Impact of Feed Spacer Filament Spacing on Mass Transport and Fouling Propensities of RO Membrane Surfaces

Abstract

Material build-up on membrane surfaces is one of the vital challenges faced by Reverse Osmosis (RO) operations leading to many operational and maintenance issues. To date, several modelling studies dealt with flow behaviour and concentration patterns for crossflow membrane operations. However, the relative fouling propensities of top and bottom membrane surfaces are never addressed in any study for narrow channels filled with ladder type spacers. In the present work, fluid flow patterns through different spacer configurations are visualized using ANSYS FLUENT by varying the dimensionless filament spacing, L (ratio of top or bottom filament spacing and channel height). Results clearly indicated that average shear stress values for the top membrane surface are always higher (3 to 8 times) than bottom membrane surface but yielded approximately similaraverage values of mass transfer coefficient for the two walls, for low to moderate filament spacings of L≤3 (SP22, and SP33) indicating similar fouling propensities of membrane surfaces. Further increase in filament spacing with L≥4 (SP44 and SP66), the average mass transfer coefficient for the top membrane indicated a sharp decline suggesting increased fouling propensity compared to bottom membrane which is not a desirable feature. Among the four spacer arrangements studied, SP44 (with L=4) was found to be the optimal arrangement yielding moderate pressure drop with nearly equal/higher area weighted values of mass transfer coefficient for the two walls and would lead to lower and equal fouling tendencies for top and bottom membrane surfaces respectively.