Numerical Study On Electron Effect In Interaction Of Gas Plasma With Aqueous Solution

For the past few years,the application of the cold atmospheric-pressure plasmas in biomedicine(called plasma biomedicine)has become an attractive research field.More and more experimental studies show that the cold atmospheric-pressure plasmas have a broad application prospect in biomedicine,such as in medical disinfection,surgery,wound healing,and even cancer treatment.In these clinical applications,the targets to be treated by plasma is biological tissue which is often covered with the water layer with the thickness of tens to hundreds of microns.Due to this,before acting on the biological tissue,plasmas will interact with aqueous solutions,in which both the complex physical effects and diverse chemical reactions will occur.Accordingly,for the targets immersed in aqueous solutions,the reactive species finally reaching the targets as well as their concentrations may be evidently different.Thus,the interactions of plasma with aqueous solutions and the mass transfer of the reactive species become a crucial topic in plasma biomedicine.Using experimental diagnosis,it has been proved that aqueous solution can significantly influence the composition,density,and distribution of the reactive species in the mass transfer process.However,because of the limited diagnosis technology,to completely determine and quantitatively analyze the influence of aqueous solution on the mass transfer of reactive species in the plasma is still a question left open and depending on an advanced diagnosis technology.In this context,a feasible solution to analyses on the mass transfer of the reactive species in aqueous solution is to utilize numerical simulation.In this thesis,a one-dimensional drift-diffusion model has been used to investigate the mass transfer of the reactive oxygen species from the gaseous plasma in the aqueous solution by means of the numerical simulation.In the gas region,electrons in the plasma can be removed from the gas plasma by adding an appropriate magnetic deflection device with little influence on the other reactive species.Thus,in the two cases with and without electrons in the gas plasma,the mass transfer and depth distributions of five main reactive oxygen species,O2-,O3,OH,HO2,and H2O2,have been investigated.This thesis shows the following results.Removing electrons from the plasma injected into the liquid phase,the penetration depth of O2-is considerably reduced,and those of O3 and OH are evidently increased.When only the electrons removed from the gas plasma are allowed to enter the liquid phase,the penetration depths of O2-and H2O2 are the same as those without the electrons removed,while only a slight penetration depth of other species is observed.In addition,the dominant generation and removal reactions of the main reactive species under the above simulation conditions have also been calculated and analyzed.