The dust collectors has some obvious advantages, such as high efficiency, if it is constructed properly, easily maintained as three are no moving parts, and, furthermore, it is easy to clean, if the construction is with a fully welded centre cyclone.
The operation theory is based on a vortex motion where the centrifugal force is acting on each particle and therefore causes the particle to move away from the cyclone axis towards the inner cyclone wall. However, the movement in the radial direction is the result of two opposing forces where the centrifugal force acts to move the particle to the wall, while the drag force of the air acts to carry the particles into the axis. As the centrifugal force is preciominant, a separation takes place.
Power and air pass tangentially in to the cyclone at equal velocities. Power and air swirl in a spiral from down to the base of the cyclone separating the powder out to the cyclone wall. Powder leaves the bottom of the cyclone via a locking device. The clean air spirals upwards along the centre axis of the cyclone and passes out at the top.
The centrifugal force each particle is exposed to can be seen in this equation:
C = m * Vt2 / r ( 16 )
C = centrifugal force
m = mass of particle
Vc = tangential air velocity
r = redial distance to the wall from any given point
From this equation it can be concluded that the higher particle mass, the better efficiency. The shorter way the particle has to travel the better efficiency, and the closer the particle is to the wall the better efficiency, because the velocity is highest and the radial distance is short.
However, time is required for the particles to travel to the cyclone wall, so a sufficient air residence time should be taken into consideration when designing a cyclone.
From above equation it is evident that small cyclones ( diameter less than 1 m ) will have the highest efficiency, a fact generally accepted.