Computational fluid dynamics modeling for performance assessment of permeate gap membrane distillation

The critical factors and interactions which affect the module-level performance of permeate gap membrane distillation (PGMD) were investigated. A three-dimensional computational fluid dynamics (CFD) model was developed for the PGMD configuration, and the model was validated using experimental data. The realizable k- ε turbulence model was applied for the flow in the feed and coolant channels. A two-level full factorial design tool was utilized to plan additional simulation trials to examine the effects of four selected parameters (i.e., factors) on permeate flux and thermal efficiency, both of which represent performance indicators of PGMD. Permeate gap conductivity (k_gap), permeate gap thickness (δ_gap), module length (L_module), and membrane distillation coefficient (B_m) were the selected factors for the analysis. The effect of each factor and their interactions were evaluated. B_m was found to be the most influential factor for both performance indicators, followed by k_gap and δ_gap. The factorial analysis indicated that the influence of each variable depends on its interactions with other factors. The effect of k_gap was more significant for membranes with higher B_m because the gap resistance becomes dominant at high B_m. Similarly, δ_gap is inversely proportional to the permeate flux and only significant for membranes with high B_m.