Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session S46: Drops and Bubbles III |
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Sponsoring Units: DFD Chair: Lailai Zhu, Princeton Univ Room: LACC 506 |
Thursday, March 8, 2018 11:15AM - 11:27AM |
S46.00001: A Multiscale Lattice Boltzmann Model for Simulating Drainage in Wet and Dry Foams Subhabrata Das, Zi-Xiang Tong, Eberly Lauren, Xi Chen, Charles Maldarelli, Ponisseril Somasundaran We use a systematic, two-component, 2D, Lattice Boltzmann Model (LBM) with frustrated short range attractive and mid/long-range repulsive-interactions to simulate the capillary and gravity-driven drainage of wet and dry foams in a confined geometry. From the assigned LBM interactions, the gas/liquid surface tension, film elasticity and capillary disjoining pressure are computed to characterize the simulated foam. First, LBM simulations of a Poiseuille flow of the foam are performed as a verification of our model, and these demonstrate a reduction in the maximum velocity with increase in the air area fraction of the foam, and a Non-Newtonian rheology. In the drainage simulations, as gas separates from the foam in the computational domain, the temporal evolution of the foam height shows a rapid collapse followed by a regime in which the foam is more stable. These results compare favorably with experiments on SDS stabilized glycerol/water foams, demonstrating the ability of the LBM method to capture the realistic behavior of foams. |
Thursday, March 8, 2018 11:27AM - 11:39AM |
S46.00002: Understanding the Nature of Nanoscale Wetting through All-atom Simulations Oliver Evans, Selemon Bekele, Mesfin Tsige Wetting plays an important role in many areas of science and engineering, including adhesion, corrosion, and ice formation among others. While macroscale wetting is well understood, a sufficient characterization of nanoscale wetting remains to be developed. Since the experimental limit of droplet spreading is presently on the order of seconds and micrometers, we turn to all-atom molecular dynamics simulations to study this phenomenon on the nanoscale. We focus our attention to simulations of pure water on atomically flat substrates such as sapphire and quartz, in which we observe significant qualitative deviations from macroscale wetting dynamics. In particular, we observe the formation of a one-molecule-thick ``monolayer'' which spreads significantly faster than the bulk of the droplet. Our interest lies in the relationship between the radius of the monolayer and other features of the droplet such as bulk radius, contact angle, and droplet height over time in both spherical and cylindrical droplets. Using a combination of first principles and constitutive relationships, we construct and analyze a model for the observed behavior in order to explain the causes and implications of the unique dynamics of wetting at this scale. |
Thursday, March 8, 2018 11:39AM - 11:51AM |
S46.00003: Oscillatory Wetting under Drops Impacting on a Hot Plate Kirsten Harth, Michiel Limbeek, Chao Sun, Andrea Prosperetti, Detlef Lohse The Leidenfrost phenomenon, where an evaporating drop levitates above a layer of its vapour on sufficiently hot plates is well-known for gently deposited drops. For impacting drops, the additional impact pressure can cause much thinner vapour layers in the nanometer range, and conventional side or bottom view imaging is incapable of detecting substrate contact. Using frustrated total internal reflection (FTIR), three main regimes were distinguished: contact, nucleate boiling at low temperatures (drop spreads in contact with substrate), Leidenfrost (film) boiling without contact and a broad transition regime. Then, the outer parts of the spreading lamella levitate, while the central region of the drop touches the substrate. |
Thursday, March 8, 2018 11:51AM - 12:03PM |
S46.00004: Slip effects on forced dewetting Tak Shing Chan, Martin Brinkmann, Ralf Seemann The forced dewetting of a viscous liquid confined in a cylindrical |
Thursday, March 8, 2018 12:03PM - 12:15PM |
S46.00005: Water-holey graphene interactions Kunal Ahuja, Yanbin Wang, Shayandev Sinha, Parth Rakesh Desai, Siddhartha Das We employ Molecular Dynamics (MD) simulations to probe the interaction of a water nanodrop with a holey graphene (HG) matrix. HG is a particular form of structurally defective nanoporous graphene, where multilayers of nanoporous graphene get arranged in form of vertically separated stacks with inter-stack separation of several nanometers. |
Thursday, March 8, 2018 12:15PM - 12:27PM |
S46.00006: Snap evaporation of droplets on smooth topographies Marc Pradas, Gary Wells, Elfego Ruiz-Gutierrez, Rodrigo Ledesma-Aguilar The evaporation of droplets on solid surfaces is important for a broad range of applications, including ink-jet printing, surface cooling, and micro-structure assembly. Despite its apparent simplicity, the precise configuration of an evaporating droplet on a solid surface has proven notoriously diffcult to predict and control. This is because droplet evaporation typically proceeds as a `stick-slip' sequence, which is a combination of pinning and de-pinning events, caused by microscopic structure of the solid surface. In this talk we show how smooth, pinning-free, solid surfaces of non-planar topography give rise to a different process which we dub snap evaporation. During snap evaporation the morphology of an evaporating droplet follows a reproducible sequence of steps, where the liquid-gas interface is quasi-statically reduced by mass diffusion until it undergoes an out-of-equilibrium snap. Experimentally, we demonstrate this process using, as a model system, a water droplet evaporating on a wavy ultra-smooth lubricant-infused surface. Mathematically, we use full hydrodynamics lattice-Boltzmann simulations, and a model based on bifurcation theory that reveals the points where snap events are triggered, which obey a strict hierarchy dictated by the underlying surface topography. |
Thursday, March 8, 2018 12:27PM - 12:39PM |
S46.00007: Impact and Spreading of Superfluid and Normal Fluid Helium Droplets Matthew Wallace, David Mallin, Andres Aguirre Pablo, Kenneth Langley, sigurdur thoroddsen, Michael Milgie, Peter Taborek We present the results of our investigation of superfluid and normal fluid helium droplets impacting on a solid dry surface in an optical cryostat at temperatures between 1.2 K and 5.1 K at saturated vapor pressure. We use high-speed video to image the impacting drops over a large range of Reynolds numbers and Weber numbers. We also use high-speed interferometry to measure the thickness and curvature of the droplets. |
Thursday, March 8, 2018 12:39PM - 12:51PM |
S46.00008: Self-Similar Taylor Cone Formation in Conducting Viscous Films: Computational Study of the Influence of Reynolds Number Theodore Albertson, Sandra Troian Previous studies by Zubarev (2001) and Suvorov and Zubarev (2004) have shown that above a critical field strength, an inviscid conducting fluid film will deform into a singular profile characterized by a conic cusp. The governing equations for the electrohydrodynamic response beneath the cusp admit self-similar solutions leading to so-called blow-up behavior in the Maxwell pressure, capillary pressure and kinetic energy density. Runaway behavior in these variables reflects divergence in time characterized by an exponent of -2/3. Here we extend the physical system to include viscous effects and conduct a computational study of the cusp region as a function of increasing electrical Reynolds number ReE. We employ a finite element, moving mesh algorithm to examine the behavior of the film shape, Maxwell pressure and capillary pressure upon approach to the blow-up event. Our study indicates that self-similarity establishes at relatively low ReE despite the presence of vorticity, which is localized to the cusp region. With increasing ReE, the period of self-similiarity extends further in time as the exponent changes from about -4/5 to the ideal value of -2/3, with slightly different values for the Maxwell and capillary stresses. |
Thursday, March 8, 2018 12:51PM - 1:03PM |
S46.00009: Instability and bifurcation of a particle-encapsulating droplet in creeping shear flow Lailai Zhu, Francois Gallaire In this study, we investigate a novel model system in order to understand the flow behavior of fluid particles such as nucleated cells and double-emulsions. The model consists of a finite-size particle encapsulated in a deforming droplet and we ask whether this composite system will stay concentric or not in a creeping shear flow. By performing numerical simulations based on a versatile boundary integral method, we find in addition to the concentric particle-droplet configuration, other eccentric and time-periodic equilibrium solutions emerge spontaneously via supercritical pitchfork and Hopf bifurcations. The loci of these solutions are presented around the codimenstion-two point. We adopt a dynamic system approach to model and characterize the two bifurcations and their interactions. By scrutinizing the flow fields and hydrodynamic forces, we identify the role of hydrodynamic particle-droplet interaction which gives rise to these bifurcations. |
Thursday, March 8, 2018 1:03PM - 1:15PM |
S46.00010: Partial coalescence of a soap bubble with a soap film Giuseppe Pucci, John Bush, Daniel Harris When a droplet is gently deposited on a liquid bath, it may coalesce only partially thereby releasing a daughter droplet of approximately half the size of the parent droplet. While the partial coalescence of droplets has been extensively studied, recent numerical simulations have suggested that partial coalescence should also be possible for soap bubbles. We present here the first experimental study of the partial coalescence of a soap bubble with a soap film. The coalescence process occurs over a timescale comparable to the inertial-capillary time, which is the time for the capillary waves generated during the process to span the bubble. A simple model that captures the time variation of the bubble's size during the air evacuation phase is presented. Through dynamic similarity, the process for bubbles is remarkably similar to that for droplets. In particular, daughter bubbles are observed to be approximately half the size of their parents and can exhibit a coalescence cascade, which arises as a succession of partial coalescence events. Future directions and ongoing work will be discussed. |
Thursday, March 8, 2018 1:15PM - 1:27PM |
S46.00011: Magnetization as a Stabilizing Influence on Ferrofluid Electrosprays Aaron Madden, Juan Fernandez de la Mora, Nirmesh Jain, Brian Hawkett, Hadi Sabouri Electrospray fills a gap for satellite propulsion, producing more thrust per weight or power than present alternatives. Useful thrust requires many electrospray emitters and multiplexing emitters to a useful scale often erodes performance. Current technologies like porous beds experience hurdles of repeatability. We exploit ferrofluids’ self-assembly into arrays of sharp tips as an alternative route to multiplexing electrosprays, demonstrating separations as low as 150um and tip curvatures as sharp as 5um. A novel, low volatility, low conductivity ferrofluid is produced, characterized and electrosprayed. Magnetization drastically expands spray stability, reducing the minimal stable flow rate by up to 99%, halving the onset voltage and showing distinctly non-Taylor morphology. |
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