Dendritic deposition of aerosol particles in fibrous media by inertial impaction and interception

Abstract

When an aerosol of fine solid particles flows through a fibrous filter, particles deposit on fibers and form chainlike agglomerates known as dendrites (see for instance, Fig. 1). These dendritic structures grow relatively unhindered for an initial period of time, but eventually they begin to interfere with each other's growth and to intermesh (Fig. 2). This pattern of deposition has profound effects on the filtration efficiency and pressure drop, both of which increase rapidly with time. Therefore, rational design, optimization, operation, troubleshooting and innovation require intimate understanding and accurate analysis of the dendritic deposition process. A theoretical model of dendritic deposition for the period during which dendrites do not intermesh was developed by Payatakes [1], subject to the assumption that interception is the dominant capture mechanism. In the present work the model is extended to include deposition by inertial impaction and interception, mechanisms which are dominant for particles larger than about 1 μm. The “shadow effect” is also incorporated in the analysis.