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

Plasma–liquid interactions represent a growing interdisciplinary area of research involving plasma science, fluid dynamics, heat and mass transfer, photolysis, multiphase chemistry and aerosol science. This review provides an assessment of the state-of-the-art of this multidisciplinary area and identifies the key research challenges. The developments in diagnostics, modeling and further extensions of cross section and reaction rate databases that are necessary to address these challenges are discussed. The review focusses on non-equilibrium plasmas.

/pdf/plasma-liquid-interactions-a-review-and-roadmap-4kfoerpjnh.pdf

Plasma-liquid interactions: A review and roadmap

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

The spectacular progress made during the last few years in reaching high energy densities in fast implosions of annular current sheaths (fast Z pinches) opens new possibilities for a broad spectrum of experiments, from x-ray generation to controlled thermonuclear fusion and astrophysics. Presently Z pinches are the most intense laboratory X ray sources (1.8 MJ in 5 ns from a volume 2 mm in diameter and 2 cm tall). Powers in excess of 200 TW have been obtained. This warrants summarizing the present knowledge of physics that governs the behavior of radiating current-carrying plasma in fast Z pinches. This survey covers essentially all aspects of the physics of fast Z pinches: initiation, instabilities of the early stage, magnetic Rayleigh-Taylor instability in the implosion phase, formation of a transient quasi-equilibrium near the stagnation point, and rebound. Considerable attention is paid to the analysis of hydrodynamic instabilities governing the implosion symmetry. Possible ways of mitigating these instabilities are discussed. Non-magnetohydrodynamic effects (anomalous resistivity, generation of particle beams, etc.) are summarized. Various applications of fast Z pinches are briefly described. Scaling laws governing development of more powerful Z pinches are presented. The survey contains 36 figures and more than 300 references.

/pdf/the-physics-of-fast-z-pinches-4lywwp72os.pdf

The physics of fast Z pinches

The propagation features of a streamer discharge in water have been investigated. Based on the experimental data obtained in the study of water discharges in a nonuniform electric field, due propagation of streamers is explained as the evaporation of water at the tip of the streamer and around it. The energy balance in the process of the streamer propagation is calculated for a sub-microsecond discharge in distilled water. It is shown that the energy released in the pre-breakdown process is sufficient to evaporate the liquid in the streamer channels. Similar velocity of the streamer propagation in both tap and distilled water substantiates negligible effect of ionic current density onto the streamer propagation process. These estimations, based on experiment, have relevance to the discussion of the nature of the dielectric breakdown of water.

Thermal processes in a streamer discharge in water

The drilling and demolition by low-duration, high-voltage electric pulses is based on the fact that, for very short times, the breakdown inside the solid dielectric occurs faster than the surface flashover benveen the electrodes. It was shown that most solid dielectrics could be broken down in insulating liquids, such as transformer oil, diesel fuel, and even in water. This study includes experimental and theoretical results on the drilling of rocks in insulating liquids, including transformer oil and diesel fuel.

Drilling of hard rocks by pulsed power

A mechanism explaining the breakdown of dielectrics with high intrinsic inhomogeneity like natural rocks and concrete is proposed and proved experimentally. This work has a very promising industrial application in the drilling and demolition of natural and artificial solid materials by electric pulses. The mechanism includes the breakdown of gas cavities inside the dielectric and on its surface. At a very high applied voltage, the high electric field causes the breakdown in the cavities. The displacement and conduction currents flowing through a number of such cavities result in the heating of the plasma and high pressure pulse generation. The pulsed pressure results in crack formation and finally, in the destruction of a solid material.

Breakdown and destruction of heterogeneous solid dielectrics by high voltage pulses

The streamer discharges are effectively used for biological and chemical cleaning of air and water. Uniform streamer discharges were obtained in water at pulsed electric loading. The volume of these discharges exceeds 400 cm3 and the energy delivered to the discharge reached 40–400 J depending on the applied voltage. The reliable and durable reactor for water treatment by pulsed streamer discharges is designed and tested. High voltage pulse amplitude applied to the reactor requires improved electric insulation to prevent flashover along the reactor surface both in water and air. High mechanical stress due to high discharge current adds the requirements to the mechanical durability of the system. A small-size reactor with the volume of approximately 1 l withstands successfully both high electrical and mechanical stresses. The reactor is designed for research purposes, however it can be upgraded to use in a high repetition-rate regime necessary for industrial applications.

Streamer discharge reactor for water treatment by pulsed power

There are various methods of rock drilling and demolition. Recently, a method utilizing pulsed power technology has appeared. This method is based on the difference of the dynamic breakdown field strength of liquid and solid dielectrics. The applicability of this method was examined. The features of the rock destruction have been studied. The mechanism explaining the breakdown of the dielectrics with high intrinsic inhomogeneity like natural rocks and concrete is proposed and proved experimentally. An inductive energy storage-opening switch system for the destruction of solid materials is designed allowing higher destruction efficiency. The experimental results using advanced diagnostics such as an image converter camera and X-ray computer tomography of samples are presented. High pulse energy experiments (up to 60 kT in pulse) have been conducted.

I.V. Lisitsyn

Papers

Thermal processes in a streamer discharge in water

Drilling of hard rocks by pulsed power

Breakdown and destruction of heterogeneous solid dielectrics by high voltage pulses

Streamer discharge reactor for water treatment by pulsed power

Drilling and demolition of rocks by pulsed power