| Material classification is an important process of the powder engineering. As the important air classification equipment, the turbo air classifier is widely used. With the rapid development of materials science, higher demand for classification efficiency and accuracy has been raised. Therefore, measures must be taken to improve the classification performance. Operating conditions and internal structure are the two important factors for the classification performance. Based on this case, in order to improve the classification performance, the operation parameters and structure parameters optimization of turbo air classifier has been studied in this paper.Air inlet velocity and rotor cage’s rotating speed are the main operation parameters of a turbo air classifier. The inner flow field of turbo air classifier under different operations is simulated by Fluent software in order to find out the best match of air inlet velocity and rotor cage’s rotating speed of a turbo air classifier. It is indicated that the flow field is stable when the air inlet velocity is close to the tangential linear velocity on the outer diameter of the rotor cage. Otherwise, it is easy to produce turbulent pulse, which could reduce the stability of the flow field. Under stable flow field, when air inlet velocity and rotor cage’s rotating speed are high, the air turbulent dissipation rate is high, which is benefit to the dispersion and classification of powders. Calcium Carbonate powders experiments show that when rotating speed are 800 or 1200 r·min-1, setting air inlet velocity as 9 m·s-1 or 12 m·s-1 respectively, the accuracy and the Newton classification efficiency of the turbo air classifier are high. And when the air inlet velocity is 12 m·s-1, rotor cage’s rotating speed is 1200 r·min-1, the accuracy and the Newton classification efficiency of turbo air classifier are the highest. This provides theoretical basis to adjust the air inlet velocity and rotor cage’s rotating speed suitably for turbo air classifier.As the most important static components, the structure of guide vane and volute can directly influence the distribution of inner flow field in turbo air classifier. In this paper, the inner flow fields of the classifier with different structures have been simulated by using Fluent software. The simulation results show that axial inclined guide vanes can decrease the upward axial velocity in the annular region. Especially, when the inclined angle is 2.5°, the upward axial velocity is decreased and the tangential velocity is increased. This is favorable to keep the flow field stable. At the same time the classification force field is enhanced to improve the dispersion of the powders. Discrete phase simulation results reveal that particle residence time in the annular region of structure T-2.5 is shorter than it is in the annular region of structure T-0. This can reduce the collision probability of particles and the energy cost is reduced. Calcium Carbonate classification experiment results also show that the cut size decreases by 0.97～8.42 μm and the accuracy increases by 6%～9% for the structure T-2.5, compared to the structure T-0. That means the classification performance is improved with the new structure.The inner flow fields of turbo air classifier with five kinds of volute tongue position are simulated. The simulation results show that velocity distribution under different position is uneven, when the volute tongue opening angle is too small or too large. This is due to the influence of boundary layer and the impact of the inlet flow. However, when the volute tongue opening angle is 20°～30°, the flow field is stable. Discrete phase simulation results reveal that the particles with the same size, which release from different position of annual region, have the similar trajectory, when the volute tongue opening angle is 20°～30°. That means, in this case, the flow field in annular region is stable. This is corresponding with the flow field simulation results. |
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