Experimental and theoretical analysis of scaling mitigation for corrugated PVDF membranes in direct contact membrane distillation

Abstract

To combat membrane scaling in membrane distillation (MD), corrugated surface patterned PVDF membrane have been designed for controlling the surface hydrodynamic properties as an engineering solution for preventing scaling. This paper attempted to correlate the CaSO4 scaling behavior of tailor-made flat PVDF (F-PVDF) and corrugated PVDF membrane (C-PVDF) in DCMD. We evaluated two feed flow modes: flow in parallel to the ridge(C-PVDF-p), and perpendicular to the ridge(C-PVDF-v). The experimental results demonstrated that C-PVDF-p exhibits the best of scaling resistance compared other two cases as well as flux. A 3D computational fluid dynamics (CFD) multiphysics model of DCMD was built by encompassing the conservation equations for mass, species, momentum, and energy. The hydrodynamic and thermal characteristics were analyzed. Modeling showed that C-PVDF-p exhibits higher flow velocity in the bulk and near the feed-membrane interface due to instabilities from feed turbulence; this enhances heat and mass transfer, feed mixing, and reduces residence time. Conversely, C-PVDF-v exhibited flow confinement within the grooves, resulting in a limited contribution to heat and mass transfer with the bulk solution. This flow behavior, coupled with the presence of recirculation vortices within the grooves, leads to an increased occurrence of CaSO4 scaling on the membrane surface. Additionally, C-PVDF-p exhibited high thermal efficiency, which explains a significant 48% increase in experiment, despite a modest 30% increase in the membrane surface area. This work demonstrated the successful module-scale CFD simulation for DCMD, and we expect future reliable modeling of large systems which provides tremendous savings in both time and cost for DCMD design for realistic applications.