A novel approach to detailed modeling and simulation of water-gap membrane distillation: Establishing a numerical baseline model

In water-gap membrane distillation (WGMD), natural convection within the water gap significantly impacts performance and thermal efficiency. Previous studies have used empirical or modified empirical correlation models to predict the Nusselt number within the water gap, investigating how natural convection affects WGMD performance and thermal efficiency. However, these models are specific to certain operating conditions, limiting their application in developing a comprehensive numerical model for the WGMD process. To address this limitation, we developed a numerical model by integrating a two-dimensional natural convection model within the water gap. Experimental investigations were conducted across a wide range of feed temperatures and water gap sizes to assess the influence of key operating parameters on performance. To validate the effectiveness of the proposed numerical model, the experimental results were compared with those from the proposed model and with results from numerical models used in previous studies. The proposed numerical model demonstrated a maximum deviation of 8.5 % from the measured data, whereas the numerical models used in previous studies exhibited deviations of 22.9 %. In addition, the flow characteristics within the water gap were analyzed through isotherms and streamlines, and the improved thermal efficiency of WGMD compared to direct contact membrane distillation (DCMD) was explored.