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Helical vortex formation in three-dimensional electrochemical systems with ion-selective membranes
Sang V Pham1,2,3, Hyuckjin Kwon1,4, Bumjoo Kim1
1Research Laboratory of Electronics, Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Physical Review. E
|April 15, 2016
Summary
The third dimension is critical for overlimiting transport in ion-selective membranes. Helical vortices, not planar ones, drive this phenomenon in wider channels, impacting electrochemical system efficiency.
Area of Science:
- Electrochemistry
- Fluid Dynamics
- Membrane Science
Background:
- Overlimiting transport across ion-selective membranes enhances electrochemical system efficiency.
- This phenomenon is attributed to electroconvectively induced vortex formation.
- Previous studies primarily used 2D models, neglecting the role of the third dimension.
Purpose of the Study:
- To investigate the critical role of three-dimensional (3D) effects in overlimiting transport.
- To characterize the helical vortex patterns observed in wider channels.
- To understand the impact of channel width on overlimiting behavior and electrokinetic instabilities.
Main Methods:
- Experimental characterization of a device exhibiting 3D electrokinetic instability.
- 3D numerical simulations of fluid flow and ion transport.
- Analysis of vortex patterns, overlimiting current, and conductance as a function of channel width.
Main Results:
- The vortex pattern in wider channels is helical, not planar, a 3D phenomenon.
- The number of helical vortices, overlimiting current, and conductance exhibit jump-discontinuous dependencies on channel width.
- Overlimiting transport is triggered at lower electric fields in wider channels due to helical vortices.
Conclusions:
- The third dimension significantly alters overlimiting transport behavior compared to 2D models.
- Helical vortices in 3D systems are more readily triggered than planar vortices in 2D systems.
- Findings have important ramifications for optimizing electrochemical desalination and other membrane systems.
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