奈米微粒與健康風險研究─子計畫三：奈米微粒控制技術研究(III)(2/2)
Date Issued
2005-07-31
Date
2005-07-31
Author(s)
陳志傑
DOI
20060725120958812309
Abstract
Due to the partial charging effect, the collection efficiency of an ESP tends to decrease with
decreasing particle size. In other words, the collection efficiencies in terms of number
density for nanoparticles of an ESP may be relatively low, although high mass collection
efficiency is well achieved by a conventional ESP. The main objective of this study was to
search the right types of filter foams that could efficiently collect those fugitive uncharged
nanoparticles. In order to conduct the aerosol penetration tests of filter foams, a constant-output
aerosol atomizer was used to generate challenge aerosol particles in the size range of
7 to 100 nm. A scanning mobility particle sizer (SMPS 3085) was used to measure the
aerosol concentrations upstream and downstream of the ESP unit and/or the filter foams.
Among the operation parameters were the foam porosity, foam solidity, foam thickness and filtration velocity. The results showed that aerosol penetration through filter foams decreased with increasing
foam porosity, apparently due the more surface area for aerosol deposition by diffusion.
Aerosol penetration increased with increasing filtration velocity due to shorter retention time.
The effect of foam packing density on aerosol penetration was very similar to foam porosity
(fiber diameter) because higher packing density means more filter materials and therefore,
more surface area for aerosol deposition. To take into account the air resistance together
with aerosol penetration, we found that low porosity, low packing and low filtration velocity
resulted in higher filter quality factor. The ESP unit tested in this work had a designed flow
rate of 100 L/min. For particles smaller than the most penetrating size (about 0.3 µm), the
aerosol penetration through ESP decreased with decreasing aerosol size until the size
reached about 15 nm (19%). Aerosol penetration of particles smaller than 15 nm increased
due to partial charging. Filter foam (110 ppi, packing density of 0.04 and thickness of 25.4
mm) removed most of the fugitive ESP nanoparticles (penetration from 19% down to 2.5%).
The air resistance induced by the ESP was almost negligible. Therefore, ESP is superior to
the filter foams from the perspective of filter quality, even for small particles with partial charging effect.
Subjects
Filtration
Nanoparticles
Filter foams
Publisher
臺北市：國立臺灣大學公共衛生學院職業醫學與工業衛生研究所
Type
report