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Hydrodynamics of the hydrocyclone flow field : effects of turbulence modelling, geometrical and design parameters Zaman, Ehsan

Abstract

This thesis describes a numerical study of the effect of swirl on the flow hydrodynamics in hydrocyclones and rotating pipes. Kinetic (force balance) and kinematic (velocity field) analysis were performed to identify the relative importance of turbulence, convective, and pressure forces in these flows. We showed that convective and pressure forces in hydrocyclones are three orders of magnitude larger than the size of turbulent forces, and seven orders of magnitude greater than the viscous forces. We derived a new dimensionless parameter based on a ratio of Euler numbers that gave a unique relationship for pressure along the axis of a hydrocyclone for all the cone angles tested. This finding enables rigorous scaling of hydrocyclones of differing cone angles. A complementary numerical study of flow in rotating pipes was carried out to elucidate the relative importance of convection and turbulence. We identified a dimensionless rotation parameter that delineates the condition at which decreasing turbulence force equals increasing convective force as rotational speed increases. This dimensionless number establishes a criterion for knowing which forces are dominant, and thereby a rational basis for choosing CFD (Computational Fluid Dynamics) models that are both cost-effective and accurate. Lastly, we conducted a sensitivity study to determine the effects of varying values of constants in the quadratic pressure-strain (QPS) Reynolds Stress turbulence model (RSM) for CFD modelling of swirl in hydrocyclones. The results identified the changes necessary to attain accurate predictions, such as overcoming the under-prediction problems of RSM. In addition, these findings laid the groundwork for a swirl-specific turbulence model for hydrocyclones.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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