“…As such, spacers of different types and geometries have been compared in terms of local shear stress and mass transfer coefficient [1-2, 5, 7, 9, 38-40]. A commonly used approach to account for solute permeation is to specify a constant membrane rejection combined with water flux and wall concentration [6,12,15,18,21,26,30,31]. This can be expressed as: J s = J w c m (1−R s ) where J s is the solute flux, J w the water flux (or flow velocity on the membrane wall), c m the solute concentration on the membrane wall and R s the membrane rejection.…”