Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session A04: Suspensions: General I |
Hide Abstracts |
Chair: Parisa Mirbod, University of Illinois Chicago Room: 203 |
Saturday, November 23, 2019 3:00PM - 3:13PM |
A04.00001: Segregation modeling of binary suspensions Stany Gallier, Mathieu Plaud This study proposes a continuum model able to describe particle segregation in bidisperse non-colloidal suspensions. It is based on the Morris-Boulay suspension balance model [Morris and Boulay, J. Rheol., 1999] which has been here extended to two classes of particles with different sizes. Doing so gives rise to new quantities (basically, normal or shear viscosity by particle class) that are not available experimentally. Indeed, only the overall suspension normal and shear viscosity are reported and it is not known how they split with respect to particle size class. We therefore consider particle-resolved Stokes simulations of binary suspensions to address this point. Parametric simulations are conducted for different size ratio, total volume fraction and large/small fraction ratio. We show that both shear and normal viscosities are approximately proportional to volume fraction ratio. This allows to provide a simple closure for the model. It is then incorporated in a flow solver and successfully compared to available experiments of segregation in channel flows. [Preview Abstract] |
Saturday, November 23, 2019 3:13PM - 3:26PM |
A04.00002: Simulating cross stream migration of hard spheres in a dilute suspension Nilanka I. K. Ekanayake, Joseph D. Berry, Anthony D. Stickland, David E. Dunstan, Steven K. Dower, Ineke L. Muir, Dalton J. E. Harvie In flowing suspensions, hydrodynamic forces can move particles across the streamlines and cluster at certain radial positions within a pipe. In the biological flow context, this cross-stream migration is widely used in cell sorting microfluidic applications to separate diseased cells based on size and other physical characteristics. This study employs a multi-fluid model to predict the solid concentration profiles of a mono-disperse suspension of hard spheres flowing at low particle Reynolds numbers. The lateral migration is modelled using wall-shear and shear rate gradient hydrodynamic lift forces and inter-particle hydrodynamic collision forces. Brownian and shear induced diffusion forces are modelled as functions of solid concentration gradients and shear rate gradients. The effect of bulk concentration on solid distribution is examined and compared against experimental data. At highly dilute conditions particles accumulate at 0.6 radius away from the centerline exhibiting the ``tubular pinch" effect caused by lift forces. With increasing bulk concentration, particles gradually move towards the centerline due to diffusion forces. This study demonstrates that the bulk concentration has a significant impact in determining solid distribution profiles. [Preview Abstract] |
Saturday, November 23, 2019 3:26PM - 3:39PM |
A04.00003: Lubrication Corrections for Brownian Suspensions Above a Wall brennan sprinkle, Aleksandar Donev, Yixiang Luo Lubrication effects play an important role in the dynamics of dense suspensions of passive or active microscale particles. In order to quantitatively measure bulk properties in these types of suspensions, the near--field lubrication flows must be accurately resolved. We present an efficient numerical method to simulate dense Brownian suspensions of many particles above a bottom wall. Our method includes lubrication effects while maintaining a computational complexity which scales linearly in the number of particles. Examples to demonstrate the effectiveness of our method include: the sedimentation of particles over an inclined plane, as well as collective motion in a suspension of magnetic `rollers'. [Preview Abstract] |
Saturday, November 23, 2019 3:39PM - 3:52PM |
A04.00004: Modeling and Stokesian-Dynamics Simulations of Friction in Colloidal Suspensions Gerald Wang, James Swan As the gap between particles in a suspension approaches zero, inter-particle frictional forces can become non-negligible. These forces may strongly influence structure and transport in systems with a significant number of particle-particle contacts, such as sticky colloid suspensions. Understanding the influence of microscopic frictional contacts on macroscopic suspension properties is vital for modeling many rheological phenomena, including discontinuous shear thickening. In this talk, we present computational and theoretical work exploring the role of friction in colloidal suspensions, in which friction is treated as a hydrodynamic resistance to sliding between particles near contact. Our Stokesian-Dynamics simulations demonstrate that the frictional suppression of both the translational and rotational diffusivities can be related to the friction coefficient using a simple power-law scaling. To explain this result, we develop a spectral model that quantifies the impact of friction on the hydrodynamic resistance tensor. We then show that a mathematical model of the suspension as a graph, which tracks connections between neighboring particles, can be used to explain the observed dynamics. We also discuss connections between our work and several recent experimental results. [Preview Abstract] |
Saturday, November 23, 2019 3:52PM - 4:05PM |
A04.00005: Particle migration of colloidal and Brownian suspensions in both Poiseuille and circular Couette flow Changwoo Kang, Parisa Mirbod The flow of neutrally buoyant and hard-sphere colloidal particles concentrated in a Newtonian viscous fluid is examined by direct numerical simulations (DNS) at various bulk particle volume fraction (0.1$\le \phi _{b}\le $0.5) and Peclet number (10$^{\mathrm{-2}}\le $\textit{Pe}$\le $10$^{\mathrm{3}})$. We use the diffusive flux model (DFM) to describe the behavior of suspensions and employ the viscosity introduced by de Kruif et al. [J. Chem. Phys. 1985] which is given as a function of shear rate and volume fraction. First, we consider pressure-driven flow of colloidal particles in a channel. For low \textit{Pe} number the concentration profile flattens, as \textit{Pe} grows the influence of Brownian motion diminishes and the distribution of concentration reaches the profile of non-colloidal suspensions flow. Also, as Brownian motion becomes dominant, the volume flow rate decreases steadily. We then study a circular Couette flow of colloidal suspensions where the inner cylinder rotates with a constant angular velocity and the outer one is fixed. The concentration profile flattens out and the local shear rate decays with the reduction of \textit{Pe} number. The torque acting on the inner cylinder builds up due to colloidal suspensions. [Preview Abstract] |
Saturday, November 23, 2019 4:05PM - 4:18PM |
A04.00006: Graphene nanoplatelets attain a stable orientation in a shear flow: an investigation on the role of Brownian fluctuations Catherine Kamal, Simon Gravelle, Lorenzo Botto We study theoretically the rotational dynamics of a rigid graphene nanoplatelet suspended in a simple shear flow. We have recently shown that in the infinite Peclet number limit a rigid platelet presenting the interfacial hydrodynamic slip properties of graphene does not follow the periodic rotations predicted by Jeffery’s theory, but rather aligns itself at a small inclination angle $\alpha_c$ with respect to the flow. This unexpected result is due to the low tangential friction at the graphene-solvent surface (the slip lengths for many 2D materials/solvent combinations can amount to several tens of nanometers). By analyzing the Fokker-Plank equation for the orientational distribution function for decreasing Peclet numbers, we show that the platelet fluctuates about $\alpha_c$ until a slip length dependent critical Peclet number is reached. Below this value, Brownian forces are large enough to produce full rotations, bringing the particle outside of a “hydrodynamic potential well”. In the stable region, the effective viscosity of a dilute suspension of graphene platelets is predicted to drop by at least a factor of 2 for typical slip length values. [Preview Abstract] |
Saturday, November 23, 2019 4:18PM - 4:31PM |
A04.00007: Shear-induced exfoliation of graphite nanoplatelets into graphene: insights from non-equilibrium molecular dynamics Simon Gravelle, Catherine Kamal, Lorenzo Botto Graphite nanoplatelets suspended in a shear flow can be exfoliated into single-layer or few-layers graphene. Such liquid-phase exfoliation method is a promising technique for the production of graphene on large scales, but the micro and nanoscale fluid-structure processes controlling exfoliation are not understood. Here we use molecular dynamics simulations of a defect-free graphite nanoplatelet suspended in a shear flow to characterise the exfoliation dynamics and measure the critical shear rate above which exfoliation occurs, comparing the effect of using different solvents (water and NMP). The measured critical shear rates are compared with a simple theoretical model due to Chen et al. (Chem. Commun., 48. (2012) 3703-3705) based on a balance between the work done by viscous shearing forces and the change in interfacial energies upon layer sliding. We found it difficult to reconcile the molecular dynamics results with the model. The results obtained so far highlight the importance of hydrodynamic slip at the liquid-graphene interface, and the effect of graphene edges on hydrodynamics and interfacial mechanics. Both effects are incompletely included in the model. [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. |
© 2020 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
1 Research Road, Ridge, NY 11961-2701
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700