Bubble plume dynamics in non-Newtonian ambient fluid mixture

The present study investigates the effects of controlling parameters such as air discharge, nozzle diameter, and the rheological characteristics of non-Newtonian ambient fluid mixtures in bubble dynamics. The tested ambient fluid mixtures were shear-thinning with different apparent viscosities and yield stresses. The geometrical characteristics of the air bubbles, specifically their dimensions and upward motions, were quantitatively analyzed at both the pinch-off and equilibrium stages. These measurements were systematically correlated with the governing parameters to elucidate the underlying physical mechanisms influencing bubble morphology and evolution. Direct correlations were found between air discharge and nozzle diameter with bubble width, height, and bubble aspect ratio. At relatively low air discharge, the width and height of bubbles were nearly identical, resulting in a width-to-height ratio of unity, whereas, at relatively high air discharge, the aspect ratio of bubbles reduced from unity to 0.5, indicating that bubbles were significantly elongated in the vertical direction. The results showed that bubbles become shorter and wider when passing through an ambient with higher viscosity. A strong relationship was found between bubble rising velocity and air discharge, as bubble velocity increased by more than 40% when air discharge increased by four times. The effects of controlling parameters on the occurrence of bubble coalescence were studied by measuring the Probability Mass Function (PMF). It was found that air discharge increased the probability of coalescence, while increasing nozzle diameter and apparent viscosity reduced it.