Numerical Study of Vortex Flow in a Classifier with Coaxial Tubes

Centrifugal air classifiers are one of the most used separation devices in particle technology. The study aims to obtain a detailed description of the bulk material classification mechanism in the developed centrifugal classifier. The classifier design and the mechanism of the stable vortex structure formation in the inter-tube space of the device are described. Velocities within and between the vortices are studied to identify regions with inverse flows, which serve as transport channels for particles. The computational fluid dynamics modeling results indicate three channels with negative or near-zero axial velocities: between the vortices, near the outer wall of the internal tube, and the inner wall of the external tube. The selectivity of the device decreases when transport channels are disrupted due to flow mixing, which is caused by the height shifting of the vortex centers.