Dean vortices: comparison of numerical simulation of shear stress and improvement of mass transfer in membrane processes at low permeation fluxes

In order to rationalize the effect of Dean vortices on mass transfer improvement during membrane filtration, we present preliminary calculations of the wall shear stress in curved tube with non-porous walls. Previous experimental work has already shown strong positive effect of Dean vortices on mass transfer. In this paper, a numerical simulation of shear stress is proposed in order to determine the influence of the geometric parameters in four different tubes: straight, torus, helical and woven tube. The simulation results are tested against the analytical solutions which are available for velocity and pressure distributions in straight tubes. The simulation gives local values from which the location of Dean vortices in cross-section can be deduced and which depends on geometry and Reynolds number. Moreover, published results dealing with oxygenation of water by a membrane process and pervaporation of organic volatile compounds are considered using the present simulation results. (C) 2001 Elsevier Science B.V, All rights reserved.