A Comparative Study On The Calculation Of One-Dimensional Fluid Model Reaction Rate Coefficients Of Dielectric Barrier Discharge In N₂ Plasma

Dielectric barrier discharge(DBD)can produce relatively stable and uniform non-thermal equilibrium discharge plasma under different discharge conditions,so it has extensive industry application prospects.Compared with the traditional DBD with sinusoidal excitation,the DBD excited by the pulsed voltage at atmospheric pressure(also called the pulsed DBD)is of higher energy conversion efficiency,higher discharge current density,enhanced stability,and uniformity and higher concentration of reactive species.Due to these,the investigation on the pulsed DBD has become a hot spot of research in the fields of gas discharge and discharge plasma.However,some microscopic phenomena of discharge are difficult to observe in experiments because of the limited experimental conditions.Therefore,numerical simulation becomes an effective method to study the characteristics and mechanisms of gas discharge plasma.The fluid model has been widely used for the investigation of low temperature plasmas produced by the DBD due to its convenience and higher accuracy in calculation.It has been a goal pursued by researcher to select reliable reaction rate coefficients when using fluid model to simulate gas discharge.The selection of electron energy distribution function(EEDF)on the basis of collision cross-section data is of importance for reliable theory evaluation of reaction rate coefficients.In general,the EEDF is assumed to be in the Maxwellian distribution.But,this may result in errors in numerical simulations of the DBD at atmospheric pressure because of electrons in nonequilibrium.In this thesis,the energy distribution of electrons in the discharge is described by Maxwellian distribution function and Boltzmann distribution function,respectively,and following this a comparison investigation of the effects of these two distributions on the simulation of the pulsed DBDs with the use of one-dimensional fluid model has been performed.The spatiotemporal average density of particles and the axial distribution of the electric field has been calculated and compared.In the simulations,reaction rate coefficients are obtained by solving the Boltzmann equation(BE)for electrons using the classical two-term expansion.This thesis includes the following contents and results:1.A one-dimensional fluid model has been developed and are solved numerically by the Scharfetter-Gummel method.Using FORTRAN programming software,the pulsed DBDs have been simulated.2.Based on a freely available software named BOLSIG+ and using the classical two-term expansion in six dimensional phase space and velocity space for solving the electron Boltzmann equation,the reaction rate coefficients suitable for non-thermal equilibrium plasmas have been obtained and compared with those due to Maxwellian distribution function.It is shown that there is obvious difference between the two distribution functions at atmospheric pressure.For N2,the electron energy distribution due to Boltzmann equation is in better agreement with the experiment than that from Maxwellian distribution function.This indicates that the former is well suitable for the simulation of non-equilibrium pulsed dielectric barrier discharge in N2 at atmospheric pressure.3.In the one-dimensional fluid model,using the two sets of reaction rate coefficients obtained by solving Boltzmann equation and given by Maxwellian distribution function,respectively,the discharge current densities and spatial distributions of the particle densities and electric field have been systematically calculated and compared.It is shown that the pulsed DBDs in N2 at atmospheric pressure are in typical Townsend mode,the densities of electrons,ion,and metastable state molecule N2(A)due to use of Boltzmann equation are obviously high,and mean electron energy is low,compared to those based on the Maxwellian distribution function.