Periodically Structured Coalescence of Bubbles in a Vertical Stream Rising Through Dense Suspensions

Bubble rise in dense suspensions exhibits unusual behaviors due to the highly non-Newtonian rheology. We report the periodically structured coalescence of succeeding bubbles in a bubble stream in corn starch-water and glass bead-soybean oil dense suspensions. The coalescence behavior is examined and characterized systematically over a wide range of packing fractions and bubble injection conditions in a pseudo-2d system through video analysis. We further employed magnetic resonance imaging (MRI) to characterize similar coalescence behaviors under different conditions in a fully 3D system. The periodically structured coalescence is attributed to the leading bubbles decelerating in the shear-thickening regime, while the trailing bubbles accelerate in the shear-thinning regime, leading to coalesce.