Collection Efficiency of Indoor Suspended Particulates by Using the Electrostatic Charged Filters
Date Issued
2005
Date
2005
Author(s)
Yang, Shin-Hao
DOI
zh-TW
Abstract
This study elucidates the effects of using a surfactant-pretreated filter (SPF) as an electret filter on the aerosol penetration. Surfactants (dimethyl dioctadecyl ammonium bromide, DDAB; sodium oleate, SO; sodium dodecyl sulfate, SDS) were used to pretreat polypropylene fibrous filters to make them charged. Various factors, including the particle size (0.05 to 0.5 μm), the aerosol charge state (Boltzmann-equilibrium charge, neutral and singly charge), the face velocity (0.1, 0.3, 0.5 and 1.0 m/s), the species of aerosol, the relative humidity (RH 30% and RH 70%) and the concentration of surfactant (0.01 M, 0.05 M and 0.08M) were considered to evaluate their effects on the aerosol collection characteristics. The Loading behaviors of these SPFs were also evaluated in this study. Furthermore, this study investigated the collection characteristics of the SPFs for bioaerosols.
Experimental results from our study demonstrate that the aerosol penetrations through SPFs were lower than through the untreated filter. The 0.3 μm-aerosol penetrations through an untreated, 0.05 M DDAB, SO and SDS-pretreated filters with Boltzmann-equilibrium charged aerosol were about 76%, 37%, 45% and 60%. Pretreating the filter with anionic surfactant did not change the structure of the filter and the mechanical capture force. The electric field measured by an electrofieldmeter of the SPFs was larger than that of untreated filter obviously. These findings imply that pretreatment with surfactant made the filters charged. The surface charge of the SPFs increased with the surfactant concentration. Aerosol penetrations through the SPFs increased with the face velocity. SPFs performed better against solid aerosol than against liquid aerosol. SPFs performed better when the tested aerosol had a larger dielectric constant. Relative humidity has no effect on the aerosol penetration through the SPFs. Regression equations for Coulombic and dielectrophoretic single-fiber efficiencies in terms of the dimensionless parameters could be fitted by the experimental measurements of SPFs in this work.
The results also demonstrate pretreatment of the filter with surfactant increases its particle-loading capacity. The clogging points of the 0.05 M DDAB and SO pretreated filters and untreated filter are 30, 28 and 18 g/m2. When a filter pretreated with a higher concentration of surfactant has a larger loading capacity, and a filter cake is formed as more mass is deposited. Additionally the loading behavior of the SPFs also depended on the size of the particle. The smaller particle more seriously clogs the SPFs. The loading capacity of the SPFs is lower at a higher face velocity.
Results of this study indicate that the bioaerosol penetrations through SPFs were lower than that through the untreated filter. Penetrations through an untreated, 0.05 M SO and DDAB-pretreated filters with E-Coli bioaerosol were about 66%, 28% and 22%, and Candida famata var. flareri bioaerosol penetration through an untreated, 0.05 M SO and DDAB-pretreated filters were about 60%, 21% and 21%. The data also imply that the surfactant on the SPFs has the restraint on bioaerosols. The penetrations through the SPFs with bioaerosol increased with the face velocity.
Subjects
帶電濾材
界面活性劑
穿透率
表面風速
介電常數
相對濕度
微粒載負
阻塞點
生物氣膠
electret
surfactant
aerosol penetration
face velocity
dielectric constant
relative humidity
aerosol loading
clogging point
bioaerosol
Type
thesis
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