A three-dimensional model for the heat and mass transfer in air-gap membrane distillation

in Desalination and Water Treatment (2021)

Membrane distillation (MD) is a process to desalinate sea water. Pilot plants are operated aiming at increasing the modules’ efficiency for large-scale applications. In air-gap membrane distillation (AGMD ... [more ▼]

Membrane distillation (MD) is a process to desalinate sea water. Pilot plants are operated aiming at increasing the modules’ efficiency for large-scale applications. In air-gap membrane distillation (AGMD) the state-of-the-art modeling of mass and heat transfer is one-dimensional, combining evaporation and diffusion through the membrane and the condenser channel in one correlation. In this work, a numerical model is developed which computes AGMD modules in three dimen- sions. For evaporation and condensation, energy conservation equations at the interfaces are solved. Simulation results are compared to experimental data and a good agreement is found. The model is then employed to compare numerically two air-gap MD module configurations and evaluate their performance at different feed inlet temperatures, velocities and air-gap thicknesses. In the upside configuration, the hot feed flows above the membrane, while in the downside configura- tion it flows below the air-gap and membrane. In the latter, the feed solution is not in contact with the membrane but separated by the air-gap which is expected to improve the fouling resistance of the membrane. The three-dimensional computational fluid dynamic computation allows the visu- alization of the velocity profile in the air-gap due to buoyancy in the downside configuration [less ▲]