Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session E2: Suspensions: Confined Flows |
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Chair: Roseanna Zia, Cornell University Room: 3002 |
Sunday, November 23, 2014 4:45PM - 4:58PM |
E2.00001: Diffusion and rheology in a suspension of hydrodynamically interacting colloids enclosed by a spherical cavity Christian Aponte-Rivera, Roseanna Zia We study diffusion and rheology of a suspension of hydrodynamically interacting colloidal spheres enclosed by a spherical cavity, utilizing the Stokesian Dynamics framework to account for long-range many-body and pairwise lubrication interactions between the particles and between particle and enclosure. Previous studies of 1D- and 2D-confined suspensions have revealed that boundaries exert a pronounced qualitative influence on microstructure, dynamics, and rheology. While studies of the motion of a point particle in a cavity have been reported, the neglect of finite size sacrifices significant qualitative information, resulting in an incorrect coupling between torque and velocity, among others. We have derived new hydrodynamic mobility functions for finite-size particles confined by a spherical boundary that faithfully capture the physics of the boundary and its influence on particle dynamics. We obtain the full grand-mobility matrix and, from these, the position-dependent short-time self-diffusivity for an isolated particle and the dynamics of a hydrodynamically interacting pair suspended in the cavity. Both of these are studied over a range of particle-to-cavity size ratios. [Preview Abstract] |
Sunday, November 23, 2014 4:58PM - 5:11PM |
E2.00002: Effective viscosity of 2D suspensions - Confinement effects Philippe Peyla, Stephane Priem, Doyeux Vincent, Alexander Farutin, Mourad Ismail We study the rheology of a sheared 2D suspension of non-Brownian disks in presence of walls. Although, it is of course possible today with modern computers and powerful algorithms to perform direct numerical simulations that fully account for multiparticle 3D interactions, the analysis of the simple case of a 2D suspension, provides valuable insights and helps to understand 3D results. For instance, we examine the role of particle-wall and particle-particle interactions in determining the rheology of confined sheared suspensions. In addition we evaluate the intrinsic viscosity as well as the contribution of hydrodynamic interactions to the dissipation as a function of a wide range of confinements. Thanks to the direct visualisation of the whole 2D Stokes flow, we are able to give a clear interpretation about the rheology of semi-dilute confined suspensions. [Preview Abstract] |
Sunday, November 23, 2014 5:11PM - 5:24PM |
E2.00003: Immersed collision of a sphere with a textured wall: from sticking to bouncing dynamics Thibault Chastel, Anne Mongruel We investigate experimentally the dynamics of a sphere immersed in a viscous fluid and impacting a wall decorated with square micro-pillars. High frequency laser interferometry is used for measuring small displacements of the sphere with spatial resolution of 200 nm. For creeping flow, the classical lubrication force on the sphere is regularized by an effective slip length that can be correlated to the texture geometry. For Reynolds number of the order of 1 to 10, the sphere can either stick to or bounce off the wall. We show how the micro-textures affect the critical Stokes number for bouncing transition. A simple model using the slip length is presented to describe the near-wall dynamics of the sphere. [Preview Abstract] |
Sunday, November 23, 2014 5:24PM - 5:37PM |
E2.00004: Growth of clogs in microchannels Emilie Dressaire, Alban Sauret, Emmanuel Villermaux, Howard A. Stone Porous membranes are used to detect and remove contaminants suspended in a fluid phase, e.g. to filter water. A typical filtration membrane allows the fluid to pass through but traps contaminants. Once a clog is formed in a pore, incoming particles aggregate upstream. This aggregate grows over time, which leads to a dramatic reduction of the flow rate. We consider a model that predicts the growth of the colloidal aggregate formed upon clogging of a microchannel. We present an analytical description to capture the time-evolution of the volume of the aggregate. We then focus on multiple parallel channels to model membrane filtration. In this situation, the growth dynamics of the aggregates are intrinsically coupled. The results of this modeling are compared with experimental data. Our work illustrates the critical influence of clogging events on the flow rate of porous membranes used in practical applications. [Preview Abstract] |
Sunday, November 23, 2014 5:37PM - 5:50PM |
E2.00005: Simulation study of suspension plugs in unsteady microchannel flows Amanda Howard, Martin Maxey, Francis Cui, Anubhav Tripathi The analysis or processing of particles in suspension may often involve a sample of finite length that is moving in a microchannel flow. Using numerical simulations, we examine the development of such a suspension plug of non-Brownian particles in unsteady, low Reynolds number shear flows in a microchannel. We focus on the early development in an oscillating Poiseuille flow, the distortion of the plug and the degree to which the motion is reversible relating this to prior work on oscillating suspension flows. For an initial particle volume fraction of 30{\%} in the plug, the forward and then reversed flow leads to minimal net forward motion of the plug front at the centerline even after several oscillations. However a forward migration is seen near the walls. This net flux of particles is balanced by a flux of particles towards the wall within the plug. The exact response depends on the strain amplitude of the oscillation, the particle volume faction and other parameters of the flow. We are also able to examine the shear-driven particle fluxes at the tail of the plug. Both regions illustrate the effect of strong inhomogeneities in particle concentration on transport. We will relate the results to our recent experimental observations. [Preview Abstract] |
Sunday, November 23, 2014 5:50PM - 6:03PM |
E2.00006: Transport of a viscoelastic particle suspension in tortuous geometries Alexander Barbati, Gareth McKinley Particle transport in viscoelastic fluids is of paramount importance in a variety of physical and industrial processes. We consider the transport of rigid particles through varied and microscale tortuous sections to model larger-scale particle transport, as commonly occurs in many reservoir stimulation processes. Beginning with the development of dynamic and geometric similarity parameters, we construct a rigid microfluidic device to probe the effects of fluid elasticity, fluid inertia, particle size, and particle volume fraction on particle transport. We characterize the microchannel flows with a combination of particle image velocimetry of embedded tracer particles and direct observation of particle accumulation and occlusion within the device. These on-chip experiments are accompanied by off-chip measurements of fluid rheology, and numerical computations of the flow field. [Preview Abstract] |
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