Numerical Simulation Of Cyclone Separator's Flow Field And Structural Improvement

The cyclone separator is one of the dust collectors, which makes use of the centrifugal force generated by rotating airflow to separate and trap the particles. The cyclone separator has been widely used in many fields such as chemical engineering, machinery, environmental protection, and architecture because of its simple structure, compact equipment, easy maintenance, convenient operation and many other advantages. The collection efficiency is often limited by the unreasonable design, mismatch size and other factors, and it cost much energy. With the development of computer fluid dynamics (CFD), more and more numerical simulations are used to rationalize the cyclones'structure.The cyclone separator's three-dimensional flow fields are mainly studied in this paper, which includes the pressure distribution, velocity characteristics in gas phase and the relationship between particles and pressure loss. The CFD commercial software FLUENT 6.3.26 is used in this paper. The turbulence model is RSM model, pressure-velocity coupling method is SIMPLE algorithm, and discretization method is QUICK format, convection and pressure gradient term is PRESTO format. The numerical simulation results are compared with the experiments, and the conclusions are as follows:(1) The mainstream within the cyclone separator is a double-vortex. With zero axial velocity surfaces as the boundary, the internal vortex is upward and the external vortex is downward and the two rotations are in the same direction. Tangential velocity plays a major role in the separator. It shows an obvious hump-shaped distribution, and the axial symmetry is good. Above 75% of the tangential velocity is 0.7~1.5 times of the inlet velocity. In the separation space, the maximum tangential velocity is 1.6~1.8 times of the inlet velocity; the velocity near the wall is about 0.9~1.3 times the speed.Axial velocity presents a saddle-shaped distribution, and with a good axial symmetry except the inlet position. Radial velocity is less an order of magnitude with a non-axisymmetric distribution. The static pressure distribution is similar to the total pressure, and they all show symmetry along the radius direction. The dynamic pressure distribution and tangential velocity characteristic present a good similarity.(2) Besides the mainstream, there are still some secondary flow phenomena, such as short-circuit flow, vertical eddy and eccentric circulation vortex. Because of the existence of the secondary flow, the particles show different trajectories due to different particle size and different inlet positions, in the same time, it affects collection efficiency.(3) Numerically simulate the relationship between vortex finder length and pressure loss in the separator. The results indicate that the length of vortex finder has an obvious effect on cyclone performances. When the vortex finder is about the gas entrance height, the cyclone pressure drop is minimal, and the pressure drop will increase whether vortex finder length is less than the entrance height or larger than it.(4) The experimental data and simulated results have a great correlation in the gas phase. The pressure loss increases gradually along with the increase of the inlet velocity. The inlet velocity and the pressure loss also have a good correlation between the gas phase and the gas-solid two-phase in experiment. The correlation coefficient between experimental and simulated value is 0.96 in the gas phase, and in the particle phase, the correlation coefficient is 0.85 between experiment and simulation.