A CFD Study on Different Configurations of Spacer-Filled Membrane Distillation System Using OpenFOAM

Circular economy initiatives like the EC funded iWAYS project (grant agreement: 958274) promote the reuse of waste heat in industrial sites. This presents opportunities and challenges for technological adaptation. Membrane distillation (MD) is a thermally driven process for water treatment that can use waste heat. However, effectively treating complex industrial wastewater requires adapting MD units to achieve reliable and efficient performance. Filament spacers within the MD units play a key role in structural maintenance and flow mixing. CFD simulations can help to characterize filament spacer configuration impacts on the hydrodynamic of feed and permeate channels, which affects both trans-membrane temperature gradient and membrane fouling control. Here, we performed a CFD study on a direct contact membrane distillation (DCMD) sub-unit with the goal of evaluating impact on robustness and performance of a set of designed filament spacer configurations. The modeled membrane distillation system has an overall length of 200 mm, width of 10 mm and height of 4.1 mm, containing two layers of filaments in each of the feed and permeate channels. The diameter of the filaments was 1 mm, and they had a 45 degrees angle to the flow direction in the channels. Variations of this standard filament configuration were also tested and simulated to optimize their mixing performance. The numerical simulations to approximate in a 3D solution of Navier-stokes equations for steady state conditions were performed using OpenFOAM code. The computational domains were meshed using OpenFOAM snappyHexMesh utility, and finite-volume based simulation relying on the chtMultiRegionFoam solver was executed in parallel over 40 CPU cores. Comparing the CFD analysis of different filaments' configurations lead to an assessment of an improved spacer structure. The selected configuration is to be 3D printed for laboratory-scale experimental confirmation of the validity of the CFD model and the optimal configuration finding.