Numerical simulations of the effect of spacer filament geometry and orientation on the performance of the reverse osmosis process

Abstract

Momentum and mass transfer in reverse osmosis membrane modules must be optimized to design efficient and economical designs. The feed spacers are used to improve mixing, to minimize fouling and concentration polarization. This computational study analyses fluid flow, mass transfer, concentration polarization and pressure drop in the feed channel of a reverse osmosis membrane module with different spacer filament geometry (cylindrical, diamond, pentagonal, and triangular), orientation and Reynolds numbers. The computational model solves three-dimensional fluid flow and mass transfer while considering the complex water and solute flux boundary conditions. The cylindrical spacer filaments configurations showed the lowest water flux, followed by pentagonal, diamond, and triangular spacer filaments configurations. The concentration boundary layer thickness was high near the spacer surface due to the stagnant velocity zone. The results indicated that the concentration polarization on the membrane surface increases with a decrease in Reynolds numbers. The channel containing triangular filament spacers gave the maximum water flux and minimum concentration polarization. The spacer configurations with an attack angle of 45° and a transverse angle of 135° showed the highest water flux; however, the pressure drop was also high. The channel containing triangular spacer filament (T1A0) showed the least CP. However, the concentration boundary layer thickness was higher at the bottom side of the channel. The developed model could be useful for predicting the reverse osmosis membrane process performance.