How slug flow can improve ultrafiltration flux in organic hollow fibres

The study deals with the use of a gas-liquid two-phase flow to reduce particle membrane fouling in organic hollow fibres by injecting air directly into the feed stream. A theoretical approach of slug flow in fibres demonstrates that the slugs created inside the fibres induce high wall shear stresses. Moreover, the membrane surface is alternately submitted to positive and negative shear stresses. This succession of stresses is expected to prevent filtered particles from settling on the membrane surface and then enhance the ultrafiltration mass transfer. Experiments were carried out with clay suspensions in hollow fibre membrane, A range of various air velocities and particle concentrations was examined and the effect of a steady gas flow was compared to that of an intermittent one. As expected, the injecting air process leads to an increase of the permeate flux by up to 110% for U-g=1 m s(-1) (flux multiplied by 2.1), for all the various concentrations studied. Furthermore, even at a low air velocity a significant enhancement can be achieved (+60% for U-g=0.1 m s(-1), flux multiplied by 1.6). An intermittent gas flow seems to be less effective than a steady one in similar experimental conditions.