Simplified flux prediction in direct-contact membrane distillation using a membrane structural parameter

• Membrane structural parameters were evaluated for use in predicting water flux.
• Membrane constant containing non-coupled membrane properties was introduced.
• Membrane constant requires simple measurements and inexpensive analytical equipment.
• Membrane constant correlates well with experimental water flux.
• Comprehensive collection of MD membrane properties and water fluxes made available.

A priori water flux prediction is desirable when conducting membrane distillation (MD) studies, however existing models are complicated with inconsistent mass transfer mechanism assumptions. To develop a simplified model that can be used to predict the relative magnitudes of water fluxes for a group of MD membranes, correlation analyses were performed between water flux and 28 structural parameters. Four parameters were found to be highly correlated with water flux: ε/δ, ε/τδ, 1/τδ, and Cm. Cm is a newly introduced structural parameter that contains non-coupled membrane properties but still carries the physical meaning of a relationship between δ (thickness) and ε (porosity) and is determined by simple and reliable measurements using inexpensive analytical equipment. The correlation result between water flux and Cm suggests that Cm is a good structural parameter for MD flux prediction. The flux prediction errors for membranes with pore sizes from 0.1 to 0.9 μm were generally smaller for the model developed with Cm than for the dusty gas model. In addition to the new structural parameter and model, this study also makes available to the literature a detailed collection of MD membrane properties and their water flux values that will assist others in membrane selection, development, and application.