Performance Characterization of Hollow Fiber Direct Contact Membrane Distillation Module

Computational fluid dynamics (CFD) simulations were carried out to study the performance of a single hollow fiber in a direct contact membrane distillation (HF-DCMD) module for a desalination process. The feed solution is seawater with a salt (NaCl) concentration of 35 g/L. The Navier-Stokes, mass and energy transport equations are considered, with a coupled boundary condition imposed by the membrane. The system is investigated to examine sensitivity toward the membrane thickness, pore size, and inner hollow fiber diameter based on existing commercial fibers. Two membrane thicknesses (300 μm, 500 μm), two membrane pores sizes (0.2 μm, 0.45 μm), and two inner diameters (1.2 mm, 1.8 mm) are studied in the laminar regime at fixed operating conditions. The presence of temperature polarization causes a significant drop in the water permeation in the DCMD system due to reduced driving force across the membrane. The characterization of polarization inside the hollow fiber will be the focus of this work. It was found that the vapor flux was most sensitive to the membrane thickness (a 30% flux increase) versus the inner diameter (2% flux increase). The pore size is also a very influential parameter (20% flux increase), moving from optimal to less-optimal properties.