(354f) Collective Effects in the Sedimentation of Particles in Viscoelastic Fluids

Murch, W. L., Stanford University
Krishnan, S., Stanford University
Shaqfeh, E. S. G., Stanford University
Particle suspensions are widely used in engineering processes, and examples can be found in oil field applications, separations, and additive manufacturing. In many of these applications, it is important to predict and control the settling rates of solid particles. When the suspending fluid is viscoelastic, e.g. in many polymeric fluids, the motion of a particle and its resultant settling rate can be significantly different than in a Newtonian fluid. Multiple particle effects in viscoelastic fluids have been less explored, but are clearly important to the applications listed above.

This talk thus focuses on the collective settling behavior of a suspension of rigid, non-Brownian spheres in viscoelastic fluids under two flow conditions. First, we address the settling behavior of particles in a quiescent fluid, where the particles settle due to gravity in the absence of an external flow. As reviewed recently, hydrodynamic interactions between particles in viscoelastic fluids under quiescent conditions can result in concentration heterogeneities and associated large velocity fluctuations during sedimentation [1]. We present a study that attempts to quantify and explain these concentration and velocity fluctuations, using new experiments and large scale numerical simulations. For the numerical simulations, we utilize a recently developed Immersed Boundary (IB) method for 3D viscoelastic flows [2]. We show that the settling process in a quiescent viscoelastic fluid can be characteristically different than that observed in Newtonian fluids [3]. The second part of this talk focuses on the settling of particles in a viscoelastic fluid with a shear flow imposed in a plane perpendicular to gravity (referred to as orthogonal shear). We examine the effects of fluid elasticity, applied shear rate, and particle concentration, which can each have a significant influence on the average particle settling rate.

[1] Zenit, R. & Feng, J. J. Annu. Rev. Fluid Mech. 50 (2018): 505–534

[2] Krishnan. S., Shaqfeh, E. S. G., & Iaccarino, G. J. Comput. Phys. 338 (2017): 313–338

[3] Guazzelli, E. & Hinch, J. Annu. Rev. Fluid Mech. 43 (2011): 97-116