Flow uneven-distribution and its impact on performances of forward osmosis module

[Display omitted] •The flow maldistribution in modified spiral wound module is demonstrated.•At equal volumetric velocity, modified spiral wound module has higher flux.•Flow maldistribution decreases the flux significantly.•The impact of flow maldistribution is more dominant under high flux conditions.•The impact of flow maldistribution is minimal on fouling at low fluxes. Progresses on development of forward osmosis (FO) membrane should be accompanied with development of acceptable FO modules. Most flat-sheet FO membranes are assembled into the modified spiral wound module by introduction of an internal baffle which results in a U-shape flow path that allows flow uneven-distribution. This study assesses the flow uneven-distribution and its impact on a U-shape flow path and compares it with a straight flow path (I-shape), like the one in the plate-and-frame module. The flow distribution was visualized through the salt tracing test, dye tracing, computational fluid dynamics (CFD) simulation and particle image velocimetry (PIV). The performance of a bench-scale module of I-shape and U-shape was then assessed. Results from all visualization methods demonstrate large spatial flow variations in the U-shape flow path. However, it does not really affect the overall flux. The U-shape flow path benefits over the Ishape when operated at equal volumetric velocities. The I-shape path only shows higher fluxes by 21 % and 3 % when operated under equal cross flow velocities under active layer facing feed solution and active layer facing draw solution modes, respectively. The low fluxes in the U-shape flow path occur in the dead-zones. The flux variations in the U-shape flow path does not significantly affect the short-term membrane fouling but is expected to be more intense in the larger modules. A simple approach to combat flow uneven-distribution via inclusion of internal baffle can reduce uneven-distribution of flow.