Mohammadigoushki Hadi, Ghigliotti Giovanni, Feng James J
Department of Chemical and Biological Engineering, University of British Columbia, Vancouver, British Columbia, V6T 1Z3 Canada.
Phys Rev E Stat Nonlin Soft Matter Phys. 2012 Jun;85(6 Pt 2):066301. doi: 10.1103/PhysRevE.85.066301. Epub 2012 Jun 1.
We report an experimental study on shearing a monolayer of monodisperse bubbles floating on liquid in a narrow-gap Couette device. The bubbles in such a "bubble raft" coalesce only if the shear rate exceeds a threshold value. This is in contrast to the conventional wisdom that bubbles and drops coalesce for gentler collisions, at shear rates below a critical value. Furthermore, the threshold shear rate increases with the bubble size and the viscosity of the suspending liquid, contravening reasoning based on capillary number. Through visualization and scaling arguments, we investigate several plausible mechanisms for the anomalous coalescence. None explains all aspects of the observations. The most promising model is one based on inertial forces that compress the bubbles radially inward and accelerate film drainage.
我们报告了一项在窄间隙库埃特装置中对漂浮在液体上的单分散气泡单层进行剪切的实验研究。在这样一个“气泡筏”中的气泡，只有当剪切速率超过阈值时才会合并。这与传统观点相反，传统观点认为在低于临界值的剪切速率下，气泡和液滴会因更温和的碰撞而合并。此外，阈值剪切速率随气泡大小和悬浮液体的粘度增加，这与基于毛细管数的推理相矛盾。通过可视化和标度论证，我们研究了几种可能导致异常合并的机制。但没有一种能解释观测结果的所有方面。最有前景的模型是基于惯性力的模型，惯性力使气泡径向向内压缩并加速液膜排水。
