Vaclav Babicky

Generation of ozone by pulsed corona discharge over water surface in hybrid gas–liquid electrical discharge reactor

Ozone formation by a pulse positive corona discharge generated in the gas phase between a planar high voltage electrode made from reticulated vitreous carbon and a water surface with an immersed ground stainless steel plate electrode was investigated under various operating conditions. The effects of gas flow rate (0.5–3 litre min−1), discharge gap spacing (2.5–10 mm), applied input power (2–45 W) and gas composition (oxygen containing argon or nitrogen) on ozone production were determined. Ozone concentration increased with increasing power input and with increasing discharge gap. The production of ozone was significantly affected by the presence of water vapour formed through vaporization of water at the gas–liquid interface by the action of the gas phase discharge. The highest energy efficiency for ozone production was obtained using high voltage pulses of approximately 150 ns duration in Ar/O2 mixtures with the maximum efficiency (energy yield) of 23 g kW h−1 for 40% argon content.

Ultraviolet radiation from the pulsed corona discharge in water

Quantitative analysis of ultraviolet radiation from the pulsed corona discharge in water with needle-plate electrode geometry (~1?3?J?pulse?1) was performed using the potassium ferrioxalate actinometry. Photon flux J190?280 and radiant energy Q190?280 of the UV light emitted from the discharge at spectral region 190?280?nm was determined in dependence on the applied voltage (17?29?kV, positive polarity) and the solution conductivity (100?500??S?cm?1). The intensity of the UV radiation strongly increased with increasing water conductivity and applied voltage. Depending on the applied voltage the determined photon flux varied by more than two orders of magnitude within the range of solution conductivities 100?500??S?cm?1. It was found that photon flux from the discharge may be directly related to the discharge pulse mean power Pp as J190?280 = 44.33 (quanta?pulse?1). A significant role of UV radiation in the production of hydrogen peroxide and bacterial inactivation by the corona discharge in water has been identified. As the solution conductivity increased the yield of H2O2 produced by the discharge decreased due to increasing photolysis of H2O2 accounting for up to 14% of the total decomposition rate of H2O2. As regards bactericidal effects, it was estimated that the UV radiation contributes about 30% to the overall inactivation of Escherichia coli.

Pulsed Electrical Discharge in Water Generated Using Porous-Ceramic-Coated Electrodes

A special metallic electrode covered by a thin layer of porous ceramic prepared by the technology of thermal plasma spraying has been developed and used for the generation of large-volume nonthermal plasma in water. Images of multichannel pulsed electrical discharge generated in water at the composite electrode as a function of solution conductivity are presented.

Localized damage of tissues induced by focused shock waves

A novel method for generation of focused shock waves has been developed. A cylindrical pressure wave, created by a high-voltage multichannel discharge in water with an increased electrical conductivity, is focused by a metallic parabolic reflector. The discharge is formed on a composite anode consisting of a cylindrical stainless steel electrode covered by a thin porous ceramic layer. In such an arrangement at the applied voltage of 30 kV, a large number of short discharge channels distributed homogeneously on the anode surface is initiated. Each discharge channel creates a semi-spherical pressure wave, and by superposition of all of the waves, a cylindrical pressure wave propagating from the anode is formed. The cylindrical pressure wave is focused by a metallic parabolic reflector (cathode) and near the focus it is transformed into a strong shock wave. The focal volume is 2.5 mm in diameter and 32 mm long. We have demonstrated that the focused shock waves destroy human red blood cells (erythrocytes) very efficiently. Interaction of the focused shock waves with fresh potatoes that have high water content have been used to assess the mechanical effects of the waves. The 6-cm-thick slab of potato was placed next to the focal region and exposed to 10 shocks at 30 kV. The experiment demonstrated that only the focal region inside the potato had been damaged and no damage was seen between the potato surface and the focal region. Local injury of animal liver tissues exposed to the shock waves were observed in vitro. Livers of three rabbits have been exposed in vivo. Histological analysis of the exposed tissues revealed injuries and hemorrhages at the focal region of the shock waves.

Discharge Filamentary Patterns Produced by Pulsed Corona Discharge at the Interface Between a Water Surface and Air

Pulsed corona discharge in atmospheric air was generated above a water surface using a reticulated vitreous carbon planar electrode. The effects of the discharge gap spacing and solution conductivity on the characteristics of the discharge were studied. Images of the discharge filamentary patterns propagating over the water surface are presented.

The catalytic role of tungsten electrode material in the plasmachemical activity of a pulsed corona discharge in water

The effects of tungsten material used as a high-voltage needle electrode on the production of hydrogen peroxide and the degradation of dimethylsulfoxide (DMSO) caused by a pulsed corona discharge in water were investigated. A reactor of needle?plate electrode geometry was used. The erosion of the tungsten electrodes by the discharge was evaluated. The yields of H2O2 production and the decomposition of DMSO by the discharge, which were obtained using the tungsten electrodes, were compared with those determined for titanium electrodes. The electrode erosion increased significantly with an increase in the solution conductivity. A large fraction (50?70%) of the eroded tungsten electrode material was released into the solution in dissolved form as tungstate ions. A correlation between the amount of eroded tungsten material released into the solution and the chemical effects induced by the discharge was determined. Lower yields of H2O2 and a higher degradation of DMSO by the discharge were obtained using the tungsten electrodes than were determined using titanium electrodes. Tungstate ions were shown to play a dominant role in the decomposition of H2O2, which was produced by the discharge using a tungsten electrode. The higher degradation of DMSO that was determined for tungsten was attributed to the tungstate-catalyzed oxidation of DMSO by H2O2, in addition to the oxidation of DMSO by OH radicals. Such a mechanism was supported by the detection of degradation by-products of DMSO (methanesulfonate, sulfate and dimethyl sulfone). The catalytic role of tungstate ions in the plasmachemical activity of the discharge generated using a tungsten electrode was also demonstrated on a pH-dependent decomposition of H2O2 and DMSO.

Pressure distribution measurements at the shock wave focus in water by schlieren photography (kidney/gall stone lithotripsy)

A shock wave in water was generated by an electric spark in the first focus of a truncated ellipsoidal reflector. From schlieren pictures of the reflector second focus region, taken at the moment the shock wave has reached it, radial pressure profiles of the focused shock wave were evaluated. The accuracy of the method used was tested by ray tracing through a semi-spherical layer inhomogeneity and by inverse reconstruction of the refractive index. The method was found to be useful for a qualitative indication of the pressure distribution at the second focus but laborious and inaccurate for a quantitative evaluation of the pressure.

Bacterial Inactivation by Pulsed Corona Discharge in Water

The decontamination effect of underwater pulsed corona discharge on gram-negative bacteria Escherichia coli and gram-positive bacteria Enterococus faecalis has been investigated. The reactor of needle-plate electrode geometry was used. The concentration of both types of bacteria decreased exponentially with increasing discharge treatment time and supplied energy input. The contribution of UV radiation and hydrogen peroxide in the overall bacterial inactivation efficiency of the discharge has been determined. UV light emitted from the discharge plasma channels was found to have significant effect on the bacterial inactivation and its contribution was estimated to be about 30%. Effect of hydrogen peroxide was small, however, under influence of high electric field its lethal activity was greatly enhanced.

Determination of electrical characteristics of nanosecond discharge in liquid

Method of determining nanosecond pulse parameters and energy deposited to the nanosecond discharge in liquids using back current shunt mounted in the middle of the supply coaxial cable is presented. A simple simulation of the discharge chamber circuit with respect to the parasitic impedances was performed for better understanding of the shape of the reflected pulse and to verify limitations of this method.

Bipolar High Voltage Pulse Power Generator

Bipolar high voltage pulse power generator is a device that generates alternately positive and negative pulses of the same amplitude and waveform. It consists of a variable high voltage DC source, a rotating spark gap and a low inductance capacitor. The spark gap allows switching both the charging and discharging phases of the capacitor into the load. The time delay between positive and negative pulses is one half of the repetition period, which is controlled by revolutions of the rotating spark gap. The amplitude of output voltage pulses can be varied up to 35 kV with the repetition frequency up to 100 Hz. Shape of output pulse is determined by used capacitor and the load value. For typical parameters (capacitor 14 nF, average load value ~100 Omega) pulses with exponential slope, rise time 40 ns and pulse duration ~3 mus are generated. The potential applications of such system include in particular generation of the pulse electrical discharges in the liquid phase. This paper describes design and performance of the bipolar high voltage pulse power generator. The high voltage measurements of the generator output pulsed into resistive load are presented and compared with the results of circuit simulations.