Bubble formation, growth and rise in non-Newtonian xanthan gum.

Xanthan gum (XG) assists in modifying the rheology (flow behavior) of flotation systems, particularly by forming finer and slower bubbles at the sparger or impeller in high-viscosity pulp, resulting in better attachment for fine or hydrophilic particles. Here, bubble formation through an orifice, subsequent growth, and rise in non-Newtonian XG solutions are studied using a computational fluid dynamics (CFD) model. The volume of fluid (VOF) formulation and the continuum surface force (CSF) with the power-law model are used to track and calculate the bubble-liquid interface motion, respectively. The CFD-predicted departure bubble sizes are validated and compared with modified correlations for three different concentrations of XG at three different inlet gas velocities of 0.1-0.3 m s-1. The lowest relative error of 0.31-8.93% has been noted against one of the correlation equations. This analysis was extended for the study of contact angle, aspect ratio, and bubble velocity. It is found that XG concentrations and inlet gas velocity have a significant impact on bubbles' growth, expansion, elongation, and pinch-off time. The influence of five distinctive dimensionless numbers (Re, Ar, Ca, We, and Mo) and corresponding forces on bubble formation and growth is also examined. At the end, a comparative study is carried out on the outcomes achieved by using the non-Newtonian power-law model and the Carreau model.