A comprehensive dynamic model consisting of 66 reactions and 24 species is developed to investigate the dynamic characteristics of ozone generation by positive pulsed dielectric barrier discharge(DBD) using parallel-plate reactor in air.The electron energy conservation equation is coupled to the electron continuity equation,the heavy species continuity equation,and Poisson's equation for a better description.The reliability of the model is experimentally confirmed.The model can be used to predict the temporal and spatial evolution of species,as well as streamer propagation.The simulation results show that electron density increases nearly exponentially in the direction to the anode at the electron avalanche.Streamer propagation velocity is about 5.26×104m/s from anode to cathode in the simulated condition.The primary positive ion,negative ion,and excited species are O_2^+,O_3^-and O_2(1?g) in pulsed DBD in air,respectively.N_2 O has the largest density among nitrogen oxides.e and N_2^+densities in the streamer head increase gradually to maximum values with the development of the streamer.Meanwhile,the O_2^+,O,O_3,N_2(A^3Σ) and N_2 O densities reach maximum values in the vicinity of the anode.
The influence mechanism of a small amount of SF6 on ozone generation in oxygen or air discharge is investigated.Some results are obtained by probing into the number of the high-energy electrons,which have the sufficiency energy for generating ozone.Introducing a small amount of SF6 into oxygen sharply decreases the number of high-energy electrons,because the electron density decreases sharply while the mean electron energy remains constant due to higher breakdown voltage and lower discharge power,and some high-energy electrons are consumed by the excitation and attachment of SF6.In contrast,when a small amount of SF6 is added into dry air discharge,despite the consumption of the excitation and attachment of SF6,the number of high energy electrons increases sharply,which is attributed to the higher mean electron energy and electron density resulted from higher breakdown voltage and discharge power.When the volume fraction of SF6 increases from 0 to 2.22%,the ozone mass concentration and the ozone yield increase by 45.7% and 29.7%,respectively.Therefore,though the oxygen source should avoid the presence of SF6,adding a small amount of SF6 can improve the ozone mass concentration and the efficiency of ozone generation.
WEI Linsheng DONG Guopan ZHANG Yafang YUAN Dingkun HU Zhaoji FU Chunyi
