Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session L28: Surface Tension Effects: Interfacial Phenomena |
Hide Abstracts |
Chair: Linda Smolka, Bucknell University Room: 309 |
Monday, November 23, 2015 4:05PM - 4:18PM |
L28.00001: Oil capture from a water surface by a falling sphere Linda Smolka, Clare McLaughlin, Thomas Witelski When a spherical particle is dropped from rest into an oil lens that floats on top of a water surface, a portion of the oil adheres to the sphere. Once the sphere comes to rest at the subsurface, the oil forms a pendant drop that remains attached in equilibrium to the sphere effectively removing oil from the water surface. Best fit solutions of the Laplace equation to experimental profiles are used to investigate the parameter dependence of the radius of curvature and the filling and contact angles at the three-phase contact line of the pendant drop for spheres with different wetting properties, densities and radii. The volume of oil captured by a sphere increases with a sphere's mass and diameter. However, lighter and smaller spheres capture more oil relative to their own volume than do heavier and larger spheres (scaling with the sphere mass $\sim M^{-0.544}$) and are thus more efficient at removing oil from a water surface. [Preview Abstract] |
Monday, November 23, 2015 4:18PM - 4:31PM |
L28.00002: Keeping warm with fur in cold water: entrainment of air in hairy surfaces Alice Nasto, Marianne Regli, Pierre-Thomas Brun, Christophe Clanet, Anette Hosoi Instead of relying on a thick layer of body fat for insulation as many aquatic mammals do, fur seals and otters trap air in their dense fur for insulation in cold water. Using a combination of model experiments and theory, we rationalize this mechanism of air trapping underwater for thermoregulation. For the model experiments, hairy surfaces are fabricated using laser cut molds and casting samples with PDMS. Modeling the hairy texture as a network of capillary tubes, the imbibition speed of water into the hairs is obtained through a balance of hydrostatic pressure and viscous stress. In this scenario, the bending of the hairs and capillary forces are negligible. The maximum diving depth that can be achieved before the hairs are wetted to the roots is predicted from a comparison of the diving speed and imbibition speed. The amount of air that is entrained in hairy surfaces is greater than what is expected for classic Landau-Levich-Derjaguin plate plunging. A phase diagram with the parameters from experiments and biological data allows a comparison of the model system and animals. [Preview Abstract] |
Monday, November 23, 2015 4:31PM - 4:44PM |
L28.00003: Simulation of drop tipstreaming in a flow focusing geometry with a hybrid numerical method Michael Booty, Michael Siegel, Jacek Wrobel, Qiming Wang A hybrid numerical method that is designed to resolve the influence of soluble surfactant in the limit of large bulk Peclet number is used to simulate tipstreaming from a drop in the Stokes flow regime in a simple, axisymmetric flow focusing geometry. Examples are presented of the influence of flow focusing on tip-thread formation and tipstreaming, and of the influence of various dimensionless flow parameters on flow dynamics. [Preview Abstract] |
Monday, November 23, 2015 4:44PM - 4:57PM |
L28.00004: Drinking in Space: The Capillary Beverage Experiment Andrew Wollman, Mark Weislogel, Ryan Jenson, John Graf, Donald Pettit, Scott Kelly, Kjell Lindgren, Kimiya Yui A selection from as many as 50 different drinks including coffees, teas, and fruit smoothies are consumed daily by astronauts aboard the International Space Station. For practical reasons, the drinks are generally sipped through straws inserted in sealed bags. We present the performance of a special cup designed to allow the drinking operation in much the same manner as on earth, only with the role of gravity replaced by the combined effects of surface tension, wetting, and special container geometry. One can finally `smell the coffee.' Six so-called Space Cups are currently in orbit as part of the Capillary Beverage Experiment which aims to demonstrate specific passive control of poorly wetting aqueous capillary systems through a fun mealtime activity. The mathematical fluid mechanical design process with full numerical simulations is presented alongside experimental results acquired using a drop tower and low-g aircraft before complete characterization aboard the Space Station. Astronaut commentary is both humorous and informative, but the insightful experimental results of the potable space experiment testify to the prospects of new no-moving-parts capillary solutions for certain water-based life support operations aboard spacecraft. [Preview Abstract] |
Monday, November 23, 2015 4:57PM - 5:10PM |
L28.00005: Bow and Oblique Shock Formation in Soap Film Ildoo Kim, Shreyas Mandre, Aakash Sane In recent years, soap films have been exploited primarily to approximate two-dimensional flows while their three-dimensional character is relatively unattended. An example of the three-dimensional character of the flow in a soap film is the observed Marangoni shock wave when the flow speed exceeds the wave speed. In this study, we investigated the formation of bow and oblique shocks in soap films generated by wedges with different deflection angles. When the wedge deflection angle is small and the film flows fast, oblique shocks are observed. When the oblique shock cannot exists, bow shock is formed upstream the wedge. We characterized the oblique shock angle as a function of the wedge deflection angle and the flow speed, and we also present the criteria for transition between bow and oblique Marangoni shocks in soap films. [Preview Abstract] |
Monday, November 23, 2015 5:10PM - 5:23PM |
L28.00006: Blowing a liquid curtain H. Lhuissier, P. Brunet, S. Dorbolo We study the response of a steady free-falling liquid curtain perturbed by focused air jets blowing perpendicularly against it. Asymmetric and symmetric perturbations are applied by using either a single pulsed jet or two identical steady jets facing each other. The response strongly depends on the curtain flow rate, and the location and strength of the perturbation. For pulsed asymmetric perturbations of increasing amplitude, sinuous wave, drop ejection, bubble ejection, and hole opening are successively observed. For steady symmetric perturbations, a steady hole forms downstream in the wake. For this latter case, we present a model for the curtain thickness and the location of the hole inthe wake which compares favorably to the experiments providing the perturbation is small enough (jet stagnation pressure smaller than curtain stagnation pressure) and the liquid viscosity is negligible. [Preview Abstract] |
Monday, November 23, 2015 5:23PM - 5:36PM |
L28.00007: Dynamic wetting failure in surfactant solutions Chen-Yu Liu, Eric Vandre, Marcio Carvalho, Satish Kumar The influence of insoluble surfactants on dynamic wetting failure during displacement of Newtonian fluids in a rectangular channel is studied in this work. A hydrodynamic model for steady Stokes flows of dilute surfactant solutions is developed and evaluated using three approaches: (i) a one-dimensional (1D) lubrication-type approach, (ii) a novel hybrid of a 1D description of the receding phase and a 2D description of the advancing phase, and (iii) an asymptotic theory of Cox. Steady-state solution families in the form of macroscopic contact angles as a function of the capillary number are determined and limit points are identified. When air is the receding fluid, Marangoni stresses are found to increase the receding-phase pressure gradients near the contact line by thinning the air film without significantly changing the capillary-pressure gradients there. As consequence, the limit points shift to lower capillary numbers and the onset of wetting failure is promoted. The model predictions are then used to interpret decades-old experimental observations concerning the influence of surfactants on air entrainment. The hybrid modeling approach developed here can readily be extended to more complicated geometries where a thin air layer is present near a contact line. [Preview Abstract] |
Monday, November 23, 2015 5:36PM - 5:49PM |
L28.00008: Dewetting of microliquid film via vapor-mediated Marangoni effect Seungho Kim, Ho-Young Kim It is generally conceived that water film residing on a hydrophilic layer is much more stable than one on a hydrophobic layer. Here we show that the film on a hydrophilic layer can be punctured just by placing an alcohol drop near the film. It is because the concentration gradients of alcohol vapor deposited on water give rise to the Marangoni effect, which pulls the water film away from the alcohol drop. We term this behavior the vapor-mediated Marangoni dewetting. Two different film flow types are observed depending on the thickness of film. For a thin water film, a bulk film recedes from the center where the alcohol vapor concentration is the highest but leaves a thin fringe film. The nanoscale fringe film is then dried, leading to continuous growth of the hole. For a thick water film, no nanoscale fringe films are observed, but the hole growth is limited to a certain radius. The maximum hole radius in the thick film regime is determined by the balance between the hydrostatic pressure and the Marangoni stress. We visualize such novel film dewetting dynamics with a high-speed camera and characterize their salient features by combining experimental and scaling analysis. [Preview Abstract] |
Monday, November 23, 2015 5:49PM - 6:02PM |
L28.00009: Dynamic contact angle at the advancing contact line on an accelerating vertical rod Takahiro Ito, Kenta Yokoi, Kenji Katoh, Tatsuro Wakimoto, Yasufumi Yamamoto, Yoshiyuki Tsuji The motion of the contact line is a critical boundary condition for the prediction of the interface geometry in the wetting or dewetting processes. The estimation of the contact angle is essential to predict the motion of the contact line, since, following the previous theories, the contact angle can be expressed by the parameters including the velocity of the contact line. However, most of the previous theories are based on the assumption of the steady state. In this study, the dynamic contact angle is investigated both experimentally and numerically for a transient state in which a vertical glass rod penetrating the free surface of the test liquid (ethylene glycol) is submerged into the liquid with acceleration motion. The experimentally measured contact angle was smaller than those obtained in the steady state for the corresponding contact line velocity. The deviation is found to increase with the acceleration of the rod. Numerical simulation showed the acceleration term affects only the surface profiles for $x$ / $l_{s}$ \textgreater 10$^{\mathrm{-2}}$ with $x$ the distance from the rod surface and $l_{s}$ the Laplace length. This indicates that the inertia effect would not responsible for the deviation of the dynamic contact angle. [Preview Abstract] |
Monday, November 23, 2015 6:02PM - 6:15PM |
L28.00010: A fluid-dynamical model for the ''anti-surfactant'' behaviour of salt solutions Stephen Wilson, Justin Conn, David Pritchard, Brian Duffy, Peter Halling, Khellil Sefiane We formulate and analyse a novel fluid-dynamical model for the flow of a solution with a free surface on which surface tension acts. This model, which uses the concept of surface excess, can describe both classical surfactants and aqueous salt solutions. These latter solutions have the anomalous property that in thermodynamic equilibrium the surface tension increases with increasing salt concentration, i.e., so-called ``anti-surfactant'' behaviour. We demonstrate the utility of the model by considering the stability of a deep layer of initially quiescent fluid, and identify the possibility of an anti-surfactant instability driven by Marangoni effects. [Preview Abstract] |
Monday, November 23, 2015 6:15PM - 6:28PM |
L28.00011: Influence of Marangoni-driven flows on A + B $\rightarrow$ C reaction fronts Laurence Rongy, Reda Tiani When the two reactants of an A + B $\rightarrow$ C reaction are brought into contact, a reaction front is formed and the spatially localized zone where the reaction occurs evolves in time due to the interdiffusion of A and B. The properties of such fronts are well studied in reaction-diffusion systems where no flow can affect the dynamics. Here we consider horizontal aqueous solutions where the three species A, B, and C can affect the surface tension of the solution, thereby driving Marangoni flows. The resulting dynamics is studied by numerically integrating the incompressible Navier-Stokes equations coupled to reaction-diffusion-convection equations for the three chemical species. We show that the front propagation cannot be predicted anymore on the sole basis of the reaction-diffusion properties as was still possible in the presence of buoyancy-driven flows around such fronts. We relate this observation to the structure of the Marangoni-driven flow and propose a classification of the convective effects on A + B $\rightarrow$ C reaction fronts as a function of the different Marangoni numbers quantifying the effect of each species on the surface tension. [Preview Abstract] |
Monday, November 23, 2015 6:28PM - 6:41PM |
L28.00012: Towards unravelling surfactant transport Mathieu Sellier, Satyananda Panda Surfactant transport arises in many natural or industrial settings. Examples include lipid tear layers in the eye, pulmonary surfactant replacement therapy, or industrial coating flows. Flows driven by the surface tension gradient which arises as a consequence of surfactant concentration inhomogeneity, also known as Marangoni-driven flows, have attracted the attention of fluid dynamists for several decades and has led to the development of sophisticated models and the undeniable advancement of the understanding of such flows. Yet, experimental confirmation of these models has been hampered by the difficulty in reliably and accurately measuring the surfactant concentration and its temporal evolution. In this contribution, we propose a methodology which may help shed some light on surfactant transport at the surface of thin liquid films. The surface stress induced by surfactant concentration induces a flow at the free surface which is visible and measurable. In the context of thin film flows for which the lubrication approximation hold, we demonstrate how the knowledge of this free surface flow field provides sufficient information to reconstruct the surfactant tension field. From the surface tension and an assumed equation of state, the local surfactant concentration can also be calculated and other transport parameters such as the surfactant surface diffusivity indirectly inferred. In this contribution, the proposed methodology is tested with synthetic data generated by the forward solution of the governing partial differential equations in order to illustrate the feasibility of the algorithm and highlight numerical challenges. [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