INFLUENCE OF LONGITUDINAL DIFFUSION ON LI QUID-WALL MASS-TRANSFER IN DEVELOPING AXIAL LAMINAR-FLOW IN AN ANNULUS

This work deals with the numerical modelling of hydrodynamics and mass transfer in developing laminar axial flow in an annulus. Complete mom entum and mass conservation equations are solved by a finite element m ethod using the FIDAP code. Concerning the diffusional problem. the re sults are in keeping with numerical predictions and experimental data available in the literature. We have particularly confirmed the fact t hat the axial velocity profile is characterized by velocity peaks in t he vicinity of each cylinder of the annulus. This phenomenon is mainly due to the influence of the momentum longitudinal diffusion term. Res olution of the complete diffusion-convection equation allowed us to cl arify the influence of the mass longitudinal diffusion term, neglected when using hypotheses of the boundary layer theory. The diffusion ter m must be taken into account for a correct prediction of the mass tran sfer in developing hydrodynamic and diffusional flow regimes. (C) 1997 Elsevier Science Ltd.