Entropy generation analysis of electrodialysis

Abstract

Electrodialysis (ED) is a desalination technology with many applications. In order to better understand how the energetic performance of this technology can be improved, the various losses in the system should be quantified and characterized. This can be done by looking at the entropy generation in ED systems. In this paper, we implement an ED model based on the Maxwell-Stefan transport model, which is the closest model to fundamental equations. We study the sources of entropy generation at different salinities, and locate areas where possible improvements need to be made under different operating conditions. In addition, we study the effect of the channel height, membrane thickness, and cell-pair voltage on the specific rate of entropy generation. We express the second-law efficiency of ED as the product of current and voltage utilization rates, and study its variation with current density. Further, we define the useful voltage that is used beneficially for separation. We derive the rate of entropy generation that is due to the passage of ions through a voltage drop, and we investigate whether voltage drops themselves can provide a good estimate of entropy generation.

Optimal design and operation of electrodialysis for brackish-water desalination and for high-salinity brine concentration

“…In addition, the stack power consumption is linearly proportional to the average current density. This is consistent with the fact that the dominant resistance at high salinity is that of the membranes [24], which is assumed constant. Further, the pumping cost is negligible for all system sizes.…”

“…Our numerical implementation of this model was validated with experimental results from Kraaijeveld et al [23,29]. The validation was presented in a previous work [24], and is shown again in Fig. B.…”

“…In addition, the diffusion coefficients inside the membrane are different than those in the free solution. The details of this model are available in previous studies [23,24,29]. Our numerical implementation of this model was validated with experimental results from Kraaijeveld et al [23,29].…”

“…The details of this model have been laid out in previous studies [23,24], and the major points of the model are summarized in Appendix B.1.…”

Integrated Valorization of Desalination Brine through NaOH Recovery: Opportunities and Challenges

“…[29][30][31] Electro-osmosis is the migration of water molecules that solvate the ions.Since the ions are transported across the ionexchange membranes,the water molecules are co-transported with the ions,t hus increasing the effective resistance in the system. Fori nstance,t he migration of ions from the feed to the concentrated stream is not the only transport phenomenon that can occur;o ther transport phenomena are known to decrease the efficiencyo fE D, specifically electro-osmosis,b ack diffusion, and osmosis.…”