Chemistry in a spinneret — Sinusoidal-shaped composite hollow fiber membranes

Composite membranes are highly permeable and used with great success in nanofiltration, reverse osmosis and gas separation. However, the higher the membrane permeability gets, the more pronounced becomes the role of the laminar boundary layer. Common approaches to overcome boundary layer limitation include the use of spacers or inserts, which induce secondary mixing. In contrast, we use composite hollow fiber membranes with an altered geometry to generate mixing effects on the lumen side without integrating spacers. In the sinusoidal-shaped lumen channel of our fibers, secondary flows and vortices evolve. To fabricate the hollow fibers, we combine two technologies. With the chemistry in a spinneret approach, we fabricate composite hollow fibers in a single-step process. Pulsating the bore fluid flow creates the sinusoidal geometry of the fiber. The superposition of a sinusoidal pulsed bore fluid flow and the chemistry in a spinneret approach fabricates sinusoidal-shaped composite hollow fiber membranes in a single step. This geometric feature reduces the boundary layer resistance and we demonstrate that the sinusoidal-shaped fibers excel the straight fibers in their performance of drying compressed air.