The stream-wise vibration effect of a fibrous filter is studied experimentally and numerically for the purpose of evaluating filtration efficiency. The particle sizes range from 0.02 to 10 μm and the face velocity ranges from 3 to 10 cm/s. The vibrational peak velocity also varied from 0 to 50 cm/s. The filtration efficiency for this wide size range is obtained by combining the individual test results for fine particles (0.02 to 0.5 μm) and large particles (0.5 to 10.0 μm). For the fine particle experiment, Arizona Road Dust (ARD) test particles are generated by an atomizer after an ultrasonic process and measured by a Scanning Mobility Particle Sizer (SMPS). For the large particle experiment, the test particles are generated by a fluidized bed and measured by an Aerodynamic Particle Sizer (APS). When the particles are generated by the atomizer after ultrasonicating, the majority of the particles are in nano scale without the agglomerates on the large particle surface, while particles generated by the fluidized bed are mostly in micro-scale because many nanoparticles are agglomerated on large particle surface. The filtration efficiency increases with the vibrational peak velocity in the impaction-dominant region (Dp> 0.1 μ m) and diffusion-dominant region (Dp< 0.1 μm), due to the increased relative velocity between the particle and the filter fiber and the increased diffusion intensity from turbulence around the fiber, respectively. A model for the filter vibration effect is established with a modified Stokes number for the impaction-dominant region and an empirical analysis for the diffusion-dominant region.
Bibliographical noteFunding Information:
This work was supported by the Post-doctoral Fellowship Program of Korea Science & Engineering Foundation (KOSEF) and Center for Filtration Research in University of Minnesota.