10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Comparison of Non-Radioactive Bipolar Charge Conditioners for Particle Ionization
SIQIN HE, Derek Oberreit, Kanomax FMT, Inc.
Abstract Number: 1603 Working Group: Instrumentation
Abstract Electrical mobility method has been widely used as a primary standard for size characterization of submicron aerosol particles, and it usually has a bipolar charge conditioner as an essential component because of the predictable steady-state charge distributions it can condition the particles with. Majority of bipolar charge conditioners used in aerosol researches are radioactive sources, such as Kr85, Po210, and Am241, because of their advantages in simple operation, stable performance, and low maintenance. However, as aerosol research extends from laboratory into real field environment, problems have arisen when using or transporting electrical mobility instruments because of the safety regulations over radioactive sources, and caused these instruments to be considered as unsuitable for field studies. To overcome the hurdle and extend the application of such characterization technique, alternative bipolar charge conditioning methods haven been developed using non-radioactive ionization sources, with the most representative two as corona discharge and soft x-ray.
To better understand the ionization performance of non-radioactive bipolar charge conditioners, three non-radioactive bipolar ionizers were evaluated and discussed in this study, with one based on corona discharge and two using soft x-ray. The ionizers were first evaluated and compared for their capabilities in establishing steady-state charge distributions with the same incoming particles from with or without pre-existing charges. Subsequently, effect of the (N∙t) value on ionization efficiency was experimentally investigated at various residence time for each respective ionizer, and the results were compared to the Fuchs limiting sphere diffusion charging theory. Finally, fractions of singly charged particles exiting each charger were measured using monodisperse neutral particles within the size range of 5 to 100 nm, and the results were compared to theoretical values reported by Wiedensohler in 1988.