Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session E4: Drops III: Experiments |
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Chair: David Hu, Georgia Institute of Technology Room: 307 |
Sunday, November 20, 2011 4:40PM - 4:53PM |
E4.00001: Dynamics of a Disturbed Sessile Drop measured by AFM Patricia McGuiggan, Daniel Grave, Jay Wallace, Shengfeng Cheng, Andrea Prosperetti, Mark Robbins A new method for studying the dynamics of a sessile drop by atomic force microscopy (AFM) is demonstrated. A hydrophobic microsphere (radius, r =20 micrometers) is brought into contact with a small sessile drop resting on a hydrophobic surface. When the microsphere touches the liquid surface, the meniscus rises onto the microsphere due to capillary forces. Although the microsphere volume is six orders of magnitude smaller than the drop, it excites the lowest normal resonance modes of the liquid interface. The sphere is pinned at the interface whose small (less than 100 nm) oscillations are readily measured with the AFM. Resonance oscillation frequencies were measured for drop volumes between 5 microL and 200 microL. The results for the two lowest normal modes are quantitatively consistent with continuum calculations for resonance of hemispherical drops with no adjustable parameters. The method may enable sensitive measurements of volume, surface tension and viscosity of small drops. [Preview Abstract] |
Sunday, November 20, 2011 4:53PM - 5:06PM |
E4.00002: Investigation of drop motion through circular orifices Ankur Deep Bordoloi, Ellen K. Longmire, Xiangzhao Kong, Martin O. Saar The motion of drops though porous media occurs in numerous science and engineering fields including multiphase fluid flow in the subsurface during groundwater flow, geothermal energy recovery, and geologic carbon dioxide sequestration. Here, we simplify the porous medium to a thin plate with an orifice to study the interactions between the drop and the solid medium. Drops of water/glycerin with diameter, D, are released in a tank of silicone oil with matched refractive index and allowed to fall downward by gravity. After reaching terminal speed, the drops encounter a thin plate with orifice diameter, d, placed horizontally within the surrounding tank. Drop deformation, contact with the orifice, and breakage are investigated using high-speed imaging, and velocity fields are determined by particle image velocimetry (PIV). Effects of diameter ratio d/D, drop Reynolds number, and drop offset with respect to the orifice center are examined. The experimental results are compared to results from numerical simulations using an immiscible, two-color BGK lattice-Boltzmann method performed under similar test conditions. [Preview Abstract] |
Sunday, November 20, 2011 5:06PM - 5:19PM |
E4.00003: Experimental Studies of Liquid/Liquid Droplets Transport in Curved Microchannels Zeyad Almutairi, Tomasz Glawdel, Carolyn Ren, David Johnson This study utilizes optical visualization techniques to experimentally investigate the changes in transport properties of liquid droplets while they travel through microchannel turns. This study was prompted by observations that showed the length and speed of the droplet dynamically change while it is travelling through the turn. To gain insightful understanding of this phenomenon, systematic studies were carried out experimentally where the channel width, height, and turn radius were varied together with flow conditions in the low Capillary and Reynolds number flow regimes. Experimental findings reveal that the dynamic changes in droplet transport through curved microchannels are mainly caused by geometrical properties of the turn such as radius to channel width ratio and the height ratio. We also believe that the behavior of droplets in turns may dynamically affect the pressure gradient in the microchannel. [Preview Abstract] |
Sunday, November 20, 2011 5:19PM - 5:32PM |
E4.00004: Experimental droplet dynamics and interfacial rheology characterization Kendra Erk, Jeffrey Martin, Jonathan Schwalbe, Frederick Phelan Jr., Steven Hudson Many properties of emulsions arise from interfacial rheology. Recently, a theory of droplet dynamics accounting for interfacial rheology, Marangoni forces and mass transport was developed. Here, we describe experimental observations of droplet dynamics in light of this theory. Using particle tracking velocimetry, we examine the dynamics of surfactant-stabilized droplets in the Poiseuille flow of a microfluidic device. Interfacial shear and dilatational properties are evaluated, and we distinguish viscous and elastic effects. We find that the shear viscosity of the interface populated by block copolymer surfactant is greater than with small molecule alcohol surfactant. Investigation of small droplets is of interest not only for their relevance to emulsion applications, but their small size has potential for improved force sensitivity and temporal resolution. Other droplet dynamic approaches will be discussed. [Preview Abstract] |
Sunday, November 20, 2011 5:32PM - 5:45PM |
E4.00005: Looking Under a Leidenfrost Drop Justin Burton, Aaron Sharpe, Roeland van der Veen, Andres Franco, Sidney Nagel The Leidenfrost effect can be observed when small water drops move around effortlessly without sticking on a hot pan. The transition to a levitated state, where the drops rest on an insulating layer of vapor, occurs at the Leidenfrost temperature. Experiment [1] and theory [2] have examined the lifetime and maximum size of Leidenfrost drops. However, the liquid-vapor interface beneath the drop has not been fully charcterized. We report experiments using laser-light interference to measure the geometry of the liquid-vapor interface. By imaging the interference fringes produced between the bottom surface of the liquid and the hot substrate, we can measure the curvature of the vapor pocket beneath the drop as well as the azimuthal undulations along the neck that sits closest to the surface. From these measurements, we can extrapolate the shape of the bottom of the drop, which fluctuates in time with a period of a few milliseconds for millimeter-sized water drops. Our measurements of the azimuthal neck radius agree with predictions [2]: the difference between the drop and neck radii, ($R_d-R_n$)$\approx$0.53$\lambda$ in the limit of large drops where $\lambda$ is the capillary length of the fluid. For small drops we recover the result found in [1] that $R_n\propto R_d^2/\lambda$. \newline [1] A. Biance, C. Clanet, D. Quere, Phys. Fluids $\textbf{15}$, 1632 (2003). \newline [2] J. H. Snoeijer, P. Brunet, J. Eggers, Phys. Rev. E $\textbf{79}$, 036307 (2009). [Preview Abstract] |
Sunday, November 20, 2011 5:45PM - 5:58PM |
E4.00006: Experimental observations of droplet trajectories for investigation of water jet breakup and atomization Joshua Z. Skolnick, Lester K. Su Experimental measurements of droplet trajectories permit investigation of the breakup and atomization processes in water jets. The jets issued at varying angles from the horizontal, with the resulting droplets being collected in a horizontal array of collection bins that provided good spatial resolution of droplet volume fluxes. The experiments encompassed varying jet diameters and exit velocities. Time-resolved imaging of the jet near-field provided information on the initial droplet size distributions, which was used in a model that generated predictions of droplet fluxes in the horizontal plane by Lagrangian tracking. The results of the experiments, interpreted with the assistance of the modeling results, allow direct assessment of the importance of secondary breakup phenomena at different run conditions. The results also reveal that droplet coalescence plays a significant role in determining the local droplet size distribution in the jet far field. [Preview Abstract] |
Sunday, November 20, 2011 5:58PM - 6:11PM |
E4.00007: Oscillatory flow measurements in the vicinity of pinned-contact capillary surfaces Joseph Olles, Amir Hirsa By coupling two pinned-contact droplets through a short tube, various devices have been demonstrated, including fast-focusing liquid lenses, pumps, and adhesion devices. The double droplet system (DDS) can be achieved on the millimeter scale with essentially spherical interfaces due to capillarity. A one-dimensional model based on the center of mass motion has been corroborated by experiments, but CFD simulations of the flow within the DDS (Ramalingam and Basaran, Phys. Fluids 2010) have yet to be experimentally validated. With PIV, we study the fluid flow in and around a DDS that is surrounded by an immiscible liquid. The flow near the corner and capillarity effects of the pinned-contact surfaces will be explored for different volumes of the DDS, oscillating frequencies, and driving amplitudes. [Preview Abstract] |
Sunday, November 20, 2011 6:11PM - 6:24PM |
E4.00008: The dynamics of impacting and coalescing Newtonian droplets Jose Rafael Castrejon-Pita, Krzysztof J. Kubiak, Eleanor S. Betton, Mark C.T. Wilson, Alfonso A. Castrejon-Pita, Ian M. Hutchings An experimental arrangement is described to study impact, coalescence and mixing between a sessile and an impacting droplet of glycerol/water striking a flat transparent substrate in air. We used high speed imaging to visualize and study the impact and coalescence of droplets from the side and from beneath. The impact parameters and liquid characteristics were chosen to match the typical dynamical conditions, based on Reynolds and Weber numbers, found in commercial drop-on-demand printing. The images were processed by particle image velocimetry and image processing algorithms to obtain velocity fields near the liquid-substrate interface, droplet geometries and contact line positions. The experimental results are compared with numerical simulations by the lattice Boltzmann method and good agreement is found. The experimental setup and its instrumentation are simple to reproduce and can be used in other practical applications. [Preview Abstract] |
Sunday, November 20, 2011 6:24PM - 6:37PM |
E4.00009: ABSTRACT WITHDRAWN |
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