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 A24: Suspensions I |
Hide Abstracts |
Chair: Jeff Morris, City College of New York Room: 327 |
Sunday, November 20, 2011 8:00AM - 8:13AM |
A24.00001: The Role of the Stokes Number, the Capillary Number, and the Centrifugal Number in Oblique Wetted Particle Collisions Carly Donahue, Robert Davis, Christine Hrenya A plethora of systems that contain solid particles coated in a liquid layer are found in nature (e.g. avalanches, pollution) and in industry (e.g. granulation, particle filtration). Previous micro-level studies of wetted collisions have been limited to normal particle-particle collisions and normal and oblique particle-wall collisions. However, for a complete understanding, a study of oblique particle-particle collisions is crucial. In the work presented here, a combination of experiments and theory are used to identify the roles of capillary and centrifugal forces in these collisions at low Reynolds number. Surprisingly, even when the capillary number is high (ratio of lubrication to capillary forces), capillary forces play an essential role in agglomeration vs. de-agglomeration. Moreover, another dimensionless number is identified to characterize the relative importance of the centrifugal forces to the capillary forces, namely the Centrifugal number, which together with the Stokes number characterizes the regime map of outcomes. This work provides the foundation for simulations of many-particle systems. [Preview Abstract] |
Sunday, November 20, 2011 8:13AM - 8:26AM |
A24.00002: Transverse alignment of fibers in a periodically sheared suspension: An absorbing phase transition with a slowly-varying control parameter Alexandre Franceschini, Emmanouela Filippidi, Elisabeth Guazzelli, David Pine Shearing fibers and polymer solutions tends to align particles with the flow direction. Here, we report that neutrally buoyant non-Brownian fibers subjected to oscillatory shear are observed to align perpendicular to the flow. This alignment occurs over a finite range of strain amplitudes and is governed by a subtle interplay between fiber orientation and short-range interactions through an athermal (non-equilibrium) process known as random organization. For a given strain amplitude and concentration, the mean field orientation defines a time-dependant control parameter that can drive the suspension through an absorbing phase transition. The slow drift of the control parameter does not influence the class of the transition. The measured critical threshold and exponents are consistent with the one reported for sphere suspensions. This work was supported by the NSF through the NYU MRSEC, Award DMR:0820341. Additional support was provided by a Lavoisier Fellowship (AF) and from the Onassis Foundation (EF). [Preview Abstract] |
Sunday, November 20, 2011 8:26AM - 8:39AM |
A24.00003: Acoustic metafluid with anisotropic mass density and tunable sound speed: An approach based on suspensions of orientable anisotropic particles Mark Seitel, Stephen Tse, Jerry Shan We investigate liquid suspensions of micron-scale, anisotropic particles as potential acoustic metafluids having anisotropic and actively controllable acoustic properties. The effective mass density (and hence the sound propagation speed) of these metafluids can vary because the added mass of an anisotropic particle suspended in the fluid changes with the particle's orientation relative to the direction of the wave propagation. A suspension with disc-like particles oriented broadside to the direction of wave propagation is thus expected to have higher effective inertia and lower sound speed than a suspension with particles with end-on alignment. To test these predictions, sound speed is measured with a time-of-flight method in suspensions of micron-size nickel flakes suspended in oil, with and without magnetic-field-induced alignment of the particles. The sound speed, relative to the unaligned case, is found to decrease for particles oriented broadside to the sound wave, and increase for edgewise alignment. We also investigate the frequency dependence of the effective sound speed, since the added mass effect is expected to diminish as the flow becomes steady at low frequencies. The experimental results are compared to the predictions of a model proposed by Ahuja \& Hardee ({\it J. Acoust. Soc. Am} 1978) for the acoustic properties of aligned oblate-spheroid suspensions. [Preview Abstract] |
Sunday, November 20, 2011 8:39AM - 8:52AM |
A24.00004: Secondary jets from high viscosity complex fluid Gustaf M{\aa}rtensson, Thomas Kurian, Gustav Graeber Jetting of high viscosity, particle filled fluids (e.g. solder paste) is of great interest in any number of industries, for example electronics manufacturing. A current problem with this technique is the presence of particle satellites outside the region of the main deposit caused partly by a secondary jet being emitted upon impact. Up to now most detailed studies of corona splashes have been performed mainly on Newtonian fluids.\footnote{Xu, L. et al. 2005 ``Drop Splashing on a Dry Smooth Surface,'' {\it PRL}, {\bf 94}, pp. 1-4} We experimentally study the impact dynamics of a non-Newtonian fluid, lead-free solder paste, with a particle volume fraction of 0.45 and particle size range between 15 and 25 \(\mu\)m. The collected films show that over a range of impact velocities, secondary jets are only emitted after impact for high velocities. These observations are important in that they indicate an upper limit on the impact velocity that can be used in a real application. A threshold criteria for the production of secondary jets as a function of viscosity, \(\eta\), surface tension, \(\gamma\), and speed, \(v\), will be presented. [Preview Abstract] |
Sunday, November 20, 2011 8:52AM - 9:05AM |
A24.00005: Controlling Heap Formation in Microsphere Suspensions Carlos Ortiz, Karen Daniels, Robert Riehn We explore how the formation of heaps of microspheres depends on the relative magnitudes of hydrodynamic, surface, and thermal forces. We assemble a heap of sub-micron polystyrene spheres by pumping a dilute ($\phi < 10^{-3}$) suspension towards a barrier in a microchannel. We map out a phase diagram to locate the heap-forming regime as a function of incoming bead velocity, controlled by driving pressure, and barrier surface charge, controlled by buffer conditions. As the barrier surface charge increases, the long-range repulsive normal force between the microspheres and the surface increases, causing the minimum driving pressure needed to form a pile to increase. We measure the static and dynamic properties of the heap as a function of system parameters. [Preview Abstract] |
Sunday, November 20, 2011 9:05AM - 9:18AM |
A24.00006: Concentrated suspensions in a homogeneous shear flow with finite fluid inertia Kyongmin Yeo, Martin Maxey The dynamics of monodisperse suspensions of neutrally buoyant particles under finite fluid inertia is investigated by numerical simulations using the force-coupling method. Here, we report on the effect of finite fluid inertia on the rheology and self-diffusion of the suspended particles for the volume fractions 0.2 - 0.4. It is found that the diffusivity is an increasing function of Reynolds number, while the particle-phase velocity fluctuations decrease at larger Reynolds number. Lagrangian velocity autocorrelation functions indicate that the motion of the suspended particles has a longer correlation under finite fluid inertia, which in turn contributes to the increase of the diffusivity. The changes in rheological parameters, such as the suspension viscosity and normal stress differences, under finite inertia are studied by analyzing pair-distribution functions. We found that the particle stresses become highly intermittent at larger Reynolds number. [Preview Abstract] |
Sunday, November 20, 2011 9:18AM - 9:31AM |
A24.00007: Clouds of particles in a periodic shear flow Bloen Metzger, Jason E. Butler We have investigated experimentally the time evolution of a cloud of non-Brownian particles submitted to a periodic shear flow in an otherwise pure liquid at low Reynolds number. This experiment is reminiscent to the famous Taylor experiment but applied to clouds of particles. It illustrates the irreversible nature of particulate systems submitted to a shear. Unlike Taylor's ink-drop, clouds of particles do not reconstitute when shear is reversed. We have found that, when repeating the cycles of shear, clouds of particles progressively disperse in the flow direction until they reach the threshold critical volume fraction. For very large initial volume fractions, clouds evolve into a ``galaxy-like" shape. [Preview Abstract] |
Sunday, November 20, 2011 9:31AM - 9:44AM |
A24.00008: Hydrodynamic effects on aggregation of colloidal particles Jeffrey Morris The effects of both hydrodynamic interaction and the form of the interparticle potential on the aggregation process for dispersed spherical particles are investigated by computational simulation. The simulation methods of Brownian Dynamics (BD) and Stokesian Dynamics (SD) are applied, over a range of solid volume fraction of $0.04\le \phi\le 0.12$. The interparticle potential is a combination of a generalized Lennard-Jones form and a Yukawa potential, the latter of which describes a screened electrostatic repulsion at longer range. Hydrodynamic interactions were found to significantly reduce the solid fraction required for percolation, with the influence depending upon the form of the potential; the difference in percolation threshold was significant, with $\phi_{c, SD} \doteq 0.06$ and $\phi_{c,BD}\ge 0.08$ a typical difference for moderate repulsion barriers. These results are for O(1000) particles in a cubic unit cell. [Preview Abstract] |
Sunday, November 20, 2011 9:44AM - 9:57AM |
A24.00009: A novel concept of dielectrophoretic engine oil filter Boris Khusid, Yueyang Shen, Ezinwa Elele A novel concept of an alternating current (AC) dielectrophoretic filter with a three-dimensional electrode array is presented. A filter is constructed by winding into layers around the core tube two sheets of woven metal wire-mesh with several sheets of woven insulating wire-mesh sandwiched in between. Contrary to conventional dielectrophoretic devices, the proposed design of electrodes generates a high-gradient field over a large working volume by applying several hundred volts at a standard frequency of 60 Hz. The operating principle of filtration is based on our recently developed method of AC dielectrophoretic gating for microfluidics. The filtration efficiency is expressed in terms of two non-dimensional parameters which describe the combined influence of the particle polarizability and size, the oil viscosity and flow rate, and the field gradient on the particle captivity. The proof-of-concept is tested by measuring the single-pass performance of two filters on positively polarized particles dispersed in engine oil: spherical glass beads, fused aluminum oxide powder, and silicon metal powder, all smaller than the mesh opening. The results obtained provide critical design guidelines for the development of a filter based on the retention capability of challenge particles. [Preview Abstract] |
Sunday, November 20, 2011 9:57AM - 10:10AM |
A24.00010: Making micro soccer balls: Spherical macro-clusters of colloidal particles by droplet evaporation on superhydrophobic surfaces Alvaro Marin, Arturo Susarrey-Arce, Han Gardeniers, Detlef Lohse Imagine a clean capillary droplet evaporating in a fakir state on a superhydrophobic micro-structured surface. When the superhydrophobicity is robust enough, the droplet will always remain on top of the micro-structure and the droplet will retain its spherical shape until its ``death.'' Very often one can observe the remains of the impurities within the droplet left on top of the structure at the end of the process. In this work, instead of using clean liquid droplets, we use dilute colloidal dispersion droplets of monodisperse polymer micro-spheres (sizes from $0.2$ to 2$\mu m$). The colloidal dispersion droplet retains its spherical shape during its whole life, even when the whole solution has been evaporated. The remaining object consist on a spherical-shaped massive cluster of particles with diameters ranging from a few tens of microns up to several hundreds of microns, depending on the amount of micro-particles present in the solution and on the final packing fraction. We will discuss on the different observed packing fractions, particle arrangements and their governing parameters. Additionally some predictions will also be introduced. [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