Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session R8: Drops XII |
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Chair: Arne Pearlstein, University of Illinois at Urbana-Champaign Room: 25A |
Tuesday, November 20, 2012 1:00PM - 1:13PM |
R8.00001: Internal flow and deformation of a liquid CO$_{2}$ drop rising through water Louis L. Steytler, Arne J. Pearlstein We report computations of the steady axisymmetric flow in and around a deformable liquid drop of CO$_{2}$ ascending through a water column under the action of buoyancy, a problem relevant to risk assessment for sub-seabed carbon sequestration and storage. In these initial computations, we consider several drop densities, corresponding to different depths in the ocean, and neglect dissolution of CO$_{2}$ into the surrounding water and formation of a hydrate film at the drop/water interface. The results, which extend our previous work (Bozzi et al., \textit{J. Fluid Mech.}, \textbf{336}, 1-32, 1997) to the case in which the dynamic viscosities of the dispersed and continuous phases are unequal, show that the degree of deformation and internal circulation depend strongly on drop size. [Preview Abstract] |
Tuesday, November 20, 2012 1:13PM - 1:26PM |
R8.00002: 3D Droplet velocities and sizes in the Ranque-Hilsch vortex tube R. Liew, J.C.H. Zeegers, J.G.M. Kuerten, W.R. Michalek The Ranque-Hilsch vortex tube is a known device that is used to generate spot cooling. In this study, we experimentally investigate the behavior of small water droplets in the vortex tube by means of Phase Doppler Particle Analysis. In an experimental vortex tube, droplets were injected together with a carrier gas to form a fast rotating (up to 80.000 rpm) droplet-gas mixture. Droplet sizes, 3D velocity components, and turbulent properties were measured, showing high intensity isotropic turbulence in the core region. To investigate the cause of the high intensity turbulence, a frequency analysis was applied on the measured velocity. The frequency spectrum of the velocity is presented and indicates that wobbling of the vortex axis is the cause of the high turbulence intensity. It was expected that larger droplets have a higher radial velocity because of the larger centrifugal force. Results show, however, that small and lager droplets behave similar. [Preview Abstract] |
Tuesday, November 20, 2012 1:26PM - 1:39PM |
R8.00003: The Polarization of a Diffuse Soft Particle Subjected to an Alternating Current Field Sebastian Uppapalli, Hui Zhao The polarization of a diffuse soft particle submerged in an aqueous electrolyte and subjected to a uniform, alternating electric field is theoretically analyzed with the standard electrokinetic model. The particle consists of a rigid uncharged core and a charged diffuse polyelectrolytic shell (soft layer), permeable to ions and solvent. Our focus is on the impact of the characteristics of the soft layer including Donnan potential, the soft layer thickness and the friction coefficient of the soft layer on the dipole coefficient, characterizing the strength of the polarization. Under the limits of thin double layers and thin polyelectrolytic shells, approximate, analytical expressions to evaluate dipole moment coefficients are derived, respectively, for high-frequency and low-frequency ranges. The analytical results are compared and agree favorably with those numerically computed by the standard model. Interestingly, we discover that when the double layer is comparable to the soft layer, the dipole moment behaves qualitatively differently at different Donnan potentials. When the Donnan potential is small, the dipole moment decreases as the double layer increases. In contrast, at large Donnan potentials, the dipole moment increases with the increase of the double layer. The distinct responses to Donnan potentials are attributed to the impact of the associated double layer on the charge distribution of mobile ions inside the soft layer. The theoretical model provides a fundamental basis for interpreting the polarization of heterogeneous systems including environmental or biological colloids or microgel particles. [Preview Abstract] |
Tuesday, November 20, 2012 1:39PM - 1:52PM |
R8.00004: Preventing droplet deformation during dielectrophoretic centering of a compound emulsion droplet Greg Randall, Brent Blue Compound droplets, or droplets-within-droplets, are traditionally key components in applications ranging from drug delivery to the food industry. Presently, millimeter-sized compound droplets are precursors for shell targets in inertial fusion energy work. However, a key constraint in target fabrication is a uniform shell wall thickness, which in turn requires a centered core droplet in the compound droplet precursor. Previously, Bei et al. (2009, 2010) have shown that compound droplets could be centered in a static fluid using an electric field of 0.7 kV/cm at 20 MHz. Randall et al. (2012) developed a process to center the core of a moving compound droplet, though the $\sim$kV/cm field induced small ($<$ 5\%) but undesirable droplet stretching. This work shows that by using macromolecular emulsifiers to strengthen the droplet's interfaces, (proteins, tunable peptides, or biotinylated streptavidin) droplet stretching can be greatly inhibited. Proof-of-principle experiments are performed in either a stagnant density-matched aquarium or a vertical channel of buoyancy-driven droplets in a $\sim$kV/cm electric field. A scaling analysis is given from a fluid mechanics and interfacial rheology perspective and we discuss the effective interfacial charge from an emulsifier and its impact on centering. [Preview Abstract] |
Tuesday, November 20, 2012 1:52PM - 2:05PM |
R8.00005: Pilot-wave dynamics in confined geometries Daniel M. Harris, John W.M. Bush Yves Couder and coworkers have demonstrated that millimetric droplets can propel themselves along the surface of a vibrating fluid bath by virtue of their pilot-wave dynamics, and that these walking droplets exhibit several features reminiscent of microscopic quantum particles. We here present the results of an experimental investigation of droplets walking in confined geometries, giving particular attention to elucidating the dynamics and statistics of the walking droplets. The behaviour depends critically on the amplitude of the vibrational forcing, specifically, the proximity to the Faraday threshold, which determines the spatio-temporal extent of the guiding wave field. Near the Faraday threshold, we demonstrate that a coherent statistical behavior emerges from the complex underlying nonlinear dynamics, and that, as in quantum mechanics, the statistics can be readily described with a linear wave equation. [Preview Abstract] |
Tuesday, November 20, 2012 2:05PM - 2:18PM |
R8.00006: Viscosity Measurement via Drop Coalescence: A Space Station Experiment Basil Antar The concept of using low gravity experimental data together with CFD simulations for measuring the viscosity of highly viscous liquids was recently validated on onboard the International Space Station (ISS). A series of microgravity tests were conducted for this purpose on the ISS in July, 2004 and in May of 2005. In these experiments two liquid drops were brought manually together until they touched and were allowed to coalesce under the action of the capillary force alone. The coalescence process was recorded photographically from which the contact radius speed of the merging drops was measured. The liquid viscosity was determined by fitting the measured data with accurate numerical simulation of the coalescence process. Several liquids were tested and for each liquid several drop diameters were employed. Experimental and numerical results will be presented in which the viscosity of several highly viscous liquids were determined using this technique. [Preview Abstract] |
Tuesday, November 20, 2012 2:18PM - 2:31PM |
R8.00007: Frictional effects on liquid marbles Guillaume Lagubeau, Antonella Rescaglio, Francisco Melo, Christophe Clanet, David Qu\'er\'e Liquid marbles are liquid drops coated with hydrophobic grains. This kind of interfaces has a dual nature as it mixes the capillar behavior of the liquid with the granular properties of the grains cap. This induces remarkable properties that have been shown recently and used for example for stabilization of liquid foams. Nevertheless, their fundamental mechanisms have yet to be fully understood. We present here an experimental study of statics and dynamics effects of the solid friction between grains on the liquid marbles properties. [Preview Abstract] |
Tuesday, November 20, 2012 2:31PM - 2:44PM |
R8.00008: Holy Balls!: Part Deux Jesse Belden, Michael Jandron, Tadd Truscott A Waboba$^{\textregistered}$ (WAter BOuncing BAll) demonstrates remarkable water skipping behavior, even at relatively large impact angles. The highly compliant nature of these elastic spheres results in significant deformation into a disk-like shape upon impact. The increased wetted area and force coefficient generates a large hydrodynamic force that more readily lifts the ball off the water surface. However, elasticity introduces some surprising phenomena, such as material waves that propagate on the sphere and interact with the water cavity. Depending upon impact conditions, material waves may propagate in various directions combining to create multiple modes of deformation and complicated fluid-structure interactions. Furthermore, the timescales of deformation and wave propagation depend on the material properties and impact conditions. In this talk, we will discuss skipping regimes in terms of impact parameters and material properties and relate failed skipping behavior to the structure-fluid interaction caused by deformation. The critical timescales for deformation, wave propagation and collision will be related to the relevant physical parameters of the problem. [Preview Abstract] |
Tuesday, November 20, 2012 2:44PM - 2:57PM |
R8.00009: The effects of the impact velocity of water droplets on the surface features in a rain field Ren Liu, Xinan Liu, James Duncan The characteristics of the shape of a water surface in response to the impact of simulated raindrops are studied experimentally. The experiment is carried out in a 1.22-m by 1.22-m water pool with a water depth of 0.3 m. Simulated raindrops are generated by an array of 22-gauge needles that are attached to a flat plate and connected to a water reservoir with soft hoses. A random translational motion is added to the plate to produce a randomness of the drop impact locations for each needle. The height of the flat plate relative to the water surface of the pool is varied from 1~m to 3~m to vary the impact velocities of the water drops. The surface features due to the impact of the drops, including the crown, stalk and ring waves are measured with a cinematic laser-induced- fluorescence (LIF) technique. It is found that the size of the crown, the height of the stalks and the wavelength of the waves vary with the impact velocity of drops. A comparison of these features with those found in a single drop impact is highlighted. [Preview Abstract] |
Tuesday, November 20, 2012 2:57PM - 3:10PM |
R8.00010: ABSTRACT WITHDRAWN |
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