Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session A2: Suspensions: Rheology I |
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Chair: Elisabeth Guazzelli, Aix-Marseille University Room: 101 |
Sunday, November 22, 2015 8:00AM - 8:13AM |
A2.00001: Rheology of dense suspensions of non colloidal spheres in yield-stress fluids Elisabeth Guazzelli, Simon Dagois-Bohy, Sarah Hormozi, Olivier Pouliquen Pressure-imposed rheometry is used to study the rheological properties of suspensions of non colloidal spheres in yield stress fluids. Accurate measurements for both the shear stress and particle normal stress are obtained in the dense regime. The rheological measurements are favourably compared to a model based on scaling arguments and homogenisation methods. The detailed account of this study can be found in Dagois-Bohy, S., Hormozi, S., Guazzelli, E., and Pouliquen, O. (2015). Rheology of dense suspensions of non-colloidal spheres in yield-stress fluids. Journal of Fluid Mechanics, 776, R2. [Preview Abstract] |
Sunday, November 22, 2015 8:13AM - 8:26AM |
A2.00002: Shear thickening regimes of non-Brownian suspensions Christopher Ness, Jin Sun We propose a unifying regime map for shear flows of dense suspensions of non-Brownian spheres that captures the onsets of particle friction and particle inertia as distinct shear thickening mechanisms, while predicting quasistatic and soft particle rheology at high volume fractions and shear rates respectively. Discrete element method simulations reveal both mechanisms of shear thickening, and we show that they can be made to occur concurrently by careful manipulation of simulation parameters. Microstructural transitions associated with frictional shear thickening are presented, and we find very distinctive divergences of both the static and dynamic microstructure with respect to volume fraction in the thickened and non-thickened states. [Preview Abstract] |
Sunday, November 22, 2015 8:26AM - 8:39AM |
A2.00003: Hydrodynamic diffusion in non-colloidal suspensions: the role of interparticle forces Nicholas Hoh, Roseanna Zia Hydrodynamic diffusion in the absence of Brownian motion is studied via active microrheology in the pure hydrodynamic limit, to elucidate the transition from colloidal microrheology to the non-colloidal limit, falling-ball rheometry (FBR). Non-Brownian force-induced diffusion in FBR is strictly hydrodynamic in nature; in contrast, force-induced diffusion in colloids is deeply connected to a diffusive boundary layer even when Brownian motion is weak. To connect these two limits, we derive an expression for the hydrodynamic force-induced diffusion via the Smoluchowski equation, where thermal fluctuations play no role. The diffusion is anisotropic, along and transverse to the line of external force. The latter is zero owing to the fore-aft symmetry of Stokes flow. We find that interparticle forces play a crucial role in the hydrodynamic limit; accounting for this force results in longitudinal force-induced diffusion $D_{\parallel}=1.26aU_s\phi$, where $a$ is probe size, $U_s$ the Stokes velocity, and $\phi$ the volume fraction, in excellent agreement with experiments and theory for macroscopic FBR. This model connects micro- and macro-scale rheology, and provides insight into the role of interparticle forces for diffusion and rheology even in the limit of pure hydrodynamics. [Preview Abstract] |
Sunday, November 22, 2015 8:39AM - 8:52AM |
A2.00004: A new state transition in the rheology of dense suspensions Rijan Maharjan, Eric Brown Dense suspensions of hard particles are known to have an effective viscosity that diverges as the packing fraction approaches the liquid-solid transition, $\phi_j$. This is typically measured based on energy dissipation in a steady state shear flow. In a Newtonian fluid, the same viscosity value also determines how long it takes for a flow to relax to steady state after a change in control. By performing transient flow measurements in a rheometer, we find the transient viscosity of suspensions start to deviate from the steady state viscosity as the packing fraction increases above $\phi_c<\phi_j$. Further, we find the ratio of the normal stress to shear stress reaches a plateau $\sim$ 1 for $\phi>\phi_c$. This identifies a new state transition. [Preview Abstract] |
Sunday, November 22, 2015 8:52AM - 9:05AM |
A2.00005: Rheology and particle dynamics near the flow-arrest transition: a constant stress and pressure approach Mu Wang, John Brady We use Brownian dynamics to investigate the relation between the rheology and the microscopic particle dynamics in dense colloidal dispersions at constant stress and pressure. For each imposed stress/pressure pair, the suspension exhibits distinct strain rate distributions depending on the observation time. We measure the long-time self-diffusivity (LTSD) corresponding to the strain rate (inverse shear viscosity) and find that the LTSD results at different imposed stresses collapse to master curves that depends only on the imposed pressure. For low-pressure suspensions, the stress-scaled LTSD diverges at a finite scaled strain rate due to its liquid-like behavior, while at high pressures the scaled LTSD emerges from zero due to the flow-arrest transition. On the other hand, we discover that the particle friction coefficient---the ratio of the particle shear stress to the particle (osmotic) pressure---is proportional to the strain rate scaled by the LTSD for \emph{all} flowing suspensions. Our results demonstrate the effectiveness of the constant stress and pressure approach for dense suspension rheology, and show that, although the flow of amorphous materials is inherently far-from-equilibrium without a linear response regime, a mean-field description should remain valid. [Preview Abstract] |
Sunday, November 22, 2015 9:05AM - 9:18AM |
A2.00006: Concentration and velocity measurements in non-Brownian suspensions using ultrasonic imaging Brice Saint-Michel, Hugues Bodiguel, Steven Meeker, Sébastien Manneville We investigate the sedimentation and the re-suspension of dense, non-Brownian particles using ultrasonic imaging in a Couette cell, coupled to rheological measurements. Our setup records the characteristic speckle signal – originating from the multitude of particles (PS, PMMA, glass) in the Couette cell scattering an initial ultrasound pulse – on a transducer array. This “speckle map” can be used to estimate the velocity field and the particle concentration in our cell. We will discuss the advantages and limitations of our device using canonical examples when the suspending fluid is Newtonian: viscous re-suspension, sedimentation, particle migration by centrifugal forces and in Taylor vortices. Finally, some results involving non-Newtonian suspending fluids will be presented. [Preview Abstract] |
Sunday, November 22, 2015 9:18AM - 9:31AM |
A2.00007: Rheological measurements of liquid-solid flows with inertia Esperanza Linares, Melany Hunt, Roberto Zenit This talk presents experimental measurements of effective viscosity for neutrally-buoyant suspensions in which the Reynolds numbers based on particle diameter varies from 1 to 1000 and for solid fractions from 10{\%} to 50{\%}. The measurements are conducted in a rough-walled, coaxial-cylinder rheometer. For Reynolds numbers from 1 to 100 and solid fractions less than 30{\%}, the effective viscosities increase with Reynolds number and are comparable with recent numerical simulations found in the literature. For higher solid fractions, the effective viscosity shows shear thinning at the lowest shear rates, followed by thickening at higher shear rates. Over this range of Reynolds numbers for a pure fluid, the flow is laminar. At higher Reynolds numbers for a pure fluid, the flow transitions to turbulence. When particles are added under these flow conditions (particle Reynolds number greater than 100), the effective viscosity continues to increase with Reynolds number but with a greater magnitude. At the highest solid fractions, the effective viscosity is independent of shear rate. [Preview Abstract] |
Sunday, November 22, 2015 9:31AM - 9:44AM |
A2.00008: Characterizing dense suspensions: two case studies from the pharmaceutical industry David J. Goldfarb, Nazia Khawaja, Irina Kazakevich, Himanshu Bhattacharjee, Michael Heslinga, Chad Dalton Liquid suspensions of Active Pharmaceutical Ingredient powders are present as pharmaceutical dosage forms in the form of oral suspensions and injectables. We present two case studies, both dense ($\sim$ 30-40{\%}) suspensions, in which the physical characterization of the product, specifically, particle size {\&} shape and rheology were key to understanding the key product attributes as pertaining to the manufacturing process and to patient administration. For the one case study, an oral suspension, identifying variations in particle morphology during the wet milling of the product was key to the product understanding necessary to modify the milling process. Rheological measurements were applied as well. For the second case study, an injectable, results from different particle size measurement techniques and rheological measurements indicated the possibility of flocculation in a formulation. Additionally, measurements were obtained to assess the ``injectability'' of the product via rheometer and texture analyzer measurements and Poiseuille flow modeling. As a result, the relevant shear rate regime for this drug product administration was identified. [Preview Abstract] |
Sunday, November 22, 2015 9:44AM - 9:57AM |
A2.00009: Wall slip in suspensions of thermo-responsive particles Thibaut Divoux, V\'eronique Lapeyre, Val\'erie Ravaine, S\'ebastien Manneville Flows of suspensions are affected by wall slip, i.e. the fluid velocity $v_{f}$ in the vicinity of a boundary differs from the velocity $v_{w}$ of the latter due to the presence of a lubrication layer. Wall slip is quantified by the slip velocity $v_s$, which is defined as $v_s=\mid v_{f}-v_{w}\mid $ and displays a power-law scaling with the stress $\sigma$ at the wall. If the slip velocity of dilute suspensions robustly follows $v_s \propto \sigma^p$ with $p\simeq 1$, there is no consensus regarding denser suspensions that are sheared in bulk, for which $v_s$ is reported to scale as a power-law of the stress with exponents inconsistently ranging between $p \simeq 0$ and 2. By means of extensive rheometry coupled to velocimetry on a suspension of thermo-responsive particles, we show that such discrepancy is only apparent, and demonstrate that $v_s$ scales as a power law of the viscous stress $\sigma-\sigma_c$, where $\sigma_c$ denotes the yield stress. Tunning the temperature reveals that such scaling holds true over a large range of packing fractions $\phi$ on both sides of the jamming point, and that the exponent $p$ increases continuously with $\phi$, from $p=1$ (dilute suspensions) to $p=2$ (dense assemblies). Our results pave the way for a unified description of wall slip. [Preview Abstract] |
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