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Jenista J.,Czech Institute of Plasma Physics
Plasma Chemistry and Plasma Processing | Year: 2017

Numerical modelling of physical properties and processes in an electric arc stabilized by a water vortex (steam torch) has been summarized in this review paper. One-fluid MHD equations are numerically solved for an axisymmetric thermal plasma flow inside a discharge chamber of the steam plasma torch. The steady state solution results are discussed for the range of currents 300–600 A with relatively low steam flow rate of about 0.3 g s−1. The maximum obtained velocities and temperatures—8500 m s−1, 26,300 K, are reported at the centre of the nozzle exit for 600 A. The evaporation of water, i.e. mass flow rate of steam, was predicted from a comparison between the present simulation and experiments. The generated plasma is mildly compressible (M < 0.7) with the inertial forces overwhelming the magnetic, viscous, centrifugal and Coriolis forces with the factor of 103. Our calculations showed that the most significant processes determining properties of the arc are the balance of the Joule heat with radiation and radial conduction losses from the arc. Rotation of plasma column due to the tangential velocity component has a negligible effect on the overall arc performance, however, the rotation of water induces fluctuations in the arc and in the plasma jet with characteristic frequency which is related to the frequency of rotation of water. Reabsorption of radiation occurs at the radial position higher than 2.5 mm from the arc axis. The amount of reabsorbed radiation is between 17 and 28%. LTE conditions are satisfied in the arc column with the 2 mm radius. Comparison between the present simulations and experiments shows good agreement with the current–voltage characteristics, radial velocity and temperature profiles, as well as with the other related numerical simulation. © 2017 Springer Science+Business Media New York

Gordillo-Vazquez F.J.,Institute Astrofisica Of Andalucia | Luque A.,Institute Astrofisica Of Andalucia | Simek M.,Czech Institute of Plasma Physics
Journal of Geophysical Research: Space Physics | Year: 2011

Spectra of sprite halos in the spectral ranges 200-500 nm and 640-1065 nm are calculated for different spectral resolutions (between 2 nm and 10 nm), rotational temperatures (220 K and 1000 K) and observation altitudes corresponding to mountain (3 km and 4.3 km), airplane (14 km), balloon (35 km) and space observation platforms. We have calculated the non-equilibrium vibrational distribution functions (VDF) of different excited electronic states of molecular nitrogen (N2) associated to sprite halo optical emissions in the ultraviolet (UV), due to the N2 Lyman-Birge-Hopfield (LBH) and Vegard-Kaplan (VK) band systems, and near UV, visible and near infrared (NIR) due to the first (1PG) and second positive (2PG) bands of N 2. Comparison of synthetic sprite halo spectra with the single sprite halo spectrum existing to date shows reasonable agreement after the observed sprite halo spectra was corrected for instrument sensitivity response. Calculated VDFs of the N2(B3 g) and N 2(C3 u) states of sprite halos show that the blue and NIR emissions produced through strong N2-1PG (B 3 g A3 u +) and N 2-2PG (C3 u B3 g) transitions are generally similar to those of known sprite spectral emission patterns, but differences may be observable at some vibrational levels. The calculated sprite halo spectra can be used as a predictive tool for the expected spectral emissions of sprite halos in different possible scenarios. Copyright 2011 by the American Geophysical Union.

Lukes P.,Czech Institute of Plasma Physics | Dolezalova E.,Czech Institute of Plasma Physics | Sisrova I.,Czech Institute of Plasma Physics | Clupek M.,Czech Institute of Plasma Physics
Plasma Sources Science and Technology | Year: 2014

The formation of transient species (OH·, NO2·, NO radicals) and long-lived chemical products (O3, H2O 2, NO3 -, NO2 -) produced by a gas discharge plasma at the gas-liquid interface and directly in the liquid was measured in dependence on the gas atmosphere (20% oxygen mixtures with nitrogen or with argon) and pH of plasma-treated water (controlled by buffers at pH 3.3, 6.9 or 10.1). The aqueous-phase chemistry and specific contributions of these species to the chemical and biocidal effects of air discharge plasma in water were evaluated using phenol as a chemical probe and bacteria Escherichia coli. The nitrated and nitrosylated products of phenol (4-nitrophenol, 2-nitrophenol, 4-nitrocatechol, 4-nitrosophenol) in addition to the hydroxylated products (catechol, hydroquinone, 1,4-benzoquinone, hydroxy-1,4-benzoquinone) evidenced formation of NO2·, NO· and OH·radicals and NO+ ions directly by the air plasma at the gas-liquid interface and through post-discharge processes in plasma-activated water (PAW) mediated by peroxynitrite (ONOOH). Kinetic study of post-discharge evolution of H 2O2 and NO2 - in PAW has demonstrated excellent fit with the pseudo-second-order reaction between H2O 2 and NO2 -. The third-order rate constant k = 1.1 × 103 M-2 s-1 for the reaction NO2 - + H2O2 + H+ → ONOOH + H2O was determined in PAW at pH 3.3 with the rate of ONOOH formation in the range 10-8-10-9 M s-1. Peroxynitrite chemistry was shown to significantly participate in the antibacterial properties of PAW. Ozone presence in PAW was proved indirectly by pH-dependent degradation of phenol and detection of cis,cis-muconic acid, but contribution of ozone to the inactivation of bacteria by the air plasma was negligible. © 2014 IOP Publishing Ltd.

Stelmashuk V.,Czech Institute of Plasma Physics
IEEE Transactions on Plasma Science | Year: 2014

Time-resolved observation of an electrical discharge in water using high-speed camera is presented. The discharge is generated in a pin to pin geometry with shock wave assistance. The shock wave generates cavitation bubbles that enhance the discharge. The initiation and growth of streamers are observed. An electric spark is generated as a result of one of the streamer reaching a counter electrode. © 2014 IEEE.

Stelmashuk V.,Czech Institute of Plasma Physics
IEEE Transactions on Plasma Science | Year: 2014

An experimental investigation has been conducted to study the morphology of electrical discharge performed in a plate-to-plate configuration. An electrical breakdown in the plate-to-plate configuration is generally difficult to produce because of a weak uniform electric field in the interelectrode region. The electrical discharge is generated when a shock wave is used. It generates a number of cavitation bubbles, which serve as locations for the streamers growth. Time-resolved observation of the electrical discharge in plate-to-plate configuration using high-speed camera is presented. © 2014 IEEE.

Dolezalova E.,Czech Institute of Plasma Physics | Lukes P.,Czech Institute of Plasma Physics
Bioelectrochemistry | Year: 2015

Electrical discharge plasmas can efficiently inactivate various microorganisms. Inactivation mechanisms caused by plasma, however, are not fully understood because of the complexity of both the plasma and biological systems. We investigated plasma-induced inactivation of Escherichia coli in water and mechanisms by which plasma affects bacterial cell membrane integrity. Atmospheric pressure argon plasma jet generated at ambient air in direct contact with bacterial suspension was used as a plasma source. We determined significantly lower counts of E. coli after treatment by plasma when they were assayed using a conventional cultivation technique than using a fluorescence-based LIVE/DEAD staining method, which indicated that bacteria may have entered the viable-but-nonculturable state (VBNC). We did not achieve resuscitation of these non-culturable cells, however, we detected their metabolic activity through the analysis of cellular mRNA, which suggests that cells may have been rather in the active-but-nonculturable state (ABNC). We hypothesize that peroxidation of cell membrane lipids by the reactive species produced by plasma was an important pathway of bacterial inactivation. Amount of malondialdehyde and membrane permeability of E. coli to propidium iodide increased with increasing bacterial inactivation by plasma. Membrane damage was also demonstrated by detection of free DNA in plasma-treated water. © 2014 Elsevier B.V.

Stelmashuk V.,Czech Institute of Plasma Physics
Physics of Plasmas | Year: 2014

When a high voltage pulse with an amplitude of 30 kV is applied to a pair of disk electrodes at a time when a shock wave is passing between them, an electrical spark is generated. The dynamic changes in the spark morphology are studied here using a high-speed framing camera. The primary result of this work is the provision of experimental evidence of plasma instability that was observed in the channel of the electric spark. © 2014 AIP Publishing LLC.

Simek M.,Czech Institute of Plasma Physics
Journal of Physics D: Applied Physics | Year: 2014

This paper reviews optical diagnostic methods and approaches applied to study the fundamentals of streamer discharges, considering the peculiarities of streamers developing in atmospheric gases at high (1 bar) as well as low (<10 mbar) pressures. A critical discussion is devoted to the cross-sections for electron-impact excitation/ionization/dissociation processes and corresponding rate constants in relation to methods used to probe streamer properties. The most important spectrometric signatures of radiative transitions of diatomic as well as atomic species are discussed on the basis of their synthetic models with a brief guide on how to simulate the most important emissions. Basic differences between UV-vis-NIR spectra produced by electron-impact and various heavy-particle energy-transfer processes during streamer evolution are presented and possible strategies based on 2D projections of cylindrically symmetric streamers to determine radial distributions of excited species within the streamer channel are discussed. The use of emission techniques to obtain the rotational temperatures and vibrational distributions of excited states of diatomics and laser-induced fluorescence techniques to probe the vibrational manifold of the lowest triplet metastable state of the nitrogen molecule is addressed. © 2014 IOP Publishing Ltd.

Stelmashuk V.,Czech Institute of Plasma Physics
IEEE Transactions on Plasma Science | Year: 2016

In this paper, a new method of generation of an electrical discharge in water using plate electrodes is proposed. The electrical discharge in plate-to-plate configuration cannot be easily generated because of a low uniform electrical field. A nitrogen bubble is injected into one of the electrodes to create a favorable condition for electrical breakdown. The generated electrical discharge is studied using a high-speed framing camera. Two interesting effects have been observed. First, the discharge is preferentially initiated on the cathode. Second, the positive streamer reveals nontypical morphology. The physical mechanisms of discharge initiation and positive streamer propagation are discussed. © 1973-2012 IEEE.

Ctibor P.,Czech Institute of Plasma Physics | Hrabovsky M.,Czech Institute of Plasma Physics
Journal of the European Ceramic Society | Year: 2010

The influence of input power on sprayed powder and final coating was quantified for a water-stabilized plasma spray torch (WSP®) and ceramic coating formed from titanium dioxide (TiO2). All other spray setup parameters were secured during the experiment with electric supply power as the only variable factor. In-flight particles were characterized by a Doppler particle velocimetry, the microstructure of the coatings was observed by microscopic techniques with computer image analysis, and phase composition was studied by X-ray diffraction. Various mechanical properties were measured - microhardness, surface roughness, and wear resistance in a slurry. Also other particular physical characteristics of the coatings - reflectivity and bandgap energy - were observed in their dependence on the supply power because they are associated with applications of the coatings. The higher the power the higher the coating quality will be: both its microstructure and mechanical performance. This substantial difference has the same trend for both power supplies utilized for the testing. © 2010 Elsevier Ltd.

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