Utilization of Hydrodynamic Forces in the Size-Based Fractionation of Spherical and Elongated Particles

Abstract. Particle motion in suspension flow results from volume and surface forces, i.e. drag force, and lift force, as well as particle-particle interaction. The force magnitude in a given flow depends thereby on the particle size. A classical example are cyclones, where larger particles of higher inertia are rejected from the flow. For elongated particles, for example flexible cellulose fibres, the particle-particle interaction which can lead to the formation of networks, gains in importance with respect to the suspension flow behavior.

This talk summarizes numerical and experimental studies which focused on the suspension flow behavior of cellulose fibres. Dilute suspension flow of individual fibres was studied numerically using OpenFOAM (CFD code), LIGGGHTS® (DEM code), and CFDEM®coupling (for CFD-DEM coupling). Dense suspension flow of flocculated fibres was studied experimentally by high-speed imaging. At moderate shear force, the suspension flow behavior is governed by the balance of the network force (fibre-fibre interaction) and dispersing fluid shear which acts on the network. It was found for this regime, that shorter fibres are present outside the network and can be removed for length-based fibre fractionation.

A smaller part of this talk presents a numerical study on the size dependent accumulation of spherical particles in coiled channels of non-circular cross section. Such is for example used in the separation of different sized cells. Combination of lift force and drag force (from secondary Dean flow) leads to a size dependent accumulation at certain position in the channel cross section.