Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session AV: Particle Laden Flows I |
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Chair: Troy Shinbrot, Rutgers University Room: Hyatt Regency Long Beach Regency B |
Sunday, November 21, 2010 8:00AM - 8:13AM |
AV.00001: A model for particle accumulation of density-matched tracers in thermocapillary flows Ernst Hofmann, Hendrik C. Kuhlmann We numerically investigate the motion of small density-matched particles in thermocapillary driven flow in a cylindrical liquid bridge under zero gravity. A model is proposed that explains the recently reported complete demixing into a \emph{Particle Accumulation Structure} (PAS) without consideration of inertial effects. We explain the paradox that optimum demixing efficiency is obtained for density-matched particles, in agreement with experiments. The PAS phenomenon depends on the flow topology in the vicinity of a certain closed streamline of the three-dimensional flow. The accumulation can be explained by a repeated particle--free-surface collision process which transfers particles among different streamlines until a stable limit cycle is reached. The given model illustrates how a closed streamline can mimic an attractor in an incompressible flow. [Preview Abstract] |
Sunday, November 21, 2010 8:13AM - 8:26AM |
AV.00002: Migration and fractionation of dense soft spheres in flow Yeng-Long Chen, Chia-Wei Hsu We investigate suspensions of elastic particles in flow. Hybrid lattice Boltzmann-Brownian Dynamics (LB-BD) approach is used to capture coupling between particle deformation and changes to the fluid field. One particle and two-particle hydrodynamic interactions are characterized and compared with experimental measurements and theoretical calculations. We further investigate the influences of particle elasticity, concentration, and shape on the average flow velocity in dense suspensions of up to 30\% particle volume fraction. It is found that the average flow velocity increases as the particle become more elastic due to wall-induced hydrodynamic migration. For binary mixtures, a novel mechanism to optimize particle fractionation based on particle elasticity is found. [Preview Abstract] |
Sunday, November 21, 2010 8:26AM - 8:39AM |
AV.00003: Sedimentation dynamics in the presence of polymer Shmuel M. Rubinstein, Mahesh M. Bandi, Tom Kodger, David A. Weitz We study the sedimentation of colloidal particles in polymer supplemented solution. The polymers enrich the dynamics of sedimentation by adding both particle attraction (caused by depletion interactions) and an elastic component to the flow. The sedimentation dynamics are governed by the formation, sedimentation and consequent breakup of poroelastic clusters of many particles. By making use of a custom built laser sheet microscope we are able to track Brownian one-micron particles at single particle resolution within a large ($\sim $cm sized) cell. This way we can resolve between bulk and boundary effects. [Preview Abstract] |
Sunday, November 21, 2010 8:39AM - 8:52AM |
AV.00004: Shear-enhanced diffusion in colloidal suspensions Ian Griffiths, Howard Stone The familiar example of Taylor dispersion of molecular solutes is extended to describe the dispersion in a colloidal suspension. In almost all standard Taylor-dispersion analysis, thermal fluctuations (Brownian motion) are assumed to be the underlying stochastic element driving solutes across streamlines. Here we consider conditions relevant to colloid suspensions, where shear-enhanced diffusion, which is a consequence of hydrodynamic interactions between particles, and is dependent on the concentration of particles, is responsible for the fluctuations transverse to the flow direction. The generic scheme is illustrated by the example of axisymmetric Poiseuille pipe flow, with a simple functional form for the diffusivity that captures both the shear-induced and Brownian contributions. This description naturally leads to a nonlinear convection-diffusion equation, which we solve analytically for a simplified model valid for low particle concentrations, and numerically for a model of higher concentrations, and the results are contrasted with regular Taylor dispersion. The approach presented here may be useful for a range of problems involving transport properties of colloidal suspensions, such as sedimentation and membrane filtration. [Preview Abstract] |
Sunday, November 21, 2010 8:52AM - 9:05AM |
AV.00005: Pattern formation and strongly nonlinear coating in Landau-Levich flow of suspensions Justin Kao, Anette Hosoi We investigate Landau-Levich coating of a solid wall by a suspension. When the suspended particle size exceeds the liquid film thickness, capillary forces lead to an effective attraction between particles, as well as pinning of individual particles against the wall. Experiments show small-scale clustering of particles, a strongly nonlinear relationship between the particle coating density and the wall speed, and under certain conditions, heterogeneous coating with long-range correlations in the particle density. We present a continuum model for particle density based on a Cahn-Hilliard formalism. [Preview Abstract] |
Sunday, November 21, 2010 9:05AM - 9:18AM |
AV.00006: Particle-laden thin film flows on an incline: experiments and equilibrium theory Jacob Bouricius, Trystan Koch, Paul Latterman, Brian Le, Samantha Mesuro, Nebojsa Murisic, Andrea Bertozzi We focus on particle-laden thin film flows on an incline. Experiments are carried out where inclination angle, bulk particle volume fraction, liquid viscosity, and particle size are varied. We classify experimental runs based on observed settling regime: settled, where particle settle out of the flow and fingering instability develops at the front (low angles and concentrations); ridged (high angles and concentrations); and well-mixed (intermediate values). We also uncover the transient nature of the well-mixed regime. In addition, in our experiments, the suspension and particulate front motion is tracked using a camera/laser set-up. Using image processing, we are able to extract the instantaneous thin film profiles and record the front motion for all observed flow regimes. The theoretical model we consider is based on equilibrium theory and it balances hindered settling of particles due to gravity against shear-induced migration. Finally, the predictions of this model are shown to be in excellent agreement with our experimental data for settling. [Preview Abstract] |
Sunday, November 21, 2010 9:18AM - 9:31AM |
AV.00007: A dynamic model for particle-laden thin film flows on an incline Nebojsa Murisic, Andrea Bertozzi Particle-laden flows are important in a variety of contexts, where transport and manipulation of suspensions occur. We consider gravity driven flows of particle-laden thin films on an incline. In the experiments, three distinct regimes are observed: particles either settle out of the flow (low bulk particle volume fraction and inclination angle), aggregate at the moving front (high bulk particle volume fraction and inclination angle), or remain well-mixed (intermediate values). Our dynamic model relies on the suspension and particle fluxes resulting from previously derived equilibrium model, where shear-induced migration balanced hindered settling due to gravity. The dynamics is modeled using a system of two scalar hyperbolic conservation laws, describing suspension and particulate front motion. We proceed by discussing a few aspects of the rich mathematical structure of these laws and their physical interpretation. Finally, the governing system is solved numerically, and simulation results are shown to agree well with the experimental data regarding front propagation and settling mode. [Preview Abstract] |
Sunday, November 21, 2010 9:31AM - 9:44AM |
AV.00008: Cross-stream migration of compliant particles in microfluidic channels Alex Kilimnik, Soojung Claire Nur, Dino Di Carlo, Alexander Alexeev Using a 3D hybrid lattice Boltzmann and lattice spring computational method, the motion of rigid and soft particles in a pressure-driven microfluidic flow was examined. The particles were modeled as neutrally buoyant fluid-filled elastic shells. The equilibrium positions of these particles were obtained in a low-Reynolds-number flow while accounting for non-linear inertial effects. Microchannels of different width were examined and it was found that the equilibrium position of the rigid particles moves away from the channel walls as the ratio between particle diameter and channel width increases. Furthermore, it was found that capsule deformability enhances the particle migration toward the channel centerline. The simulation results were compared with experimental data obtained with varying size and viscosity oil droplets suspended in water indicating favorable agreement. These findings could aid in the design of devices to sort particles based on their mechanical stiffness. [Preview Abstract] |
Sunday, November 21, 2010 9:44AM - 9:57AM |
AV.00009: Rotation and Alignment of Rods in Two-Dimensional Chaotic Flow Jerry Gollub, Jeffrey Guasto, Monica Kishore, Shima Parsa Moghaddam, Greg Voth, Nicholas Ouellette We study the dynamics of rod shaped particles in two-dimensional electromagnetically driven fluid flows. Two separate flows are compared: one with time-periodic flow and the other with non-periodic flow. Video particle tracking is used to make accurate measurements of the motion and orientation of rods along with the carrier fluid velocity field. Measured rod rotation rates are in agreement with predictions for ellipsoidal particles based on the measured velocity gradients at the center of the rods. There is little dependence on length for the rods we studied (up to 53\% of the length scale of the forcing). Rods are found to align weakly with the direction of extensional strain. However, the alignment is much stronger with the direction of Lagrangian stretching defined by the eigenvectors of the Cauchy-Green strain tensor. A simple model of the stretching process predicts the degree of alignment of rods with the stretching direction. [Preview Abstract] |
Sunday, November 21, 2010 9:57AM - 10:10AM |
AV.00010: Measuring the rotation rate of rod-shaped particles in 3D turbulence Shima Parsa, Nicholas T. Ouellette, Greg A. Voth We study the rotation of rod-shaped particles in turbulent flow using stereoscopic particle tracking with high speed video. With images from multiple cameras we are able to extract the position and orientation of rods as a function of time in a flow between oscillating grids. We work in the low density limit where rod-rod interactions can be ignored. Rod rotation is determined by the local velocity gradient so measurement of the rotation rate variance provides an indirect way to access the second moment of velocity gradient of the flow. Development of methods for tracking rods in turbulence shows great promise both for understanding many flows containing inertial rods and as a means of extracting small scale properties of the flow along Lagrangian trajectories [Preview Abstract] |
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