The secondary drop formation of nanoparticle/surfactant-stabilized water droplets under non-uniform electric fields

摘要

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. (C) 2020 Elsevier Ltd. All rights reserved.