High-Volume Aerosol Filtration and Mitigation of Inertial Particle Rebound

Abstract

The performance of electrostatically charged blown microfiber filter media was characterized for high-volume sampling applications. Pressure drop and aerosol collection efficiency were measured at air pressures of 55.2 and 88.7 kilopascals (kPa) and filter face velocities ranging from 2.5 to 11.25 meters per second (m/s). Particle penetration was significant for particles above 0.5 micrometers (μm) in aerodynamic diameter where the onset of particle rebound was observed as low as 200 nanometers (nm). Particle retention was enhanced by treating filters in an aqueous solution of glycerol. Adding this retention agent eliminated electrostatic capture mechanisms but mitigated inertial rebound. Untreated filters had higher nanoparticle collection efficiencies at lower filter face velocities where electrostatic capture was still significant. At higher filter face velocities, nanoparticle collection efficiencies were higher for treated filters where inertial capture was dominant and particle rebound was mitigated. Significant improvements to microparticle collection efficiency were observed for treated filters at all air flow conditions. At high air pressure, filter efficiency was greater than 95% for particles less than 5 μm. At low air pressure, performance enhancements were not as significant since air velocities were significantly higher through the fiber mat. Measured single fiber efficiencies were normalized by the theoretical single fiber efficiency to calculate adhesion probability. The small fiber diameter (1.77 μm) of this particular filter gave large Stokes numbers and interception parameters forcing the single fiber efficiency to its maximum theoretical value. The adhesion probability was plotted as a function of the ratio of Stokes and interception parameter similar to the works of others. Single fiber efficiencies for inertial nanoparticle collection were compared to existing theories and correlations.Received 30 September 2013; accepted 9 February 2014. Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.Address correspondence to Josh Hubbard, Sandia National Laboartaories, P.O. Box 5800 MS 1148, Albuquerque, NM 87185-1148, USA. E-mail: jahubba@sandia.gov INTRODUCTIONA large number of works have examined the performance of fibrous filtration media at filter face velocities greater than 1.0 meter per second (m/s). In a previous work, we have shown that nanoparticle collection efficiencies via impaction and interception deviate from the predictions of Stechkina et al. (1969) for viscous flow when filter face velocities are significantly higher than 0.01-0.1 m/s (Hubbard et al. 2012). Increased penetration has been observed and attributed to inertial particle rebound from the fiber surface. The objectives of this study were to (1) characterize the performance of eBMF (electrostatically charged ...

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