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 M35: Drops: General |
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Chair: Tadd Truscott, Utah State University Room: Ballroom B |
Tuesday, November 24, 2015 8:00AM - 8:13AM |
M35.00001: Unraveling expressionism Tadd Truscott, Baptiste Darbois-Texier, Benjamin Lovett, Martin Brandenbourger, Laurent Maquet, Zhao Pan, Tristan Gilet, David Strivay, Stéphane Dorbolo From the large facades of our buildings to the refinement of art canvas, paintings literally surround us and make our lives colorful. Artists are continually looking for novel methods to complement their expression and ideas, while instinctively manipulating the underlying physics. We attempt to unravel a phenomenon common to many modern canvas artists. In some paintings small droplets (0.1 - 5 mm) appear as a single color, however, on closer inspection are actually composed of multicolored spiral patterns (e.g., non-newtonian acrylic paint). High-speed imaging reveals that these assemblies occur when a droplet impinges on the edge of a small pool of paint. Upon impact, the droplet creates a crown with the falling droplet color on the inside of the crown and the pool colors on the outside. Ripping occurs in thin film feeding a rapid roll-up in the thicker ridge-line regions. These twisted formations are projected outward and break into small droplets that form the paint spirals. These beautiful formations, appreciated in their static form on canvas in museums around the world, are formed by equally beautiful physical phenomena. [Preview Abstract] |
Tuesday, November 24, 2015 8:13AM - 8:26AM |
M35.00002: 3D tomographic reconstruction of the internal velocity field of an immiscible drop in a shear flow Paul Kerdraon, Stuart B. Dalziel, Raymond E. Goldstein, Julien R. Landel, Francois J. Peaudecerf We study experimentally the internal flow of a drop attached to a flat substrate and immersed in an immiscible shear flow. Transport inside the drop can play a crucial role in cleaning applications. Internal advection can enhance the mass transfer across the drop surface, thus increasing the cleaning rate. We used microlitre water-glycerol drops on a hydrophobic substrate. The drops were spherical and did not deform significantly under the shear flow. An oil phase of relative viscosity 0.01 to 1 was flowed over the drop. Typical Reynolds numbers inside the drops were of the order of 0.1 to 10. Using confocal microscopy, we performed 3D tomographic reconstruction of the flow field in the drop. The in-plane velocity field was measured using micro-PIV, and the third velocity component was computed from incompressibility. To our knowledge, this study gives the first experimental measurement of the three-dimensional internal velocity field of a drop in a shear flow. Numerical simulations and theoretical models published in the past 30 years predict a toroidal internal recirculation flow, for which the entire surface flows streamwise. However, our measurements reveal a qualitatively different picture with a two-lobed recirculation, featuring two stagnation points at the surface and a reverse surface flow closer to the substrate. This finding appears to be independent of Reynolds number and viscosity ratio in the ranges studied; we conjecture that the observed flow is due to the effect of surfactants at the drop surface. [Preview Abstract] |
Tuesday, November 24, 2015 8:26AM - 8:39AM |
M35.00003: Dye doped micro-droplets as a sensor for fluid dynamics applications Tindaro Ioppolo, Maurizio Manzo We report that micro-droplets can be used as sensors for fluid dynamics applications. These microscale droplets in liquid or solid form are made of polymers that are doped with dyes. These tiny droplets behave has micro-scale optical cavities that support optical modes. The optical modes are excited remotely using a Nd:YAG laser with pulse repetition of 10Hz. Here we report the fabrication of the droplets and their feasibility as untethered wall pressure and temperature sensors. When the droplets are exposed to variations of temperature or pressure their morphology (size and index of refraction) change. This in turn leads to a shift of the optical modes. The optical modes and therefore their shifts are monitored using an optical spectrometer. [Preview Abstract] |
Tuesday, November 24, 2015 8:39AM - 8:52AM |
M35.00004: Harnessing Nanoparticles to Control Evaporation at Liquid-Vapor Interfaces Xin Yong It is well known that nanoparticles with appropriate size and surface chemistry adsorb to liquid-vapor interfaces and consequently modify the mechanical properties of the interfaces. However, little has been explored about the effect of nanoparticles on the heat transfer occurring at the interfaces. Using many-body dissipative particle dynamics (MDPD), we model an evaporating interface with adsorbed nanoparticles. Homogeneous and amphiphilic Janus nanoparticles, which contain hydrophobic and hydrophobic surface regions, are considered in this study. We measure the variation in the evaporation rates of the interface by gradually increasing particle loading until a hexagonal-close-packed monolayer is achieved. We explore the effect of surface chemistry and surface composition of the particles and demonstrate that evaporation can be readily adjusted by tuning the interaction parameters and amphiphilic ratio. Importantly, we observe that the evaporation suppression by adsorbed nanoparticles occurs only when the ambient vapor pressure is low. This study provides a fundamental understanding of the phase transition in multiphase interfacial systems and opens up new routes to additional control over evaporating interfaces. [Preview Abstract] |
Tuesday, November 24, 2015 8:52AM - 9:05AM |
M35.00005: Dissolution of a multicomponent droplet in an immiscible ambient fluid: Application of the distribution law Shigan Chu, Andrea Prosperetti A liquid droplet will shrink in an undersaturated ambient liquid medium due to mass transfer across the interface even when the drop liquid is only sparingly soluble in the host liquid. The dissolution rate of a single-component droplet can be accurately predicted by an adaptation of the the Epstein-Plesset theory, in which it is assumed that the droplet surface remains at saturation. This hypothesis may be violated in the case of a multi-component droplet, as the more soluble component dissolves faster than the other(s). As a consequence, the droplet surface cannot remain saturated with this component in the later stages of the process. To account for this feature a modified Epstein-Plesset theory is developed on the basis of the distribution law of liquid-liquid solutions. The implications of the teory are illustrated with several examples. [Preview Abstract] |
Tuesday, November 24, 2015 9:05AM - 9:18AM |
M35.00006: Marangoni stresses and drop breakup due to wall shear in a partially filled rotating cylinder Andrew White, Azeez Odesanya, Thomas Ward Drop deformation and breakup in a rotating cylinder partially filled with oil is studied. Experiments using a rotating cylinder are relatively new but we will demonstrate that they are analogous to studies involving tubes and other geometries. Surfactants are added to the drop phase in concentrations at and below the CMC while the rotation rate of the cylinder is varied. Of interest is the effect of interfacial surfactant transport on changes in oil film thickness, drop shape and the onset of tail streaming. Two Biot numbers comparing the importance of surfactant adsorption and desorption to convection of surfactant on the interface are estimated. As shown in previous work on drops and bubbles in tubes, the balance between surface convection, diffusion and adsorption can affect the placement of Marangoni stresses, resulting in thicker or thinner films than with clean surfaces. When surface convection is large, surfactant builds up at the tail and Marangoni stresses can lead to tail streaming when surface tensions are sufficiently small. Experimental results are compared to numerical simulations and to previous work on drops and bubbles in tubes. [Preview Abstract] |
Tuesday, November 24, 2015 9:18AM - 9:31AM |
M35.00007: Optical whispering gallery mode induced interface deformation of liquid droplets Peng Zhang, Sunghwan Jung, Yong Xu, Aram Lee In this study, we analyze nonlinear processes associated with a high-Q factor whispering gallery mode (WGM) in micro-sized liquid droplets, which can be induced by Kerr nonlinearity, thermal effect, and optical radiation pressure. Optical WGM can produce a radiation pressure on the droplet and induce droplet deformations. In our analysis, the droplet deformation will be obtained both analytically by force balance and numerically by the boundary element method. We will show that the nonlinear optofluidic effect is stronger than the Kerr effect and thermal effect. Time scales of these three nonlinear processes will also be estimated and compared. The feasibility of single photon level nonlinearities will be analyzed. [Preview Abstract] |
Tuesday, November 24, 2015 9:31AM - 9:44AM |
M35.00008: Washing wedges: a capillary instability in a gradient of confinement Ludovic Keiser, Remy Herbaut, Jose Bico, Etienne Reyssat When a drop of oil is introduced into a gradient of confinement (two glass plates forming a sharp wedge) capillary forces drive it toward the most confined regions, where the solid-fluid contact area is maximal. A surfactant solution subsequently introduced into the wedge undergoes the same movement until it reaches the oil previously added. If the aqueous phase wets the solid better than the oil, a complex exchange process between both phases occurs. The water-oil interface destabilizes, oil fingers grow in the water phase, pinch-off and lead to the formation of droplets that migrate away from the tip of the wedge. The whole oil phase is eventually extracted. A linear stability analysis of the interface is presented and captures the size of the oil droplets. The dynamics of the system is however not perfectly explained by a simple Poiseuille flow. Indeed, more refined models should account for the dissipation in meniscii and lubrication films. Finally, we suggest that our model experiment may constitute a useful tool to select optimal systems for oil recovery processes. [Preview Abstract] |
Tuesday, November 24, 2015 9:44AM - 9:57AM |
M35.00009: Generation of highly-viscous microjets Yoshiyuki Tagawa, Hajime Onuki, Yuto Oi An ink-jet printing system (or a liquid-dispensing device) has ecological and cost advantages compared to other printing systems such as offset printing and gravure printing since it requires a small amount of liquids. However, most ink-jet printers are not able to eject high-viscous liquids more than 10 cSt. This limitation severely restricts applications of the ink-jet system. Here we present a novel jet-generation system, discharging jets of high-viscous liquids up to 1,000 cSt. The system employs an impulsive force and converges the force efficiently in order to accelerate the liquid-air interface strongly for generating viscous jets: It consists of a liquid container and a thin tube partially inserted in the liquid. The liquid-air interface inside the thin tube is set deeper than that outside of the tube. We then add an impulsive force on the bottom of the container, leading to the microjet generation inside the thin tube. The pressure field under the impulsive force is estimated using pressure-impulse approach, deriving the jet velocity. The jet velocity is experimentally measured with varying the impulsive force and liquid levels in the tube and the container. It is found that the measured velocities agree with the estimation. Owing to the simple structure of the generation system and an ability for ejecting viscous liquids, it could extend the limits of existing ink-jet printers and may be applicable for next-generation technologies such as 3D printing systems and needle-free injection devices. [Preview Abstract] |
Tuesday, November 24, 2015 9:57AM - 10:10AM |
M35.00010: From bubble bursting to droplet evaporation in the context of champagne aerosols Thomas Seon, Elisabeth Ghabache, Arnaud Antkowiak, Gerard Liger-Belair As champagne or sparkling wine is poured into a glass, a myriad of ascending bubbles collapse and therefore radiate a multitude of tiny droplets above the free surface into the form of very characteristic and refreshing aerosols. Because these aerosols have been found to hold the organoleptic “essence” of champagne they are believed to play a crucial role in the flavor release in comparison with that from a flat wine for example. Based on the model experiment of a single bubble bursting in idealized champagnes, the velocity, radius and maximum height of the first jet drop following bubble collapse have been characterized, with varying bubble size and liquid properties in the context of champagne aerosols. Using the experimental results and simple theoretical models for drop and surface evaporation, we show that bubble bursting aerosols drastically enhance the transfer of liquid in the atmosphere with respect to a flat liquid surface. Contrary to popular opinion, we exhibit that small bubbles are negative in terms of aroma release, and we underline bubble radii enabling to optimize the droplet height and evaporation in the whole range of champagne properties. These results pave the road to the fine tuning of champagne aroma diffusion, a major issue of the sparkling wine industry. [Preview Abstract] |
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