Combined macroscopic and pore scale modeling of direct contact membrane distillation with micro-porous hydrophobic membranes

Abstract

The transport processes of a direct contact membrane distillation (DCMD) module are investigated with a multiscale approach in this study. A stochastic, numerical reconstruction algorithm is first developed to generate 3D virtual membranes based on the membrane's pore size and fiber orientation distributions. Pore-scale simulations are then performed on the reconstructed membrane model. The membrane's effective thermal conductivity and mass diffusivity are computed using AVIZO software and OpenFOAM solver, respectively. A 2D macroscopic, multiphysics model considering the conservation of mass, species, momentum, and energy is developed, where the effective transport properties obtained from pore-scale simulations are utilized, to study the heat and mass transfer through the membrane. Two commercially available polytetrafluoroethylene (PTFE) membranes (GE-Osmonics/0.22 μm and MS-3010/0.45 μm) are chosen as examples for the present multiscale approach. The computed transport properties of the membranes are found to yield good distillate flux predictions with data reported in the literature. The MS-3010/0.45 μm membrane is found to produce 24% higher freshwater on average than GE-Osmonics/0.22 μm membrane. Finally, the performance of DCMD of three hypothetical membranes with different specifications is compared to the reconstructed MS-3010/0.45 μm membrane to study the factors that need to be taken into account for optimal design of the membrane for DCMD applications.