Simulation of the discharge propagation in a capillary tube in air at atmospheric pressure

International audienceThis paper presents simulations of an air plasma discharge at atmospheric pressure initiated by a needle anode set inside a dielectric capillary tube. We have studied the influence of the tube inner radius and its relative permittivity ε r on the discharge structure and dynamics. As a reference, we have used a relative permittivity ε r = 1 to study only the influence of the cylindrical constraint of the tube on the discharge. For a tube radius of 100 µm and ε r = 1, we have shown that the discharge fills the tube during its propagation and is rather homogeneous behind the discharge front. When the radius of the tube is in the range 300 to 600 µm, the discharge structure is tubular with peak values of electric field and electron density close to the dielectric surface. When the radius of the tube is larger than 700 µm, the tube has no influence on the discharge which propagates axially. For a tube radius of 100 µm, when ε r increases from 1 to 10, the discharge structure becomes tubular. We have noted that the velocity of propagation of the discharge in the tube increases when the front is more homogeneous and then, the discharge velocity increases with the decrease of the tube radius and ε r. Then, we have compared the relative influence of the value of tube radius and ε r on the discharge characteristics. Our simulations indicate that the geometrical constraint of the cylindrical tube has more influence than the value of ε r on the discharge structure and dynamics. Finally, we have studied the influence of photoemission processes on the discharge structure by varying the photoemission coefficient. As expected, we have shown that photoemission, as it increases the number of secondary electrons close to the dielectric surface, promotes the tubular structure of the discharge

Removal of pollutants by plasma catalytic processes

Removal of molecular atmospheric pollutants by non-thermal plasmas is under study since the beginning of the eighties. It has been shown that pulsed electrical discharges, such as dielectric barrier or corona discharges, are powerful means to eliminate Volatile Organic Compounds (VOCs) from the ambient air, or to treat flue gases which contain nitrogen oxide. However it is now recognised that, for several pollutants, the use of the plasma alone does not allow a complete elimination of the undesirable molecule. For example NO is oxidised in the air plasma to form other oxides like NO2 and N2O5, and reactions of oxygen atoms or hydroxyl radicals produced by the discharge with VOCs can lead not only to H2O and CO2 but to a number of by-products following the partial oxidation of the molecule, which can be as undesirable than the compound to be initially removed from effluents. This is particularly the case when the electrical energy deposited in the gas flow must be kept as low as possible in order to design a low energy cost equipment. As a result addition of a catalyst together with the pulsed discharge is now investigated in various laboratories in order to achieve a complete oxidation of VOCs, i.e. the so-called de-COV process, or a complete reduction of NOX (NO and NO$_{2})$ to produce N2 and O2, i.e. the so-called de-NOX process, at low energy consumption. This paper is a short review of works which have been done these last years in that domain, specifically on NOX and some selected VOC molecules

Methane conversion in homogeneous discharge at atmospheric pressure in Ar-CH 4 mixtures

International audienceUV pre-ionized photo-triggered discharge reactor is used, its allows to work with an homogeneous plasma, a uniform electric field and a controllable deposition of electric energy in the plasma even at atmospheric pressure. The moderate values of the reduced electric field E/N, associated with the preceding properties, allows a 0D self-consistent physical and chemical modelling, without restrictive hypothesis on the physics of the energy deposition. Initial methane concentrations are in the range 250-1000 ppm at atmospheric pressure, chromatographic diagnostics are used to identify and quantify CH 4 and by-products

Naphthalene oxidation by different non-thermal electrical discharges at atmospheric pressure

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Experimental and numerical study of the propagation of a discharge in a capillary tube in air at atmospheric pressure

International audienceThis paper presents an experimental and numerical study of a pulsed air plasma discharge at atmospheric pressure propagating in a capillary glass tube. In this work, we have compared the discharge structures and the axial propagation velocities of discharges. First, we have studied a needle-to-plane configuration without tube. For applied voltages in the range 7-18 kV, we have observed in experiments and in simulations that a plasma ball starts to develop around the needle tip. Then, for applied voltages less than 14 kV, in experiments, the discharge rapidly splits into several streamer channels with a main axial streamer. In simulations, we have computed only the main axial discharge. For applied voltages higher than 14 kV, in experiments and in simulations, we have observed that the discharge propagates with a cone shape in the gap. For all studied voltages, a good experiment/modelling agreement is obtained on the axial propagation velocity of the discharge, which increases with the applied voltage. Then, we have studied the propagation of discharges inside capillary tubes with radii in the range 37.5-300 μm. In experiments and simulations, we have observed that for small tube radius, the discharge front is quite homogeneous inside the tube and becomes tubular when the tube radius increases. Experimentally, we have observed that the velocity of the discharge reaches a maximum for a tube radius slightly less than 100 μm. We have noted that for a tube radius of 100 μm, the discharge velocity is three to four times higher than the velocity obtained without tube. This clearly shows the influence of the confinement by a capillary tube on the discharge dynamics. In this work, we have only simulated discharges for tube radii in the range 100-300 μm. We have noted that both in experiments and in simulations, the velocity of the discharge in tubes increases linearly with the applied voltage. As the radius of the tube decreases, the discharge velocity derived from the simulations slightly increases but is less than the experimental one. We have noted that the discrepancy on the discharge velocity between experiments and simulations increases as the voltage increases

Odorous volatile compounds conversion by electro-ceramic barrier discharge

International audienceDecomposition of butyric acid and dimethyl sulphide diluted in dry air is studied in coaxial cylindrical geometry of Electro-ceramic Barrier Discharge (EBD). Removal rates are measured for different initial concentrations and electrical parameters. By products are identified using FTIR spectroscopy and PTR-MS diagnostic

N-hexane abatement using a non-thermal plasma

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Spatio-temporal distribution of absolute densities of argon metastable 1s 5 state in the diffuse area of an atmospheric pressure nanosecond pulsed argon microplasma jet propagating into ambient air

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