Although droplet microfluidics have attracted increasing research interest, the regulation of complex polymeric droplets remains incomplete in chemical industry. In this study, we investigate the formation of yield stress droplets in flow-focused microchannels with orifice constraints by means of numerical simulations using a volume-of-fluid method coupled with an adaptive mesh refinement technique. The results show that different orifice sizes induce various flow patterns, including dripping, quasijetting, quasijetting with droplet coalescence, and jetting. A predictive model is established for the extension length of the dispersed phase during the necking stage, considering orifice dimensions interplay. Furthermore, higher yield stress influences the droplet size and formation frequency by expanding the high viscosity distribution in the dispersed phase. The proposed predictive correlations for droplet size, velocity, and formation frequency, accounting for the effects of orifice dimensions and yield stress, are believed to have significant impacts on the preparation of polymeric droplets in microreactors.

中文翻译：

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通过孔口约束调节流动聚焦微通道中屈服应力液滴的尺寸和流动模式


尽管液滴微流控引起了越来越多的研究兴趣，但化学工业中复杂聚合物液滴的调控仍然不完整。在本研究中，我们通过使用流体体积方法与自适应网格细化技术相结合的数值模拟，研究了具有孔口约束的流聚焦微通道中屈服应力液滴的形成。结果表明，不同的孔口尺寸会产生不同的流动模式，包括滴流、准喷射、液滴聚结的准喷射和喷射。考虑到孔口尺寸的相互作用，建立了颈缩阶段分散相延伸长度的预测模型。此外，较高的屈服应力通过扩大分散相中的高粘度分布来影响液滴尺寸和形成频率。所提出的液滴尺寸、速度和形成频率的预测相关性，考虑了孔口尺寸和屈服应力的影响，被认为对微反应器中聚合物液滴的制备具有重大影响。