Bubble coalescence complex interactions

A mechanism for the long-range hydrophobic interaction is evidently hidden in the complicated matter of surface induced gas adsorption - affected by solute, electrolyte, and dissolved gas. That seems now clear from the complex behaviour of solutes on bubble coalescence, and indeed from direct force measurements and other observations mentioned above. In retrospect, that and the resulting added subtlety of molectdar forces is not a surprise. After all, nature did not put these forces to work to assemble biological entities in an aqueous environment without an atmosphere. 

Most studies on heat- and mass-transfer to or from bubbles in continuous media have primarily been limited to the transfer mechanism for a single moving bubble. Transfer to or from swarms of bubbles moving in an arbitrary fluid field is complex and has only been analyzed theoretically for certain simple cases. To achieve a useful analysis, the assumption is commonly made that the bubbles are of uniform size. This permits calculation of the total interfacial area of the dispersion, the contact time of the bubble, and the transfer coefficient based on the average size. However, it is well known that the bubble-size distribution is not uniform, and the assumption of uniformity may lead to error. Of particular importance is the effect of the coalescence and breakup of bubbles and the effect of these phenomena on the bubble-size distribution. In addition, the interaction between adjacent bubbles in the dispersion should be taken into account in the estimation of the transfer rates... 

Furthermore, the physics of the interaction between turbulence and bubbles in the complex flow of a stirred vessel, with its implications for coalescence and break-up of bubbles and drops, is still far from being understood. Up to now, simple correlations are available for scale-up of industrial processes generally, these correlations have been derived in experimental investigations focusing on the eventual mean drop diameter and the drop size distributions as brought... 

Bubble interaction in swarms is a complex process. Bubble clusters commonly form that coalesce more or less simultaneously into very large bubbles. Recent experiments have revealed some of the details behind this behavior. A bubble contacts another only by following its wake to an overtaking collision. Coalescence or breakup occurs only after the collision, when one bubble is pulled into the near wake of the other. Interaction of three or more bubbles in clusters leads to increased coalescence rates. We have also shown analytically that bubbles do not collide like solid particles, but rather are drawn together by the dynamics of the surrounding fluid. Gravity and fluid acceleration drive bubble motion small-scale turbulence tends to prevent rather than enhance coalescence. 

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