Sinusoidal shaped hollow fibers for enhanced mass transfer

- A novel method to directly produce sinusoidal shaped hollow fibers.
- One step dry wet spinning of passive mixing membranes.
- Detailed discussion of occurring phenomena and mass transfer increase.

Geometrically structured flow channels induce secondary flows and vortices enhancing mass and heat transport rates. In particular, these vortices may reduce concentration polarization and subsequent fouling in membrane transport processes. In this work we present a new method of producing hollow fiber membranes with a sinusoidal change in diameter along the fiber length. We engineered a pulsation module that imposes a sinusoidally fluctuating bore liquid flow rate. Harmonic bore flow conditions can be varied over a wide range of operational settings. The fluctuating bore liquid flow rate translates into axial membrane properties varying with respect to inner bore diameter and wall thickness.We suggest that the resulting narrowing and widening of the membrane lumen channel induces secondary vortices to the liquid feed inside the membrane lumen. In gas/liquid membrane absorption processes these secondary vortices reduce the diffusional resistance, also known as the Bellhouse effect. For the produced hydrophobic PVDF membranes, improved oxygen transport from shell-to-lumen side prove superiority over straight hollow fiber membranes in G/L absorption process by a factor of 2.5 at higher liquid flow rates. We anticipate the dynamic flow module to be easily integrated into currently existing hollow fiber membrane spinning processes.