Research On Miniature Particle Size Distribution System For In-Situ Detection Of Ultrafine Particle In Near Space

Near space generally refers to the earth’s atmospheric sphere 20km～100km away from the ground,which basically coincides with the scope of "middle atmosphere"concerned by atmospheric physics.It is a key research field in atmospheric physics.Ultrafine particles(particle size≤100nm)have complex and important effects on the atmosphere in the near space through physical and chemical effects such as radiation forcing,aerosol nucleation and cloud formation.In recent years,countries all over the world had carried out relevant research on aerosol modes and concentration distribution in near space,but due to the minimum detection limit of optical methods and aerodynamic methods,there were few researches on ultrafine particles in adjacent space.Based on the principle of particle mobility,this thesis studied and designed a small particle size distribution system for in-situ detection of ultrafine particles in near space,realized the design of ultrafine particle charging,size identification and classification,detection and particle size distribution inverted at low pressure,and preliminarily completed the integration of the whole sensing system.The main contents were as follows:(1)Based on the monopolar corona discharge diffusion charging theory,a wire plate small charging module was designed.The effects of different polarity and structure on the corona discharge characteristics were studied.It was found that the positive corona discharge is more uniform at low pressure,and its charging stability at atmospheric pressure to 5.5kPa low pressure was proved by experiments,which established a foundation for the normal operation of the whole system at low pressure..(2)A small parallel Differential Mobility Analyzer(DMA)which can be integrated with the charging module was designed by using the method of differential mobility particle size identification and classification.Through computer simulation,the effects of different structural parameters on DMA detection performance were studied.It was found that the DMA channel width should be greater than eight times the height,so as to reduce the side wall effect of the flow field;When the slit width of the carrier gas inlet is as low as 0.75 times of the channel width,the particle transfer efficiency can reach 90%;The gap size of the carrier gas inlet slot has little effect on the detection performance of DMA.Finally,the experiments proved that the small parallel DMA has the ability of particle size identification and classification in the range of atmospheric pressure to 5.5kPa low pressure.(3)According to the principle of Faraday cup detection,an integrated Faraday cup electrometer detection module was designed.Compared with the commercial detection instrument,it proved that the self-made module has good detection efficiency,and realizes the evolution from detection electrical signal to particle information by using particle size distribution inversion algorithm.(4)Finally,the sub modules of the system were integrated and the adaptability test of high-altitude environment was carried out.The design and test of a miniaturized particle size distribution system for in-situ detection of ultrafine particles in adjacent space were preliminarily completed.