Simulation of the flow around spacer filaments between narrow channel walls. 1. Hydrodynamics

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.