Enhanced mass transfer and energy efficiency by a biomimetic feed spacer in reverse osmosis membrane modules

Abstract

Inspired by the structure of seal whiskers, this study undertakes a biomimetic design of the spacer in Reverse osmosis (RO) desalination, the performance of biomimetic spacers based on parameters such as elliptical cross-sectional area ratio (SR), twist angle (φ) and Reynolds number (Re) are analysed. Spacer performance ratio on the water production per unit pressure drop (SPR) and energy loss factor (λ) are introduced to better elucidate the structural performance of the spacer. The experimental and simulation studies on the adopted commercial spacer and the improved biomimetic spacer are used to demonstrate the reliability of the simulation. The structure of commercial spacer is further obtained by using micro-CT scanning, then the performance of commercial spacer (S1), circular cross-section spacer (CS), and prototype biomimetic spacer (BS) are numerically compared, and an improved biomimetic spacer (IBS) is obtained. When Re = 50 (Re = 300), the pressure drop of IBS is reduced by approximately 38 % (35 %) compared to the CS, and 39 % (28 %) compared to the S1; SPR is increased by approximately 83 % (57.4 %) compared to the CS, and 60.8 % (37 %) compared to the S1. With a filament angle (γ) of 60°, the IBS exhibits optimal performance. Ultimately, through data and theoretical analysis, theoretical formulas are developed to reflect the energy loss factor (λ) based on the projected area of the spacer along the flow direction, Re, and pressure drop. Through optimization of design, the improved biomimetic spacer can not only significantly reduce the pressure drop, but also obtain the high water flux, which provides new insights and methods for the development of seawater desalination technology.