Moisture transport through asymmetric porous membranes with finger-like holes for indoor humidity control: A lattice Boltzmann simulation approach

Asymmetric porous membranes with finger-like holes are one sort of promising membrane materials for indoor humidity control. Moisture transport in these materials is the key factor influencing humidity control performance. To overcome the difficulties in modelling meso-scale mass transfer in these materials, a lattice Boltzmann simulation (LBM) methodology has been proposed to model the pore-scale gas flow and mass transfer in the asymmetric membranes with finger-like holes. A typical membrane is classified into three sub-layers: a porous support layer, a layer with finger holes, and a denser skin layer. Simulated annealing technique was used in our study to reconstruct the calculating domain. Then fluid flow and mass transfer in the membrane were predicted with LBM, and permeability and effective diffusivity were evaluated. The existence of finger holes in the matrix could dramatically enhance the overall mass transfer in the membranes. Besides, the inhomogeneity in membrane structures would make the macro-scale lumped parameter prediction of membrane performance questionable. Our findings show differences in comparison to previous macro-scale multi-layer analysis. The dominant resistance is in the skin layer. There should be a change in emphasis for membrane optimization with a focus on the skin layer rather than the porous layer.