Study On Flow Field Characteristics And Separation Behavior Of Ultrafine Powders Gas-Solid Swirling Classification

With the development of high technology and new material industry in China,the demand for ultrafine powder materials is increasing,and higher requirements are put forward for the technology and equipment of the production of powder products.For ultrafine powder products,classification process and equipment are particularly important..Existing studies have shown that the cutting particle size of ultrafine powder can reach 1.3μm by micro-cyclone separator,which is smaller than the cutting particle size of traditional classifying equipment.Therefore,this study by using numerical simulation and experimental study on the method of combining to under different structure parameters and operating parameters of the micro internal flow field characteristics with the movement of particles in cyclone separator are research,aims to reveal the micro cyclone separator structure parameters and operating parameters on the internal flow field and the influence law of particle movement,and then again based on the proposed can effectively improve the micro cyclone separator on the properties of ultrafine powder particles grading optimization method.1.The gas flow field in a micro cyclone separator was numerically simulated,and the effects of air velocity,vortex finder diameter and vortex finder insertion depth on the gas flow field were investigated.The results show that the gas velocity has a significant effect on the stability of the gas phase flow field in the cyclone separator.When the gas velocity is high,the vortex core oscillates seriously at the tail end of the inner cyclone,resulting in the flow field disorder in the cone and feed leg space of the cyclone separator.The diameter of the vortex finder has a significant effect on the axial velocity distribution of the gas phase flow field in the cyclone separator.When the diameter of the vortex finder is D_e>0.4D_c,there will be stagnation or even backflow phenomenon in the upward internal swirling flow.The stability of the gas flow field in the cyclone separator is relatively poor when the riser insertion depth is small2.The separation behavior of powders in swirling flow field was studied by numerical simulation.Is small,the study found that,in the tone speed incident particles after short circuit directly by the litres of trachea,and when the gas velocity is larger in the upper part of the leg to the bottom and hopper flow field particle trajectory is very intensive and stay for a long time,in the actual process of the classification of backmixing phenomena,easy to cause particles may make coarse particle by litres of tracheal discharge,Therefore,It is best that the intake air speed should be neither too high nor too low.With the increase of litres of vortex finder insertion depth,particles in the flow field of rotating flow increased gradually,until the insert depth of 0.7D_c vortex ring count the most,at this time,the classification and separation of particles in the flow field are more sufficient,so the best prediction when L=0.7D_c classification;When the vortex finder diameter is large,the movement track of particles in the flow field inside the cyclone separator is scattered and without regularity.However,when the vortex finder diameter is gradually reduced,the number of rings of particles rotating in the flow field is gradually increased.Therefore,it is predicted that the vortex finder diameter with the best grading effect may be0.5D_c or smaller3.The effects of air velocity,vortex finder diameter and insertion depth on the classification effect of micro cyclone separator on ultrafine powder were studied by experiments.The classification results obtained from the tests were explained by combining the characteristics of gas phase flow field and the movement behavior of particles in the flow field.The results show that.the classification accuracy and efficiency of the cyclone separator for ultrafine powder particles increased first and then decreased with the increase of air velocity,and the classification accuracy and efficiency reached the best when the air velocity was 15m/s.The best grading efficiency can be obtained when the insertion depth of the vortex finder is flush with the lower end of the inlet,and better grading accuracy can be obtained when the insertion depth of the vortex finder is slightly greater than the lower end of the inlet.The classification effect of the micro cyclone separator on ultrafine powder is improved obviously with the decrease of the diameter of the vortex finder.Finally,the experimental values are compared with the predicted values of numerical simulation,and the experimental results are basically consistent with the predicted results of simulation.To sum up,the operating parameters and structural parameters suitable for ultrafine powder particle classification of the micro cyclone separator used in this paper are as follows:Inlet air speed v=15m/s,feeding speed q≤27g/min,insertion depth L=0.7D_c and vortex finder diameter D_e=0.4D_c,the grading accuracy K=2.15,grading particle size D₅₀=3.30μm.There are 76 figures,9 tables and 95 references in this paper...