Semi-quantitative Analysis of Filtration Behavior on Electrets and Non-electrets Challenged by Particle Types, Sizes and Filtration Velocities

摘要

Fibrous materials are widely used for air filter media due to their high filtration efficiency (FE) and low pressure drop (PD) thanks to their highly porous structure. Electrostatically-enhanced charged materials, called electret, take the advantage of increasing the FE by electrostatic attraction of the particles without adversely decreasing the PD. However, the FE by electrostatic attraction is dramatically affected by particle types, sizes, and velocities. A number of theories and mathematical equations describe the FE of a media, charged or uncharged, with a certain fiber size when challenged by different particle sizes at different velocities by electrostatic and mechanical mechanisms. When particle size is bigger moving at a higher velocity, the FE of an uncharged media with higher fiber size is higher by inertial impaction. Conversely, its FE is lower at a slower particle velocity having the same particle size. In contrast, the FE is higher for the uncharged media with finer fiber size when challenged with smaller particles moving at a slower speed by Brownian diffusion. Conversely, its FE is lower at a higher particle velocity having the same particle size. The FE is noticeably reduced with the increase of the particle velocity on a charged media by the relative reduction of the electrostatic force with respect to the aerodynamic force. This presentation will semi-quantitatively analyze the FE of unchaged glass fiber media and charged meltblown (MB) media challenged by different types of particles and particle sizes at different velocities. The filtration theories will be discussed in comparison with the experimental results.