Experimental And Computational Study Of Dielectric Barrier Discharge For Ozone-free Nitrogen Oxides Production

Dielectric barrier discharge(DBD)had been widely used in ozone synthesis in the early stage.And most scholars were committed to studying the mechanism of ozone generation while ignoring the research work on nitrogen oxides generation.With the development of plasma biomedicine,the role of those nitrogen oxides,especially peroxynitrite(ONOO^-),in biomedical applications has gradually emerged.And peroxynitrite plays an important role in cell signal transduction and antimicrobial defense in human body,which is considered to be an environment-friendly antibacterial drug with broad application prospects.Facilitating the separate production of ozone and nitrogen oxides is the main requirement for achieving the desired plasma performance for specific purposes,hence it is very important to investigate mechanism and regulation method of product mode transition.In this paper,phenol was used as a probe to investigate the regulation mechanism under different discharge conditions.Furthermore,a zero-dimensional chemical kinetics model for atmospheric AC air DBD was developed.And there was a comparative study on whether the internal mechanism of mode conversion is caused by different discharge conditions.Firstly,alkaline phenol in the PBS solution was used as a chemical probe.With varying discharge parameters such as applied voltage,gas flow rate and oxygen content,the regulation of peroxynitrite formation was shown.The peroxynitrite concentration was found to be relatively independent of the applied voltage,while negatively correlated with the gas flow rate.The energy density was introduced as a micro-parameter to comprehensively study the coupling effects of the discharge parameters on peroxynitrite formation for better process control.Peroxynitrite concentration had a positive correlation with the energy density,demonstrating that a higher energy per area could promote peroxynitrite formation.P.digitatum was chosen as a microbial model to evaluate the microbial inactivation efficacy of thus-generated gaseous peroxynitrite.The results further showed that the gas plasma treatment effectively inhibited the germination of P.digitatum spores,with germination inhibition efficiency closely related to peroxynitrite concentration.Secondly,a zero-dimensional chemical kinetics model for atmospheric AC N₂/O₂DBD was developed,which consisted of 56 species and 672 chemical reactions.Vibrationally excited ozone was specially added to the plasma chemistry.Typical filamentary behavior was taken into account in the model by applying a large number of consecutive microdischarge pulses as a function of time.Energy density,defined as the ratio of the dissipated energy each cycle to the discharge area,together with gas temperature were the input parameters.The calculations were first performed for one microdischarge pulse and its afterglow,to study in detail the chemical pathways of the species.Subsequently,long time-scale simulations were carried out,corresponding to real residence times in the plasma,assuming a large number of consecutive microdischarge pulses,to mimic the conditions of the filamentary discharge regime in DBD.The calculated dynamics for various reactive oxygen and nitrogen species showed reasonable agreement with the experimental results obtained by FTIR.Finally,the global model was used to investigate the DBD product mode conversion mechanism.At different oxygen content,ozone concentration was negatively correlated with gas temperature.As the electron energy increased,the ozone density first reached a peak and then decreased.Besides,NO was positively correlated with electron energy and gas temperature.And the maximum ozone concentration was obtained under higher electron energy.The main production pathway for O₃ and O₃(V)is the 3-body recombination reaction of O and O₂.For O₃(V),the main destruction pathway is via collisions with O and O₂(a¹).While the main destruction pathway is via collisions with O₂(b¹)for O_3.The formation of NO is closely related to O and O₃.Product mode transition is a combined effect of electron energy and gas temperature with different internal mechanisms.The electron has an impact on the electron density and therefore the production and consumption of particles density such as O,O₂(a¹)and O₂(b¹),which leads to the total production rate increasing more rapidly than the total consumption rate.While the gas temperature affects the reaction rate coefficients for both the production and consumption of O₃ and NO.It is necessary to avoid temperature accumulation in the discharge channel when producing ozone.And higher energy efficiency will be obtained with reasonable use of the accumulated heat together with an additional heating source.