Developing lengths in woven and helical hollow fibers for Dean vortices flows

摘要

Coiling membranes enables to create in the flow Dean vortices which enhance permeate flux and bring improvements to membrane filtration processes. The Dean number enables to predict the appearance of those vortices. As it increases, a secondary flow appears with one pair of vortices. However, this flow profile only establishes when the flow is fully developed. It is useful to predict the membrane developing length to take into account the impermeable part (inlet and outlet plugs) and to calculate the real membrane area submitted to the Dean, shear stress. Austin and al. [1] , and Guan and al. [2] simulated the developing angle respectively for a parabolic and a uniform flow at a tore entrance but their conditions and their results do not fit all experimental studies. Our work consisted in determining by CFD the developing length in the case of ultrafiltration with different kinds of woven or helical membrane tubes. This simulation has a wide validity range of parameters.