Improvement of desalination productivity with intermittent impermeable segments

This study explores how to enhance productivity in membrane devices by incorporating intermittent impermeable segments within a spacer-free geometry for RO, NF, and UF applications. The model features a hybrid channel structure where a central impermeable segment of length β is seamlessly integrated between two standard membrane segments, each of length L. The productivity parameter, defined as economic flow (E, $/s), balances hydraulic losses with permeate production. Key parameters include segment lengths (L and β), inlet flow speed (Re), and permeate value (w, $/kg). Results show impact of impermeable segment use on concentration polarization and permeate flux. Optimal segment lengths (β^∗) are dependent upon Re and w. Such lengths increase monotonically with w, reflecting the growing importance of mitigating polarization as permeate value rises. For a channel length of 300 mm, at Re=4.8, the optimal segment length peaked at β^∗=160mm for w>2×10⁻⁴ $/kg. Low Re values within the laminar range are necessary for effective use of impermeable segments, while higher values are not justified (β^∗=0). Compared to a staggered-cylinder spacer arrangement, our design achieves a 99.9 % reduction in axial pressure drop for a 300-mm commercial channel at 0.5 m/s cross-flow, yielding an estimated $40 in annual savings. This configuration offers an alternative approach for advancing desalination towards greater efficiency and economic sustainability.