Influence of flow-interruption on filter performance during the filtration of liquid aerosols by fibrous filters

Abstract

This study investigated the influence of flow interruptions on the filtration performance of two different multi-layered fibrous filters during liquid aerosol filtration. It was found that both types of filters experienced a significant secondary loading stage, though they had reached a steady state for continuous flow. The filters showed distinctive increases in pressure drop and filter saturation until a second equilibrium state was reached. This second equilibrium state was attributed to a rearrangement of liquid in the filter during the breaks, clogging previously free passages. The ratio of shear and capillary forces was found to determine whether these passages were able to be “cleaned” once airflow was recommenced. Based on these findings, the airflow required to clean fully saturated filters was investigated and a phenomenological model developed to describe this behaviour. Furthermore, it was found that filters could be cleaned and reused, whereby they would return to one of the previous steady states (continuous or discontinuous flow). The experiments conducted in this work represent a more realistic test for oil-mist (or coalescing) filters than typical laboratory testing. Furthermore, it is hoped that they will help to bridge the gap between laboratory and field test results.