M. Yousfi

Coupling of chemical kinetics, gas dynamics, and charged particle kinetics models for the analysis of NO reduction from flue gases

A chemical kinetics model is developed to analyze the time evolution of the different main species involved in a flue gas initially stressed by a pulsed corona discharge at the atmospheric pressure and including N2, O2, H2O, and CO2 with a few ppm of NO. The present chemical kinetics model is coupled to a gas dynamics model used to analyze the radial expansion of the gas in the ionized channel created during the discharge phase. It is also meant to analyze the gas heating due to the Joule effect. This chemical kinetics model is also coupled to charged particle kinetics models based on a Boltzmann equation model to calculate the electron-molecule reaction coefficients in the flue gas and on a Monte Carlo code to estimate the energy and momentum transfer terms relative to ion-molecule collisions which are the input data for the gas dynamics model. It is shown, in particular, that the evolution of the radicals and the oxides is substantially affected by the gas temperature rise (from the initial value of 300...

Boltzmann equation analysis of electron‐molecule collision cross sections in water vapor and ammonia

Sets of electron‐molecule collision cross sections for H2O and NH3 have been determined from a classical technique of electron swarm parameter unfolding. This deconvolution method is based on a simplex algorithm using a powerful multiterm Boltzmann equation analysis established in the framework of the classical hydrodynamic approximation. It is well adapted for the simulation of the different classes of swarm experiments (i.e., time resolved, time of flight, and steady state experiments). The sets of collision cross sections that exist in the literature are reviewed and analyzed. Fitted sets of cross sections are determined for H2O and NH3 which exhibit features characteristic of polar molecules such as high rotational excitation collision cross sections. The hydrodynamic swarm parameters (i.e., drift velocity, longitudinal and transverse diffusion coefficients, ionization and attachment coefficients) calculated from the fitted sets are in excellent agreement with the measured ones. These sets are finally...

Improved Monte Carlo method for ion transport in ion-molecule asymmetric systems at high electric fields

An improved Monte Carlo method is developed for the simulation of the ion transport in classical drift tube in the case of ion-molecule asymmetric systems such as O−/O2 or N+/N2. The aim of this new method is to overcome the problem of incident ions which vanish at relative high electric field due to asymmetric charge transfer or electron detachment. These ion removal processes are compensated by a fictitious ion creation which improves the accuracy of the ion distribution function and swarm coefficient calculations. The classical ion-molecule collision processes occurring in weakly ionized gases at room temperature (elastic collisions including energy exchange and thermal motion of background gases and also inelastic collisions) are taken into account. This new method is then validated and the transport and reaction coefficients have been given for a large range of E/N (a part of them for the first time in the literature) in O−/O2 and N+/N2 systems.

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.

Modeling and basic data for streamer dynamics in N2 and O2 discharges

A second order hydrodynamics model of streamer dynamics is developed without using the classical restrictive approximations concerning the source term of the conservation equation of electron energy. The first three moments of the Boltzmann equation coupled to the Poisson equation for the space charge electric field are closed using the local energy approximation. The basic data needed for the present second order model for electrons and the first order model for ions are obtained from the solution of the steady state Boltzmann equation and the Monte Carlo simulation, respectively. The electron data associated with the source term of the electron energy conservation equation and which correspond to the different electron–molecule processes considered in our N2 and O2 discharges (ionization, attachment, excitation, elastic, and superelastic collisions) are explicitly given. Then, we give the results obtained with the present second order hydrodynamics model and concerning N2 and O2 gases at atmospheric pre...

RF discharge modelling in a N2O/SiH4 mixture for SiO2 deposition and comparison with experiment

The present work concerns the experimental and theoretical analysis of the electrical behaviour and N2O/SiH4 dissociation of a classical RF discharge used for SiO2 thin-film deposition. Electric and deposition rate measurements are undertaken at 0.5 and 1 Torr gas pressures. The reactor modelling involves electrical, hydrodynamic and mass transfer models. The electrical model enables the calculation of the electron impact dissociation rates required for the mass transfer model, while the gas velocities are determined by the hydrodynamic model. Only an electrical discharge model accounting for the negative-ion conversion reactions O-/SiH4 and NO-/SiH4 allows good agreement between the measured and calculated power densities particularly at 1 Torr. Furthermore, a simplified chemical scheme which includes 16 species (N2O, N2, O2, NO, NO2, N, O(3P), O(1D), SiH4, SiH3, SiH3O, H2SiO, H, H2, OH and H2O) is used in the mass transfer model. The corresponding results (deposition rates) are quite consistent with the measurements.

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.

Modeling and three-dimensional simulation of the neutral dynamics in an air discharge confined in a microcavity. I. Formation and free expansion of the pressure waves

A three-dimensional numerical analysis of the neutral dynamics is performed in the case of a short-gap (0.5 mm) spark discharge in air confined in microcavities at atmospheric pressure (760 Torr) and ambient temperature (293 K). This work is undertaken in the framework of silicon microsystems bearing a micropump actuated by pressure waves which result from a discharge. The short-gap discharge characteristics are taken from experimental results namely 470 ns for the duration and 13.5 W for the maximum injected power. The neutral gas evolution is described by the classical transport equations and solved by a powerful numerical monotonic upstream-centered scheme for conversion laws. The gas–solid interaction occurring in thermal and hydrodynamic boundary layers is taken into account assuming that the microcavity temperature remains invariant (293 K). This article (part I) is devoted to the first evolution phase of the neutral dynamics whose the duration corresponds to the discharge time. Our results clearly ...

Zero‐dimensional hybrid model for analysis of discharge excited XeCl lasers

A powerful zero‐dimensional hybrid model to study the positive column of a glow discharge used as an excitation medium for XeCl lasers is presented. This model was employed using a numerical code including three strongly coupled parts: electric circuit equations (electric model), electron Boltzmann equation (particle model), and kinetics equations (chemical kinetics model). From this hybrid model, kinetics and electrical parameters of Ne–Xe–HCl laser discharge mixtures have been discussed and analyzed. Calculated discharge current and voltage are also compared with available theoretical and experimental results. The good qualitative agreement observed shows the validity of the present model which can used as an efficient tool for the investigation of the homogeneous excimer laser discharge.