Comprehensive performance assessment of spacers in spiral-woundmembrane modules accounting for compressibility effects
Net-type spacers are essential components of the spiral-wound membrane (SWM) modules employed in reverse osmosis (RO) desalination plants. Despite progress made in designing SWM modules in recent years, key issues related to feed-spacer characteristics (particularly spacer material properties in conjunction with their geo-metry), which affect module performance and membrane integrity, have been neglected by the research com-munity. This paper focuses on the effect of compressive stresses, imposed on membrane spacers and envelopes during SWM-module fabrication to achieve module compactness and resistance to deformation during operation. A comprehensive method is presented (involving experimental and computational tools) which allows to quantify compressive stress effects, on the characteristics of spacer-filled membrane channels, and further to assess their impact on the key SWM-module operating parameters and on overall RO process performance. The method is demonstrated by assessing the performance of 26-mil commercial feed-spacer in an appropriate range of compressive stresses; it is interesting that modest nominal applied pressure, at the level of 1–2 bar, tends to cause significant feed-spacer compression, channel-gap reduction and membrane indentations impairing the active layer. The novel method is considered most helpful for selecting appropriate feed-spacer material and geometric characteristics, for a membrane of particular mechanical properties.