CFD Simulation of Mass Transfer Phenomena in Spacer Filled Channels for Reverse Electrodialysis Applications

Salinity Gradient Power via Reverse Electrodialysis is a topic of primary importance nowadays. It allows getting energy from the "controlled" mixing of solutions at different salt concentration. The performance of this technology depends on many factors such as: components properties (i.e. membranes, spacers, electrodes), stack geometry, operating conditions and feeds features. Concentration polarization phenomena may significantly affect the actual membrane potential, thus reducing the gross power produced. On the other hand, C-polarization phenomena may significantly be reduced by suitably choosing the hydrodynamic regime within the stack. Such a choice may in turn significantly require higher pumping power, thus reducing the net power output. In this work, carried out within the EU-FP7 funded REAPower project, CFD simulations were carried out in order to study the fluid flow behaviour and mass transport phenomena within spacer-filled channels for SGP-RE technology. The effect of different parameters (channel geometry, feed flow rate, feed solution concentration and current density) on concentration polarization was assessed. The well known unit cell approach was adopted for the simulations in order to reduce their computational requirements as well as to increase the level of detail. Results show that the electrical potential loss due to polarization phenomena should be regarded as little significant in the case of seawater-brine for the operating conditions and geometrical configurations investigated. Conversely, a great attention should be devoted to such phenomena when very diluted solutions are to be employed (e.g. river water).