Analysis of heat and mass transfer by CFD for performance enhancement in direct contact membrane distillation

Abstract

A comprehensive analysis on the dominant effects for heat and mass transfer in the direct contact membrane distillation (DCMD) process has been performed with the aid of computational fluid dynamics (CFD) simulations for hollow fiber modules without and with annular baffles attached to the shell wall. Potential enhancement strategies under different circumstances have been investigated. Numerical simulations were carried out to investigate the effect of the MD intrinsic mass-transfer coefficient of the membrane (C) on the performance enhancement for both non-baffled and baffled modules. It was found that the temperature polarization coefficient (TPC) decreases significantly with increasing C value regardless of the existence of baffles, signifying a loss of overall driving force. However, the higher C compensated for this and the mass flux showed an increasing trend. A membrane with a lower C value was found to be less vulnerable to the TP effect. In this case, the introduction of turbulence aids such as baffles did not show substantial effect to improve system performance. In contrast, introducing baffles into the module can greatly enhance the mass flux and the TPC for a membrane with a high C value, where the main heat-transfer resistance is determined by the fluid side boundary layers.The effect of operating temperature on heat and mass transfer in the MD process was also studied with a membrane of a lower C value (2.0×10 -7 kg·m -2 ·s -1 ·Pa -1 ). Although the TPC generally decreased with increasing operating temperatures, the mass flux N m increased significantly when operating temperature increased. A baffled module showed a more significant improvement than a non-baffle module at a higher temperature. Moreover, it was confirmed that higher operating temperatures are preferable for a substantial improvement in the heat/mass transfer as well as MD thermal efficiency, even with a relatively small transmembrane temperature difference of 10K.

Advances in Membrane Distillation for Water Desalination and Purification Applications

“…In 2012, Yu et al presented computational fluid dynamics results on the benefits of improving the flow conditions in DCMD modules [157]. They used DCMD hollow fiber modules with and without annular baffles attached to the shell wall to investigate the effect of the intrinsic mass-transfer coefficient of the membrane on the module performance.…”

Dynamic modeling and experimental validation for direct contact membrane distillation (DCMD) process

“…In [7] an intuition to consider a dynamic model for time evolution of the heat in the MD process was addressed, where the interest was focused on introducing numerical simulations for Navier-Stokes equations. Later on, the interest in dynamic modeling for the MD process continued, and followed with many studies that tackled the dynamic analysis of heat and mass transfer using Computational Fluid Dynamics (CFD) techniques [30][31][32][33][34]. For more numerical models for the MD process see [35][36][37][38][39][40] Literature models offer a predictive estimation for the temperature of the boundary layer region of the membrane, however they are unable to provide information about the temperature of the bulk solutions in the feed and the permeate sides.…”

Analysis of the effect of turbulence promoters in hollow fiber membrane distillation modules by computational fluid dynamic (CFD) simulations

“…Moreover, these prior simulation studies only focused on mass-and/or heat-transfer improvement by designing better flow channels or incorporating spacers for both non-MD and MD flat sheet or spiral wound membrane modules [37][38][39][40][41][42]. Thus far, CFD analysis for process modeling in hollow fiber MD modules has been limited to our previous work [33,43].…”