10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Collection Performance of Nanofiber/Microfiber Mixed Air Filter Prepared by Wet Paper Processing
Youichi Omori, TIANYI GU, Li Bao, Yoshio Otani, Takafumi Seto, Kanazawa University
Abstract Number: 1112 Working Group: Control and Mitigation
Abstract Recent progress in manufacturing nanometer-order fibers (nanofibers) may lead potential applications of nanofibers to air filtration media. Since nanofibers are expected to enhance the collection performance (a high efficiency at a low pressure drop), the application of nanofiber to air filter has been investigated by several research groups. The quality factor, Qf, of an air filter is a widely used index to evaluate the filter performance. From our preliminary experiment, Qf of a commercial air filter (uncharged, medium performance and HEPA grade, fiber diameter of submicron) was around 0.03 Pa-1 or less for particles of 300 nm at the filtration velocity of 5.3 cm/s. Based on the filtration theory, mixing of small amount of nanofiber is expected to increase Qf. However, the structure of nanofiber filter prepared in the most of literatures was thin film (membrane) due to the low mechanical strength of nanofibers and a high packing density. As a result, the filtration performance and the service life of nanofiber filters are not yet high enough to meet the high demand for industrial usage. In this work, a wet paper processing method was used to produce nanofiber/microfiber mixed filter media. Two kinds of nanofibers (α and β) with the average fiber diameter of 177 and 240 nm were mixed at 10 to 20 wt% with microfibers of the average diameter of 11.6 micron. The filtration experiments were conducted using polyalphaolefin (PAO), NaCl and Japanese standard dust (JIS-11) test aerosol at the filtration velocity of 5.3 cm/s. Three kinds of test filters were prepared with the collection efficiencies of (a) 80%, (b) 99.7%, and (c) 99.99% for 0.3-micron particles by changing the mixing ratio of nanofibers. The pressure drops of these filters (5.3 cm/s) were (a) 42 Pa, (b) 133 Pa and (c) 218 Pa, attaining the quality factor of 0.04, 0.044 and 0.04, respectively. The quality factor is also evaluated based on the single fiber filtration theory (Kirsch and Stechkina, 1978) taking into account the inhomogeneity of filter packing. A good agreement was found between the experimental and theoretical collection efficiencies, suggesting that the wet processing is an effective means for packing nanofibers uniformly in a micron fiber bed.