  Ultrafiltration membrane modules suffer from a permeate flow decrease arising
during filtration and caused by concentration polarization and fouling in,
e.g., fermentation broth purification. Such performance losses are frequently
mitigated by manipulating the hydrodynamic conditions at the membrane-fluid
interface using, e.g., mesh spacers acting as static mixers. This additional
element increases manufacturing complexity while improving mass transport in
general, yet accepting their known disadvantages such as less transport in dead
zones. However, the shape of such spacers is limited to the design of
commercially available spacer geometries. Here, we present a methodology to
design an industrially relevant mini-module with an optimized built-in 3D
spacer structure in a flat-sheet ultrafiltration membrane module to eliminate
the spacer as a separate part. Therefore, the built-in structures have been
conceptually implemented through an in-silico design in compliance with the
specifications for an injection molding process. Ten built-in structures were
investigated in a digital twin of the mini-module by 3D-CFD simulations to
select two options, which were then compared to the empty feed channel
regarding mass transfer. Subsequently, the simulated flux increase was
experimentally verified during bovine serum albumin (BSA) filtration. The new
built-in sinusoidal corrugation outperforms conventional mesh spacer inlays by
up to 30% higher permeation rates. The origin of these improvements is
correlated to the flow characteristics inside the mini-module as visualized
online and in-situ by low-field and high-field magnetic resonance imaging
velocimetry (flow-MRI) during pure water permeation.
