Investigation of the effect of lift and drag on air-core formation in a hydrocyclone

Abstract

Abstract: Fluidised bed reactors commonly utilise cyclones and hydrocyclones for classification of particles to or from the fluidised bed. Multiphase interactions play a dominant role in such fluidisation and ancillary separation or classification processes. Computational Fluid Dynamics (CFD) and experiment was used to determine whether drag and lift plays a significant role in air-core formation and the performance of a hydrocyclone. Four drag models and three lift models were used in the investigation. The Eulerian-Eulerian multiphase model was used in this study. With the Eulerian-Eulerian approach, the multiphase interactions such as drag and lift can be accounted for which is not the case with the Volume-of-Fluid (VOF) and Mixture models. Turbulence was accounted for using the Renormalization Group Theory (RNG) k-ε Model. The models under predicted the underflow mass flow rate by 63 % and over predicted the overflow mass flow rate by 12%. The results indicate that lift has no effect on the air-core and water mass flow split. Whilst drag does not affect the air-core or water mass flow split the choice of drag model has a noticeable effect on the stability of the solution. Thus, it is recommended that lift be neglected and that a drag model must be included to ensure stability. Either the Morsi-Alexander or the Tomiyama et al. model should be used. Future work will focus on modelling the drag and lift in a fluidised bed using the Eulerian-Eulerian Dense Discrete Phase Model