Filtration performance of novel microfibrous media embedded with nanofiber flocs for aerosol particle removal

Abstract

Ingestion and accumulation of sea salt and other impurities is a major challenge for high speed vessels, turbine engines, and other air breathing systems. The performance and reliability of filters are anticipated to be improved significantly after the rate of performance degradation is reduced via enhanced filtration media and well-designed filtration approaches. This study proposes to apply anionic surfactant to disperse the nanofibers thoroughly and employ cationic surfactant to flocculate the dispersed nanofibers into numerous small groups of nanofiber flocs. Using the wet-lay procedure in the lab, the novel porous microfiber media was then fabricated with small groups of nanofiber flocs together with activated carbon and polyester fibers. The unique nanofiber filter media was then evaluated for filtration performance using face velocity, pressure drop, and filtration efficiency parameters. Due to nanoflocced fiber inclusion, an anomalous region in the filtration efficiency versus pressure drop regime was observed where wall slip occurring at the nanostructured surface provided an unusually high level of filtration efficiency near the most penetrating particle size (MPPS) region of 0.1-0.4 μm with a concomitant reduction in the normally encountered levels of pressure drop. This anomalous increase in the filtration efficiency versus pressure drop is a novel phenomenon and it is highly beneficial to aerosol filtration. The enhanced filtration reveals that the quality factor near the MPPS region increases significantly due to the inclusion of nanofiber flocs. The unique porous filtration media is expected to increase the dirt holding capacity and prolong the lifecycle of the turbine air filter systems.

Characterization of Dirt Holding Capacity of Microfiber-Based Filter Media Using Thermal Impedance Spectroscopy

“…The VGCFs easily become bundled together to create large clumps due to the extremely large van der Waals force and high surface energy. This is the critical concern on the application of the VGCFs in the filter media . Therefore, anionic surfactant sodium dodecyl sulfate (SDS) and cationic surfactant cetrimonium bromide (CTAB) were purchased from Sigma-Aldrich.…”

“…Finally in Case C, the nanofibers are flocculated as numerous small groups, i.e., nanoflocs. These nanofiber flocs can be simply embedded within the microfiber medium during the wet-lay manufacturing process. , Thus, an essential method of nanofiber inclusion to avoid the high pressure drop is to use nanofibers that do not continuously span the filter space but are attached to larger structure fiber networks, as stated in Cases B and C. Most companies are marketing filters that have electrosprayed nanofiber layers on top of a larger-diameter-fiber filter as described in Case A. These layers of nanofibers are intentionally kept thin to lower pressure drop, but the media’s surface quickly builds up a surface layer of entrapped particulates that grows into a filter cake.…”

“…However, for Cases B and C, nanofibers are synthesized or entrapped throughout the microfiber support structure; this potentially results in high particulate filtration efficiency and reduced pressure drop. Based on the analysis and comparison of the three different nanofiber inclusion methodologies discussed, further efforts on Case C have been made for an in-depth understanding of the filtration outcomes and for potential advanced product development . Vapor-grown carbon nanofibers (VGCFs) produced from hydrocarbon gases via catalytic decomposition using nanocatalyst crystals can be obtained at relatively lower cost.…”

“…Vapor-grown carbon nanofibers (VGCFs) produced from hydrocarbon gases via catalytic decomposition using nanocatalyst crystals can be obtained at relatively lower cost. The VGCFs were consequently chosen as the applicable nanofibers for this novel filter media fabrication in our laboratories. , The large van der Waals force and high surface energy between VGCFs cause bundling of the VGCFs with bundles ranging in diameter from a few hundred microns to a few millimeters. Based on the method developed by the Auburn CM3 group, − the VGCFs have been successfully separated, flocked, and dispersed into the wet-laid nonwoven filtration media with polymers and activated carbon fibers.…”

“…The VGCFs were consequently chosen as the applicable nanofibers for this novel filter media fabrication in our laboratories. , The large van der Waals force and high surface energy between VGCFs cause bundling of the VGCFs with bundles ranging in diameter from a few hundred microns to a few millimeters. Based on the method developed by the Auburn CM3 group, − the VGCFs have been successfully separated, flocked, and dispersed into the wet-laid nonwoven filtration media with polymers and activated carbon fibers. The nonwoven nanofloc filter media has been successfully developed by embedding nanoflocs into microfiber support structures via a wet-lay process.…”