Chapter five - Filtration characteristics of nanofiber filter and multilayer nanofiber filter for depth filtration

Abstract

The conventional filter correlations for filter efficiency and pressure drop have been adopted to interpret and predict performance of nanofiber filters under depth filtration. Specifically, a detailed comparison between these correlations with a set of tests using uncharged polyethylene oxide (PEO) nanofiber filters has been worked out, wherein the efficiency is determined for nine filters with different fiber basis weights. These test filters have been challenged with sodium chloride aerosols of sizes between 50 and 500nm. Both the tests and correlations are in agreement with each other. The results reveal the U-shape behavior of the grade efficiency curves for the nanofiber filters with aerosol size and decreasing maximum penetration particle size (MPPS) with increasing fiber basis weight or fiber packing density. The test also reveals as the fiber basis weight increases, the fiber packing density first increases with reduced pore size between neighboring fibers at constant filter thickness. With further increase in fiber basis weight, the thickness starts to increase while the fiber packing density increases only modestly. Based on such peculiar behavior of a nanofiber filter, a multilayer (ML)/multimodule nanofiber filter has been developed.