The effect of fibre diameter on filtration and flux distribution - relevance to submerged hollow fibre modules

This paper examines the effect of fibre diameter on filtration and flux dis tribution with inter-fibre two-phase flow for conditions relevant to submer ged bioreactors (SMBR). Hollow fibres of different diameters fixed in a spe cially designed holder providing shell-side feed were tested for a model bi omass feed with pumping and submerged systems. The experimental results sho wed that the effect of the fibre diameter on filtration increased with the increase in turbulence around the fibres. For filtration with two-phase flo w, the performance was sensitive to changes in fibre diameter and significa ntly lower flux declines were obtained with smaller fibres. On the other ha nd, a theoretical analysis of flux distribution along the fibre in a submer ged system showed the smaller fibres to be disadvantaged. The theoretical m odel based on the simplified Navier-Stokes equations and filtration equatio ns revealed that the flux distribution along the fibre depends on fibre inn er diameter, length and fibre permeability. The effect of these factors can be related to a dimensionless coefficient zeta = 4lR(i)(-3/2)R(m)(-1/2). S ensitivity analysis demonstrated that for zeta > 2, the maximum flux along the fibre can be approximately estimated by J(max) = zetaJ(mi). Although, t he effect of high initial local flux on performance of filtration is still to be assessed, the flux distribution model is useful in design and operati on of the SMBR system. (C) 2001 Elsevier Science B.V. All rights reserved.