Hinderink Emma, Bera Bijoy, Schinkel Christiaan, Steijn Volkert van
Department of Chemical Engineering, Delft University of Technology, 2629 HZ, Delft, The Netherlands.
Multiphase Systems (ME-P&E), Delft University of Technology, 2628 CN, Delft, The Netherlands.
Sci Rep. 2025 Feb 17;15(1):5720. doi: 10.1038/s41598-025-87291-2.
Concentrated emulsions flowing through channels of varying widths are omnipresent in daily life, from dispensing mayonnaise in our kitchens to large-scale industrial processing of food, pharmaceuticals, etc. Local changes in channel geometry affect the stability of emulsions over length scales far beyond the droplet magnitude, for example through propagation of coalescence events called a coalescence avalanche. The underlying mechanisms are not well understood. In this work, we investigated the stability of concentrated emulsions flowing through microchannels featuring a constriction. We found that in this model geometry, the acceleration of the droplets induced near the entrance of the constriction triggers a coalescence event between the leading and the trailing droplet, but only above a critical droplet velocity. This separation-induced coalescence event, in turn, was found to trigger a coalescence avalanche in the upstream direction. Analysis of the flow behavior through particle image velocimetry and particle tracking velocimetry revealed that the propagation also follows a separation-induced coalescence mechanism, due to the retraction of the interface of the trailing droplet upon coalescence and the corresponding acceleration of the liquid inside the coalesced fluid thread. The constriction ratio was found to enhance the coalescence occurrence but did not affect the speed of coalescence propagation.
从我们厨房中挤蛋黄酱到食品、药品等的大规模工业加工，流经不同宽度通道的浓缩乳液在日常生活中无处不在。通道几何形状的局部变化会在远超液滴大小的长度尺度上影响乳液的稳定性，例如通过一种称为聚并雪崩的聚并事件的传播。其潜在机制尚未得到很好的理解。在这项工作中，我们研究了流经具有收缩部分的微通道的浓缩乳液的稳定性。我们发现，在这种模型几何形状中，在收缩部分入口附近诱导的液滴加速会引发前导液滴和尾随液滴之间的聚并事件，但前提是液滴速度要高于临界速度。反过来，这种分离诱导的聚并事件被发现会在上游方向引发聚并雪崩。通过粒子图像测速和粒子跟踪测速对流动行为的分析表明，由于尾随液滴在聚并时界面的回缩以及聚并流体细丝内部液体的相应加速，这种传播也遵循分离诱导的聚并机制。发现收缩比会增加聚并的发生率，但不影响聚并传播的速度。
