Analysis And Study For Geometrically Similar Turbo Air Classifier Model

The turbo air classifier is a dry classifier widely used in powder preparation industry.It has the advantages of a controllable particle size distribution range,high classification accuracy,large processing capacity,and simple structure.With the continuous expansion of powder application fields,the demand is gradually developing towards ultra-fine,for improving the classification performance of turbo air classifiers requires in-depth research.In the actual production practice,in the face of different application backgrounds,the specifications and sizes of the turbo air classifier are not the same.Therefore,it is particularly important to explore the distribution law of the internal flow field of geometrically similar turbo air classifiers to guide the design of classifiers with different specifications and the same structure.In this paper,the distribution law of the internal flow field of geometrically similar classifier model is analyzed by numerical simulation method,and the key structure is adjusted according to the problems in the flow field to achieve the purpose of optimizing the flow field.The main contents of the paper include:The influence of the size scaling factor on the flow field distribution in the annular region of the classifier is analyzed by numerical simulation.The simulation results show: under the same air inlet velocity,the tangential velocity distribution in the annular region of the geometrically similar classifier model shows the distribution of quasi-free vortices.With the increase in model size,the circumferential distribution of tangential velocity in the annular region is non-uniform,and the area weighted average tangential velocity of the cylinder surface in the annular region increases.The radial velocity distribution in the annular region conforms to the law of point flow.Except for the large difference in the radial velocity values near the outer edge of the rotor cage,the area weighted average radial velocity of the cylinder surface in the annular region does not change with the scale factor of the classifier.With the increase of the model size,the radial velocity difference between the rotor cage channels is obvious.Based on the velocity variation characteristics of the annular region of each model,the numerical simulation data of the geometrically similar classifier model are used as training samples to establish the area weighted average tangential velocity and radial velocity of the cylinder surface prediction equations in the annular region of the classifier,and to achieve the prediction of the velocity in the region of the geometrically similar turbo air classifier model and the vortex phenomenon between the rotor cage channels of the turbo air classifier.By analyzing the kinematic similarity and dynamic similarity of the geometrically similar turbo air classifier model,it is concluded that the flow fields of geometrically similar classifier models are similar.In response to the problem of uniform circumferential distribution of tangential velocity in the annular region in the large-scale classifier model,it is proposed to adjust the installation position of the guide vane.The simulation results show: with the decrease in the installation diameter of the guide vane,the width of the annular region becomes narrower,the tangential velocity of the inner edge of the guide vane becomes larger and the tangential velocity gradient becomes smaller.The narrowing of the vane channel restricts the full flow of gas,while the rotation of the rotor cage has a more significant effect on the surrounding flow field and the radial velocity fluctuations become greater.The turbulent dissipation rate near the guide vane increases,and the particles are better dispersed by the turbulent vortex.The turbulent dissipation rate near the rotor cage increases from slow to sharp,which is not conducive to the uniformity of flow distribution around the rotor cage.Combined with the discrete phase simulation,it can be seen that for the models with narrow annular region,the graded cut size increases with the increase of the width of the annular region.However,when the width of the annular region increases to a certain extent,the particle’s trajectory becomes long,the residence time becomes long and the solid concentration increases significantly to increase the probability of particle aggregation.According to the distribution law of the tangential velocity in the annular region of each model,the same prediction formula is established to predict the area weighted average tangential velocity of the cylinder surface in the annular region with different installation diameters of the guide vane for the classifier.The prediction formula can be applied to other geometrically similar models with different guide vane installation diameters.The O-Sepa desktop turbo air classifier is constructed using acrylic material.The equipment can not only realize the lightweight of the grading equipment but also directly observe the movement state of the powder inside the classifier.Through the experiment of calcium carbonate material,the following conclusions are obtained: the cut size increases with the increase of air inlet speed and decreases with the increase of rotor cage speed.Under the same working conditions,the smaller the size of the geometrically similar model,the smaller the cut size.Comparing the air inlet feeding and the upper spreader feeding,it is found that the air inlet feeding results in a smaller cut size and a narrower particle size distribution of the collected fine powder.However,this feeding method makes the residence time of particles in the classifier longer,resulting in lower classification accuracy.