HOLLOW FIBER VACUUM MEMBRANE DISTILLATION MODULES WITH CROSS-FLOW AND PARALLEL FLOW ARRANGEMENTS

2D Large Eddy Simulations (LES) were run to characterize the effect of a cross-flow configuration versus the same cross-section in parallel flow for hollow fibers with a packing fraction of 50%, Reynolds number 500, for vacuum membrane distillation modules. The enhanced nature of vortex shedding and flow separation was able to effectively mitigate temperature polarization in cross-flow in both the axial and radial directions. The flow remained attached to the fibers in the parallel configuration, leading to thick thermal and concentration boundary layers corresponding to high polarization. In the parallel configuration, there was 2% radial distribution in the flux, showing a near-uniform boundary layer thickness. In the cross-flow configuration, the radial distribution varied in time based on the transient nature of vortex shedding. The shedding mitigated radial temperature polarization by reducing the boundary layer thickness and mixing more thermal energy that would normally exit the module via the bulk solution back into the zone near the membrane, improving axial polarization. For a module length of 40mm, corresponding to 30 rows of packed fibers, there was a 50% improvement in the flux performance switching from parallel to cross-flow.