Abstract: The classification performance of a turbo air classifier is mainly affected by matching of air inlet velocity and rotating speed of rotor cage. With the same inlet velocity, increasing the rotating of rotor can decrease cut size to obtain ultra-fine powders. However, it will cause non-uniform distribution of fluid flow and decrease classifying accuracy. A model of the turbo air classifier with straight-blade rotor cage is established and the flow field is simulated by the software of Fluent. To solve the problems including non-uniform distribution of fluid flow and big angle of fluid-attack at the entrance of rotor cage, the blade’s shape and installation angle are designed and improved. A method of designing arc-blade rotor cage is proposed. The simulation results indicate that for the arc-blade rotor cage, the angle of fluid-attack at the entrance of rotor cage is decreased, the flow field of channel in rotor cage becomes uniform, and the cut size is also reduced. Calcium carbonate classification experimental results are in agreement with simulation results. In the design condition that air inlet velocity is 12 m/s and rotating speed of rotor is 1 200 r/min, compared to the straight-blade rotor cage, the cut size is reduced 11.5% by using the turbo air classifier with arc-blade rotor cage without decreasing the classifying accuracy.

Key words: arc-blade, axial vortex, cut size, rotor cage, turbo air classifier