Abstract Electrocoalescence is an energy-efficient and environmentally-friendly process for breaking water-in-oil emulsions. It has been used extensively in the oil and petroleum industries. In this study, the electrocoalescence process of nanoparticle/surfactant-stabilized water droplets with a planar interface in the presence of non-uniform electric fields was experimentally investigated. The effects of electric field patterns (i.e. uniform and non-uniform fields) and nanoparticles (i.e. concentrations) on the drop-interface electrocoalescence process were systematically examined, analyzed, and discussed. The results showed that the presence of Sodium Dodecyl Sulfate (SDS) significantly increased the volume of secondary droplets and led to the apex disintegration of the main secondary droplet because of the low surface tension. At high SiO2 concentrations, the liquid bridge between the droplet and interface was difficult to form, and the whipping filament regime, sheet breakup regime, and varicose jet breakup regime, were observed, which were determined by the accumulating surface charge. In addition, three types of non-uniform fields induced by different geometrical electrode configurations, i.e. grid electrodes, mesh electrodes, and coupled electrodes, were proposed and the electric field distributions were calculated in COMSOL Multiphysics. With increasing SiO2 concentrations, coupled electrodes produced much smaller detached droplet volumes than those of pairwise mesh and grid electrodes, which was helpful to complete the coalescence of the drop and interface. Furthermore, flat electrodes, which induced a uniform electric field, produced much larger secondary droplet volumes than those of the electrodes generating non-uniform electric fields. In summary, the utilization of coupled electrodes had a positive effect on drop-interface coalescence and increased the overall separation efficiency. The outcome of this work is potentially useful in the design of compact and efficient oil-water electro-dehydration devices.

中文翻译：

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非均匀电场下纳米颗粒/表面活性剂稳定水滴的二次液滴形成

摘要 电聚结是一种节能环保的油包水乳液破乳工艺。它已广泛用于石油和石油工业。在这项研究中，实验研究了在非均匀电场存在下具有平面界面的纳米颗粒/表面活性剂稳定水滴的电聚结过程。系统地检查、分析和讨论了电场模式（即均匀和非均匀场）和纳米颗粒（即浓度）对液滴界面电聚结过程的影响。结果表明，十二烷基硫酸钠 (SDS) 的存在显着增加了次级液滴的体积，并由于低表面张力导致主要次级液滴的顶点崩解。在高 SiO2 浓度下，液滴和界面之间的液桥难以形成，并且观察到鞭打细丝状态、片断状态和曲张射流断裂状态，这是由积累的表面电荷决定的。此外，提出了由不同几何电极配置引起的三种非均匀场，即网格电极、网格电极和耦合电极，并在 COMSOL Multiphysics 中计算了电场分布。随着 SiO2 浓度的增加，耦合电极产生的分离液滴体积比成对网格和网格电极小得多，这有助于完成液滴和界面的聚结。此外，感应均匀电场的扁平电极，产生比产生非均匀电场的电极大得多的二次液滴体积。总之，耦合电极的使用对液滴界面聚结有积极影响，并提高了整体分离效率。这项工作的结果可能有助于设计紧凑高效的油水电脱水装置。