Three-dimensional CFD analysis of hydrodynamics and concentration polarization in an industrial RO feed channel

Hydrodynamics and mass transfer characteristics in an industrial spiral wound reverse osmosis (RO) feed channel under typical plant operating conditions are investigated using fully-coupled three-dimensional computational fluid dynamic (CFD) simulations with a detailed spacer geometry. The pressure drop vs average longitudinal velocity can be approximated by ΔPc∝ū1.67 and the trend matches an empirical correlation previously derived from plant data. Substantial wall-parallel velocity near the membrane surface is observed, which suppresses boundary layer development. Rolling cells are formed in the center of the feed channel, which promote transverse mixing. Different from concentration polarization phenomenon in unobstructed flat channels, concentrated islands are isolated in regions near spacer filaments where flow is relatively stagnant. The local mass transfer coefficient km oscillates longitudinally but the cell-average k¯m appears fairly constant in cells adjacent to each other. It is shown that k¯m∝ū0.40 under typical plant operating conditions. A one-dimensional system-level model incorporating the CFD results is developed and validated by plant trial data under various operating conditions, yielding a slight improvement in accuracy as compared to the author's previously published empirical model.