A HELICAL BAFFLE FOR CROSS-FLOW MICROFILTRATION

The use of a helical-shape baffle in a mineral (Carbosep) membrane pro vided an increase of more than 50% in permeate flux compared with that obtained without a baffle at the same hydraulic dissipated power. Two types of solutions were used: bakers yeast (5% dry weight) and dodeca ne- water emulsion (0.1%, w/w). The effect of the number of helices wi th respect to baffle length shows that the permeate volume increases w ith increasing number of helices but to a lesser degree when the numbe r of helices is more than 4 per 25-mm baffle length. Also, when the ba ffle's maximum diameter was reduced by about 40% a small variation in permeate flux values was observed. More interesting results were obtai ned with experiments at very low transmembrane pressures (0.1-0.2 bar) when the permeate flux remained almost constant even from the beginin g of the experiment, indicating that progressive fouling was practical ly absent. Flow visualization was made with a video camera (VHS) and s howed that the flow was rotational around the baffle axis and that the rotational velocity increased the mixing and migration of the rejecte d particles from the membrane surface. The manufacturing and installat ion of this type of baffle was found to be easy, and the cleaning time required for membrane regeneration was found to be shorter than after unbaffled steady flow experiments; so it was possible to recover the initial membrane permeability.