The effect of the structure of the rotors with openings in the bottom plate and without openings on the classification characteristics of a turbo air classifier was investigated.Ground calcium carbonate was used in the classification tests.The cut size of classified particles became smaller and the classification precision was reduced in the case with openings.The effect of wind speed on classification particles cut size decreased with increasing rotor speed in the classification process.On the other hand

the flow field of the annular regions in both cases was measured with laser Doppler velocimeter (LDV).The results demonstrated that the radial wind speed decreased in the case with openings due to split-flow

resulting in a smaller cut size.In the vicinity of the rotor without openings

the abrupt increase of tangential wind speed and especially intensified axial turbulence brought about adequate disagglomeration and higher classification precision.