Mass transfer analysis of ultrafiltration using spacers based on triply periodic minimal surfaces: Effects of spacer design, directionality and voidage

An ideal feed spacer balances high flux and low pressure drop while minimizing fouling. In this work, several feed spacer with complex triply periodic minimal surface (TPMS) geometries were designed and fabricated using additive manufacturing (AM) processing. AM technology was employed to vary the voidage and directionality of the spacers. The fabricated spacers were tested to determine their impact on mass transfer, pressure drop and critical flux in a flat-sheet ultrafiltration (UF) setup for protein separation in aqueous medium. Dimensionless numbers analysis was conducted with dextran filtration, while critical flux was determined via the flux-stepping method by filtration of bovine serum albumin (BSA). All the tested TPMS spacers displayed an increase in mass transfer compared to a commercial spacer design, with the Gyroid spacer (84% voidage) exhibiting a 67% increase in Sherwood number. The Gyroid design also showed an 8% improvement in critical flux. Modification of the spacer voidage and direction also showed significant influence on performance. By increasing the voidage of the Gyroid spacer from 84% to 90%, we observe a 97% increase in Sherwood Number and an 18% decrease in Power number, compared to commercial spacer. The findings of this study show the advantages of TPMS architectures as candidates for spacer design in UF.