论文标题
CFD表面润湿性和流速对界面进化的影响和跨流微流体系统中液滴捏合机构的影响
CFD analysis of effects of surface wettability and flow rates on the interface evolution and droplet pinch-off mechanism in the cross-flow microfluidic systems
论文作者
论文摘要
这项研究通过有限元方法在数字上研究了表面润湿性对T通道微通道中两相不混溶的流量和液滴捏合动力学的影响。已经采用了一种保守的级别方法（CLSM）来捕获宽流量率（$ 1/10 \ leq Q_R \ leq 10 $）和接触角度（$ 1/10 \ leq q_r \ leq 10 $）和触点角度（$ 120^{$ 120^{\ leq} \ leq tuq tureq tureq 180^} \ ciccy}）的挤压状态（$ CA_C <10^{ - 2} $）中的接口拓扑（$ CA_C <10^{ - 2} $）基于瞬时相剖面，液滴形成阶段被分类为初始，填充，挤压，捏合和稳定的液滴。在填充阶段，润湿性效应微不足道。但是，在挤压和捏合阶段中，疏水作用更为明显。工程参数通常显示出对无量纲参数的复杂依赖性（$ ca_c $，$ q_r $，$θ$）。捕获瞬时界面演化已揭示了与接触角的液滴形状senstivity。接口配置文件从凸面转换为疏水（$ 120^{\ circ} \leqθ\ leq 135^{\ circ} $），而超级杂相（$ 150^{\ circ} \leqθ\leqθ\ leq 180^{\ \ \）与文献相反，分散相中的压力不是恒定的，而是在连续相压力的反相。根据压力和相位剖面比较填充时间和捏合时间，已经带来了新的见解，即即使没有流动可视化和相位剖面，也可以通过安装压力传感器来阐明液滴捏机理。当拉普拉斯压力从较小到较高的值不等时，界面曲率采用扁平的形状。界面颈部宽度（2R）显示出趋势的增加到阈值，然后以接触角线性降低。
This study has numerically investigated the effect of surface wettability on two-phase immiscible flow and dynamics of droplet pinch-off in a T-junction microchannel using finite element method. A conservative level set method (CLSM) has been adopted to capture the interface topology in squeezing regime ($Ca_c <10^{-2}$) for wide flow rate ratio ($1/10 \leq Q_r \leq 10$) and contact angle ($120^{\circ} \leq θ\leq 180^{\circ}$). Based on the instantaneous phase profiles, droplet formation stages are classified as initial, filling, squeezing, pinch-off and stable droplet. Wettability effects are insignificant in filling stage. However, hydrophobic effects are more visible in squeezing and pinch-off stages. Engineering parameters have generally shown complex dependence on dimensionless parameters ($Ca_c$, $Q_r$, $θ$). Capturing the instantaneous interface evolution has revealed droplet shape senstivity with the contact angle. Interface profiles transform from convex into concave immediately for hydrophobic ($120^{\circ} \leq θ\leq 135^{\circ}$) whereas slowly for super hydrophobic ($150^{\circ} \leq θ\leq 180^{\circ}$) conditions. In contrast to the literature, pressure in dispersed phase is not constant, but it is an anti-phase with pressure in continuous phase. Comparing the filling and pinch-off time based on the pressure and phase profiles has brought new insights that the droplet pinch-off mechanism can be elucidated by installing the pressure sensors even without the flow visualization and phase profiles. The interface curvature adopts a flattened to a more concave shape when the Laplace pressure varies from a smaller to a higher value. The interface neck width (2r) shows an increasing trend up to a threshold value and then decreases linearly with the contact angle.
