Flow-MRI to Analyze Effectiveness of Membrane Devices

Control of the hydrodynamics within the feed channel of membrane modules is a promising strategy to lower concentration polarization. The goal is to introduce secondary flows that reduce the boundary layer thickness. However, to prove that secondary flows are effective, tangible data of the local velocities are necessary. Visualizing the flow in membrane modules leads to a deeper understanding of the interaction between geometry and filtration performance.

This thesis interconnects flow-MRI, computational fluid dynamics and additive manufacturing to observe and manipulate the fluid dynamics in membrane modules. Together, these competences open the door to make new geometries, measure the filtration performance and model the fluid dynamics. This research approach was applied to medical and water filtration membrane modules combining filtration experiments with flow-MRI analysis.

In this way, flow-MRI visualized and quantified the active membrane area, vortex formation and internal flux pathways demonstrating the impact of membrane and module geometry on the filtration performance. Corresponding MRI images depicted the deposition mechanisms of silica particles on the membrane that are influenced by the feed flow. On grounds of first flow-MRI and MRI results in dialyzers, a new end cap was designed that utilizes flow straighteners. In addition, flow-MRI data were further processed to quantify shear rate patterns inflicted by staggered herringbones.

Flow-MRI is a powerful tool that enables to in situ observe flow manipulation and particle deposition in membrane modules. This thesis demonstrates that geometry matters and that the make, measure, model approach is applicable to many research fields in membrane science.