MASS-TRANSFER IMPROVEMENT IN HELICALLY WOUND HOLLOW-FIBER ULTRAFILTRATION MODULES YEAST SUSPENSIONS

Secondary flows known as Dean vortices, that appear in a curved pipe d ue to centrifugal force, are found to reduce concentration polarisatio n and fouling and increase membrane permeation rates. The influence of Dean vortices on mass transfer is studied in membrane filtration. The experimental study consists in filtering suspensions of baker's yeast with ultrafiltration hollow fibre membranes, arranged in straight or coiled modules. The effect of different operating parameters is tested : flow velocity, suspension concentration and module geometry. It is f ound that secondary flow enhances membrane permeation by a factor of u p to 5. Moreover, an energy analysis shows that for the same energy co nsumption, the permeate flux obtained in a coiled module is still far greater than that in a straight module. (C) 1998 Elsevier Science B.V. AU rights reserved.