Fundamental Study Of Atmospheric Pressure Non-thermal Plasma Applications Based On The Fluid Model

Based on the rapid development of the plasma jet and the dielectric barrier discharge(DBD)technology,the atmospheric pressure non-thermal plasma has been widely used in biomedicine and catalytic synthesis in recent years.However,due to the limitations of experimental diagnostic techniques,the generation mechanism of reactive species of micro-plasma jet,the micro-scale interaction between the dielectric barrier discharge plasma and the bacterial biofilms,and the microscopic mechanism of plasma synergistic catalysis in the field are not fully understood.Aiming at these problems,in this paper,a two-dimensional atmospheric pressure non-thermal plasma fluid model is developed.Through a series of high time-space resolution studies on the plasma development process,the model reveals the generation mechanism of plasma and the interactions between plasma and treated objects at microscale,which provides theoretical guidance for the development of atmospheric pressure non-thermal plasma applications.The main contents of this paper are as follows:1)Based on the two-dimensional micro-plasma jet model,we find the tube diameter affects the generation of the reactive species in the streamer by changing the ignition voltage.The mechanism of the influence of the tube diameter on the ignition voltage is: More electrons wall losses happen due to the faster drift movement to the inner wall of smaller tube diameter,therefore,the decreasing pre-avalanche electron density need increasing ignition voltage to facilitate the avalanche-streamer transition as the tube diameter decreases.The increasing in ignition voltage enhances the power injection to the plasma,which results in a stronger ionization and excitation process,and thus the density of the reactive species is increased by orders of magnitude.2)Based on the two-dimensional air dielectric barrier discharge model,we study the microscopic interactions between the negative streamer and the bacterial biofilm on the fruit surface.The voltage drop between the streamer head and the biofilm causes pre-ionization on the biofilm surface,which accelerates the propagation of the streamer.The strong electric field on the biofilm surface,the difference of ion flux density and the extremely high reactive species flux caused by the streamer result in more effective mechanical damage and lipid peroxidation,and consequently,cell injury.Meanwhile,since the mean free path of the charged species in the streamer discharge is on the micrometer scale,therefore,the plasma can penetrate into the cavity inside the biofilm.The data analysis shows that the peak density of most of the active particles in the plasma is located in the cavity,so it can effectively kill the bacteria at the bottom of the biofilm.Futhermore,we simulate the process of three bacterial biofilms treated by two negative streamers,and the results show that there is a synergistic effect between the steamers,which not only increases the treatment area,but also increases the density of active particles in the cavity.3)Based on the packed-bed dielectric barrier discharge(PB-DBD)reactor model under complex geometry,we analyse the discharge characteristics,conversion rate and energy efficiency of dry reforming of methane and carbon dioxide by nanosecond pulsed plasma catalysis.During the pulse on period,the plasma is expanded in a combination of surface ionization waves and filamentary microdischarges in the inner gap between the catalytic beads,while in the outer gap between the catalytic beads and the dielectric tube,the plasma is advanced in the form of a negative streamer and finally converted into a strong glow discharge.In the pulse,the high instantaneous power energy causes the electron heating which drives the inner and outer gap discharges to develop rapidly,and determines the electron collision decomposition to dominate the production of CO and H2.During the pulse off period,the extremely low duty cycle effectively reduces the gas temperature,which in turn decreases the recombination of CO and O,and eventually increases the conversion rate by means of nanosecond pulse PB-DBD.The high instantaneous power and low duty cycle of nanosecond pulse PB-DBD are the main reasons for the high conversion and high energy efficiency.