Coalescence Preference Depends on Size Inequality

Abstract

During bubble or droplet coalescence, there is a puzzling tendency for the coalesced bubble or droplet to be preferentially placed closer to the larger of its two parents. We confirm that this preference is a function of parent size ratio by directly visualizing coalescing air bubbles on an oil-water interface and coalescing water droplets immersed in oil. We find that the final position of the coalesced sphere is controlled by surface energy release and is related to the parent size ratio by a power-law relationship.

Bran‐induced effects on the evolution of bubbles and rheological properties in bread dough

“…The suggested possibility of coalescence as a potential bubble growth mechanism in dough can be corroborated by the recently revealed “coalescence preference ,” a phenomenon of bubble dynamics in soft materials. A daughter bubble that is merged from two different‐sized parent bubbles tends to be placed toward the larger parent (Weon & Je, ). The preferential orientation of the coalesced bubble toward its larger parent is explained by the mass transport due to size inequality based capillary pressure difference, Δ P = 2 Ɣ ( r S −1 – r L −1 ), where, Ɣ is the interfacial tension and r s and r L are the radii of two parent bubbles (Zhang, Li, & Thoroddsen, ), one small and the other of larger size, respectively, that undergo coalescence to form a daughter bubble of radius, R (Figure ).…”

Spatial and temporal scaling of unequal microbubble coalescence

“…In spite of the few important attempts through experimental [26][27][28] and radiological measurements 29 , the fundamentals of coalescence dynamics associated with hydrodynamics and mass transport, including the temporal/spatial scales, have not been well understood. For example, "coalescence preference" has been a puzzling tendency observed in experimentation 29,30 for the merged bubble to be preferentially located closer to the larger of its two parent bubbles. It has been found that the location of the merged bubble is linked by the parent bubble size ratio with a power-law relationship, but the dynamics to drive such a preference is not addressed.…”

“…Twelve cases, varying the size ratio of large to small bubbles, γ, from 5.33 to 1, are systematically investigated. The aforementioned coalescence preference phenomenon and its power-law scaling 29,30 are captured.…”

Four-dimensional visualization of rising microbubbles

“…The distance S [black solid triangles in Fig. 4(c)] showed a downward hump right after the coalescence, possibly due to capillary waves carrying momentum34. Meanwhile, the azimuthal angle φ A(A′)-C showed a large variation over the rising time (Fig.…”

“…Phase contrast x-ray imaging26272829 provides excellent contrasts in microbubble boundaries of gas−liquid systems3031323334. Fast x-ray microtomography using phase contrast x-ray imaging has been also developed for 4-D visualization of quasi-static microbubbles2829.…”