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 G7: Suspensions II |
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Chair: Salima Rafai, Grenoble University Room: 24C |
Monday, November 19, 2012 8:00AM - 8:13AM |
G7.00001: Cahn-Hilliard modeling of particles suspended in two-phase flows Patrick Anderson, Young Joon Choi We study the dynamics of particles suspended in two-phase flows by coupling the Cahn-Hilliard theory with the extended finite element method (XFEM). In the Cahn-Hilliard model the interface is considered to have a small but finite thickness, which circumvents explicit tracking of the interface. For the direct numerical simulation of particle-suspended flows, we incorporate an XFEM, in which the particle domain is decoupled from the fluid domain. To cope with the movement of the particles, a temporary ALE scheme is used for the mapping of field variables at the previous time levels onto the computational mesh at the current time level. The model is general, but to demonstrate and validate the technique, here the dynamics of a single particle at a fluid-fluid interface is studied. First, we apply a small disturbance on a particle resting at an interface between two fluids, and investigate the particle movement towards its equilibrium position. In particular, we are interested in the effect of interfacial thickness, surface tension, particle size and viscosity ratio of two fluids on the particle movement towards its equilibrium position. Finally, we show the movement of a particle passing through multiple layers of fluids. [Preview Abstract] |
Monday, November 19, 2012 8:13AM - 8:26AM |
G7.00002: Effect of the History Force on Particle Trajectories within an Oscillatory Rotating Flow Shujing Xu, Ali Nadim At a previous APS-DFD meeting it was reported, based on theoretical considerations, that particles denser than their suspending fluid can be made to migrate {\em toward} the rotation axis if the container undergoes oscillatory rigid-body rotation in an appropriate range of frequencies [Nadim et al., {\em Bull.\ Am.\ Phys.\ Soc.}, {\bf 53}, 191 (2008)]. This is contrary to ordinary centrifugation. However, the effect of the Basset history force was not accounted for in that analysis. It is shown here that while the history force significantly affects the dynamics of the particles, the oscillatory ``counter-centrifugation'' effect that was previously discovered continues to persist even when the history force is included in the analysis. Interestingly, inclusion of the history force can extend the parameter regime for which oscillatory counter-centrifugation might be observed. [Preview Abstract] |
Monday, November 19, 2012 8:26AM - 8:39AM |
G7.00003: Taylor-Aris dispersion in the presence of shear-enhanced diffusion and variable mean flow Gregory Rubinstein, Ivan Christov, Howard Stone Controlling the dispersion of colloidal suspensions is important in applications ranging from drug delivery to water purification. Previously, Griffiths and Stone [EPL (2012) 97, 58005] considered the influence of shear-induced diffusion on the Taylor-Aris dispersion of a colloidal suspension flowing in a cylindrical pipe. In this work, we extend their analysis to a radial outflow geometry, which features velocity variations along the flow direction. We found that the shear-induced diffusion due to the hydrodynamic interactions between the colloidal particles tends to decrease dispersion in the flow direction, as does the decrease in the velocity as the fluid flows radially outward. Using the method of multiple time scales, we derived an averaged dispersion equation that demonstrates the impact of these two effects. We also extended our methodology to coupled dispersion problems, in which the suspended particulate phase releases heat into the ambient fluid or the colloidal particles dissolve into the solvent medium. [Preview Abstract] |
Monday, November 19, 2012 8:39AM - 8:52AM |
G7.00004: Dispersion of suspension plugs in microchannels Martin Maxey, Glareh Azadi, Anubhav Tripathi, Kyongmin Yeo Plugs of beads can be used as a model for understanding the behavior of suspensions in microfluidic devices. Despite a large volume of literature in the field of microfluidic suspension flows; the fundamental understanding of the dispersion of hard and soft particle suspension plugs of finite length has not be studied in detail. Here we focus on the dispersion characteristics of non-Brownian, low Reynolds number bead suspensions in microfluidic channels. The effect of initial plug length, bead size and dilution on the early stages of dispersion of these beads in a pressure driven flow will be presented. Numerical simulations of suspension shear flow for test configurations relevant to plug dispersion have been performed in order to present a new level of continuum models for particle stresses and particle fluxes in confined shear flows. These results can contribute to the design of high throughput microfluidic systems for cell screening and bio-separation. [Preview Abstract] |
Monday, November 19, 2012 8:52AM - 9:05AM |
G7.00005: Hydrodynamics of confined suspensions Nicolas Desreumaux, Raphael Jeanneret, Jean-Baptiste Caussin, Eric Lauga, Denis Bartolo We investigate experimentally and theoretically the dynamics of suspensions flowing in quasi-bidimensional channels. Specifically, we focus on the role of the hydrodynamic interactions on the large-scale behavior of the suspensions. Our experiments demonstrate that density fluctuations propagate on large distances with a non-linear dispersion relation. We then model our system as a collection of interacting potential dipolar singularities. By focusing on the large-scale dynamics, we show that density waves do propagate and that the dispersion relation depends on the local curvature of the density field. This model yields good agreement with our experiments. [Preview Abstract] |
Monday, November 19, 2012 9:05AM - 9:18AM |
G7.00006: Hydrodynamic particle interactions in sheared microflows Alvaro Marin, Massimiliano Rossi, Mauricio Zurita-Gotor, Christian J. K\"ahler Multiphase flows in micro-confined geometries are non-trivial problems: drops and particles introduce a high degree of complexity into the otherwise linear Stokes flows. Very recently, new mechanisms of instability have been identified in simulations in shear-flows of non-Brownian particle solutions (Zurita-Gotor et al., J. Fluid Mech. 592, 2007, and Phys. Rev. Lett. 108, 2012), which might be the cause for anomalous self-diffusion measured experimentally by Zarraga and Leighton (Phys. Fluids 14, 2002). Using a 3D particle tracking technique (Astigmatism-PTV), we perform experiments in a microconfined cone-plate couette flow with a dilute suspension of non-brownian particles. The A-PTV technique permits us to track individual particles trajectories revealing particle-particle hydrodynamic interactions. Our experiments show an abnormal dispersion in the velocity field and non-homogeneous particle distribution which can be related with the swapping mechanism (JFM 592, 2007;PRL 108, 2012). [Preview Abstract] |
Monday, November 19, 2012 9:18AM - 9:31AM |
G7.00007: The Effect of Particle Deformation on the Collective Dynamics of Confined Rigid Spheres and Deformable Drops J. Blawzdziewicz, M. Loewenberg, P.J.A. Janssen, M.D. Baron, P.D. Anderson, E. Wajnryb The evolution of linear arrays of rigid spheres and deformable drops in a Poiseuille flow between parallel walls is investigated to determine the effect of particle deformation on the collective dynamics in confined particulate flows. We find that linear arrays of rigid spheres aligned in the flow direction undergo a particle-pairing instability and are unstable to lateral perturbations. Linear arrays of deformable drops, in addition to the pairing instability, exhibit other dynamical features, including formation of transient triplets, cascades of pair-switching events, and formation of pairs with equal interparticle spacing. Particle deformation also stabilizes drop arrays to lateral perturbations. These pairing and alignment phenomena are qualitatively explained in terms of hydrodynamic far-field dipole interactions (insensitive to particle deformation) and quadrupole interactions (deformation induced). We suggest that quadrupole interactions underlie the spontaneous formation of droplet strings in confined emulsions under shear [{\it Phys.\ Rev.\ Lett.}, 2001, {\bf 86}, 1023]. [Preview Abstract] |
Monday, November 19, 2012 9:31AM - 9:44AM |
G7.00008: Shape asymmetric particles self-assemble under flow in quasi-two-dimensional microchannels William Uspal, H. Burak Eral, Patrick Doyle Emerging applications in microfluidics increasingly require the imposition of spatial and temporal order on flowing suspensions of particles. In on-chip flow cytometry, for instance, cells must be individually distinguishable and addressable as they flow through a scanning region. Via combined theoretical and experimental approaches, we consider how particle shape can be tailored for flow induced assembly in a shallow, ``quasi-two-dimensional'' microchannel. Our main finding is that when fore-aft symmetry is broken, a single rigid particle will spontaneously align with the external flow field and migrate laterally to the channel centerline. Via a simple theoretical model, quantitatively borne out by experiments, we show how assembly arises from the interplay of lateral confinement by side walls and a particle's hydrodynamic self-interaction. This mechanism is unique to the quasi-two-dimensional channel geometry: strong confinement in one spatial direction and weak confinement in another. Moreover, assembly does not require time reversal symmetry breaking, as is commonly supposed. Building on this understanding of a single particle, we show that clusters of multiple asymmetric particles likewise assemble into spatially ordered, ``crystalline'' states. [Preview Abstract] |
Monday, November 19, 2012 9:44AM - 9:57AM |
G7.00009: Rheological measurements in liquid-solid mixtures Esperanza Linares-Guerrero, Melany Hunt In a previous investigation by Koos {\emph{et al.}} (2012), the torque measurements of mixtures of non-cohesive, neutrally buoyant, relatively large particles (order of mm diameter size) in aqueous glycerine at high shear rates were presented. These measurements showed a linear dependence on the range of shear rates tested ($\dot{\gamma} \approx 1-110 s^{-1}$) and a nonlinear dependence on the solid fraction. For this range of shear rates, previous studies have shown a transition from a linear to a nonlinear dependence on $\dot{\gamma}$. However, most of these studies considered smaller particle size (the order of $\mu$m) and therefore small Stokes number, or the measurement devices were dominated by secondary flows as shown by Hunt {\emph{et al.}} (2002). To analyze further this rheology, experiments for suspensions with particle densities higher than the liquid density were performed, which increased the Stokes number. To avoid slip at the walls, the rheometer walls were roughened. At higher Stokes number the particle collisions become important and change the rheology of the suspension. Preliminary results show an increased dependence on Stokes number compared with the earlier study. [Preview Abstract] |
Monday, November 19, 2012 9:57AM - 10:10AM |
G7.00010: Particle Migration and Interaction in Confined Flows Kaitlyn Tuley, Sungyon Lee, Marcus Roper Inertial microfluidic principles are widely applied in flow cytometry, microfluidic chips, and cell filtration. The hydrodynamic nonlinearity caused by inertia regulates the location of and separation between particles in these devices. Yet, there is no theory to explain these phenomena. We describe asymptotic and numerical models for the fundamental fluid mechanics of particle migration and interaction with applications to: (i) inertial focusing and (ii) the dynamic self-assembly of particles into uniformly spaced flowing lattices. [Preview Abstract] |
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