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Energy efficiency enhancement of electromembrane desalination systems by local flow redistribution optimized for the asymmetry of cation/anion diffusivity

Title
Energy efficiency enhancement of electromembrane desalination systems by local flow redistribution optimized for the asymmetry of cation/anion diffusivity
Author
곽노균
Keywords
Electrodialysis; Mass transport enhancement; Spacer engineering; Concentration polarization; Ion concentration visualization
Issue Date
2017-02
Publisher
ELSEVIER SCIENCE BV
Citation
JOURNAL OF MEMBRANE SCIENCE, v. 524, page. 280-287
Abstract
In an electrochemical system, ion transport near ion exchange membranes or electrodes induces inevitable concentration polarization (i.e., formation of diffusion boundaries), which impedes the mass transport and worsens the energy efficiency. To mitigate the effect of concentration polarization (CP), various efforts towards mass transport enhancement employed structures, often called spacers, which promote mixing and modify the flow velocity distribution in the channel. In this work, we employed an electrodialysis (ED) system as a model to investigate the mass transport effects of embedded microstructures, which can redistribute the local flow velocity. We placed a row of cylindrical posts inside the diluate channel and varied the distance from the posts to the membranes. We studied the effect of this post-to-membrane distance on the mass transport by measuring the current-voltage responses and visualizing ion concentration and flow velocity profiles. The study was done through microfluidic ED model experiments and direct numerical simulation based on the coupled Navier-Stokes and Poisson-Nernst-Planck equations. Our results indicate that when the posts are positioned near the center of the channel, the mass transport is enhanced due to the increase in local convection near the concentration boundary layers. More importantly, we discovered that the mass transport is maximized when the location of the posts is slightly off-centered, due to the asymmetry of the cation/anion diffusivity (DNa+ < DCl-). Compared to a system without any structures, the embedded posts can improve both the electrical energy efficiency and the salt removal.
URI
https://www.sciencedirect.com/science/article/pii/S0376738816311590?via%3Dihubhttps://repository.hanyang.ac.kr/handle/20.500.11754/112742
ISSN
0376-7388; 1873-3123
DOI
10.1016/j.memsci.2016.11.046
Appears in Collections:
COLLEGE OF ENGINEERING[S](공과대학) > MECHANICAL ENGINEERING(기계공학부) > Articles
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