CFD analysis of mass transfer in spacer-filled channels for reverse electrodialysis

Abstract

Reverse electrodialysis (RE) is a promising technology for electric power generation by converting the chemical potential difference of a salinity gradient, within a stack equipped by selective ion-exchange membranes. Concentration polarization phenomena and pressure drop affect strongly the power output obtainable; therefore the channel geometry is a fundamental operating parameter for the optimization of the system. In this work, Computational Fluid Dynamic simulations were performed to predict fluid flow and mass transfer in spacer-filled channels for RE applications. A parametric analysis for different spacer geometries was carried out; in particular, woven and non woven spacers were simulated, with different pitch to height ratios, at various Reynolds numbers typical of RE channels, and with two different orientation. From the rigorous Stefan–Maxwell equation along with the assumptions of binary electrolyte and local electroneutrality, the transport equation was obtained. Periodic boundary conditions were adopted to simulate a fully developed flow. Simulation results show how the parameters investigated influence pressure drop and concentration polarization, thus suggesting the features that a spacer should have in order to obtain high process performance.