MODELLING OF CYCLONE SEPARATORS USING CFD

Abstract

Cyclones are devices that employ the resulting force between the drag, gravitational, inertial and centrifugal force to separate particles from the carrier gas. Due to these they follow a high turbulence. The CFD (Computational Fluid Dynamics) appears to be a strong engine to predict engineering projects. They are capable of modelling the high turbulence in the cyclones by the use of the equations of continuity and momentum balance. These equations are applied to the problem of the cyclone flow and were solved using FLUENT 6.2.16. This study investigates the effect of cyclone outlet (vortex finder) length and the cylindrical portion length on cyclone pressure drop A series of numerical experiments were performed by using the computational fluid dynamics technique (CFD) for the evaluation and validation of three-dimensional models for cyclones. The cases sought to reproduce the simulated geometry and operating conditions given by Lapple (1951)and that of Stairmand. The simulations were out using the CFD software FLUENT, the discrete phase model was used along with the RSM model of turbulence (Reynolds Stress Model) and second order upwind for the variables descriptive. The first part of the preliminary study involved simulations of a cyclone with geometric characteristics given by Stairmand using the RNG k-C model and the RSM. As values calculated by the RSM model were much closer to the experimental values, the same was used for further studies. The computed pressure drop values from six different geometries clearly indicates that at low cylinder heights, the pressure drop was high and at less vortex length the pressure drop were less. Hence for cyclones operating at high velocity, the pressure can be greatly reduced by increasing the cylinder height or by decreasing the vortex length. This may be due to the additional parts which exceed cyclone natural vortex length. Although there is no vortex they may serve as a chamber to release air pressure It was also found that, the vortex length increases the swirl flow inside the cyclone separators and thereby showing the greater chances for high separation efficiencies.