On the Filtration Efficiency of Composite Media Composed of Multiple Layers of Electret Media

Abstract

The intention of this study is to find out the reasoning for the discrepancy between the measured and calculated filtration efficiencies of composite media composed of multiple layers of base electret media reported in previous studies. Size-fractionated particles in neutral, single-charged, and Boltzmann-stationary-charge-distributed were prepared to measure the filtration efficiency of multi-layered electret media. It was found that the reported discrepancy was attributed to the charge distribution of the test particles. This result further suggests that the charge distribution of the test particles must be taken into consideration for the filtration efficiency prediction of multilayered electret media.

Importance of Dipole Orientation in Electrostatic Aerosol Filtration

“…Note that unlike the case of mechanical capture mechanisms, no corrections exist for the single-fiber efficiency correlations to address the interplay between the electrostatic particle capture and that due to the other mechanisms. Therefore, in the present study, the total single-fiber efficiency, η SFE ( n ), is calculated using the individual electrostatic efficiencies, as given in eq η normalS normalF normalE ( n ) = 1 − ( 1 − E σ D false( n false) ) ( 1 − E σ C false( n false) ) Finally, the collection of the filter (due only to electrostatic attraction) can be calculated using eq . η E ( n ) = 1 − prefix∑ n = − ∞ n = ∞ [ f ( n ) 0.25em exp true( − 4 α η normalS normalF normalE ( n ) H π d f ( 1 − α ) true) ] where f ( n ) is obtained from eq based on the particle charge distribution (see refs ,,,− for additional information about the applications of the above empirical equations).…”

“…This justifies the need for further research on electrostatic particle capture for future filtration applications. Theoretical research on electrostatic aerosol filtration started decades ago with the pioneering work of Lathrache and Fissan, Kanaoka et al, and Podgórski et al and has continued to this date by various groups (see, e.g., refs − ). Nevertheless, electrostatic aerosol filtration has remained a poorly understood process due to the lack of quantitative information about the distribution and density of charges of different polarities in a fibrous filter. − …”