Jetting to dripping transition: Critical aspect ratio in step emulsifiers
Jetting to dripping transition: Critical aspect ratio in step emulsifiers
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DOI：
10.1063/1.5084797
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发表时间：
2018-12
影响因子：
4.6
通讯作者：
A. Montessori;M. Lauricella;Elad Stolovicki;D. Weitz;S. Succi
中科院分区：
文献类型：
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作者：
A. Montessori;M. Lauricella;Elad Stolovicki;D. Weitz;S. Succi
完全三维的，时间相关的，直接模拟的非理想的Navier-Stokes方程的两组分流体，揭示了机制，抑制液滴破碎步骤乳化器低于临界阈值的宽度-高度（$W/H$）比的微流体喷嘴。低于$W/H \sim 2.7$，模拟提供了从受限矩形通道几何形状到喷嘴台阶下游流体的各向同性（球形）膨胀的流体的平滑拓扑过渡的证据。超过这个阈值，从内部空间到外部空间的过渡涉及一系列动态重排，使自由表面保持机械平衡。这种重排还引起周围流体的回流，这又导致射流收缩并最终导致其破裂，即液滴形成。模拟结果与实验值的阈值，这是发现约$w/h \sim 2.4$显着协议。
Fully three-dimensional, time-dependent, direct simulations of the non-ideal Navier-Stokes equations for a two-component fluid, shed light into the mechanism which inhibits droplet breakup in step emulsifiers below a critical threshold of the the width-to-height ($w/h$) ratio of the microfluidic nozzle. Below $w/h \sim 2.7$, the simulations provide evidence of a smooth topological transition of the fluid from the confined rectangular channel geometry to an isotropic (spherical) expansion of the fluid downstream the nozzle step. Above such threshold, the transition from the inner to the outer space involves a series of dynamical rearrangements which keep the free surface in mechanical balance. Such rearrangements also induce a backflow of the ambient fluid which, in turn, leads to jet pinching and ultimately to its rupture, namely droplet formation. The simulations show remarkable agreement with the experimental value of the threshold, which is found around $w/h \sim 2.4$.