Computational Study of Seawater Desalination Using Hollow Fiber Direct Contact Membrane Distillation

Abstract

Computational fluid dynamics simulations were conducted to examine transport phenomena in a direct contact membrane distillation module comprised of hollow fibers (HF-DCMD) for desalination applications. Navier-Stokes, mass, and energy transport equations were used to simulate three-dimensional steady laminar flows. The Dusty Gas model calculates the vapor transport through the membrane in HF-DCMD modules. The vapor pressure difference between the two sides (lumen and shell) induced by the temperature difference drives the vapor transport. The effect of membrane properties and thickness on the membrane flux performance and the temperature and concentration polarization characteristics was assessed. The findings showed that hollow fiber membranes using direct contact membrane distillation configuration are more sensitive to the membrane thickness than other parameters. Moreover, an investigation of the effect of the feed inlet and outlet on the HF-DCMD module performance was carried out. The results prove that when the feed water flows parallel to the hollow fiber, it performs better than when the inlets or outlets are placed at the sidewalls of the shell. The effect of the packing density of fibers in the shell on the module performance was investigated. The outcomes demonstrated that the performance of the HF-DCMD module at a higher packing ratio was affected considerably, especially at a lower feed flow rate. The length degradation in highly packed HF-DCMD was investigated using modules with various lengths. It was demonstrated that temperature and concentration polarizations profoundly influence the module performance as the module length increases. Fins as a parallel flow disruptor were used to mitigate polarizations and increase vapor flux by enhancing mixing. Fins improve vapor flux by about 10%, and decrease polarization by 7%.