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Title: Self similarities in desalination dynamics and performance using capacitive deionization

Abstract

Charge transfer and mass transport are two underlying mechanisms which are coupled in desalination dynamics using capacitive deionization (CDI). We developed simple reduced-order models based on a mixed reactor volume principle which capture the coupled dynamics of CDI operation using closed-form semi-analytical and analytical solutions. We use the models to identify and explore self-similarities in the dynamics among flow rate, current, and voltage for CDI cell operation including both charging and discharging cycles. The similarity approach identifies the specific combination of cell (e.g. capacitance, resistance) and operational parameters (e.g. flow rate, current) which determine a unique effluent dynamic response. We here demonstrate self-similarity using a conventional flow between CDI (fbCDI) architecture, and we hypothesize that our similarity approach has potential application to a wide range of designs. We performed an experimental study of these dynamics and used well-controlled experiments of CDI cell operation to validate and explore limits of the model. For experiments, we used a CDI cell with five electrode pairs and a standard flow between (electrodes) architecture. Guided by the model, we performed a series of experiments that demonstrate natural response of the CDI system. We also identify cell parameters and operation conditions which lead to self-similar dynamicsmore » under a constant current forcing function and perform a series of experiments by varying flowrate, currents, and voltage thresholds to demonstrate self-similarity. Based on this study, we hypothesize that the average differential electric double layer (EDL) efficiency (a measure of ion adsorption rate to EDL charging rate) is mainly dependent on user-defined voltage thresholds, whereas flow efficiency (measure of how well desalinated water is recovered from inside the cell) depends on cell volumes flowed during charging, which is determined by flowrate, current and voltage thresholds. Results of experiments strongly support this hypothesis. Results show that cycle efficiency and salt removal for a given flowrate and current are maximum when average EDL and flow efficiencies are approximately equal. We further explored a range of CC operations with varying flowrates, currents, and voltage thresholds using our similarity variables to highlight trade-offs among salt removal, energy, and throughput performance.« less

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [2];  [2];  [1]
  1. Stanford Univ., CA (United States)
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1497314
Alternate Identifier(s):
OSTI ID: 1526165; OSTI ID: 1548441
Report Number(s):
LLNL-JRNL-745800; LLNL-JRNL-769873
Journal ID: ISSN 0043-1354; 930428
Grant/Contract Number:  
AC52-07NA27344
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Water Research
Additional Journal Information:
Journal Volume: 140; Journal Issue: C; Journal ID: ISSN 0043-1354
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Materials science

Citation Formats

Ramachandran, Ashwin, Hemmatifar, Ali, Hawks, Steven A., Stadermann, Michael, and Santiago, Juan G. Self similarities in desalination dynamics and performance using capacitive deionization. United States: N. p., 2018. Web. doi:10.1016/j.watres.2018.04.042.
Ramachandran, Ashwin, Hemmatifar, Ali, Hawks, Steven A., Stadermann, Michael, & Santiago, Juan G. Self similarities in desalination dynamics and performance using capacitive deionization. United States. doi:10.1016/j.watres.2018.04.042.
Ramachandran, Ashwin, Hemmatifar, Ali, Hawks, Steven A., Stadermann, Michael, and Santiago, Juan G. Sat . "Self similarities in desalination dynamics and performance using capacitive deionization". United States. doi:10.1016/j.watres.2018.04.042. https://www.osti.gov/servlets/purl/1497314.
@article{osti_1497314,
title = {Self similarities in desalination dynamics and performance using capacitive deionization},
author = {Ramachandran, Ashwin and Hemmatifar, Ali and Hawks, Steven A. and Stadermann, Michael and Santiago, Juan G.},
abstractNote = {Charge transfer and mass transport are two underlying mechanisms which are coupled in desalination dynamics using capacitive deionization (CDI). We developed simple reduced-order models based on a mixed reactor volume principle which capture the coupled dynamics of CDI operation using closed-form semi-analytical and analytical solutions. We use the models to identify and explore self-similarities in the dynamics among flow rate, current, and voltage for CDI cell operation including both charging and discharging cycles. The similarity approach identifies the specific combination of cell (e.g. capacitance, resistance) and operational parameters (e.g. flow rate, current) which determine a unique effluent dynamic response. We here demonstrate self-similarity using a conventional flow between CDI (fbCDI) architecture, and we hypothesize that our similarity approach has potential application to a wide range of designs. We performed an experimental study of these dynamics and used well-controlled experiments of CDI cell operation to validate and explore limits of the model. For experiments, we used a CDI cell with five electrode pairs and a standard flow between (electrodes) architecture. Guided by the model, we performed a series of experiments that demonstrate natural response of the CDI system. We also identify cell parameters and operation conditions which lead to self-similar dynamics under a constant current forcing function and perform a series of experiments by varying flowrate, currents, and voltage thresholds to demonstrate self-similarity. Based on this study, we hypothesize that the average differential electric double layer (EDL) efficiency (a measure of ion adsorption rate to EDL charging rate) is mainly dependent on user-defined voltage thresholds, whereas flow efficiency (measure of how well desalinated water is recovered from inside the cell) depends on cell volumes flowed during charging, which is determined by flowrate, current and voltage thresholds. Results of experiments strongly support this hypothesis. Results show that cycle efficiency and salt removal for a given flowrate and current are maximum when average EDL and flow efficiencies are approximately equal. We further explored a range of CC operations with varying flowrates, currents, and voltage thresholds using our similarity variables to highlight trade-offs among salt removal, energy, and throughput performance.},
doi = {10.1016/j.watres.2018.04.042},
journal = {Water Research},
issn = {0043-1354},
number = C,
volume = 140,
place = {United States},
year = {2018},
month = {4}
}

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