Numerical Simulation And Stability Analysis Of Gas-particle Two-phase Flows In Cyclone Separators

Cyclone separators are extensively used for particle controlling and process industries, such as, air pollution control, aerosol sampling and particulate matter control, due to their simple structure, inexpensive manufacturing cost, ease in maintenance and strong adaptability. The flow in cyclone separator is three-dimensional turbulent flow with two-phase separation motion, the flow process is very complicated and is always accompanied many physical phenomena including interaction between gas and solid, coherence, adsorption and static electricity. And there also exists secondary flow(short-circuiting flow, vortex, mixing et al.) besides the mainstream. Although the cyclone separator is widely used and has been researched for many years, the mechanism of two-phase separation and flow instability has not been understood clearly.In this thesis, the numerical simulation is used to obtain the rule of turbulent flow field and two-phase separation characteristic. In order to describe two-phase, the Reynolds stress model(RSM) in Euler coordinate system and the discrete phase model(DPM) in Lagrange coordinate system are adopted. The main research contents and results of this thesis are as follows:(1) Using the standard k-e model, RNG k-e model and RSM to simulate the strongly swirling turbulent flow in cyclone separator, and the results of prediction for the velocity distribution were compared with those of experiment. Among the three models, the prediction results of the RSM have been found to be most rational, which gives clear vortex structure..(2) Numerical simulation is carried out for the tangential inlet cyclone separator with different dimensionless rate(the ratio of vent diameter and cylinder diameter is 0.342, 0.355, 0.368, 0.382 and 0.395). Then, the stability of the vortex flow in the separator is analyzed with the energy gradient theory. Results show that the tangential velocity distribution in the outer vortex is the most close to velocity distribution characteristics of free vortex at the dimensionless rate of 0.355.(3) Unsteady numerical simulation is adopted to study the effects of the insertion depth of vortex finder on the velocity distribution, vortex characteristics and precession vortex core in cyclone separator. Results show that the deeper insertion depth of vortex finder will reduce short-cut flow occurrence, which is good at the stability of the flow. However the deeper insertion depth of vortex finder will lead to the increase of the resistance coefficient.(4) Numerical study of cyclone separator has been performed to investigate the detailed flow information about particle trajectories by altering the particle diameter and injection location of particles. It is found that with the increasing of the particle diameter, the separation efficiency increases. However, when the particle diameter exceeds a critical size, the particles will deposit on the conical wall, which leads to lower separation efficiency.