Study On Flow Field Distribution And Structure Comparison Of Turbo Air Classifier

Turbo air classifier is one of the important equipment in powder preparation,it is popular in industrial production because of its simple operation,controllable particle size and high economic benefit.However,with the increasing demand for ultra-fine powder particles in various industries,it is particularly important to improve the classification performance.The flow field in classifier was numerical simulated,and the simulation results were analyzed by combing with the theory to explore the distribution law of flow field.The influence of flow fields in annular region with different structure parts in the classifier was compared.According to the existing problems in the flow field,the structure was improved to optimize the flow field and improve the classification performance.The main contents include:The flow fields in the classifiers with or without the guide vanes are compared to study the effect of the guide vanes on the flow field.The simulation results show that the guide vanes change the velocity field distribution of the annular region through guiding the airflow.The tangential velocity of airflow decreases and the radial velocity increases.The change of velocity field can reduce the energy loss in the classifier.The decrease of the airflow tangential velocity at the outer edge of the rotor cage can influence the vortex distribution in the channel of the rotor cage.And the decrease of the radial velocity fluctuation and turbulence dissipation rate near the outer edge of the rotor cage is helpful to improve the classification accuracy.The calcium carbonate classification experimental results show that the cut size is increased and the classification accuracy is improved for the turbo air classifier with the guide vanes.The large turbulent dissipation rate near the guide vanes is conducive to dispersing the powder,weakening the fish-hook effect obviously.The numerical simulations of both gas phase and discrete phase indicate that the annular region of the prototype classifier exist the non-uniform circumferential flow field distribution,the radial and tangential velocity of the airflow in the area close to the inlet channel in the annular region is greater,resulting in different trajectories of particles with the same particle size in the annular region,and different classification results.To settle the problem,the new guide vanes with 100 setting angle and log spiral guide vanes are designed based on the analyses of airflow motion in the classifier.The CFD simulation results show that the standard deviation of airflow circumferential velocity in the annular region of the new guide vanes is small.The classification results of the particles with same size are consistent.And the new guide vanes can decrease the cut size and improve fine particle size distribution.So the new guide vanes are conducive to improving the non-uniform circumferential flow field distribution in the annular region and the classification performance.Besides,compared with the guide vanes with 10° setting angle,the log spiral guide vanes has a better classification results.The flow fields of four kinds of rotor cage chassis with different opening size in classifier are compared,the results show that the rotor cage with an open chassis has a "shunt" phenomenon at the bottom of the annular region,compared with the rotor cage with a closed chassis.The "shunt" phenomenon can change the airflow velocity distribution of the annular region.Besides,with the increase of the opening size,the axial and radial velocities in the top and middle area of annular area and cut size show a trend of decreasing first and then increasing.The opening size of the rotor cage chassis has little influence on the flow field and the classification performance,while the open or closed chassis rotor cage have more influence on it.The calcium carbonate classification experimental results show that the open rotor cage chassis can reduce the cut size and improve the content of fine particles in the fine powder.The closed rotor cage chassis can improve the classification accuracy and reduce the content of coarse particles in the fine powder.