An alternative cyclone design uses a secondary air flow within the cyclone to keep the collected particles from striking the walls, to protect them from abrasion.
The primary air flow containing the particulates enters from the bottom of the cyclone and is forced into spiral rotation by stationary spinner vanes.
It is in the opposite direction to the particle's centrifugal force because it is on a volume of fluid that is missing compared to the surrounding fluid.
Using is equal to the volume of the particle (as opposed to the velocity).
The air in a cyclone is initially introduced tangentially into the cyclone with an inlet velocity .
Assuming that the particle is spherical, a simple analysis to calculate critical separation particle sizes can be established.
Similar separators are used in the oil refining industry (e.g.
for Fluid catalytic cracking) to achieve fast separation of the catalyst particles from the reacting gases and vapors.
In non-equilibrium conditions when radial acceleration is not zero, the general equation from above must be solved.
Rearranging terms we obtain , possibly based upon the injection angle, and a cutoff radius, a characteristic particle filtering radius can be estimated, above which particles will be removed from the gas stream. For example, the geometry of the separator is not considered, the particles are assumed to achieve a steady state and the effect of the vortex inversion at the base of the cyclone is also ignored, all behaviours which are unlikely to be achieved in a cyclone at real operating conditions.