Interactions Between Unequal Parallel Bubbles Rising in a Non-Newtonian Fluid

The interactions between three unequally sized parallel bubbles rising in a non-Newtonian liquid with power-law rheology are investigated numerically using the volume of fluid interface capturing method. The critical horizontal interval for bubble coalescence is obtained by varying the initial bubble spacing in the simulations and observing the subsequent motion and interaction. The results indicate a substantial increase in this critical interval when compared to equally sized bubbles that can be attributed to the characteristic flow field in the vicinity of the bubbles. While lateral coalescence is observed for small bubble intervals, the coalescence is observed to occur in the wake of the larger bubble as the spacing approaches the critical interval. Beyond the critical interval, a repulsive effect leads to a gradual increase in the horizontal bubble interval similar to equally sized bubbles. This increase however subsides eventually but is compensated by a continuous increase in the vertical distance thereby avoiding coalescence.