Structure Optimization Of Multineedle-to-cylinder Reactor In Dielectric Barrier Discharge At Atmospheric Pressure And Experimental Study Of Formaldehyde Removal

Dielectric barrier discharge (DBD) can produce large volume and high-energy-density non-thermal plasma (NTP) at atmospheric pressure over a wide range offrequencies without expensive vacuum equipment, so it has a number of industrialapplications, such as surface modification, environmental protection, medicine, andplasma displays. Gaseous organic pollutant removal through DBD is a new techniquethat has appeared promising application prospect because of high efficiency andnon-selectivity. Reactor configuration has a major effect on DBD characteristics andpollutant removal efficiency, thus reactor configuration optimization and the match ofthe DBD reactor structure and the power supply is of great significance for large-scaleindustrial application of DBD.To decrease initial discharge voltage and operating voltage, increase electrondensity and pollutant removal efficiency, multineedle-to-cylinder (MC) corona-DBDreactor is designed at first in this thesis. Experimental discharge currents and imagesshow the discharge pattern at atmospheric air is filament (streamer). According todischarge theory, the life cycle of one such filament can be discerned three separate steps:the formation of the avalanche, i.e., the electrical breakdown; the ensuing current pulse ortransport of charge across the gap; and simultaneously the excitation of the atoms andmolecules present and thus initiation of the reaction kinetics. Researches have been madeaiming at the three separate steps of the filament:①Based on the quasi-static maxwell equation, a quasi-static field model ispresented to calculate the electric field distribution in the reactor using finite-elementmethod. The critical electric field strength of avalanche production is adopted as thecriterion to optimize the structure and parameters of MC reactor, which is validated byfurther experiments.Simulation results also show that mutual effect among adjacent needles influenceDBD characteristics. Therefore, the fluid-hydrodynamic model is employed toinvestigate the the influence of the mutual effect on the multi-needle streamerpropagation. The comparison and analysis between the electric field, electrons andpositive ions number density, electron average energy of streamer discharge insingle-needle geometry (SNG) and three-needle geometry (TNG) show that the averagepropagation velocities, electric fields distribution, electron average energy, the electron density along the streamer propagation axis in TNG decreas compared with those in theSNG. However, the corona character is weakened in TNG. Meanwhile, the electric field,electrons and the electron average energies out of streamer domain in TNG are greaterthan those in SNG, which is favorable to gasous pollutant removal.②The matching of electrode configuration and power supply parameters is studiedby orthogonal design in combination with Lissajous figures, in which the value oftransported charges per cycle is adopthe as the goal factor. The results of the varianceanalysis interpret that the influence of Upis the most remarkable. The next influencingfactor is f while NL and INRA do not affect the charges transferred remarkably. Theoptimal experiment plan is f=21kHz, and NL is3.5mm and2mm alternatively spacedwith INRA of45°. Orthogonal experiment results are experimentally validated byfurther experiments involved with all NL and INRA combinations.③The orthogonal experiment is used to optimize the matching between MCstructure and the power supply to achieve the highest removal efficiency. Densityfunctional theory (DFT) is used to study the pathways of formaldehyde removal underDBDs plasma conditions through molecular simulation package. The calculation modelof the relative energy of the reactions is defined, in which adjustment term concerningthe actual experiment conditions is considered. Possible radical reactions and theformation reactions of radicals are designed and investigated with DFT. The previouslycorrelative theoretical or experimental results are also included in this work.Comparative results between the previous investigation and the present workdemonstrate that theoretical calculation with DFT is an efficient and reliable supplementfor experimental research.