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Insights into the effect of spacer filaments in membrane systems on the flow pattern were obtained using a computational fluid dynamics code. The flow patterns were examined for a single filament adjacent to the wall and centered in the channel and for three different spacer configurations, the cavity, zigzag, and submerged spacers, with variations in both the mesh length and filament diameter for Reynolds numbers ranging from 90 to 768. Large recirculation regions were formed behind the filaments, and the flow around the filament increased the shear stress on the wall. For an identical Reynolds number and filament diameter, a single filament adjacent to a membrane wall produced a larger recirculation region than a single filament in the center of the channel. For the cavity and submerged spacers, above a critical Reynolds number or mesh length, the recirculation regions between sequential filaments influenced each other and merged to form one large recirculation region between sequential filaments. In contrast, the zigzag spacer forced the channel flow into a zigzag pattern, which caused the recirculation region to reattach to the wall.

A computational fluid dynamics (CFD) code was used to study the effects of Reynolds number, mesh length, and filament diameter on mass-transfer enhancement for three spacer configurations, a cavity, a zigzag, and a submerged spacer. For the cavity and zigzag spacers, masstransfer enhancement first increases with a decrease in the mesh length, reaches a maximum, and then decreases with a further decrease in the mesh length, while pressure loss showed a continuous increase with a decrease in the mesh length. The submerged spacer shows a continuous increase of the mass-transfer enhancement and pressure loss with a decrease in the mesh length. For all spacer types, mass transfer increases with the filament diameter. However, at a smaller filament diameter, the overall spacer performance increases, as indicated by a high mass-transfer enhancement to pressure loss ratio. Overall, the CFD simulations reveal that the zigzag spacer is the most efficient spacer type for a spiral-wound membrane module.

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