A Numerical Study of the Influence of Particle Density on Lift Force-Induced Separation in a Micro-Separator/Classifier by a Macroscopic Particle Model

抄録

A Macroscopic Particle Model (MPM), which can be regarded as a quasi direct numerical simulation and hence does not need any drag and lift force models, is applied to examine the effect of particle density on lift force-induced separation in a micro-separator/classifier. The computational domain is a 30-degrees arc channel with a radius of 20 mm connecting to 5-mm straight channels at the both ends. In this study the modeled is an upper-half of the channel with a width of 200 μm and a depth of 75 μm. The particle diameter was chosen to be 20 μm, which is well separable in experiments and is suitable for MPM in which a particle should contain several fluid cells. The density was examined in the range of slightly lighter to denser, compared with water. The particle trajectories from representative points are predicted by MPM and also by a traditional particle tracking method (DPM) for comparison. The DPM without a lift force model predicted that the trajectories expanded over the cross-sectional plane with an increase of particle density since a secondary flow pattern called Dean vortices caused strong centrifugal force acting outwards from its center. On the other hand, the trajectories predicted by MPM were almost confined in the outer-half of the plane due to the lift force acting inwards to the vortex center. It seems that encountering lift force due to a steep shear and centrifugal force due to the Dean vortices are balanced regardless of the particle density since both forces likely increase with particle inertia. It is notable that particles can be hydraulically separable regardless of the density ranging slightly lighter to denser compared to the medium.