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DYNAMICS OF ACCELERATING STREAMER IN BARRIER DISCHARGE IN AIR.
Hoder, T.; Bonaventura, Z.; Prukner, Václav; Šimek, Milan
2016 - English
An accelerating streamer in barrier discharge is generated in 10 torr pressure air. Using the complex voltage waveform, the stable and reproducible discharge is triggered. From the ratio of two spectral bands of molecular nitrogen the electric field is determined in 2D. These results are well resolved in time and space thus suitable as a benchmark for computation of the streamer initiated plasma-chemistry in air.
Keywords:
streamer; air; electric field
Available at various institutes of the ASCR
DYNAMICS OF ACCELERATING STREAMER IN BARRIER DISCHARGE IN AIR.
An accelerating streamer in barrier discharge is generated in 10 torr pressure air. Using the complex voltage waveform, the stable and reproducible discharge is triggered. From the ratio of two ...
Arc–Anode Attachment Area in DC Arc Plasma Torch at Low Pressure
Ondáč, Peter; Mašláni, Alan; Hrabovský, Milan
2016 - English
Studying the processes in the anode attachment area of a DC arc plasma torch helps to extend the lifetime of the anode, stabilize the plasma flow for plasma spraying and better understand the movement of the anode attachment. In this work, such processes were studied at low pressure, by a non-disturbing method, using a high-speed camera and a high voltage probe. We also found pressure ranges, in which the following transitions were observed: the constricted/diffuse anode attachment, and subsonic/supersonic plasma jet\n
Keywords:
Arc Plasma Torch; Arc–Anode Attachment; Low Pressure
Available at various institutes of the ASCR
Arc–Anode Attachment Area in DC Arc Plasma Torch at Low Pressure
Studying the processes in the anode attachment area of a DC arc plasma torch helps to extend the lifetime of the anode, stabilize the plasma flow for plasma spraying and better understand the movement ...
Infrared measurements in medium and long wavelength on COMPASS
Vondráček, Petr; Horáček, Jan; Pánek, Radomír; Gauthier, E.
2016 - English
The experimental study of radial profiles of parallel heat flux in the scrape-off layer (SOL) of the COMPASS tokamak shows a systematic discrepancy between medium (MWIR) and long (LWIR) wavelength infrared (IR) thermographic measurements. Significant temperature and heat flux overestimation is observed in the MWIR range, whilst the LWIR range is almost not affected. It is assumed to be caused by a presence of dust particles creating sub-pixel sized micro hot-spots. Significant inhomogeneity of the surface conditions across the limiter is observed, resulting in local disturbance of the derived heat flux profiles (decay length variation up to ~ few tens of percent). Influence of the inhomogeneously distributed micro hot-spots is suppressed using correction factors (the heat transmission coefficient α) for each pixel separately in the heat flux calculation. Procedure of the α coefficient estimation is described.
Keywords:
IR; MWIR; LWIR; Dust; COMPASS; SOL
Available at various institutes of the ASCR
Infrared measurements in medium and long wavelength on COMPASS
The experimental study of radial profiles of parallel heat flux in the scrape-off layer (SOL) of the COMPASS tokamak shows a systematic discrepancy between medium (MWIR) and long (LWIR) wavelength ...
Photocatalytic Decomposition of Wastewater from the Production of Explosives
Brom, Petr; Brožek, Vlastimil; Březina, Václav; Hlína, Michal; Mastný, L.; Novák, M.
2016 - English
Water stabilized plasma generator WSP® H-500, operating on the principle of Gerdien arc was used for the photocatalytic decomposition of furazan- and picraminate-based explosives. The generator emits intensive radiation in the range of 300-660 nm, which allows not only to activate photocatalysts based on TiO2, but also other semiconductor oxides with a narrower band gap, such as tungsten oxide. The photocatalytic decomposition of sewage and slurries containing the potassium salt of 4-hydroxy-4,6-dihydro-5,7- dinitrobenzofurazane-3-oxide (KDNBF) or sodium picraminate (NaC6H4N3O5) was performed using the anatase paste and newly developed photocatalyst produced by the company Precheza a.s. The photocatalytic reactor was built using a quartz tube coil with an internal volume of 650 ml, with a nominal size of the irradiated area of 7.5 dm2 (value reduced by the area of the gaps between coil turns) to enable the flow the processing solution or suspension of up to 10 l / min. The centre of the coil is exposed to the plasma jet with the intensity\nof 80 kW; of which 15 kW is transformed into the light radiation. 11% of the radiation output was used for the presented experiments. The time of exposition was 45 mins and 20 l of solution were treated. In the case of KDNBF, 90% of the compound was decomposed. Moreover, 100% of sodium picraminate were decomposed after 15 minutes into low-molecular inorganic compounds. Advantage of the assembly is the ability to treat highly dangerous chemical compounds in a closed cycle and test selective catalyst
Keywords:
plasma generator; photocatalytic decomposition; sodium picraminate; dinitrobenzofurazane
Available at various institutes of the ASCR
Photocatalytic Decomposition of Wastewater from the Production of Explosives
Water stabilized plasma generator WSP® H-500, operating on the principle of Gerdien arc was used for the photocatalytic decomposition of furazan- and picraminate-based explosives. The generator emits ...
COMPARISON OF S-CO2 POWER CYCLES FOR NUCLEAR ENERGY
Veselý, L.; Dostál, V.; Entler, Slavomír
2016 - English
The supercritical carbon dioxide (S-CO2) is a possible cooling system for the new generations of nuclear reactors and fusion reactors. The S-CO2 power cycles have several advantages over other possible coolants such as water and helium. The advantages are the compression work, which is lower than in the case of helium, near the critical point and the S-CO2 is more compact than water and helium. The disadvantage is so called Pinch point which occurs in the regenerative heat exchanger. The pinch point can be eliminated by an arrangement of the cycle or using a mixture of CO2. This paper describes the S-CO2 power cycles for nuclear fission and fusion reactors.
Keywords:
S-CO2; power cycle; fusion
Available at various institutes of the ASCR
COMPARISON OF S-CO2 POWER CYCLES FOR NUCLEAR ENERGY
The supercritical carbon dioxide (S-CO2) is a possible cooling system for the new generations of nuclear reactors and fusion reactors. The S-CO2 power cycles have several advantages over other ...
ELECTRON BEAM REMELTING OF PLASMA SPRAYED ALUMINA COATINGS
Matějíček, Jiří; Veverka, J.; Čížek, J.; Kouřil, J.
2016 - English
Plasma sprayed alumina coatings find numerous applications in various fields, where they enhance the properties of the base material. Examples include thermal barriers, wear resistance, electrical insulation, and diffusion and corrosion barriers. A typical structure of plasma sprayed coatings, containing a multitude of voids and imperfectly bonded interfaces, gives them unique properties - particularly low thermal conductivity, high strain tolerance, etc. However, for certain applications such as permeation barriers or wear resistance, these voids may be detrimental.\nThis paper reports on the first experiments with remelting of plasma sprayed alumina coatings by electron beam technology, with the purpose of densifying the coatings and thereby eliminating the voids. Throughout the study, several parameters of the e-beam device were varied - beam current, traverse velocity and number of passes. The treated coatings were observed by light and electron microscopy and the thickness, structure and surface morphology of the remelted layer were determined and correlated with the process parameters. Based on the first series of experiments, the e-beam settings leading to dense and smooth remelted layer of sufficient thickness were obtained. In this layer, a change of phase composition and a marked increase in hardness were observed.\n
Keywords:
Plasma sprayed coating; alumina; electron beam; remelting; post-treatment
Available at various institutes of the ASCR
ELECTRON BEAM REMELTING OF PLASMA SPRAYED ALUMINA COATINGS
Plasma sprayed alumina coatings find numerous applications in various fields, where they enhance the properties of the base material. Examples include thermal barriers, wear resistance, electrical ...
Evolution of Point-To-Plane Nanosecond Discharge in Deionized Water
Šimek, Milan; Pongrác, Branislav; Člupek, Martin; Babický, Václav; Lukeš, Petr
2016 - English
We employed techniques of time-resolved ICCD microscopy and spectroscopy to register basic morphologic and emission fingerprints of micro-discharges produced in deionized water. Fast risetime high-voltage pulses (duration of 5 ns and amplitude of ~110 kV) applied in a point-to-plane electrode geometry produced micro-discharges either periodically or in a single-shot regime. Time resolved ICCD images evidence typical streamer-like branched filamentary morphology while emission spectra show a broad-band continuum evolving during the first few nanoseconds followed by the well-known HI/OI atomic lines (tens of ns).
Keywords:
nanosecond discharge; water; ICCD imaging
Available at various institutes of the ASCR
Evolution of Point-To-Plane Nanosecond Discharge in Deionized Water
We employed techniques of time-resolved ICCD microscopy and spectroscopy to register basic morphologic and emission fingerprints of micro-discharges produced in deionized water. Fast risetime ...
THE INVESTIGATION OF AN Al7075 ALLOY PREPARED BY SPARK PLASMA SINTERING OF MILLED POWDERS
Molnárová, O.; Málek, P.; Nemeth, G.; Kozlík, J.; Lukáč, František; Chráska, Tomáš; Cinert, Jakub
2016 - English
Atomized powder of an Al7075 alloy was high energy ball milled at room and cryogenic temperatures and compacted by spark plasma sintering (SPS) method. The influence of processing parameters on phase composition and microstructure was studied by X-ray diffraction, light and scanning electron microscopy. The mechanical properties were characterized by microhardness measurements. The atomized powder contained a large volume fraction of intermetallic phases located predominantly in continuous layers separating cells or dendrites in the interior of individual powder particles. Consolidation by SPS destroyed partially this morphology and replaced it by individual particles located at boundaries of original powder particles, at cell boundaries or arranged in chains in previous dendritic regions. High energy milling destroyed most intermetallic particles and enriched the matrix by solute atoms. The high deformation energy introduced into the powder during milling enhanced microhardness up to 220 HV. Consolidation of milled powders by SPS led to the formation of very fine-grained structure with the grain size even below 1 μm and with the fraction of high-angle boundaries about 0.9. Two main types of heterogeneously distributed precipitates were found. The irregularly shaped precipitates with a size about 1 μm seemed to encompass areas with rod like nano-precipitates in most samples. A drop in microhardness to 118HV was observed after SPS, predominantly due to a release of introduced deformation energy.
Keywords:
Cryo-milling; Spark plasma sintering; Ultrafine-grained materials; Milling
Available at various institutes of the ASCR
THE INVESTIGATION OF AN Al7075 ALLOY PREPARED BY SPARK PLASMA SINTERING OF MILLED POWDERS
Atomized powder of an Al7075 alloy was high energy ball milled at room and cryogenic temperatures and compacted by spark plasma sintering (SPS) method. The influence of processing parameters on phase ...
ATMOSPHERIC JET BASED ON SURFACE STREAMER DIELECTRIC BARRIER DISCHARGE
Šimek, Milan; Prukner, Václav
2016 - English
We designed novel axisymmetric atmospheric jet formed by effluents produced by surface streamers suitable for various applications. Filamentary streamers are produced by the amplitude-modulated AC surface dielectric barrier discharge. The SDBD-based jet makes use of the tangential injection of the working gas into a cylindrical chamber that induces a fast vortex flow through the discharge zone and expells excited/ionized/reactive species out of the discharge area through the axial orifice in the form of a jet spinning around its axis. The jet may be easily used to treat surfaces, expose biological samples or even be injected in liquids.
Keywords:
atmospheric pressure; jet; surface barrier discharge
Available at various institutes of the ASCR
ATMOSPHERIC JET BASED ON SURFACE STREAMER DIELECTRIC BARRIER DISCHARGE
We designed novel axisymmetric atmospheric jet formed by effluents produced by surface streamers suitable for various applications. Filamentary streamers are produced by the amplitude-modulated AC ...
Synthesis and applications of Intermetallics
Novák, P.; Salvetr, P.; Kříž, J.; Kubatík, Tomáš František
2015 - English
Intermetallic compounds, intermetallics, are characterized by interesting properties, such as e.g. excellent high -temperature oxidation resistance, shape memory or ability to store hydrogen reversibly. Their positive, but also negative, properties are a combination of the behaviour of metals and ceramics. Their wider application in industry is limited due to low room-temperature ductility and problematic production, associated with high melting points of many intermetallics, high reactivity of metals at high temperatures and problematic processing. In this paper, the overview of the methods for synthesis of intermetallic compounds is presented, ranging from conventional casting processes to modern powder metallurgy technologies. Selected interesting applications from industry and medicine, where their unique properties are used
Keywords:
Intermetallic compounds; powder metallurgy technologies
Fulltext is available at external website.
Synthesis and applications of Intermetallics
Intermetallic compounds, intermetallics, are characterized by interesting properties, such as e.g. excellent high -temperature oxidation resistance, shape memory or ability to store hydrogen ...
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