Analysis and prediction of SWM feed spacer performance based on CFD results with an emphasis on the effect of micro-scale lateral and longitudinal washing flows

Abstract

In reverse osmosis applications, feed spacers are used in spiral wound membranes to separate the membrane surfaces and enhance mass transfer while incurring an acceptable pressure drop. In this study, an attempt has been made to understand the effect of spacer characteristics, such as arrangement and size, on mass transfer and pressure drop. Power-law equations were successfully developed to describe different spacer performance measures as a function of Reynolds number (Re), where both the multiplier of the Re term and the Re exponent vary for each spacer arrangement. Although at the macro level, it was not possible to adequately correlate the equation parameters with the spacers’ geometrical parameters (such as porosity), examining the post-processed CFD results at the micro level led to explanations for the observed concentration profiles, trends in spacer performance and changes in the equation parameters. A key observation was the importance of lateral flow recirculation, which was termed side-washing. Overall, based on the Spacer Configuration Efficacy performance measure and by assessing the trade-off between Sherwood number and pressure drop, the Woven configuration shows the best performance among the spacer arrangements and range of flowrates studied.