Migration of particles undergoing pressure-driven flow in a circular conduit

Abstract

This study focuses on the demixing of neutrally buoyant suspensions of spheres during slow, pressure driven flows in circular conduits. Distributions of the solid fraction of particles, φ, and the suspension velocity, ν, are measured at different lengths from a static in-line mixer. Experiments were conducted over a range of volume average solids fractions, φbulk (0.10⩽φ⩽0.50), and at two different ratios of the particle radius, a, to the radius of the circular conduit, R (a/R=0.0256 and a/R=0.0625). At φbulk⩾0.20, the particles rapidly migrate to the low-shear-rate region in the center of the conduit. This migration results in a blunting of the ν profile, relative to the parabolic profile observed in homogeneous Newtonian fluids. For the flow geometry with the smaller ratio of a/R, the φ profile builds to a sharp maximum or cusp in the center. Particle structures are observed in the experiments with the higher a/R. The entrance lengths for the development of the φ and ν fields, Lφ and Lν, respectively, are strong functions of a/R and φbulk. Lφ and Lν rapidly decrease as φ and a/R increase. Over the range of our data, the ν profiles are observed to develop more rapidly than the φ profiles. The experimental results are compared with fully developed flow predictions from the shear-induced migration (SIM) model and the suspension balance (SB) model. At the smaller a/R, the SIM model more accurately predicts the experimental results. At larger a/R, some qualitative features of the experimental results are better predicted by the SB model, however, neither model provides good quantitative predictions, especially at low φbulk.

Modelling Shear Induced Diffusion Based Particle Segregation: A Basis for Novel Separation Technology

“…To be complete, we used a different method than the method introduced by Hampton and coworkers [24] because high correlations between the different parameters were obtained when using their method. Figure A5.…”

Transition to Turbulence in Particulate Pipe Flow

“…In conditions of very low Reynolds number and high concentration, particles migrate towards the center of the pipe and blunt the velocity profile, see for instance [10]. This effect which would tend to reduce the effective viscosity in the pipe is suspected to be present for the 780 µm particles in pipe D 1 for φ ≥ 0.25 (see in figure 3).…”

Heterogeneous Multiscale Simulations of Suspension Flow

“…Over all ranges of the shear-rate and all volume forces applied, we find for the ratio of the characteristic time scales ν app ∕ D ≫ 1, and therefore t equil;diff ≫ t equil;flow . This is also known from experiments [72].…”

“…The channel has a width of L M;y ¼ 50 mm. From experimental studies [72], we can expect that with a resolution of approximately 40 lattice points, the characteristics of profiles of u and ϕ can be resolved in sufficient detail. We therefore chose Δx M ¼ 1.25 mm.…”