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 E7: Suspensions I |
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Chair: Joe Goddard, University of California, San Diego Room: 24C |
Sunday, November 18, 2012 4:45PM - 4:58PM |
E7.00001: Microstructure and Rheology of Particle Suspension in a Yield Stress Fluid Stephanie Deboeuf, Lucie Duclou\'e, Nicolas Lenoir, Guillaume Ovarlez Numerous industrial and natural fluids, such as fresh concrete or debris flows, are made of particles suspended in a yield stress fluid. Such suspensions exhibit complex rheological behaviours: elasto-plasticity, strain hardening, shear-thinning (non constant viscosity), normal stress difference, ... In the light of results about shear-induced microstructure in concentrated suspensions of spheres in Newtonian fluids [Parsi {\&} Gadala-Maria 1987, Brady 1997, Morris 2009, Blanc et al 2011], we experimentally addressed the role of the particle microstructure in this complex rheology. Our model system is made of non-Brownian spherical hard particles suspended in a concentrated emulsion. We associate rheological measurements to microtomography X imaging techniques allowing for high resolution pair distribution functions in three dimensions. We characterize this microstructure for various shear histories (squeeze flow and rotational flow, transient and steady state, various low and high shear rates) and we relate it to their elastic and plastic properties. [Preview Abstract] |
Sunday, November 18, 2012 4:58PM - 5:11PM |
E7.00002: Effect of sheared-induced diffusion on the transfer of heat across a sheared suspension Bloen Metzger, Xiaolong Yin Suspensions of non-Brownian particles undergoing shear provide a quasi-unique system where mixing occurs spontaneously at low Reynolds number. In essence, particles behave in the fluid as so many ``stirrers.'' The questions raised are how do they affect the transport of heat/mass across sheared suspensions? What will be the influence of the particle size, their volume fraction and the applied shear? By using an index matched suspension and a laser induced fluorescence imaging technique, we were able to measure individual particle trajectories and correlate the particle diffusion motion to the thermal diffusion of the suspension. Particles cause a significant enhancement ($>$ 300\%) of the suspension transport properties. Simulations which combine a Lattice Boltzman technique to solve the flow and a passive Brownian tracer algorithm to solve for the transfer of heat are in very good agreement with experiments. [Preview Abstract] |
Sunday, November 18, 2012 5:11PM - 5:24PM |
E7.00003: Effects of inertia on the steady shear rheology of concentrated emulsions: sign reversal of normal stress differences Priyesh Srivastava, Kausik Sarkar The shear rheology of moderately concentrated emulsions (5-27{\%} volume fraction) in the presence of inertia is numerically investigated. Typically, an emulsion of viscous drops experiences positive first normal stress difference (N$_{1})$ and negative second normal stress difference (N$_{2})$, as has also been predicted by perturbative analysis (Choi-Schowalter model) and numerical simulation. However, recently using single drop results we have shown [Li and Sarkar, 2005, J. Rheo, 49, 1377] that introduction of inertia reverses the signs of the normal stress difference in the dilute limit. Here, we numerically investigate the effects of interactions between drops in a concentrated system. The simulation is validated against the dilute results as well as analytical relations. It also shows the reversal of signs for N$_{1}$ and N$_{2}$ for small Capillary numbers above a critical Reynolds number. The physics is explained by the inertia-induced orientation of the individual drops in shear. Increasing volume fraction increases the critical Reynolds number at which N$_{1}$ and N$_{2 }$change sign. The breakdown of linearity with volume fraction with increasing concentration is also analyzed. [Preview Abstract] |
Sunday, November 18, 2012 5:24PM - 5:37PM |
E7.00004: Buckling of particle-laden interfaces Theo Kassuga, Jonathan Rothstein Particle-laden interfaces have been shown to have very interesting physical behavior, such as being able to resist compressive and shear stresses, and helping stabilize emulsions and foams. In this work, we study the buckling of an oil-water interface populated by micron-sized latex particles using a Langmuir trough. We extend pre-existing results to the micron-sized range with different density ratio and show that the existing theoretical framework still applies as a prediction of the dominant wrinkle wavelength. However, histograms show that the wavelength distribution has two peaks, which indicates that there occurs a cascading phenomenon similar to that observed in thin solid sheets. We can characterize this by tracking the position within the particle raft where cascading occurs, the wavelength of the resulting wrinkles, and their width along the crest. [Preview Abstract] |
Sunday, November 18, 2012 5:37PM - 5:50PM |
E7.00005: Suspensions with a tunable effective viscosity Philippe Peyla, Salima Rafai, Levan Jibuti In this work, we conduct a numerical investigation on sheared suspensions of non-colloidal spherical particles on which a torque is applied. Particles are mono-dispersed and neutrally buoyant. Since the torque modifies particles rotation, we show that it can indeed strongly change the effective viscosity of semi-dilute or even more concentrated suspensions. We performed our calculations up to a volume fraction of 0.28. And we compare our results to data obtained at 0.40 by other authors with a totally different numerical method. Depending on the torque orientation, one can increase (decrease) the rotation of the particles. This results in a strong enhancement (reduction) of the effective shear-viscosity of the suspension. We construct a dimensionless number Q which represents the average relative angular velocity of the particles divided by the vorticity of the fluid generated by the shear flow. We show that the contribution of the particles to the effective viscosity can be suppressed for a given and unique value of Q independently of the volume fraction. In addition, we obtain a universal behavior (independent of the volume fraction) when we plot the relative effective viscosity divided by the relative effective viscosity without torque as a function of Q. Finally, we show that a modified Faxen law can be equivalently established for large concentration. [Preview Abstract] |
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