Qian Lijuan, Cong Hongchuan, Zhu Chenlin
College of Mechanical and Electrical Engineering, China Jiliang University, Hangzhou 310018, China.
Polymers (Basel). 2020 Jan 24;12(2):263. doi: 10.3390/polym12020263.
Binary droplet collisions are a key mechanism in powder coatings production, as well as in spray combustion, ink-jet printing, and other spray processes. The collision behavior of the droplets using Newtonian and polymer liquids is studied numerically by the coupled level-set and volume of fluid (CLSVOF) method and adaptive mesh refinement (AMR). The deformation process, the internal flow fields, and the energy evolution of the droplets are discussed in detail. For binary polymer droplet collisions, compared with the Newtonian liquid, the maximum deformation is promoted. Due to the increased viscous dissipation, the colliding droplets coalesce more slowly. The stagnant flow region in the velocity field increases and the flow re-direction phenomenon is suppressed, so the polymer droplets coalesce permanently. As the surface tension of the polymer droplets decreases, the kinetic and the dissipated energy increases. The maximum deformation is promoted, and the coalescence speed of the droplets slows down. During the collision process, the dominant pressure inside the polymer droplets varies from positive pressure to negative pressure and then to positive pressure. At low surface tension, due to the non-synchronization in the movement of the interface front, the pressure is not smooth and distributes asymmetrically near the center of the droplets.
二元液滴碰撞是粉末涂料生产以及喷雾燃烧、喷墨打印和其他喷雾过程中的关键机制。采用耦合水平集和流体体积法（CLSVOF）以及自适应网格细化（AMR）对使用牛顿液体和聚合物液体的液滴碰撞行为进行了数值研究。详细讨论了液滴的变形过程、内部流场和能量演化。对于二元聚合物液滴碰撞，与牛顿液体相比，最大变形得到促进。由于粘性耗散增加，碰撞液滴的聚结更慢。速度场中的停滞流动区域增加，流动重新定向现象受到抑制，因此聚合物液滴永久性聚结。随着聚合物液滴表面张力降低，动能和耗散能量增加。最大变形得到促进，液滴的聚结速度减慢。在碰撞过程中，聚合物液滴内部的主导压力从正压变为负压，然后再变为正压。在低表面张力下，由于界面前沿运动的不同步，压力不平稳且在液滴中心附近不对称分布。
