During the last two decades atmospheric (or high) pressure non-thermal plasmas in and in contact with liquids have received a lot of attention in view of their considerable environmental and medical applications. The simultaneous generation of intense UV radiation, shock waves and active radicals makes these discharges particularly suitable for decontamination, sterilization and purification purposes. This paper reviews the current status of research on atmospheric pressure non-thermal discharges in and in contact with liquids. The emphasis is on their generation mechanisms and their physical characteristics.

http://iopscience.iop.org/article/10.1088/0022-3727/42/5/053001/pdf

Non-thermal plasmas in and in contact with liquids

The application of strong electric fields in water and organic liquids has been studied for several years, because of its importance in electrical transmission processes and its practical applications in biology, chemistry, and electrochemistry. More recently, liquid-phase electrical discharge reactors have been investigated, and are being developed, for many environmental applications, including drinking water and wastewater treatment, as well as, potentially, for environmentally benign chemical processes. This paper reviews the current status of research on the application of high-voltage electrical discharges for promoting chemical reactions in the aqueous phase, with particular emphasis on applications to water cleaning.

/pdf/electrohydraulic-discharge-and-nonthermal-plasma-for-water-bcogyk507r.pdf

Electrohydraulic Discharge and Nonthermal Plasma for Water Treatment

Review on electrical discharge plasma technology for wastewater remediation

Electrostatic enhancement of coalescence of water droplets in oil: a review of the technology

The technology for electrostatic enhancement of coalescence of water droplets in oil emulsions is critically reviewed. Historically, the electrostatic coalescer was invented for the petroleum-related industries in California [US Patent 987 115 (1911)]. Nowadays, this technology is generally considered for the separation of an aqueous phase dispersed in a dielectric oil phase with a significantly lower dielectric constant than that of the dispersed phase. Various designs have been introduced, with most using alternating current (AC) electric fields with mains frequency (50 or 60 Hz). The direct current (DC) electric field has been less common in the past as compared to the AC. In 1981, the concept of pulsed DC electric fields was introduced, together with insulated electrodes [Trans. IChemE 59 (1981) 229–237; UK Patent 217 1031A (1986)]. Since then, this has become more common in the electrocoalescence technology. Pulsed DC and AC fields are especially useful, when the aqueous phase content of the emulsion is high, to prevent short-circuiting between the pair of electrodes. Processing of oil from old wells is a good example, where the volumetric water content could vary significantly. Reported work by some workers indicates the existence of an optimum frequency, which depends on the electrode coating material, its thickness and the liquid emulsion composition. This is however, a contentious issue which has not been completely resolved. The characteristics and geometry of the electrode system (generally cylindrical or plate) influence the performance of the electrostatic coalescer, and are closely related to the type of the applied electric field and the emulsion used. There are basically two types of electrode: uninsulated electrode and insulated electrode. Combination of electrocoalescence and mechanical separation (e.g., centrifugal force) has also been introduced. Heating and the addition of chemicals have been shown to further enhance the electrocoalescence of water droplets. Other methods that can be combined with the electrical treatment are filtration, methods employing high pressure and temperature, and mixing. This review paper also looks at some of the current specific industrial applications using the electrocoalescence technology. Besides the oil and petroleum industries, this technology has potential applications in the edible oil industries such as palm oil, sunflower oil and vegetable oil processing. Most of the currently available equipment is very big and bulky, having a large inventory of emulsion. Therefore, we see the future trend for new developments to be in the direction of inventing small portable devices, incorporating features such as optimum electric fields and combined electrical and centrifugal forces to further enhance the separation of water-in-oil emulsions. Furthermore, a better understanding of the fundamentals of electrocoalescence will enable a better design of the geometry of the electrodes, of the flow field with respect to the electric fields, the type of dispersion used and the type of the applied electric field. © 2002 Elsevier Science B.V. All rights reserved.

Short communication Electrostatic enhancement of coalescence of water droplets in oil: a review of the technology

Ozonation using microbubbles formed by electric fields

Ozone is widely used to deactivate microorganisms and remove organic contaminants in water industries. However, interest also exists in using radical species, which are stronger oxidants than ozone...

A Pulseless Corona-Discharge Process for the Oxidation of Organic Compounds in Water

The mechanism of electrostatic spraying of insulating fluids, such as air or organic solvents, into relatively conductive fluids, such as water, is investigated in this work. Experiments with air sprayed into water through an electrified capillary showed that the pressure inside the capillary increases, reaches a maximum, and then decreases as the applied voltage is increased. The initial pressure increase is due to the electric stress on the fluid interface, while the decrease is due to the Coulombic electrohydrodynamic flow generated near the end of the capillary. It is shown that electric fields can cause simultaneous pumping, spraying, and mixing of fluids. This phenomenon is demonstrated for air and kerosene in water.



On etudie dans ce travail le mecanisme de vaporisation electrostatique de fluides isolants, tels que l'air ou des solvants organiques, dans des fluides relativement conducteurs, tels que l'eau. Les experiences d'air vaporise dans l'eau dans un capillaire electrifie montre que la pression dans le capillaire augmente, atteint un maximum, puis diminue lorsqu'on augmente le voltage applique. L'augmentation de la pression initiale est due a la contrainte electrique sur l'interface du fluide, tandis que sa diminution est due a l'ecoulement electrohydrodynamique Coulombien induit pres de l'extremite du capillaire. On montre que les champs electriques peuvent causer un pompage, une vaporisation et un melange simultanes des fluides. Ce phenomene est demontre pour l'air et le kerosene dans l'eau.

Pumping, spraying, and mixing of fluids by electric fields

In many chemical and environmental applications, the use of bubble column reactors is common and often essential in such processes as absorption, coal liquefaction, catalytic slurry reactions, and bioreactions. The objective of this work is to investigate bubble generation of air in water through electrified metal capillaries. Many important factors that affect the formation of bubbles, including capillary size, capillary tip configuration, electrode distance, and flow rate, are studied. It is found that the bubble size decreases with increasing applied voltage and decreasing airflow rate. A dimensional analysis of the system parameters is also pursued. The dimensionless numbers are correlated into an empirical model that can be used for the prediction of the bubble size as a function of the applied voltage and airflow rate. It is found that the bubble size decreases with decreasing Reynolds number and increasing Weber number. Three different modes of bubble formation are observed: a spraying mode obtained at low airflow rate and high applied voltage, a dripping mode observed at high flow rate and low applied voltage, and a mixed spraying-dripping mode.

Won-Tae Shin

Papers

Ozonation using microbubbles formed by electric fields

A Pulseless Corona-Discharge Process for the Oxidation of Organic Compounds in Water

Pumping, spraying, and mixing of fluids by electric fields

Experiments on electrostatic dispersion of air in water

Kinetics of soil ozonation: an experimental and numerical investigation.