Computational study of desalination by reverse osmosis — Three-dimensional analyses

• Characterization of three-dimensional binary fluid flows in a desalination module
• Membrane performance is enhanced by the presence of spacers.
• Spacers help in mitigating concentration polarization and fouling buildup.
• Spacers have more favorable influence on membrane performance at higher flow rates.
• The net of spacers in the 30° arrangement is the most efficient one.

A computational study has been conducted to examine three-dimensional steady multicomponent fluid flows in the reverse osmosis membrane module. The module contains a net of spacers. The SST k-ω turbulence model is employed to simulate flow and concentration fields at Re = 400 and 800, while the laminar model is employed to characterize flow and concentration fields at Re = 100. Spacer grids with 30°, 45° and 60° are considered as three different geometries. The membrane is treated as a functional surface where water flux, concentration and local pressure are coupled. The nature of concentration polarization in each membrane module is determined. Characteristics of potential fouling buildup are determined from the wall shear stress distribution. Correlations between potential fouling regions and the concentration distribution are presented. The coefficient of performance for each membrane module is determined at all flow rates considered. It has been illustrated that all membrane modules perform better at higher flow rates. The membrane module containing the net of spacers in the 30° arrangement is shown to be the most efficient membrane module. This study proves that the configuration of spacers is an important optimization parameter for the design of reverse osmosis membrane modules.