(418c) Desalination Performances of Large Hollow Fiber-Based DCMD Devices

Membrane distillation (MD) can be utilized to desalt highly saline waters that have considerable osmotic pressure. Current reverse osmosis desalination technology is not designed for saline waters having high osmotic pressure. Realization of this goal requires MD membranes to be highly fouling resistant. Fouling is a major obstacle that MD technique should potentially eliminate or control by selecting appropriate membrane material/surface, flow manipulation, additional force field and cleaning procedure. In direct contact membrane distillation (DCMD), Song et al. (2008) have shown that a rectangular cross-flow hollow fiber membrane configuration with a specific type of plasma polymerized superhydrophobic coating on the membrane outside surface and a novel method of operation ensured no precipitation based fouling from CaCO₃ and CaSO₄. We dwell on this novel aspect compared to conventional methods of fouling control. The simulation model of Song et al. (2008) assumed the membrane mass transfer coefficient, k_m, as an adjustable parameter for large hollow fiber modules with crossflow in a given range guided by estimated values and Zukauskas equation for predicting heat transfer coefficients in the two boundary layers. Here k_m was predicted from an enhanced model from Li and Sirkar (2016) without any adjustable parameters. To develop efficient designs, the model further simulated the performance of hollow fiber modules where the fiber ID was varied. Effects of fiber length on water vapor flux and water production rate were also modeled. This analysis will help design optimum hollow fiber membrane modules for desalination by DCMD for brines with low as well as high salinity.