A process model of electrodialysis including membrane deformation effects

Abstract

Electrodialysis (ED) is an electro-driven process that makes use of ion exchange membranes (IEMs) under an applied electric field. The main application of ED is the desalination for drinking water production. A transmembrane pressure (TMP) distribution may arise in ED stacks due to an uneven pressure distribution in the two fluid channels, thus causing membrane/channel deformation and flow redistribution. This can occur in large-scale non-parallel configurations, e.g. crossflow arrangements. Detrimental effects of membrane deformation have widely been studied with reference to several membrane processes. However, this aspect has been neglected in ED applications. In this work, a novel process model of ED units including the effects of membrane deformation is presented. The model was developed with a multi-scale architecture. The model simulates the fluid-structure interaction (i.e. membrane deformation and flow redistribution) in a cell pair based on correlations from small-scale numerical simulations (structural mechanics and computational fluid dynamics). Then, transport and electrochemical phenomena occurring in ED systems are simulated. Cross-flow ED units were simulated in two-dimensions (length and width). Results showed that mild deformations have a negligible impact on the ED process performance. However, configurations prone to larger deformations (e.g., thin membranes) exhibited more significant effects, with an increase in the specific energy consumption. The same approach can be used for other configurations (e.g. counter-flow and asymmetrical channels in parallel flow) and for reverse electrodialysis.