Helical-Ridge-Membranes from PVDF for enhanced gas-liquid mass transfer

New membrane geometries have the potential to increase mixing at the feed and permeate side to counteract concentration polarization and fouling. Such membrane geometries can be of very different architecture. Here, we address a new class of hollow fiber membranes having helical ridges. We focus on gas-liquid mass transfer, which is significantly slowed down by a liquid-side diffusion resistance. We present hydrophobic polyvinylidene fluoride (PVDF) helical ridge hollow fiber membranes produced by a rotating needle spinneret. Conceptually, the wet spinning methodology builds upon our Rotation-in-a-Spinneret platform technology, featuring customized microstructured rotating needles. The microstructured needle orifice includes two grooves to initiate ridge formation on the lumen side of the hollow fiber, while the ridges twist helically upon needle rotation. The new generation spinneret device produces hollow fiber membranes with reduced fiber diameter as compared to previous versions. It is specifically designed such that rotating spinning parameters enable an adjustable helical ridge pitch. Ridge formation and ridge shape strongly depend on rotational speed. The latter affects characteristic membrane properties such as membrane permeability and molecular selectivity. The helical ridges induce secondary flow in the lumen of the hollow fiber membranes, proven by pressure drop manipulation and experimental flow streamline visualization. In-depth analysis by flow simulation identifies rotational flow patterns as the governing flow phenomena. Ultimately, application in gas-liquid membrane contactors for oxygenation and CO2 capture revealed up to 10-fold improved transmembrane gas fluxes. Hence, the helical ridges cause turbulence promotion to introduce significant mass transfer enhancement.