A novel retentate spacer geometry for improved spiral wound membrane (SWM) module performance, Journal of Membrane Science

Year : 2015

Author : Chrysafenia P.Koutsou, Anastasios J.Karabelas

The investigated novel retentate-spacer design comprises spherical nodes symmetrically connected with cylindrical filaments, thus forming a net-type structure with parallelogram unit-cells.Key feature of this configuration is the contact points (or small contact-regions) of nodes with bounding membranes, instead of filament-membrane contact lines characterizing the conventional unwoven-filament geometries; undesirable contact  lines create “dead-flow” zones, that promote reduced mass-transfer(i.e. increased concentration polarization-CP) and fouling.Direct numerical simulations of the flow field and mass transfer,complemented by pressured rop and mass-transfer coefficient measurements,reveal the advantages of novel spacers.The flow field, and local shear-stress and mass-transfer-coefficient distributions on membranes,are rather uniform. The novel spacers,considering also the extensive flow constrictions between filaments and membranes,exhibit broader distributions of these time-averaged transport parameters,which extend to higher values (compared to conventional spacers), with insignificant percentage of zero values;a fairly uniform shear-stress distribution is also identified on spacer filaments. Thus,significant benefits are expected in mitigating CP and fouling phenomena in membrane operation.Friction lossess how increased dependence on cross-flow velocity (compared to conventional designs), as they are affected more by flow-shearing at the membrane surfaces,than by form-drag. Useful pressure drop and mass-transfer correlations are obtained.