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Flow Distribution in a Hydrocyclone Fibre Separation Predictions Influence of Particle Diameter on Separation

Hydrocyclones use the principle of centrifugal separation to remove or classify solid particles from a fluid, based on size, shape, and density. In order to improve the design and operation of hydrocyclones, it is important to have a good understanding of the flow and particle motion. PSL licenses the UBC hydrocyclone model developed to predict particle separation and to model fractionation in hydrocyclones according to specific fibre properties, including but not restricted to coarseness.

Particle Separation

The first step is to predict the three-dimensional flow field, as the three-dimensional geometry near the inlet pipe influences significantly the accuracy of separation predictions. Computation of the flow filed in the hydrocyclone is done using block structured curvilinear grids; turbulence is modelled using a k-e model specially modified for highly curved turbulent flows. The swirling flow pattern, imparted to the incoming fluid, is the dominant flow feature in the hydrocyclone. Several minor flow patterns are also associated with the rotational flow and influence the trajectories of the particles. The computation of the liquid-phase velocities and particle motion is carried out independently. Fibres experience a centrifugal force in the rotational flow field, which is balanced by the pressure force and a drag force associated with the fibre motion. The centrifugal force is directly dependent on the tangential velocity and therefore its correct determination is critical in predicting the fractionation performance of hydrocyclones. The trajectories of the particles of different size, shape, and injection location can be calculated and the separation efficiency estimated.

Model Usage

The developed model can be used to evaluate the influence on fractionation of fibre density, fibre diameter, fibre length, fibre specific surface, and coarseness. In addition, the influence of hydrocyclone geometry and flow conditions on fractionation can be successfully address by the model.