Abstract
Vehicle cabin air filters are exposed to humid air more frequently than any other air filters during routine use. The filtration performance of several commercially-available cabin air filters was investigated, along with the humid exposure period, using laboratory-based measurements. The averaged filtration efficiency and pressure drop were measured at ~70% and 75 Pa, respectively. Significant increases in filtration efficiency (up to 15%) and pressure drop (up to 250 Pa) were observed as the humid exposure time increased. Filtration efficiency increased ~15% and pressure drop increased 250 Pa as 140 g water was absorbed, which represents ~60 minutes humid exposure at a relative humidity of 90%. The pressure drop increased significantly at the beginning of the humid exposure due to the greater water absorption capacity of dryer dust in the filter. The dust load had a significant effect on the changes in filtration efficiency and pressure drop. The filtration efficiency and pressure drop of the 12-month used filter increased 2 times faster than that of the new filter at the same exposure conditions. The filtration efficiency and pressure drop were explicitly expressed as functions of the water absorption mass in the filter. Two coefficients were empirically derived and successfully accounted for the effects of humid exposure on filtration efficiency and pressure drop.
Highlights
In the last decade, many studies have identified vehicle cabin as a microenvironment for human exposure to Particulate Matters (PM) (Zhu et al, 2007; Kaminsky et al, 2009; Geiss et al, 2010; Knibbs and de Dear, 2010; Bigazzi and Figliozzi, 2012; Hudda et al, 2012)
Since the vehicle cabin air filters were designed as a medium-efficiency filter, the filtration efficiency was measured in the fine particle size range from 0.3 μm to 5 μm
For particles larger than 5 μm, the filtration efficiency is close to 100%, which implied the fact that the dust collected in the cabin air filter contains substantial large suspended dust that are enriched in metal elements (e.g., Zn, Cu and Cr) and ions (e.g., SO42–) (Zhao et al, 2006)
Summary
Many studies have identified vehicle cabin as a microenvironment for human exposure to Particulate Matters (PM) (Zhu et al, 2007; Kaminsky et al, 2009; Geiss et al, 2010; Knibbs and de Dear, 2010; Bigazzi and Figliozzi, 2012; Hudda et al, 2012). Extensive studies have been conducted to investigate the parameters that determine the PM entry to the in-cabins and measures to reduce the in-cabin PM concentrations (Xu and Zhu, 2009; Knibbs et al, 2010; Hudda et al, 2011). Both experimental and numerical studies have reported a positive effect of cabin air filter on reducing the in-cabin PM concentration (Pui et al, 2008; Qi et al, 2008; Xu et al, 2011; Xu and Zhu, 2013). Xu et al (2013) conducted extensive measurements on the performance of air filters that were used in the airliner cabins and reported a much greater filtration efficiency (86%–99%) and pressure drop (150–250 Pa) than vehicle cabin filters’.
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