CFD prediction of scalar transport in thin channels for reverse electrodialysis

Reverse electrodialysis (RED) is a very promising technology allowing the electrochemical potential difference of a salinity gradient to be directly converted into electric energy. The fluid dynamics optimization of the thin channels used in RED is still an open problem. The present preliminary work focuses on the computational fluid dynamics simulation of the flow and concentration fields in these channels. In particular, three different configurations were investigated: a channel unprovided with a spacer (empty channel) and two channels filled with spacers, one made of overlapped filaments and the other of woven filaments. The transport of two passive scalars, representative of the ions present in the solution, was simulated in order to evaluate concentration polarization phenomena. Computational domain effects were also addressed. Results show that: (i) the adoption of a computational domain limited to a single unit cell along with periodic boundary conditions provides results very close to those obtained in a larger domain; (ii) the woven spacer-filled channel is the best compromise between pressure drop and concentration polarization. Future work will address the inclusion of electrical effects along with the migrative transport of the ions in the channel.