The present work involves the simulation and optimization of the ladder-type spacer mesh length (ML) ratio in spiral wound membranes (SWMs), using a two-dimensional (2D) integrated computational fluid dynamics (CFD) approach. The permeation properties, incorporated with a transient unsteady hydrodynamics modeling approach, were used to analyze and optimize the ML value for SWM feed spacers. The influence of unsteady hydrodynamics on the development of the concentration polarization in the membrane channel was also investigated. The optimum ML ratio was determined to be 3, because of its ability to generate a high intensity of unsteady hydrodynamics with the lowest effective concentration polarization factor and the results were further validated using velocity vector plots, wall shear stress analysis, and the localized concentration polarization factor. © 2010 American Chemical Society.