Atmospheric Pressure Humid Argon DBD Plasma for the Application of Sterilization - Measurement and Simulation of Hydrogen, Oxygen, and Hydrogen Peroxide Formation

Hydrogen, oxygen, and hydrogen peroxide have been measured downstream of an atmospheric pressure humid argon dielectric barrier discharge. The yield of the three species was studied as a function of the discharge power and gas flow rate. Hydrogen peroxide was measured after dissolution into water downstream of the discharge, while hydrogen and oxygen were measured in the gas phase. The production rates of both hydrogen and oxygen were found to be at least one order of magnitude greater than that of hydrogen peroxide. In all cases, the molar rate of molecular hydrogen production was more than twice that of molecular oxygen. At various total gas flow rate, and over a range of energy density of 0 to 1500 J/L, the concentration of hydrogen found at the reactor outlet varied from 0 to 1000 ppm, while oxygen reached a maximum concentration of about 400 ppm. The corresponding concentration of hydrogen peroxide that was calculated to have been in the reactor outlet gas did not exceed 11 ppm. Mechanisms for this system based on experiments and a numerical model are presented. The results of experiments on the use of post-discharge effluent gas of humid argon plasma for sterilization purposes (inactivation of E. Coli) bacteria are also presented and discussed in relation to the results of the chemical measurements and simulations

CHARACTERIZATION OF MEDIUM VOLTAGE EQUIPMENT AGEING BY MONITORING OF PARTIAL DISCHARGES CHEMICAL AND ACOUSTICAL EMISSION

International audienceDuring the ageing of in service medium voltage equipments, electrical losses are mainly due to partial discharges. These partial discharges can lead to the electrical failure of industrial equipments. Partial discharges include (i) bulk discharges occurring in insulating material voids, (ii) corona discharges affecting or not the insulator and (iii) surface discharges developing on an insulator surface from a triple point (conductor/insulating material/air). Bulk and surface discharges can respectively lead to a final volume or surface breakdown whereas corona discharges may only induce in a long term chemical surface ageing. Surface discharges and corona discharges produce chemical species in atmospheric air, i.e. ozone and nitrogen oxides. These products can be identified and quantified by a periodic sampling of the ambient air in the medium voltage equipment enclosure during accelerated ageing cycles. In previous studies, it was demonstrated that the nature and relative distribution of concentration of these stable gaseous products was closely correlated to the discharge regime (glow, streamer, spark regimes). Measurements have been carried out on a distribution cell and transformer using low cost electrochemical and semi conductive sensors; acoustic measurements were simultaneously performed. It is shown that gas discharges can be detected within a few minutes from their onset. The discharge regime can also be characterized thanks to the specific detection of nitrogen oxides while low regime corona discharges are simultaneously occurring. The change in the surface discharge regime is evidence of accelerated insulator surface ageing (risks of surface breakdown) ; equipment enclosure ambient air sampling can then be an accurate method for determination of the state of health of this type of equipment

BIOLOGICAL APPLICATIONS OF ATMOSPHERIC PRESSURE DIELECTRIC BARRIER DISCHARGES

International audienceA reduction of more than 4 orders of magnitude of survivors was obtained by exposing a Bacillus Stearothermophilus spores - contaminated surface to an atmospheric pressure DBD post-discharge for 20 minutes. Decontamination mechanisms are investigated assuming that (i) inactivation is obtained when the bacteria DNA is fragmented, (ii) the protein coats are the main protection of the cell core DNA in the case of bacteria spores. The degradation of DNA (plasmid) and protein (RNAse A) samples submitted to the postdischarge is evaluated according to the operating conditions: gas composition, treatment time and sample state, i.e. hydrated or dried samples

CURRENT DISTRIBUTION OF AC SURFACE DISCHARGES AND ASSOCIATED CHEMISTRY

It is shown that ac discharges propagating at an air / dielectric interface, though of planar structure, behave, till a critical voltage Vcrit, as corona discharges in an air gap, with similar propagation fields for the filamentary discharge components and similar glow components. This leads to consider the surface discharges as gas discharges propagating above the dielectric surface. Beyond Vcrit, the retention of charges by the dielectric surface becomes ineffective, due to the gas heating in the filamentary channels and to the heat subsequently transferred from these channels to the surface. In return, the surface gives its energy excess back to the discharge, so opening the way, on the surface, to leader-like discharges of higher conductivity, needing about 10 times lower fields to propagate

RADIATION KINETICS AND CHEMICAL REACTIVITY OF BARRIER DISCHARGES IN HUMID ARGON

International audienceThe technique of spatially resolved cross-correlation spectroscopy was used to record two-dimensional luminosity distributions for the selected spectral bands of molecular nitrogen (λ=337.1 nm), OH-radical (λ=308 nm), and two spectral lines of excited Ar (λ=750.4 nm and λ=763.5 nm) emitted by the microdischarges of the barrier discharge in flowing humid argon at atmospheric pressure. Concentrations of two stable reaction products of H2O decomposition (H2 and O2) in argon plasma were determined experimentally as functions of humidity. Comparison of these results with the corresponding measurements of radiation kinetics permitted a detailed analysis of the influence of the discharge mechanism on its chemical reactivity in humid argon to be accomplished

A new discriminating high temperature fission chamber filled with xenon designed for sodium-cooled fast reactors

Xenon high temperature fission chamber, designed for sodium-cooled fast reactors, unlike the argon filled fission chambers, can operate at temperatures greater than 500◦C without partial-discharges and discriminate neutrons and partial-discharges at temperatures up to 650◦C

Paschen’s law in extreme pressure and temperature conditions

Paschen’s law gives the inception voltage for an electrical discharge as a function of the product of gas pressure and the gap distance between two infinite planar electrodes. It is known that deviations from Paschen’s law occur when temperature is increased. Historically two theoretical corrections, the Peek and Dumbar corrections, are proposed to predict the deviation from Paschen’s law by increasing temperature. To carry out an experimental investigation on the deviation from Paschen’s law by increasing temperature a customized system was designed which can operate at temperatures up to 400°C and at pressure up to 1MPa, calculated at room temperature; with an inter-electrode distance between 100μm and 6.6mm and with an error on the inter-electrode distance measurement of 20μm. In this article, firstly, the results from the experimental investigation on the deviation from Paschen’s law at temperature up to 400°C are presented. The results are then compared with theoretical corrections, and finally a theory to explain the results is proposed and discussed

Characterization and localization of partial-discharge-induced pulses in fission chambers designed for sodium-cooled fast reactors

During the operation of the Superphenix and Phenix reactors, an aberrant electrical signal was detected from the fission chambers used for neutron flux monitoring. This signal, thought to be due to partial electrical discharge (PD) is similar to the signal resulting from neutron interactions, and is generated in fission chambers at temperatures above 400°C. This paper reports work on the characterization and localization of the source of this electrical signal in a High Temperature Fission Chamber (HTFC). The dependence of the shape of the PD or neutron signal on the various experimental parameters (nature and pressure of the chamber filling gas, electrode gap distance, and fission chamber geometry) are described. Next, experiments designed to identify the location within the chambers where the PD are being generated are presented in way to propose changes to the fission chamber in order to reduce or eliminate the PD signal

Propriétés physicochimiques de décharges électriques à pression atmosphérique. Application à la décontamination biologique de surface.

La recherche menée depuis la thèse porte sur l'étude des dispositifs à décharges électriques produisant un plasma froid à pression atmosphérique. L'approche choisie est essentiellement expérimentale, traitant à la fois des aspects fondamentaux et des perspectives applicatives. Le domaine d'application choisi est celui de l'environnement et de la sécurité sanitaire. En effet, les technologies plasma froid constituent une réponse innovante pour la réduction du risque chimique (émissions toxiques dans l'atmosphère) et du risque biologique (infections nosocomiales). La recherche portant sur la conception et l'étude de procédés plasma froid dédiés à ces applications a été menée au cours de ce travail dans un contexte international compétitif, ces thèmes constituant actuellement les deux axes majeurs de recherche dans le domaine des plasmas froids. Deux types d'applications ont été, et sont toujours actuellement développées : la décontamination biologique de surface et le traitement d'effluents gazeux de combustion. Par ailleurs, ces deux axes d'application reposent sur une connaissance approfondie des propriétés physicochimiques des décharges électriques à pression atmosphérique, développée grâce à des études « amont » et transverses effectuées au cours de deux thèses encadrée et/ou dirigée

Atmospheric pressure argon-based discharges for surface decontamination purposes

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