Abstract Liquid–liquid dispersion by head-on impingement in a cross-slot microfluidic device to form oil-in-water emulsion is experimentally investigated at broad range of flow rate conditions. Reynolds number based on the continuous aqueous phase flow is changed from 1000 to 7000 and the oil dispersed volume fraction varies between 3% and 30%. The flow patterns are observed in the vicinity of impinging region to characterize the effect of Reynolds number and oil volume fraction on the water-oil interaction and thus emulsification process. Based on the measured droplet size and size distribution, two geometries are compared, aimed at evaluating the advantages and disadvantages of swirl flow in the collision region for producing high quality emulsion. One configuration, “600–600”, corresponds to inlet channels of identical size (600 μm × 600 μm), while the other one, “600–300”, has a smaller channel for dispersed phase which is off-axis with the water channel. The results show that flow characteristics during dispersing process are significantly different for viscous and turbulent conditions. Dominated by Reynolds number, the flow patterns are classified into three regimes. The more turbulent the flow is, the finer and more monodispersed droplets will be in the o/w emulsion. In the medium Reynolds number regime, characteristics of flow are closer to laminar flow using higher oil volume fraction, compared to small oil volume content. It is particularly evident with 600–300 system because of lowering velocity gradient between two phase streams. Based on results of drop mean diameter and polydispersity index, 600–300 system which generates swirl flow structure only exhibits a superior performance, compared to the conventional equal-size geometry, at relatively higher Reynolds number.

中文翻译：

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使用正面撞击配置的微通道中的快速水包油乳化：涡流运动的影响

摘要 在宽范围的流速条件下，通过在交叉槽微流体装置中正面撞击形成水包油乳液的液-液分散进行了实验研究。基于连续水相流的雷诺数从 1000 变为 7000，油分散体积分数在 3% 和 30% 之间变化。在撞击区域附近观察流动模式，以表征雷诺数和油体积分数对水油相互作用和乳化过程的影响。根据测得的液滴尺寸和尺寸分布，比较了两种几何形状，旨在评估碰撞区域涡流对生产高质量乳液的优缺点。一种配置，“600–600”，对应于相同尺寸的入口通道 (600 μm × 600 μm)，而另一个，“600-300”，有一个较小的分散相通道，它与水通道离轴。结果表明，在粘性和湍流条件下，分散过程中的流动特性有显着差异。以雷诺数为主，流动模式分为三种状态。流动越湍流，O/W 乳液中的液滴越细，越单分散。在中等雷诺数范围内，与小油体积含量相比，使用较高油体积分数的流动特性更接近于层流。由于降低了两相流之间的速度梯度，这在 600-300 系统中尤为明显。基于液滴平均直径和多分散指数的结果，