Large eddy simulation of hydrocyclone - prediction of air-core diameter and shape

Hydrocyclones are widely used in the mining and chemical industries. An attempt has been made in this study, to develop a CFD (computational fluid dynamics) model, which is capable of predicting the flow patterns inside the hydrocyclone, including accurate prediction of flow split as well as the size of the air-core. The flow velocities and air-core diameters are predicted by DRSM (differential Reynolds stress model) and LES (large eddy simulations) models were compared to experimental results. The predicted water splits and air-core diameter with LES and RSM turbulence models along with VOF (volume of fluid) model for the air phase, through the outlets for various inlet pressures were also analyzed. The LES turbulence model led to an improved turbulence field prediction and thereby to more accurate prediction of pressure and velocity fields. This improvement was distinctive for the axial profile of pressure, indicating that air-core development is principally a transport effect rather than a pressure effect. An increase in feed flow rate will increase the air-core diameter by increasing the centrifugal force on fluid elements, which in turn increases the tangential velocity component, thereby lowering the pressure at the hydrocyclone axis near the apex. It has been observed that when the spigot diameter increased, the air-core diameter increased, since the tangential velocity increases when underflow diameter increases. As expected, a rise in the viscosity of liquid reduces the air-core diameter at constant feed velocity, by lowering the pressure drop over the cyclone. This LES turbulent multi-phase CFD model, once extended to particulate phase flow in hydrocyclone, would be a useful tool for studying design dimensions. More importantly, alternative geometries may be examined swiftly. (c) 2006 Elsevier B.V. All rights reserved.