Double filament feed spacers for enhanced performance in reverse osmosis modules

Optimizing feed spacer geometry can significantly improve the efficiency of reverse osmosis (RO) modules through enhanced hydrodynamics. In this study, a novel symmetrical spacer is developed to mitigate concentration polarization and enhance RO performance. The proposed double filament spacer design features double elliptical or circular filaments separated by a slit along their length, connected by column-type nodes. Flow simulations, a type of computational fluid dynamics simulation in which the Navier-Stokes equations are numerically solved without relying on turbulence models, provided a fundamental analysis of double filament spacer performance. These reveal an even velocity distribution and increased flow mixing induced by the double filament, regardless of the cross-section type. Moreover, additional vortices were promoted downstream of the double filament spacer nodes, producing a jetting effect. This phenomenon helped to reduce the polarization region on the membrane surface and improve the permeation potential, as confirmed by salt concentration and permeation velocity computations. Although both double filament spacers outperformed the commercial design, the circular double filament spacer exhibited higher permeation and lower salt deposition capabilities than the elliptical-shaped filaments. Furthermore, the practical effectiveness of a double filament spacer was experimentally assessed in the RO system. Both spacers showed the potential to enhance flux production and specific flux relative to commercial design, with an enhancement reaching 68 % in the case of the circular double filament spacer. Utilizing this spacer also demonstrated a substantial reduction in pressure drop by 35 %. Therefore, the novel double filament spacer design, particularly the circular filament type, appears well-suited for achieving highly efficient and low-energy performance in RO module elements.