The effect of weir angle on bubble motion in a flotation froth: Visual modelling and verification

Abstract A computer model of flowing foam has been. developed This provides a dynamic, visual simulation of the motion, deformation and coalescence of bubble between the pulp froth interface and either bursting on the surface or overflowing the weir. The model combines the flow model of Murphy et al. [1] based on Laplace's equation and the visualisation techniques of Weaire and Kermode [2]. Murphy et al. [3] verified the prediction of the flow trajectories of bubbles in a rectangular system. Their visualisation was based on elliptical bubbles. Here the method of Weaire and Kermode [2], developed to describe the deformation of bubbles in a diffusing system, has been used. In addition, the model has been extended to allow the simulation of flowing foams in systems of arbitrary dimensions. An experimental system has been developed which allows investigation of bubble motion and coalescence in a flowing foam when changing the weir angle from 30° to 60°. It was found that the model satisfactorily describes bubble trajectories and residence times. Further, the fraction of air leaving the foam as unburst bubbles is a maximum at a specific weir angle. A coalescence criterion has been defined that determines the extent of bubble deformation required to lead to coalescence and which appears to be largely independent of system configuration. Qualitative, visual comparison of experimental and predicted coalescence zones show close agreement.