Mass Transport Limitations in High-Performance Water-Vapor Selective Membranes: A Multiphysics Simulation Approach

The pursuit of high-performance, water–vapor selective membranes remain a focal point, as membranes often emerge as energy-efficient alternatives for psychrometric processes. Recent literature results on membranes fabricated from specialised polymers, 2D materials, and metal–organic frameworks (MOFs) as selective layers, have demonstrated unprecedented water vapour permeance and selectivity. However, few studies have examined how such high intrinsic permeances interplay with transport limitations governing the overall membrane performance in common test-cell geometries. This study aims to assess the theoretical limits of diffusion-based membranes by studying the impact of various transport resistances on the overall system permeance. Multiphysics simulations are used to model both fluid dynamics and mass transport within a simplistic geometry versus a commercially available sweep cell. A non-uniform flux pattern emerges, highlighting the substantial impact of non-uniform flow fields and fluid boundary layers, which were previously deemed inconsequential in gas separations. This leads to the underutilization of the membrane, yet unexpectedly increases the overall process permeance by approximately 20 % when compared to a simple planar geometry. As researchers engineer better selective layers, future advancements could push this difference as high as 36 %. By utilizing dimensionless groups and fitting parameters (0.76 Re^0.438Sc^0.33), the true membrane permeance can be extracted from the test configuration within a 5 % margin of error. This approach is essential for assessing permeances, scaling membranes, and enabling accurate comparisons.