Numerical analysis of real-scale reverse electrodialysis with microscale structures and electrode segmentation

Abstract

Here we present an improved numerical method by exploiting periodicity to analyze a real-scale reverse electrodialysis (RED), including an unlimited number of microstructures and electrode segmentations. Flow and current (or voltage) distributions are calculated for a unit cell with on-demand adjustment of applied voltage (or current), and the calculations are repeated by mapping the outflow's data to the inflow's one. By laying end to end those results, a real-scale RED with vast microstructures and segmented electrodes can be simulated. 4-mm length RED was analyzed by exploiting periodicity and a conventional method, and we verified that the errors were within 1%, requiring 1/n memory usage and < 50% computing time (n: number of repeating units). Such reduced computational cost allows us to calculate 400-mm length RED filled with 4,000 microstructures of woven mesh spacer, 2D horizontal or 3D cross patterns and 10 segmented electrodes. We confirmed that the relative superiority of the local power generation of spacers/patterns varies from location, and the net power density (and net energy efficiency) can be enhanced up to 251 % by optimizing a system's size and 352 % by electrode segmentation. In addition, we verified that the degree of performance enhancement as segmenting the electrode is proportional to the Sherwood number, which represents the convective mass transfer governed by a flow velocity and spacer/pattern structures. To be best of our knowledge, this is the first numerical analysis of a real-scale RED with spacer/patterns and electrode segmentations simultaneously, and it firmly established the existence of coupled effects of patterns and electrode segmentation.