Oes Investigation Of The Temperature Characteristics Of Atmospheric-Pressure Waveguide-Based Microwave Oxygen Plasma Torch

Atmospheric microwave plasma torch not only has the characteristics of high temperature as the thermal plasma,but also has the advantages of no plasma contamination for the electrodeless configuration and the high microwave energy-to-plasma coupling efficiency.And it can generate a stable large-volume discharge in a variety of working gases.Therefore atmospheric-pressure microwave-induced plasma has been widely applied in practice.We designed a microwave plasma device?APPLAS-MPT3I?that can produces large volumes with high-energy plasma torches at atmospheric pressure.In order to strike the discharge in the microwave plasma torch,we develop a self-made ignitor which can provide seed electrons in the discharge tube for the plasma excitation.The ignitor not only reduces the cost of the experimental device,but also makes the operation more convenient and safer.Moreover,a stabilized microwave torch is achieved inside the quartz tube by a swirl gas.First,we investigated the characteristics of atmospheric pressure waveguide based microwave plasma torch with different working gases.It is found that the discharge morphology is different significantly with respect to different working gases.When the working gas is argon,filaments are observed in the plasma discharge and it is infeasible to achieve a stable discharge.In the case of oxygen,nitrogen and air,respectively,the discharge can achieve a stable plasma discharge.The nitrogen discharge is faint and behaves as a diffusive glow.In comparison,there is the brighter cylindrical region of radial of several mm along the tube axe in the oxygen plasma discharge,from which the glow diffuses and occupies the space in the tube.At the same time,the coupling efficiency of microwave energy to plasma has been studied for nitrogen,oxygen,and air,respectively.Under the same conditions,the microwave coupling efficiency of oxygen is found to approach the highest value of almost 100%.Experiments are carried out with respect to oxygen to study the plasma formation and its stability with varying flow rate and microwave power.The dependence of the plasma volume on the absorbed power and the gas flow rate is investigated experimentally with the photograph recording of the plasma morphology.In addition,we measured the gas temperature of the afterglow of the microwave oxygen plasma torch by means of optical emission spectroscopy?OES?.From the application point of view,the gas temperature is one of the most important parameters for atmospheric microwave plasma.Owing to the fact that the gas temperature is closely related with the rotational temperature of the oxygen in the atmospheric plasma,the rotational temperature of the excited state O₂?b ¹?_g⁺,v=0?in an oxygen glow discharge is measured from the intensity distribution of the atmospheric A-band O₂?b ¹?_g⁺,v=0??O₂?X³?_g^-,v=0?at ?=760 nm.On the basis of the energy balance equation,the dependence of the afterglow gas temperature on the absorbed power and the gas flow rate is investigated experimentally as well as the axial variation of the gas temperature in the afterglow zone.Finally,we conducted a preliminary study on waste water remediation.We treated the organic wastewater with Brilliant Blue dye by making use of the microwave plasma torch with different carrier gases,oxygen,nitrogen,and air,respectively.We found that the best removal efficiency is achieved in oxygen microwave plasma torch,which is mainly due to the high densities of oxidized active species in the oxygen plasma torch.But much effort has to be devoted to improve the remove efficiency,degrade the energy consumption,and enhance the competition with other methods for using this method in the future.