Frequency Effects And Generation Mechanisms Of Reactive Oxygen Species On Atmospheric-pressure Pulsed Dielectric Barrier Discharge In Helium/Oxygen And Argon/Oxygen

Dielectric barrier discharge is a kind of gas discharge way,where insulating dielectric is placed in discharge space so as to produce artificial plasma.Atmospheric-pressure pulsed dielectric barrier discharge is a kind of burgeoning dielectric barrier discharge.It is excited by high-voltage pulsed source and is of the excellent properties due to both pulsed discharge and dielectric barrier discharge.Also,it can effectively generate non-thermal equilibrium discharge plasma with high chemical activity at atmospheric pressure.Especially,the features and advantages of atmospheric-pressure pulsed dielectric barrier discharge plasmas can meet actual needs in the fields of non-thermal equilibrium discharge plasma applications.Thus,the researches,including the discharge mechanisms and characteristics as well as the actual applications such as the plasma biomedical engineering and plasma surface modification,have aroused wide attentions of domestic and aboard scholars.In this dissertation,a one-dimensional fluid model has been developed and used for numerically investigating the frequency effects of atmospheric-pressure pulsed dielectric barrier discharge plasmas in helium/oxygen and argon/oxygen mixture,respectively.In addition,the generation mechanisms of reactive oxygen species of the pulsed dielectric barrier discharge in argon/oxygen at atmospheric pressure have also been explored.This dissertation includes the following contents and results:（1）Using a one-dimensional fluid model and under the oxygen concentration below 2%,the comparative study on the frequency effects of the discharge current density,the electric field,the averaged electron temperature and the averaged particle density in space-time in the atmospheric-pressure pulsed dielectric barrier discharges in helium/oxygen and in argon/oxygen have been performed.Furthermore,the frequency effects of the pulsed dielectric barrier discharge in argon/oxygen under high oxygen concentration below 5%at atmospheric pressure has also been investigated.The obtained main conclusions are as follows:For the two gases,there are two bipolar discharges in one period of applied voltage pulse under the considered frequency range and oxygen concentrations.The frequency affects the two discharges in helium/oxygen,but in argon/oxygen it induces strong effect only on the first discharge.For the first discharge in each gas,there is a characteristic frequency at which the characteristics quantities reach their respective minimum,and this frequency appears earlier for argon/oxygen.In addition,the discharge in argon/oxygen is strong and the averaged electron temperature is low,compared to those in helium/oxygen The total averaged particle density of the reactive species in argon/oxygen is larger than those in helium/oxygen by about one order of magnitude.For the two discharges occurred in one period of applied voltage pulse in argon/oxygen,there is a characteristic frequency,at which the peak value of each discharge current density reaches its minimum under high oxygen concentration.Under the oxygen concentration below 4%and with the increase of oxygen concentration,the characteristic frequency of the first discharge first increases and then decreases,while that of the second discharge always increases.With the oxygen concentration above 4%,the characteristic frequency of the two discharges remain unchanged generally.（2）Based on the optimized one-dimensional fluid model of non-thermal equilibrium discharge plasmas,the generation mechanisms of reactive oxygen species of the pulsed dielectric barrier discharge in argon/oxygen at atmospheric pressure have been studied.The study includes the dominated reaction pathways for the generation and loss of the four reactive species（O,O（1D）,O₂（1△g）and O₃）as well as the corresponding reaction pathway contributions at the oxygen concentration of 3%and the evolution mechanisms of long-lived species（O,O₂（1△g）and O₃）in a discharge period at the oxygen concentration of 1%.The obtained main conclusions are as follows:The main producing pathways of O,O（1D）and O₂（1△g）are the electron impact reactions between electrons and O₂.Secondly,O comes from the reaction between O（1D）and O₂.The reaction between neutral particles,i.e.,O₂+O₂+O→O₃+O₂ generates the vast majority of O₃.The main consuming pathway of 0（1D）is the reaction between O（1D）and O₂.The generations of 0,O（1D）,O₂（1△g）and O₃ and the loss of O（1D）are slightly affected by the frequency.The frequency mainly affects the consuming pathways of O,O₂（1△g）and O₃.Electron e,Ar+,Arr,Arm and Ar*are generated mainly at the rising and falling edge of the applied voltage pulse and are consumed rapidly in the pulse-off time,while reactive oxygen species O,O₂（1△g）and O₃ still exist largely in the gap in the pulse-off time.In a discharge period,the increase of the Nave2 of O₃ comes from the reaction between O₂ and O.The increase of the Nave2 of O and O₂（1△g）are attributed to the effect of the applied voltage,making more collisions between electron and O₂ at the two discharges.