Validation and characterisation of mass transfer of 3D-CFD model for twisted feed spacer

3D-CFD simulations of a membrane channel with several variations of twisted feed spacer geometry are performed for a Re-h range of 50-200 using a fine meshing approach. Although previous studies could not accurately simulate its performance, the current CFD model shows good agreement with previous experimental data. The validated model reveals that twisted spacers present higher Sherwood number (similar to 55 %) and lower friction factor (similar to 8 %) than conventional ladder-type spacers because the twisted features promote vortex generation and minimise the appearance of stagnant zones. Furthermore, the RR-twisted spacer outperforms the LL- and LR-twisted spacer types in terms of Sh because the concave surfaces of the spacers face towards the centre of channel, causing stronger vortices downstream of the filaments. With respect to the number of twists, Sh reaches a minimum at l(m)/l(twist) = 3 due to relatively stagnant zones. However, Sh increases at l(m)/l(twist) = 4 due to the formation of strong vortices in the region between the filaments. In terms of attack angle, Sh reaches a maximum at alpha = 45 degrees due to the formation of stronger vortices behind the filament intersection. This paper shows that CFD modelling tools have evolved to a stage that they can be used to understand membrane phenomena with complex spacer designs.

Automated summary

3D-CFD simulations are conducted on a membrane channel with different twisted feed spacer geometries. The results show that twisted spacers enhance vortex generation and reduce stagnant zones, resulting in a higher Sherwood number and lower friction factor compared to conventional ladder-type spacers. The RR-twisted spacer outperforms the LL- and LR-twisted spacer types due to the alignment of concave surfaces towards the channel center, creating stronger vortices downstream. The study also reveals that the number of twists and attack angle have an impact on the performance of the membrane channel.