Pore-Level Multiphase Simulations of Realistic Distillation Membranes for Water Desalination

Membrane distillation (MD) is a thermally driven separation process that is operated below boiling point. Since the performance of MD modules is still comparatively low, current research aims to improve the understanding of the membrane structure and its underlying mechanisms at the pore level. Based on existing realistic 3D membrane geometries (up to 0.5 billion voxels with 39nm resolution) obtained from ptychographic X-ray computed tomography, the D3Q27 lattice Boltzmann (LB) method was used to investigate the interaction of the liquid and gaseous phase with the porous membrane material. In particular, the Shan and Chen multi-phase model was used to simulate multi-phase flow at the pore level. We investigated the liquid entry pressure of different membrane samples and analysed the influence of different micropillar structures on the Wenzel and Cassie-Baxter state of water droplets on rough hydrophobic surfaces. Moreover, we calculated the liquid entry pressure required for entering the membrane pores and extracted realistic water contact surfaces for different membrane samples. The influence of the micropillars and flow on the water-membrane contact surface was investigated. Finally, we determined the air-water interface within a partially saturated membrane, finding that the droplet size and distribution correlated with the porosity of the membrane.

Automated summary

Membrane distillation (MD) is a thermal separation process operated below boiling point. Current research focuses on improving the performance of MD modules by studying the membrane structure and underlying mechanisms. Using realistic 3D membrane geometries obtained from X-ray computed tomography, the interaction between liquid and gas phase with the porous membrane material was investigated. The influence of different microstructures on water droplets and the air-water interface within the membrane were also studied.