, due to small thermal conductivity of the gas phase, and the reduction of the effective slip length at the channel wall due to the presence of the liquid-gas interface segments in the grooves. Criteria for heat transfer enhancement are formulated for different parameters of the structuring. [Preview Abstract] |
Wednesday, March 23, 2011 1:27PM - 1:39PM |
Q9.00012: Utilizing an Automated Home-Built Surface Plasmon Resonance Apparatus to Investigate How Water Interacts with a Hydrophobic Surface Adele Poynor By definition hydrophobic substances hate water. Water placed on a hydrophobic surface will form a drop in order to minimize its contact area. What happens when water is forced into contact with a hydrophobic surface? One theory is that an ultra-thin low- density region forms near the surface. We have employed an automated home-built Surface Plasmon Resonance (SPR) apparatus to investigate this boundary. [Preview Abstract] |
Wednesday, March 23, 2011 1:39PM - 1:51PM |
Q9.00013: Quantification of slip at a liquid-solid interface -- a novel approach Aleks Ponjavic, Mourad Chennaoui, Janet Wong Much effort has been spent recently on experimentally proving the existence of interfacial slip of a Newtonian fluid. A constant limitation is the proximity to the surface at which the velocity of a fluid can be measured. A new technique is developed to maximise this proximity. The objective is to acquire velocity measurements of a fluid as close as possible to the liquid-solid interface while still using a direct method of observation. To ensure proximity to the surface the technique of photobleaching is adopted. Dye-doped water is pumped through a microfluidic channel. A short, intense pulse from a laser causes dye within the focal volume to bleach, creating a spot. The geometry of this spot evolves depending on the velocity profile of the fluid. By fitting the evolution of the spot with a Poiseuille velocity profile with slip the slip length is extracted. The hydrophobicity of the channel is varied by flowing silane through the channel prior to measurement, forming a self-assembled monolayer. Effects of shear rate and wettability on interfacial slip length are investigated. [Preview Abstract] |
Wednesday, March 23, 2011 1:51PM - 2:03PM |
Q9.00014: Effects of Interfacial Translation-rotation Coupling for Confined Ferrofluids Angbo Fang Ferrofluids have wide applications ranging from semiconductor fabrications to biomedical processes. The hydrodynamic spin diffusion theory for ferrofluids has been successful in explaining many experimental data, but it suffers from some fatal flaws. For example, it fails to predict the incorrect flow direction for a ferrofluid confined in a concentric cylinder channel in the presence of a rotating magnetic field. In this work we develop a method to establish the general hydrodynamic boundary conditions (BCs) for micro-polar fluids such as ferrofluids. Through a dynamic generalization of the mesoscopic diffuse interface model, we are able to obtain the surface dissipation functional, in which the interfacial translation-rotation coupling plays a significant role. The generalized hydrodynamic BCs can be obtained straightforwardly by using Onsager's variational approach. The resulted velocity profile and other quantities compares well with the experimental data, strikingly different from traditional theories. The methodology can be applied to study the hydrodynamic behavior of other structured fluids in confined channels or multi-phase flows. [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