This zone may be created in an air vortex for example
in a cylindrical chamber with inlet and outlet placed on the
opposite sides of the chamber axis (Fig. 1d). The fed particles
enter with the air stream through whirl blades, which
create a screw-type flow. The blade profiles should be designed
such that the radial component of the air velocity
everywhere vanishes. Particles rotate while drifting radially
towards the chamber walls with size-dependent velocities.
As they simultaneously proceed along the chamber axis they
reach the wall in different locations. Larger particles arrive