Miniaturization of Electrical Ultrafine Particle Sizers.

摘要

Nanoparticles, or ultrafine particles, have potential risks for human health, and the adverse health effects caused by ultrafine particles have been proven to be size related. To meet the increasing demanding for personal exposure monitoring and spatial distribution measurements of ultrafine particles, this dissertation studied the development and miniaturization of electrical ultrafine particle sizers (EUPS). There are three essential components for developing a EUPS unit: a charger to electrically charge the sample particles, an electrical mobility classifier to classify the charged particles, and a downstream particle count detector to measure the number concentrations. Two generations of EUPS were developed in this dissertation.;The first generation was a precipitator--type (p--type EUPS, which was assembled with a miniature corona--discharge unipolar charger, a miniature disk--type precipitator, and a portable condensation particle counter. All three components were calibrated under the optimized operation conditions. By combining the component calibration results, a data inversion scheme was developed to retrieve particle size distribution from measured signals. Size distribution measurement performance of the p--type EUPS prototype was then evaluated with both laboratory generated aerosols and field ambient aerosols. Evaluation results solidly verified the size distribution measurement reliability and flexibility of the p--type EUPS.;Several possible improvements were implied, for a more precise EUPS size distribution measurement, based on the p--type EUPS development. These improvements were realized in the second part of this dissertation, as the component development and evaluation for a second generation EUPS. A new corona--discharge based, miniature unipolar aerosol charger was developed and evaluated. The new charger design made significant improvements in both intrinsic and extrinsic charging efficiency, and it also maintained a more stable charging performance.;To improve the electrical mobility classification resolution, a miniature electrostatic aerosol classifier (EAC) prototype, named the Dumbbell EAC, was designed as an improved replacement of the mini--disk precipitator for the next generation EUPS. It had a novel axial--symmetric dumbbell--shaped curved classification channel design, to achieve an extended classification length within the compact overall device size. The Dumbbell EAC classification performance was evaluated both numerically and experimentally. According to both evaluation results, this palm size device, with its higher aerosol to sheath flow ratio as up to 1:5, and extended detectable size range from 10 to 850 nm, provided an improved solution for more precise portable size distribution measurements by the next generation EUPS.