This paper reports a breakup regime of bubbles and droplets that is caused by a sudden channel expansion in a microfluidic device. In this regime, bubbles or droplets generated at a flow-focusing geometry periodically breakup into smaller bubbles or droplets, respectively, upon entering an expansion. In addition to Capillary number $Ca$, which is previously shown to govern the dispersion breakup in such geometries, we find that, at a high-inertia regime, the Weber number $We$ also plays a significant role in specifying the transition from non-breakup to breakup regimes. Furthermore, we identify different periodic breakup modes, for example, symmetric and asymmetric breakup, which are dictated by the Ohnesorge number. A power law of $f^{0.5}\propto W{e}^{0.1}C{a}^{0.2}$, where $f$ denotes the frequency at which the dispersions arrive at the expansion region, governs when the droplets and bubbles breakup. This power law highlights the importance of inertia to the dispersion breakup in an expansion-mediated geometry. Our results demonstrate that, without modifying the geometry and by only tuning several dimensionless parameters related to the fluid flow, a microchannel expansion region can produce mono-, bi-, or tri-disperse bubble or droplet populations. These discoveries may find utility in the design of multi-disperse bubble or droplet populations using microfluidics.

中文翻译：

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膨胀介导的微流体中气泡和液滴的破裂

本文报道了由微流控设备中突然的通道膨胀引起的气泡和液滴的破裂状态。在这种情况下，以流动集中的几何形状产生的气泡或液滴在进入膨胀时分别周期性地分裂为较小的气泡或液滴。除毛细管数$C\mathrm{一种}$，如先前所示，它可以控制这种几何形状的色散破裂，我们发现，在高惯性状态下，韦伯数 $\mathrm{w\; ^}Ë$在规定从非解体政权向解体政权的过渡中，也起着重要作用。此外，我们确定了不同的周期性破坏模式，例如对称和不对称破坏，这由Ohnesorge数决定。的幂定律$F^{0.5}\propto \mathrm{w\; ^}{Ë}^{0.1}C{\mathrm{一种}}^{0.2}$，在哪里 $F$表示分散液到达膨胀区域的频率，决定了液滴和气泡何时破裂。该幂定律凸显了惯性对扩展介导的几何形状中的色散破裂的重要性。我们的结果表明，在不更改几何形状且仅调整与流体流动相关的几个无量纲参数的情况下，微通道扩展区域可以产生单分散，双分散或三分散的气泡或液滴种群。这些发现可能在使用微流控技术设计多分散气泡或液滴群体中有用。