Numerical study of two-dimensional multi-layer spacer designs for minimum drag and maximum mass transfer

Based on the insights gained from previous published works, a series of multi-layer spacer designs for use in spiral wound membrane modules are proposed and evaluated via computational fluid dynamics simulations. The filament diameter to channel height ratio of traditional cylindrical filaments is reduced from 0.6 to 0.4 and 0.3, and one or two layers of elliptical filaments with various attack angles are introduced in the middle region of the channel. The mass transport equations are solved in conjunction with the momentum and continuity equations for a solute with Schmidt number of 600, and the hydraulic Reynolds number is varied from 50 up to 800. Spacer performance is evaluated via a basic permeate processing cost analysis. The proposed designs did not lower processing costs when operating at hydraulic Reynolds numbers above 200, but showed potential for reducing costs in the steady laminar flow regime, at hydraulic Reynolds numbers equal to or less than 200. Implications for design improvements of spacer meshes, such as extra layers of spacer filaments to direct the bulk flow towards the membrane walls, and changes to the filament profiles to reduce form drag are discussed. (C) 2008 Elsevier B.V. All rights reserved.