Effect Of Inlet And Outlet Structure And Inlet Gas Velocity On Unstable Characteristics Of Swirl Flow In Cyclone Separator

The internal flow field of cyclone separator is a three-dimensional strong turbulent flow field.The internal flow field of cyclone separator with different structures is studied and analyzed,which can provide the basis for improving the capture efficiency of cyclone separator.The modern high-efficiency cyclone separator has been able to basically remove particles whose particle size is more than 10?m,but the capture ability of ultra-fine particles below 5?m still needs to be further excavated.In the inner flow field of the cyclone separator,the rotation characteristics of the precession vortex core(PVC)can obviously affect the escape of small particles.In this paper,the computational fluid dynamics simulation method is used to simulate the flow field in cyclone separator with different vertex finder diameter De and the ratio of cross-sectional area to inlet area of cyclone separator K_A.The inlet gas velocity and exhaust structure size are obtained in relation to tangential velocity and axial velocity,short circuit flow rate,and so on.The influence of the rotation frequency of vortex core and the distance of vortex core center away from the geometric center of the separator.Furthermore,they affect particle collection efficiency,backmixing entrainment rate and short-circuit escape rate.By means of computational fluid mechanics analysis,it is found that the vortex core oscillation can be weakened by adding a top cone to the dust vent.The quantitative relationships among inlet gas velocity,vortex core rotation frequency,swing amplitude and particle backmixing are quantitatively described by comparing the steady vortex structure with the non-stationary vortex structure.At the same time,the cause of the instability of the vortex core at the dust vent is also discussed.The main contents and results of the thesis are as follows:(1)The distribution of the maximum tangential velocity in the flow field in the cyclone separator is analyzed by the change of the inlet and outlet structure and the gas velocity,and the variation trend of the tangential velocity with De,K_A and the influence of the top cone on the tangential velocity are obtained.(2)The distribution trend of axial velocity in the flow field in cyclone separator is studied by comparing the inlet and outlet structure of the equipment.The influence of De,K_A and top cone on the interface diameter of stagnant layer and upper and lower flow is found.(3)The influence degree of equipment geometry parameters on short-circuit flow of cyclone separator is investigated,and the variation rule of short-circuit flow size,position and occurrence area with De and K_A and the effect of top cone on short-circuit flow are summarized.At the same time,the influence of the three factors on downgoing flow is analyzed.(4)The rotation characteristics of precession vortex core with different structural parameters and gas velocity are described and the variation rules are summarized.(5)The relationship between particle collection efficiency,backmixing entrainment rate and escape rate of short-circuit flow and structural parameters is refined,and a model of vortex-core rotation and back-mixing entrainment rate is established.(6)The concept that radial confluence flow loss exceeds a certain threshold will cause instability of the vortex nucleus at the dust vent.