Flux improvement by Dean vortices: ultrafiltration of colloidal suspensions and macromolecular solutions

Coiled and straight hollow-fibre modules have been built and tested; the pe rmeate flux obtained in ultrafiltration with these two geometries is compar ed for two feeds: a colloidal bentonite suspension and a dextran solution. In the case of colloidal suspensions, the secondary flows induced by the co iled geometry allow fouling to be reduced and the permeate flux is multipli ed by a factor of up to 2. An empirical relationship is proposed to express the limiting flux of permeate as a function of both the velocity and some geometrical parameters of the coiled modules. Analogous results are obtaine d during the ultrafiltration of dextran. It is also shown that under certai n conditions almost no deposit was formed; the permeate flux under these co nditions is three times higher for coiled modules than for straight ones. F or a given energy expenditure and ultrafiltration process, the gain in perm eate flux can reach a factor of 1.8. (C) 1999 Elsevier Science B.V. All rig hts reserved.