A numerical model of fibrous filters containing deposit

Abstract

This work is aimed at developing numerical methods to model the effects that particle deposit collected by fibrous filters has upon the flow field within the filter and hence upon further deposition. A numerical model of the flow field has been developed using the Boundary Element Method. The model contains a two dimensional single fibre with the boundary conditions applied on the computational domain accounting for the neighbouring fibres. A layer of porous material is assumed to cover the fibre modelling deposited particulate. The width of the porous layer, which varies along the fibre surface, is defined by particle behaviour determined in earlier work, Dunnett and Clement 1 . Once the flow field is known the motion of the particles in the flow is modelled. Small particles are considered where diffusion is the main mechanism by which they are captured by the fibres. Various situations are considered and the flow and particle behaviour investigated.In particular the effect of existing porous deposit on the fibres upon further deposition is studied.

Assessing the Protection Provided by Facepiece Filtering Respirator: New Model Involving Spherical Porous Layer with Annular Peripheral Opening

“…In addition, the model can be expanded to include the particle penetration dynamics due to the filter loading with the particles deposited on the fibers. This can be done by utilizing approaches presented in Kirsch (2006) and Dunnett and Clement (2009).…”

On the filtration performance of dust-loaded trilobal fibers

“…As a result, the flow experiences higher resistance and the deposited particles enhance the collection mechanisms. The effect of particle deposition on the filtration performance (i.e., collection efficiency and pressure drop) of fibers with circular cross-section has been investigated previously in many studies (e.g., [7][8][9][10][11][12][13][14][15][16]). Although trilobal fibers are becoming increasingly more available [17][18][19][20][21], the literature is very scarce (and controversial sometimes) when it comes to using such fibers for aerosol filtration [22][23][24][25][26].…”

Critical trajectories for aerosol particles: Their determination for impaction in fibrous filters and in oscillating bubbles

“…In our previous work on filtration ( Dunnett and Clement 2006, 2009and 2012, the boundary element method was used to calculate the flow field for aerosol particles incident on a fibre. The deposition mechanisms examined for a growing deposit were diffusion ( Dunnett and Clement 2006) and also interception Clement 2009, 2012 ).…”

“…The determination of particle trajectories by solution of their equation of motion in a given flow field was discussed by Davies (1973), and here we describe a very efficient method for reaching the limiting critical trajectory for impaction in a fibrous filter by a process of iteration. We also describe a direct method for their determination applicable to impaction in an oscillating gas bubble inside a liquid in which the equations in a time-dependent velocity field can be transformed into an integral equation.In both cases the flow field in which the particles move must be known or calculable, and we assume the particles are subject to Stokes' drag in conditions such that the Stokes number, St so that diffusion can be neglected in describing the particle motion.In our previous work on filtration ( Dunnett and Clement 2006, 2009and 2012, the boundary element method was used to calculate the flow field for aerosol particles incident on a fibre. The deposition mechanisms examined for a growing deposit were diffusion ( Dunnett and Clement 2006) and also interception Clement 2009, 2012 ).…”