Characteristics of settling of dilute suspension of particles with different density at high Reynolds numbers--颗粒学报PARTICUOLOGY

Zaidi, A. A. (2021). Characteristics of settling of dilute suspension of particles with different density at high Reynolds numbers. Particuology, 56, 62-74. https://doi.org/10.1016/j.partic.2020.10.015

Characteristics of settling of dilute suspension of particles with different density at high Reynolds numbers

Ali Abbas Zaidi ^*

Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland

10.1016/j.partic.2020.10.015

Volume 56, June 2021, Pages 62-74

Received 28 May 2020, Revised 13 October 2020, Accepted 14 October 2020, Available online 7 January 2021, Version of Record 8 March 2021.

E-mail: zaidi@ethz-u.ch

Highlights

• Effect of particle density on clustering is studied using simulations.

• Very dilute suspension is allowed to settle at Reynolds number more than 250.

• In mixture, larger density particles dominated the settling characteristics.

• Physics behind the studied anomalies is explained using the vortical structures.

Abstract

Dilute suspension of particles with same density and size develops clusters when settle at high Reynolds number ( $≥$ 250). It is due to particles entrapment in the wakes produced by upstream particles. In this work, this phenomenon is studied for suspension having particles with different densities by numerical simulations. The particle-fluid interactions are modelled using immersed boundary method and inter-particle collisions are modelled using discrete element method. In simulations, settling Reynolds number is always kept above 250 and the suspension solid volume fraction is nearly 0.1 percent. Two particle density ratios (i.e. density of heavy particles to lighter particles) equal to 4:1 and 2:1 and particles with same density are studied. For each density ratio, the percentage volume fraction of each particle density is nearly varied from 0.8 to 0.2. Settling characteristics such as microstructures of settling particle, average settling velocity and velocity fluctuations of settling particles are studied. Simulations show that for different density particles settling characteristics of suspension is largely dominated by heavy particles. At the end of paper, the underlying physics is explained for the anomalies observed in simulation.

Graphical abstract

Keywords

Particle clustering at high reynolds number; Suspension with different density particles; Particle microstructure due to settling; Immersed boundary method

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