Structured hollow fiber membranes for enhanced mass transfer

This thesis describes the development and evaluation of three technologies to structure hollow fibers in a manner such that passive mixing is directly coupled with the fluid flow through these novel hollow fiber structures. The aim of this thesis is to provide production technologies that are applicable to large-scale membrane fabrication beyond the laboratory scale as well. The first principle is based on the phenomenon of liquid rope coiling, which is consequently applied to the spinning process of hollow fibers, resulting in spiral structures. The influencing parameters are evaluated. Different batches of hollow fibers are prepared from three polymer solutions, varying in viscosity. Finally, membrane geometry, morphology, and potential Dean numbers are discussed. The second principle creates hollow fibers with variating diameter, caused by periodic flow conditions during the membrane formation process. The flow field in such membrane channels studied by means of CFD. The fabrication principle is applied to different material systems. The spun fibers are experimentally characterized in terms of geometry, morphology, mass transfer, and pressure loss. The third principle uses rapid prototyping to allow for the customization and optimization of spinnerets. On this basis, a rotation is superimposed on the spinning process, giving twisted membranes in a single step production. Different spinneret geometries are designed and 3D-printed. The rotational spinning is applied with a PES-based material which results in twisted multi-channel fibers. These fibers are investigated with regard to their geometry, morphology, and potential applications. Finally, the three novel technologies are compared in terms of applicability and performance potential.