10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Filtration Performance of Electret Filter Composed of Nano/Micron Fibers
TOSHIKI MURAKAMI, Takafumi Seto, Yoshio Otani, Kanazawa University
Abstract Number: 648 Working Group: Control and Mitigation
Abstract Air filters composed of electrostatically charged fibers (electret filters) are commonly used for respirators. In the present work, mixed nanofiber/microfiber electret filters were investigated in term of the filter quality factor. The mixed nano/microfiber electret filters were prepared by an electrospinning process. From the scanning electron micrographs of prepared filters, it was found that both nanofiber and microfiber were well mixed to form uniform packing structure. The average fiber diameter of nanofibers was 200 to 1200 nm depending on the spinning condition, while that of microfiber was controlled to be 1800 nm.
The filtration performance of filters was investigated by measuring the collection efficiency, E (=1-P, where P is the penetration) and the pressure drop. Test NaCl particles were generated by an evaporation-condensation method and they were classified by the differential mobility analyzer (DMA) into the monodispersed particles of 30 to 300 nm in the electrical mobility diameter. The number concentrations of DMA-classified aerosol at the inlet and outlet were measured by a condensation particle counter (CPC). The penetration through the electret was measured with and without electrical neutralization by soaking it with isopropanol. The filtration velocity was varied from 1 to 10 cm s-1.
The filtration performance of charged and neutralized filters was evaluated by the filter quality factor, qf, defined as the ratio of logarithm of particle penetration to the pressure drop: qf = -lnP/ΔP, where, ΔP, is the pressure drop across the filter media. As the nanofiber diameter becomes smaller, qf of charged filters increased and reached over 0.25 at the nanofiber diameter of 600 nm, however, qf decreased when the fiber diameter was smaller than 600 nm. The total charge on the filter was estimated by comparing the collection efficiencies with/without neutralization. Q of the 600-nm fiber was estimated to be more than of 4x10-4 Cm-2 but it decreased with decreasing the fiber diameter.
Filtration performance of the electret was also analyzed by the single fiber filtration theory by taking into account the bimodal distribution of fibers. The filtration performance of the mixed fiber filter after neutralization was in good agreement with those predicted by introducing the inhomogeneous factor calculated from the bimodal distribution of fibers. As the fiber diameter decreases, qf of neutralized filter increased as predicted.