How does porosity heterogeneity affect the transport properties of multibore filtration membranes?

TL;DR

This study uses computational simulations and experimental imaging to analyze how heterogeneity in porosity affects the transport and performance of multibore filtration membranes, revealing anisotropic permeability and lumen contributions.

Contribution

It introduces a combined experimental and computational approach to characterize and simulate the effects of spatial porosity variations on membrane transport properties.

Findings

Porosity heterogeneity causes anisotropic permeability in membranes.

Different lumen channels contribute variably to membrane performance.

Simulation results align with MRI measurements of membrane behavior.

Abstract

The prediction of pressure and flow distributions inside porous membranes is important if the geometry deviates from single-bore tubular geometries. This task remains challenging, especially when considering local porosity variations caused by lumen- and shell-side membrane skins and macro- and micro-void structures, all of them present in multibore membranes. This study analyzes pure water forward and reverse permeation and backwashing phenomena for a polymeric multibore membrane with spatially-varying porosity and permeability properties using computational fluid dynamics simulations. The heterogeneity of porosity distribution is experimentally characterized by scanning electron microscopy scans and reconstructed cuboids of X-ray micro-computed tomography scans. The reconstructed cuboids are used to determine porosity, pore size distribution, and intrinsic permeability in the membrane's porous structure in all spatial directions. These position-dependent properties are then applied to porous media flow simulations of the whole membrane domain with different properties for separation layer, support structure, and outside skin layer. Various cases mimicking the pure water permeation, fouling, and backwashing behavior of the membrane are simulated and compared to previously obtained MRI measurements. This work reveals (a) anisotropic permeability values and isoporosity in all directions and (b) differing contributions of each lumen channel to the total membrane performance, depending on the membrane-skin's properties. This study encourages to pertain the quest of understanding the interaction of spatially distributed membrane properties and the overall membrane module performance of multibore membranes.