Analysis and optimisation of mixing in binary droplet collisions
Analysis and optimisation of mixing in binary droplet collisions
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DOI：
10.1017/jfm.2023.749
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发表时间：
2023-10-23
影响因子：
3.7
通讯作者：
Chakraborty，Nilanjan
中科院分区：
文献类型：
--
作者：
Ruiz-Gutierrez，Elfego;Hasslberger，Josef;Chakraborty，Nilanjan
二元液滴的碰撞在许多工业、化学和生物过程中起着关键作用。在这些过程中，所需结果的质量强烈依赖于液滴在半空中碰撞时的混合。在这项工作中，多相直接数值模拟的基础上的体积的流体方法已被用来调查的混合过程和分析的参数，如注射速度，定时和碰撞角度的影响。由于对流和不可逆扩散过程而导致的混合演变已通过分离参数进行量化。为了综合碰撞的结果，重新定义了碰撞参数，以考虑非球形液滴的碰撞。已经发现，最佳混合不发生对称的迎面碰撞，而是在适度的非对称配置。通过对速度梯度张量的分析，解释了这种现象。它已被证明，通过打破对称性，局部拓扑结构的流动被改变，所产生的对流增加了液体之间的接触面积，从而增强了混合过程。然而，还观察到横向未对准将初始动能转化为合并液滴的旋转，从而防止增强的混合。
The collision of binary droplets plays a key role in several industrial, chemical and biological processes. In these processes, the quality of the desired outcome is strongly dependent on the mixing of the liquid droplets as they collide in mid-air. In this work, multiphase direct numerical simulations based on the volume-of-fluid method have been used to investigate the process of mixing and analyse the effects of parameters such as injection velocity, timing and collision angles. The evolution of mixing due to convection and irreversible diffusive processes has been quantified by means of the segregation parameter. To synthesise the outcome of a collision, the impact parameter has been redefined to account for the collision of non-spherical droplets. It has been found that the optimal mixing does not occur for symmetric head-on collisions, but rather at moderately asymmetrical configurations. This behaviour has been explained by analysing the velocity gradient tensor. It has been demonstrated that by breaking the symmetry, the local topology of the flow is altered and the resulting convective flows increase the contact area between the liquids, thereby augmenting the mixing process. However, it was also observed that lateral misalignment transforms the initial kinetic energy into the spinning of the merged droplets, thus preventing an enhanced mixing.