We experimentally study the transition from droplet to wave regimes in microfluidic liquid–liquid multiphase flows having large differences in viscosity. A unified approach based on periodic pattern analysis is employed to study relationships between dispersed and separated flow regimes, including dripping, jetting, capillary waves, inertial waves and core–annular flows over a wide range of flow rates and viscosity contrasts. We examine the morphology and dynamics of each flow regime based on wavelength, frequency and velocity of repeating unit cells to elucidate their connections and to develop predictive capabilities based on dimensionless control parameters. We demonstrate in particular that pattern selection is contingent upon the propagation velocity of droplets and waves at the transition. We also investigate microfluidic wave breaking phenomena with the formation of ligaments and droplets from wave crests in both capillary and inertial wave regimes. This work expands conventional multiphase flow regimes observed in microchannels and shows new routes to disperse highly viscous materials using interfacial waves dynamics in confined microsystems.

中文翻译：

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从液滴到波：高粘性微流体流动中的周期性不稳定模式

我们通过实验研究了粘度差异很大的微流体液-液多相流中从液滴到波浪状态的转变。采用基于周期性模式分析的统一方法来研究分散和分离流态之间的关系，包括在各种流速和粘度对比下的滴落、喷射、毛细波、惯性波和核-环流。我们根据重复晶胞的波长、频率和速度检查每个流态的形态和动力学，以阐明它们的联系并开发基于无量纲控制参数的预测能力。我们特别证明了模式选择取决于过渡时液滴和波的传播速度。我们还研究了在毛细管和惯性波状态下从波峰形成韧带和液滴的微流体波破碎现象。这项工作扩展了在微通道中观察到的传统多相流态，并展示了在受限微系统中使用界面波动力学分散高粘性材料的新途径。