Cyclones (or centrifugal collectors) create a ‘cyclonic’ or centrifugal force, similar to water going down a drain, to separate dust from the polluted air stream. The centrifugal force is created when dust filled air enters the top of the cylindrical collector at an angle and is spun rapidly downward in a vortex (similar to a whirlpool action). As the air flow moves in a circular fashion downward, heavier dust particles are thrown against the walls of the collector, collect, and slide down into the hopper.

Cyclone Collector Design Considerations:

Cyclone dust collector efficiencies depend on,

1. particle size (particles with larger mass being subjected to greater force),
2. force exerted on the dust particles and,
3. time that the force is exerted on the particles

Cyclone dust collectors can be designed with either large or narrow diameters depending on the application. Small diameter cyclones have high dust collection efficiencies at low dust loads (0.1 to 6 grains per cubic foot) and high pressure drop of 6 to 10 inches w.c. (water column). Owing to the small diameter they have the tendency to plug at high dust loads. Large diameter cyclones can handle high dust loads (50-100 grains per cu.ft) with low pressure drops (1.5 to 3 inch w.c.) efficiently. They are not very efficient at low dust loads.

To improve efficiencies, design considerations are,

1. high narrow inlets reduce distances traveled by dust to the wall and thereby improve collection efficiencies
2. small diameters have higher forces than larger diameter cyclones
3. smooth transition ensures maximum efficiency.

Use of expansion hoppers in dust discharge:

In high pressure drop cyclones, dust collecting at the discharge point could be swept upward to the outlet tube. This phenomenon occurs due to the powerful inner vortex that is formed inside the main swirling stream at the discharge point. Use of expansion hoppers allows dust to be discharged through an airtight feeder. Expansion hoppers effectively squeeze out moisture in some heavy moisture applications.

http://www.dustcollectorexperts.com/cyclone/