Dean vortices applied to membrane process: Part I. Experimental approach

In order to demonstrate the interest of using Dean vortices at the industrial scale, three quite different types of water, two sizes of membrane module and two pilot plants are used. For bentonite suspensions and semi-industrial modules, the relation between limiting flux and wall shear stress for a Dean module is the same as the one obtained at the lab scale, whatever the shape and length of the helix. Secondary flow effects on permeate flux are maintained in the case of modules of greater size. Although for these semi-industrial modules, the limiting flux obtained in a straight module differs from that obtained in a woven module for a same wall shear stress, in the case of industrial modules the two types of modules seem to exhibit the same behavior. The whole of the results obtained for industrial modules is represented by a phenomenological relation that expresses the decrease in the fouling when the wall shear stress increases. In industrial conditions, an influence of the hydrodynamics is observed which is lower than at the lab scale.