Sedimentation of Two Side-by-Side Heavy Particles of Different Density in a Shear-Thinning Fluid with Viscoelastic Properties

Abstract

Particle sedimentation has widely existed in nature and engineering fields, and most carrier fluids are non-Newtonian. Recently, the manipulation of a settling particle in liquid has been a topic of high interest to those involved in engineered processes such as composite materials, pharmaceutical manufacture, chemistry and the petroleum industry. Compared with Newtonian fluid, the viscosity of non-Newtonian fluid is closely related to the shear rate, leading to a single settling particle having different dynamic behaviors. In this article, the trajectories and velocities of two side-by-side particles of different densities (heavy and light) settling in a shear-thinning fluid with viscoelastic property were studied, as well as that for the corresponding single settling particle. Regardless of the difference in the particle density, the results show the two-way coupling interaction between the two side-by-side settling particles. As opposed to a single settling particle, the wake of the heavier particle can clearly attract or rebound the light particle due to the shear-thinning or viscoelastic property of the fluid. Regarding the trajectories of the light particle, three basic path types were found: (i) the light particle is first attracted and then repelled by the wake of the heavy one; (ii) the light particle approaches and then largely traces within the path of the heavy one in the limited field of view; (iii) the light particle is first slightly shifted away from its original position and then returns to this initial position. In addition to this, due to the existence of a corridor of reduced viscosity and negative wake generated by the viscoelastic property, the settling velocity of a light particle can exceed the terminal velocity of a single particle of the same density. On the other hand, the sedimentation of the light particle can induce the distinguishable transverse migration of the heavy one.

Settling velocity variation induced by a sphere moving across a two-layer stratified fluid with different rheological characteristics

“…The shear thinning and viscoelastic properties of the PAAm solution are specically described in our recent paper. 23 The density of the PAAm solution is 1005 kg m −3 , which is very close to that of water. The shear thinning and viscoelastic properties of 0.5% PAAM solution are shown in Fig.…”

“…The shear thinning and viscoelastic properties of the PAAm solution are specifically described in our recent paper. 23 …”

“…For the 0.5 wt% PAAm solution, n is 0.484, and k is 0.572 (goodness-of-t is 0.997) obtained by tting the above equation and rheogram of 0.5 wt% PAAm solution. 23 The Reynolds number (Re) is dened as…”

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