| Summary: | <span>Spacer design in spiral-wound membranes (SWMs) significantly affects the axial pressure<br />drop in the flow channel but also the deposit layer removal. However, the effects of the spacer<br />design and feed flow distribution in the module on the filtration performance have not yet been<br />investigated during the highly fouling-susceptible fractionation of proteins from skim milk by<br />SWMs. Therefore, a parallel spacer with no turbulence promotion and a less homogeneous feed<br />flow distribution in the SWM was compared to a diamond spacer with regard to its impact on<br />deposit formation and filtration performance. The experiments were conducted in a flat sheet test<br />cell and in SWMs. The parallel spacer induced a more homogeneous deposit layer formation.<br />However, no difference in filtration performance could be observed in the experiments with the test<br />cell. Even though deposit layer formation dominates the microfiltration, its amount and spatial<br />distribution could not be directly linked to the filtration performance. Furthermore, both spacers<br />were assessed in SWM. Despite the higher crossflow velocity applicable in the more open channels<br />of the parallel spacer, the performance of the parallel spacer was inferior to the diamond spacer.<br />This was independent of the viscosity of the feed. Due to the high curvature of the membrane sheets<br />close to the permeate collection tube, the cross-section of the flow channels in the SWM equipped<br />with the parallel spacer was reduced. This resulted in a distinctly lower deposit layer control and<br />performance, which could not be compensated by the resulting higher crossflow velocity far from<br />the permeate collection tube.</span>
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