RESUMO
Electroemulsification methods use electrohydrodynamic (EHD) forces to manipulate fluids and droplets for emulsion formation. Here, a top-down method is presented using a contactless corona discharge for simultaneous emulsion formation and its pumping/collection. The corona discharge forms using a sharp conductive electrode connected to a high-voltage source that ionizes water vapor droplets (formed by a humidifier) and creates an ionic wind (electroconvection), dragging them into an oil medium. The nonuniform electric field induced by the corona discharge also drives the motion of the oil medium via an EHD pumping effect utilizing a modulated bottom electrode geometry. By these two effects, this contactless method enables the immersion of the water droplets into the moving oil medium, continuously forming a water-in-oil (W/O) emulsion. The impact of corona discharge voltage, vertical and horizontal distances between the two electrodes, and depth of the silicone oil on sizes of the formed emulsions is studied. This is a low-cost and contactless process enabling the continuous formation of the W/O emulsions.
RESUMO
This paper discusses an experimental approach to study the effects of a contactless method on electrocoalescence of water-in-oil mixture/emulsion. A positive corona discharge is utilized using a sharp conductive needle without direct contact with the mixture/solution to avoid potential corrosion of the electrode. This creates a nonuniform electric field, which is further used for the coalescence of water droplets in the range of micro to macro in oil. Two approaches are employed in this study: qualitative analysis conducted by visually studying coalescence patterns in videos captured with a high-speed camera and a quantitative analysis based on calculations obtained from dynamic light scattering measurements. From the behavior of the water droplets under the electric field, it is observed that dipole-dipole interaction, migratory coalescence/electrophoresis, and dielectrophoresis have major roles in promoting the coalescence events. The effects of oil viscosity and power consumption on the coalescence rate are also investigated, suggesting an optimal oil-water separation process. The results of this study pave a path for developing a safe, contactless, rapid, and low-power-consuming separation process, potentially suitable for an offsite application.
RESUMO
Current oil-water separation methods require a significant power, a high processing time, and costly equipment, which typically yield low treatment efficiency. Pulsed direct current (dc) electric fields and recently nonuniform electric fields caught considerable attention in the petroleum industry research in order to address the most common oil-water separation issues such as chain formation, partial coalescence, and low efficiency in either the energy consumption or coalescence rate. Here, a contact-less charge injection method induced by corona discharge is utilized to investigate the impacts of nonuniform and pulsed dc electric fields on the coalescence of water droplets inside an oil medium. The operating process parameters were experimentally calibrated and optimized with the goal of increasing the effectiveness and energy consumption efficiency of the coalescence process. High-speed imaging and image processing techniques were used in order to investigate the effect of different active forces (i.e., dipole-dipole interaction, migratory coalescence, or electrophoresis, and dielectrophoresis) during the coalescence process. Different pulsed dc frequencies and pure dc waveforms were utilized and their impact on the coalescence of water droplets was investigated. An optimal coalescence recipe was proposed by continuous measurement of the distance, velocity, and acceleration of the coalescing water droplets. The results of this study suggest use of pulsed dc and pure dc electric fields for coalescence of water droplets in concentrated and dispersed emulsions, respectively.
