M Benhenni

Ion swarm data for electrical discharge modeling in air and flue gas mixtures

The first step of this work is the determination of the elastic and inelastic ion-molecule collision cross sections for the main ions (N2+, O2+, CO2+, H2O+ and O−) usually present either in the air or flue gas discharges. The obtained cross section sets, given for ion kinetic energies not exceeding 100 eV, correspond to the interactions of each ion with its parent molecule (symmetric case) or nonparent molecule (asymmetric case). Then by using these different cross section sets, it is possible to obtain the ion swarm data for the different gas mixtures involving N2, CO2, H2O and O2 molecules whatever their relative proportions. These ion swarm data are obtained from an optimized Monte Carlo method well adapted for the ion transport in gas mixtures. This also allows us to clearly show that the classical linear approximations usually applied for the ion swarm data in mixtures such as Blanc’s law are far to be valid. Then, the ion swarm data are given in three cases of gas mixtures: a dry air (80% N2, 20% O2...

Chemical kinetics with electrical and gas dynamics modelization for NOx removal in an air corona discharge

A non-stationary reactive gas dynamics model in a mono-dimensional geometry, including radial mass diffusion, gas temperature variation and chemical kinetics, is developed in this paper. The aim is to analyse the spatio-temporal evolution of the main neutral species involved in a corona discharge used for NO pollution control in polluted air at atmospheric pressure and ambient temperature. The present reactive gas dynamics model takes into account 16 neutral chemical species (including certain metastable species) reacting following 110 selected chemical reactions. The initial concentration of each neutral species is obtained from a 1.5D electrical discharge model. The gas temperature variations are due to direct Joule heating during the discharge phase, and also result from the delayed heating due to the relaxation of the vibrational energy into a random thermal energy during the post-discharge phase. The simulation conditions are those of an existing experimental setup (anode voltage of 10 kV in the case of a point to plane geometry with an interelectrode distance of 10 mm). The obtained results show that the diffusion phenomena and the gas temperature rise affect quite well the gas reactivity and the neutral species evolution. This allows us to better understand the different reaction processes and transport phenomena affecting the NO concentration magnitude inside the discharge channel.

Basic data for atmospheric pressure non-thermal plasma investigations in environmental and biomedical applications

The aim of this paper is to discuss some aspects of the optimization of the active species generated by corona or DBD discharges at atmospheric pressure which are very useful in the field of plasma environmental and biomedical applications. For such an optimization, this paper targets, in particular, the use of discharge modeling tools and the problem of accuracy of the required basic data. First of all, an overview on the different experimental diagnostics used for the characterization of these non-thermal plasmas is given followed by a short description of the different models (streamer dynamics, gas dynamics and chemical kinetics coupled with models of basic data calculation) required for complementing such experimental investigations. Then, emphasis is placed on the basic data of charged particles (electrons and ions) needed for streamer dynamics modeling and particularly on the necessity to use accurate and validated basic data in order to have a quantitative (not only qualitative) description of the phenomena and processes occurring in such discharges. An overview is given on the calculations and the fitting methods of collision cross sections and swarm coefficients of the data of charged particles and their validation using, in particular, pulsed Townsend measurements for experimental comparisons. Swarm coefficients are calculated from a multi-term solution of the Boltzmann equation or from Monte Carlo simulation. Some illustrative results are given in the case of the simulations of a dc positive point-to-plane corona discharge in air at atmospheric pressure. The effect of consideration of some basic data, particularly those of polyatomic ions, is shown on the discharge development and the radical production. (Some figures in this article are in colour only in the electronic version)

Drift and reactions of positive tetratomic ions in dry, atmospheric air: Their effects on the dynamics of primary and secondary streamers

The ion swarm data, namely, the reduced mobility, diffusion, and reaction rates of the positive tetratomic ions O4+ and N2O2+ in N2 and O2 have been determined from a Monte Carlo simulation using calculated and fitted elastic and inelastic cross sections. The elastic momentum transfer cross sections have been determined from a semiclassical Jeffreys-Wentzell-Kramers-Brilouin (JWKB) approximation based on a rigid core potential model well adapted for polyatomic ions. The inelastic cross sections have been approximated from considerations based on the N4+/O2 and N4+/N2 systems. The validated cross section sets in pure N2 and O2 have been used to determine the O4+ and N2O2+ swarm data in dry air over a large E/N range up to 1000 Td. However, due to the lack of experimental ion transport coefficients necessary for a more rigorous cross section validation, the present data, validated only at low E/N, should be regarded as a first approximation, susceptible to improvements as soon as measurements of ion transpo...

Basic data of polyatomic ion-molecule systems for flue gas discharge modelling

In the presence of an external electric field, ion transport coefficients (ion mobility and diffusion coefficients) are closely related to the ion-neutral interaction potential. A new generalized potential model, coupled to an optimized Monte Carlo technique, has been developed for the determination of the transport coefficients of polyatomic ions in weakly ionized gases. This corresponds to the polyatomic ion-molecule systems which can affect the electrical behaviour of the flue gas discharges used for the non-thermal plasma reactor for pollution control. The ion-molecule interaction has been described by a rigid core potential model which is adapted for both polar and non-polar systems and also symmetric and asymmetric systems. Momentum transfer cross sections are then determined using a semi-classical approach. The corresponding sets of cross sections including the dominant processes in our intermediate ion energy range (elastic and mainly charge transfer in certain cases) are used in the Monte Carlo code to calculate the ion transport coefficients over a wide range of reduced electric field E/N. These ion transport data fit quite well the drift tube measurements available in the literature for the CO2+/CO2 system, and also for certain weakly polar cases. The case of the H2O+/H2O system is then considered thus giving in this highly polar system the ion swarm data for the first time in the literature. Finally, we have considered with quite good reliability some asymmetric systems such as CO2+/N2 and N2+/CO2 whose ion data are also needed for flue gas discharge modelling.

Analysis of ion mobility and diffusion in atmospheric gaseous mixtures from Monte Carlo simulation and macroscopic laws

The reduced mobility and diffusion coefficients of and O− are calculated with a Monte Carlo simulation for the gas mixtures N2–H2O (50%, 50%) and O2–N2 (80%N2, 20%O2), respectively, from measured and calculated elastic and inelastic cross sections. These mobility and longitudinal diffusion coefficients have been compared with the standard Blancs law and with the common mean energy (CME) procedure. Good agreement between these three calculation methods was found for the mobility and diffusion of in the N2–H2O mixture at high reduced fields where inelastic processes are relatively uninfluential. However, a strong deviation between Blancs law and both CME procedure and our Monte Carlo calculations for the reduced mobility and the diffusion coefficient of in this gas mixture N2–H2O was observed at low reduced fields, because inelastic processes are significant. On the contrary, for the case of the N2–O2 mixture, where inelastic processes are small over the reduced electric field range 1–8000 Td, the three calculation methods led to similar results. The elastic collision cross sections used were determined from a semi-classical JWKB approximation by using a rigid core potential model for both symmetric and asymmetric , O−/O2 and O−/N2 ion–neutral systems. Moreover, the inelastic cross sections were extended to low energies from appropriate approximations. These cross section sets were validated from the good agreement between our Monte Carlo calculated reduced mobilities in N2 and H2O, O− in O2 and N2 and either measured values for the systems and O−/O2 or physical properties of the systems and O−/N2.

Basic data of ions in He-air mixtures for fluid modeling of low temperature plasma jets

The basic ion data such as interaction potential parameters, elastic and inelastic collision cross sections, transport coefficients (reduced mobility and diffusion coefficients) and reaction coefficients have been analysed and determined for the case of He+, N2+, and O2+ in He-dry air mixtures. The ion transport and reaction coefficients have been determined from an optimized Monte Carlo simulation using calculated elastic and experimentally fitted inelastic collision cross sections. The elastic momentum transfer cross sections have been calculated from a semi-classical JWKB (Jeffreys Wentzel Kramers Brillouin) approximation based on a (6-4) rigid core interaction potential model. The inelastic cross sections have been fitted using the measured reaction coefficients, such as, for instance, the non resonant charge transfer coefficients. The cross section sets involving elastic and inelastic processes were then validated using either the measured reduced mobility whenever available in the literature or the ...

Transport properties of {\rm SF}_{6}^{-} in SF6?Ne, SF6?N2 and SF6?O2 mixtures

The mobility of has been calculated for the gas mixtures SF6?Ne, SF6?N2 and SF6?O2 using an optimized Monte Carlo code for the ion transport simulation in a drift tube. The elastic momentum transfer collision cross sections needed for the calculation were determined from a semi-classical JWKB approximation, while the inelastic ones (detachment, dissociative charge transfer and conversion to and F?) were taken from the literature for the case of the collision system. The resulting sets of collision cross sections were validated by comparing the calculated mobilities with those measured in the above mixtures with a time-resolved pulsed Townsend technique. The longitudinal and transverse density-normalized diffusion coefficients were calculated for these mixtures for the case where the share of SF6 in the mixture was 50%. Finally, the validity of Blancs law was discussed at low and high electric fields, whereby we show that it fails at high fields, where inelastic processes are dominant.