Characteristics of permeate-side spacers of spiral wound membrane modules

• Methodology for accurate determination of permeate-side spacer permeability.
• Typical effective lateral permeabilities of SWM spacers reported for the first time.
• Spacer/fabric thickness variation with imposed pressure accurately measured.
• Permeate-side permeabilities are essential for SWM design/performance simulation.

Reliable estimates of the effective lateral permeability (k) of permeate-side spacers of spiral wound membrane (SWM) elements are required in order to design them and simulate module and plant performance. Such permeability data are not available at present. A straightforward approach is recommended for determining k of spacers under modest pressure, which involves pressure drop measurements in a spacer-filled channel coupled with separate accurate data on the effect of normal pressure on spacer thickness. Application of this approach to typical spacers from commercial SWM modules shows that k is at the level of 2 to 3.5 × 10− 10 m2, for measured thickness 0.20 to 0.25 mm. The tested spacers exhibit modest compaction under pressure, with a tendency to approach asymptotically a minimum thickness at a pressure smaller than that prevailing in tightly wound membrane envelopes of commercial modules. Recommendations are also outlined regarding R & D directions on the selection of appropriate permeate spacers in the context of overall optimization of SWM module design and desalination process performance.