Particle Collection of Electret Media under Different Filtration Pressures

Electret media have the advantage of enhancing the particle collection efficiency while keeping/reducing the media pressure drop by the electrostatic mechanisms in addition to the mechanical ones. This study investigated the effect of operational pressure on the filtration performance of electret filter media. Experiments was conducted at the pressures in the range of 0.33-3 atm and using DMA-classified particles ranging in electrical mobility sizes of 10-600 nm. The penetration of particles in the neutral, singly charged and Fuchs' bipolar charge states of two electret media (both charged and discharged) were measured. The single fiber efficiency due to the induced and Coulombic forces, i.e., eta In and eta C, were obtained. It is found that both efficiencies are a function of the filtration pressure (i.e., fiber Kn#) in addition to those parameters already included in existing models. A simple modification was also proposed for the existing model (based on the single fiber theory), enabling it to predict the particle collection efficiency of electret media operated under various filtration pressures.