Study On The Structure Of Rotor Cage And Guide Blade In A Turbo Air Classifier

The turbo air classifier is widely used as a very important powder classification device. However, the conventional turbo air classifier produces a wide particle size distribution which is difficult to meet the requirement of reducing the particle size and making fine powder uniformly to arrange fine powder particles because of the constraints in the sectional structure and process of the classifier. Therefore, the structure of a turbo air classifier should be optimized. In recent years, In line with the development of research on the flow field characteristics of a turbo air classifier, it provides theoretic foundation for optimizing structure. In this paper, the rotor cage and guide vane of a turbo air classifier was modified. The structural effects on the inner flow field of a turbo air classifier were all simulated with the FLUENT(?) software and the numerical simulations results were compared and analyzed. Eventually, the numerical simulations results were confirmed by actual material experiments.The blades in rotor cage are streamlined in design to minimize the differential pressure because of maintaining equality of cross-sectional area between two blades. According to the simulation results, the positive whirling vanishes and flow field become stable. The full blades in conventional rotor cages were improved to splitter style. The effect of the structure of the rotor cage with full blades and with splitter blades on the inner flow field of a turbo air classifier was investigated with the software Fluent. The result from numerical simulation indicates that air velocity fluctuations on outer cylinder of the improved rotor cage are decreased in the height direction, while, the radial velocity is decreased and the tangential velocity is increased compared with the conventional rotor cage, so, the cut size of classified particles is smaller. The deviation of tangential velocity and radial velocity distribution on outer circle of horizontal section of the rotor cage is greatly improved, compared with the conventional rotor cage. When the ratio of the short blade length to the long blade length is 0.77, the flow field between blades is stable, and the velocity distribution on outer circle of the rotor cage is uniform. The experiment results on material classification demonstrate that the rotor cage with splitter blades is helpful in improving the classification precision and decreasing the cut size. When the revolving bar is fixed on the rotor cage, it's helpful to disperse the raw material. However, due to the increase of velocity fluctuation in annular region, the cut size also increases.The modification involved positively or negatively curving the straight blade. The structural effects of the straight, positively bowed, and negatively bowed blades on the inner flow field of a turbo air classifier were all simulated with the FLUENT(?) software. The numerical simulations indicate great improvement in the annular region tangential and radial velocity distributions of the positively bowed guide blade, compared with the straight and negatively bowed blades. Air velocity fluctuations on the outer cylinder of the improved guide blade are decreased in the height direction. Also, the radial velocity is decreased and the tangential velocity is increased using the positively bowed blade. As a result, the classified particles are cut smaller than with the straight and negatively bowed blades. The inertia rotating vortex between blades is decreased, and the flow field becomes stable. Material classification performance experiments were also performed. The results thereof demonstrate that the positively bowed guide blade improves the classification precision and decreases the particle cut size. These actual experimental results confirm the computational fluid dynamics simulation results, and the feasibility of the modified guide vane in engineering applications.The dry classification technology about narrow class of ultra-fine powders was studied on two-stage series turbo air classifier. Raw materials can be classified twice when two turbo air classifiers are connected in series effectively. The classification experiments of aluminum oxide were conducted. The results show that the particle size distribution of fine powder is below 10μm.