Corona Plasma Generation And Its Application For Air Purification

In the face of the more and more serious air pollution,a series of environment policies focusing on the contamination reduction such as coal-fired boiler,have been introduced from 2015 and obtained well effects.The traditional ESP has poor removal efficiency on the fine particles including PM 10 and PM 2.5.Hence,the remaining outdoor fine particles result in a serious indoor air pollution.However,the indoor air purifiers have quite different purifying effects.The fine particles can be charged and agglomerated by the high-energy electrons induced by the plasma discharge,resulting in a well collection on the precipitating electrode plate via electrohydrodynamic(EHD)and viscous force.Meanwhile,the generated active particles have a strong oxidation and degradation effects on the organic,the inorganic and microbial aerosol.In this dissertation,the plasma discharge has been investigated systematically,including the charges of dusts,dust removal,ionic wind,electrical agglomeration and back corona and so on.The main contents and conclusions are summarized as follows:(1)The charging and removal processes act simultaneously in a single-stage ESP.The DC or pulsed power can charge the particles with the same polarity,a larger particle diameter results in greater charge.Under a constant pulsed voltage,the charge of the particles increases with the increase of frequency,whereas a higher frequency can produce a more intensive ironic wind resulting in a poorer removal efficiency.Therefore,r,the greatest charge of particles can not generate a largest removal efficiency under DC overlapped pulse power.(2)In the wire-plate and single-stage ESP,the DC discharge induces more intensive electrohydrodynamic forces and vortexes than pulsed discharge.A symmetric vortex pair is induced by the EHD forces near the collection plate corresponding to the head and tail of the wire electrode.EHD/Re2 ranges from 1 to 20 at the inception of the vortex pair with the increase of the applied voltage,the electric intensity and vortex are strongest in the vicinity of the electrode wire in terms of the DC overlapped pulse power with a constant total applied voltage,a stronger vortex is generated especially under higher DC voltage.(3)The particles are removed with a previous charging process in a two-stage ESP.The removal efficiency can be improved by the increasing collecting voltage and charging voltage during a certain range.When plate voltage is increased to a certain higher level,the edge of plate begins to discharge with the collecting voltage reaching a certain value,thus the removal efficiency decreases by the ionic wind induced by the strong electrical field.However,a plate-plate ESP can produce a more uniform electric field and weaker ironic wind than the wire-plate ESP.(4)In terms to the electrical agglomerate reactor with stagger wires,applying DC,pulse or AC voltage can induce agglomeration and improvement of the removal efficiency,and the decreasing effects order are AC,pulse and DC.DC voltage has an agglomeration with weak sensitivity to the particle diameter,and around a 5%improvement of the removal efficiency.Pulse voltage can especially increase the particle agglomeration of the smaller diameter,and the removal efficiency increases 13%,approximately.However,AC voltage improves greatly removal efficiency of all particles diameters by 10%.(5)Plasma discharge can increase the air flow rate.The fastest rate induced by the discharge in the needle-cylindrical,needle-net and needle-hole reactor are 2 m/s,1.4 m/s,1 m/s,respectively.Moreover,the high-speed air flow mainly locates in a small region near the outlet of the reactor,whereas the flow rate decreases dramatically in the other region.(6)The back corona discharge can be stably generated on the honeycomb ceramics with high specific resistance.Meanwhile,the obvious air flow can be observed around the honeycomb ceramics and utilized to drive the air flow.DC discharge can generate back corona easier than pulsed discharge.More intensive back corona discharge can be induced by higher DC voltage with a constant total voltage of the DC overlapped pulse power.Meanwhile,the additional pulsed voltage on a constant DC voltage can generated more dramatic back corona discharge as well.