Experimental Investigation on Continuous Filtration of Sub-Micron Aerosol by Filter Composed of Dual-Layers Including a Nanofiber Layer

This study concerns filtration of sub-micron aerosol using dual nanofiber and microfiber layers. The first part compares the filtration performance of nanofiber (300 nm diameter fibers) and microfiber (1.8 mu m diameter fibers) filters. Test aerosol is sodium chloride (NaCl) particulates ranging from 41 to 514 nm generated from atomization. Experimental results show that the fractional efficiency and quality factor of nanofiber filter is higher than microfiber filter, but microfiber filter has lower rate of increase in pressure drop under continuous loading. The second part aims to utilize the dust holding capacity of microfiber filter to relieve the rapid clogging and skin formation of nanofiber filter. In this work, three types of filters formed by stacking of microfiber and nanofiber layers are tested to investigate the loading characteristics of inhomogeneous dual-layer fibrous filter under the challenge of sub-micron NaCl aerosol. Experimental results show that the filter with microfiber layer upstream of nanofiber layer has a lower increase rate in pressure drop than the filter with constituent layers in reversed arrangement. The semi-empirical model of polydisperse aerosol loading, as modified from the version of monodisperse aerosol, predicts deposition profile across filter depth that explains the pressure drop results. Serving two purposes, the dual-layer filter with microfiber (upstream) and nanofiber (downstream) is able to utilize the strength of nanofibers in clean stage filtration and microfibers in loaded stage filtration. Moreover, a lower pressure drop increase implies that the filter does not require frequent cleaning by backpulses of compressed air, which might destroy the fragile nanofibers.