3D CFD study and optimisation of static mixer type feed spacer for reverse osmosis

Innovative designs of feed spacers for various applications of membrane-based separation processes are required to be identified. We proposed the static mixer type flat sheet of feed spacer and studied the shear stress and mass transfer around it in the flow channel. The enhanced mass transfer could be obtained by increasing the feed flow velocity at the expense of increased pressure drop. Box-Behnken design (BBD) of response surface methodology (RSM) along with desirability function analysis was used for the optimisation of the geometry with the average mass transfer at the membrane surfaces, pressure drop along the flow direction and channel Reynolds number as the optimisation parameters. The optimum geometry found corresponds to (lh) = 0.5 and θ = 45° at the channel Reynolds number of 78. The spacer configuration efficacy of the optimised geometry was found to be 20.7 × 10−6, which is in line with the reported data. However, the variation in the values of the average Sherwood number with the power number is slower than the commercial as well as other state-of-the-art geometries reported, opening up an opportunity to operate the system at lower Re, thereby increasing the permeate recovery at the same operating pressure.