A dust-collecting device consisting of a cylindrical chamber the lower portion of which is tapered to fit into a cone-shaped receptacle placed below it. The dust-laden air enters through a vertical slotlike duct on the upper wall of the chamber at the rate of at least 100 f/sec. Since the particles enter at a tanget, they whirl in a circular or cyclonic path within the chamber. The centrifugal force exerted on the particles is proportional to their weight and to the square of their velocity. The particles slide along the walls of the chamber and gradually circulate down into the conical receptor while the clean air escapes through a central pipe at the bottom. The dust accumulates in the cone and is discharged at intervals or continuously. The larger the particles, the more efficient the removal; in simple cyclones particles those less than 50 microns in diameter are not retained, but improved models retain particles as small as 20 microns. Cyclones are also used in cleaning and firing pulverized coal.
