An assessment of reverse electrodialysis for application to small-scale aquatic systems

Abstract

Reverse electrodialysis (RED) is a means by which to produce electrical power through the flow of Na+ and Cl- ions from seawater to fresh water across ion selective membranes. While current research has largely focused on utilizing RED for large-scale commercial power, this thesis explores the feasibility of using RED as a power source for remote sensing devices and unmanned underwater vehicles, with a specific focus on the Arctic Ocean. A parameter sweep is developed using MATLAB in order to estimate the ideal dimensions and flow rates for an RED stack with respect to its volumetric power density. Unlike previous models, this model accounts for considerations unique to RED's application to unmanned underwater vehicles and remote sensing devices in variable environmental conditions. The model maintains broad generality for use with a variety of RED design configurations, while also demonstrating agreement with empirical data collected from specific experimental tests. The computational model is validated by empirical data from three previous studies and used to find a specific and volumetric power density for RED of 2.35 W/kg and 206 �10⁻³ W/cm³ at 298K with salt concentrations of 0.7 and 35 g NaCl/ kg H₂O. This thesis then compares RED to other environmental energy harvesting systems and determines RED to be a competitive power source within the environmental constraints of the Artic. Regarding the use of RED as a secondary power source to charge lithium ion batteries, it is found that it would require an RED stack over four days to recharge a lithium ion battery of equal mass and over thirteen days for a battery of equal volume. For use with low power systems requiring constant power, an RED stack could supply more power than a lithium ion battery of equivalent mass for durations longer than three days and ten days for one of equivalent volume.