干微泡沫：在受限通道中的形成和流动
Dry microfoams: Formation and flow in a confined channel
摘要：
我们提出了一个实验研究的微气泡凝聚成二维微泡沫和它的流动在矩形微通道。使用流动聚焦方法，我们在微流控芯片上原位产生泡沫，用于大范围的液体分数，低至液体中的百分之几。我们可以监测从分离的气泡到所需微泡沫的转变，其中气泡被紧密地包装并被薄膜分离。我们发现，气泡的形成频率是有限的液体流量，无论气体压力。形成频率产生泡沫流的调制，沿着通道迅速衰减。平均泡沫流率非线性地依赖于所施加的气体压力，由于毛细作用而显示阈值压力。当通道宽度中的气泡数量变化时，流速出现强烈的不连续性，反映了泡沫拓扑结构的离散性。我们还生产了一种超扁平泡沫，将通道高度从250 $μ$ m降低到8 $μ$ m，导致高度与直径比为0.02;我们注意到在流动过程中气泡形状发生了显著变化。
英文摘要：
We present an experimental investigation of the agglomeration of microbubbles into a 2D microfoam and its flow in a rectangular microchannel. Using a flow-focusing method, we produce the foam in situ on a microfluidic chip for a large range of liquid fractions, down to a few percent in liquid. We can monitor the transition from separated bubbles to the desired microfoam, in which bubbles are closely packed and separated by thin films. We find that bubble formation frequency is limited by the liquid flow rate, whatever the gas pressure. The formation frequency creates a modulation of the foam flow, rapidly damped along the channel. The average foam flow rate depends non-linearly on the applied gas pressure, displaying a threshold pressure due to capillarity. Strong discontinuities in the flow rate appear when the number of bubbles in the channel width changes, reflecting the discrete nature of the foam topology. We also produce an ultra flat foam, reducing the channel height from 250 $μ$m to 8 $μ$m, resulting in a height to diameter ration of 0.02; we notice a marked change in bubble shape during the flow.
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