Hi gonzalito,

In a self aspirated cell such as a Wemco, the agitator/impeller rotates inside of 3 tubes or cylinders:  the draft tube is slightly larger in diameter than the impeller and sits at the bottom of the impeller with a slight vertical overlap; the standpipe is typically over 2X the impeller diameter and sits above the impeller, with a portion submerged in the top of the pulp; and the disperser is approximately the same diameter as and is attached to the standpipe and overlaps the top ~2/3 of the impeller.

When the impeller spins, the slurry in its vicinity begins to rotate and creates a vortex in the surface of the pulp.  When the air column in the center of the vortex reaches the impeller blades, the air is broken up into small bubbles as it mixes violently with the slurry and the mixture is flung outward radially from the impeller by centrifugal inertia and into the quiescent zone of the cell.  A similar vortex on the bottom of the impeller draws slurry up to the impeller through the draft tube.  The rotational velocity of the mixture is halted when it flows outward through holes in the disperser, so the pulp in the quiescent zone typically does not spin.

The air that escapes the agitation zone into the quiescent zone is then continuously replaced through the draw-hole in the top of the standpipe.

I hope this helps...feel free to ask additional questions for clarification, if necessary.

Craig

Thank you very much. Now I understand, then how do I calculate the airflow? and How do I calculate the diameter of the impeller?