Reverse osmosis issues relating to pressure drop, mass transfer, turbulence, and unsteadiness

Numerical simulation has been used to investigate a number of significant physical processes for reverse osmosis in a spiral-wound membrane, including fluid-flow regimes, flow unsteadiness, and fluid-flow periodicity. The independent variables included the feed spacer strand angle, feed spacer thickness, inter strand spacing, strand radius, radius of the center cylinder, and Reynolds number. Results extracted from the numerical solutions were post-processed to provide algebraic correlations for both the dimensionless pressure drop and the Sherwood number. For the range of Reynolds numbers relevant to practice, turbulence was found to be nonexistent. Flow unsteadiness was identified for certain ranges of the Reynolds number and the geometrical parameters. The extent of the unsteadiness was sufficiently moderate so as not to have any practical effect on the dimensionless pressure drop and Sherwood number. Fluid-flow periodicity was verified.