Abstract for presentation at Chemeca 2005

Overall flotation kinetics in a flotation cell is largely governed by the motions of air bubbles and solid particles and their collisions. As a result, prediction of flotation kinetics has not been possible because of the complexity of these particle-bubble interactions in the turbulent three-phase process. Principles of flotation cell design and operation have therefore been mostly empirically based. CFD models are now being developed, but because typical industrial-scale flotation cells may contain millions of bubbles and particles, a direct 3D numerical modelling approach resolving bubble and particle scales would require far more computational power than will be available for many years. CFD models have therefore been developed using time-averaged RANS and multi-fluid techniques. These models require input on bubble-particle collisions in turbulent flow. Research has been carried out in the past to investigate bubble-particle collisions, but has been restricted to the two extreme situations that can be treated theoretically, Stokes flow and potential flow. More realistic situations have not been considered. To address this problem, a multi-scale modelling approach is proposed in this paper, whereby CFD modelling is carried out at both the macro (cell) scale and micro (bubble) scale with closure relations for the macro-scale models determined through analysis of the micro-scale models.

In this paper, a methodology will be developed to investigate the elementary characteristics of bubble-particle collisions in turbulent flows using CFD modelling, and the use of these characteristics, primarily collision frequency and efficiency, will be demonstrated in a macro-scale model of a flotation cell.