Barriers to electrodialysis implementation: maldistribution and its impact on resistance and limiting current density

Electrodialysis is an emerging low-energy membrane-based water-treatment technology with strong potential for industrial use. However, various engineering challenges have prevented widespread utilisation. The flow maldistribution in electrodialysis has been evaluated through computational fluid dynamics simulations in Ansys Fluent. A typical lab-scale stack geometry with ten cell pairs was simulated, and significant flow non-uniformity was found. An analytical model showed good agreement with simulations and was used to quantify the maldistribution through a single dimensionless number. The inlet flow rate and stack geometry were varied to investigate the distribution of flow. Maldistribution was exacerbated when the inlet flow rate, channel width, distributor angle, or number of cell pairs was increased. Further, the effect of maldistribution on the limiting current density (LCD) and stack resistance was evaluated using a one-dimensional model. Maldistribution was found to significantly impact the LCD, with a reduction of 23% found for the typical geometry relative to uniformly distributed flow. The resistance was impacted much less, showing an increase in resistance of only 2%. This highlights that maldistribution is a localised issue rather than a global one and goes some way to explaining why there has been a distinct lack of research into flow maldistribution in electrodialysis.