Numerical investigation into the loading behaviour of filters operating in the diffusional and interception deposition regimes

Using a previously developed theory, which allows for changes in gas flow from deposit growth, calculations are performed for deposition on an initially cylindrical fibre. The deposit is given a specified porosity through which the flow is calculated from Darcy's equation using the Beavers and Joseph (1967) boundary condition at the outer boundary. Results are obtained for different porosities phi the volume fraction of space in the deposit, for flow conditions such that deposition occurs by the mechanisms of diffusion and interception, but not impaction (Stk < 1). Dependencies given in the literature of the deposit permeability on phi are examined. The dominant mechanism is determined by the value of the parameter, s = R/delta where R is particle to fibre radius ratio and delta is the non-dimensional thickness of the flow diffusion layer. Where diffusion dominates, s < 1, increase in porosity does not significantly increase deposition, apart from the effect of its lower density. Where s > 1 and interception dominates, deposition increases with increase in phi and is significant for phi >= 0.9 where more streamlines pass through the deposit. The shape of the deposit remains peaked at the front of the fibre, at the forward stagnation point, but, if a deposit has an initial flat front, it grows into a shape peaked away from the stagnation point, as observed by Kanaoka et al. (1986). Possible reasons for this behaviour are discussed. (c) 2012 Elsevier Ltd. All rights reserved.