Comparative Hydrodynamic Assessment of Twill-Woven Feed Spacers in Flat-Sheet Ultrafiltration Membrane Cassettes: Balancing Hydraulic Resistance and Near-Membrane Flow Enhancement

Feed spacers can promote membrane-side transport in flat-sheet ultrafiltration channels, but the accompanying hydraulic resistance increases pumping demand. This study combined pure-water pressure-drop measurements with transient three-dimensional ANSYS Fluent simulations to compare a commercial 2/1 twill-woven spacer (T-Base) and 16 systematically varied candidate configurations. A geometry-resolved finite-volume model was evaluated through computational-domain, mesh, and time-step sensitivity assessments; the predicted pressure gradients agreed with the measurements with a mean relative deviation below 4%. The methodological novelty lies in integrating pressure-normalized near-wall efficacy, bilateral wall shear stress balance, and equal-area spatial sampling within a geometry-resolved, multi-indicator framework for comparing spacer configurations with different periodic lengths and mesh densities. At a 60° low attack angle and a superficial inlet velocity of 0.0551 m·s−1, T3823 (filament spacing 0.38 mm, filament diameter 0.23 mm, spacer thickness 0.44 mm) provided the most favorable hydrodynamic trade-off among the 16 candidates. It produced a near-membrane velocity of 0.0220 m·s−1 and a pressure gradient of 53.5 kPa·m−1; its pressure-normalized near-wall efficacy was 1.23 relative to T-Base. T3823 also reduced bilateral membrane shear deviation from 24.91% to 8.30% and near-wall velocity dispersion by 50.7%. Overall, the results highlight the value of coordinated spacer-geometry optimization for balancing near-membrane flow enhancement and hydraulic resistance, with T3823 emerging as the most promising configuration among the candidates evaluated.