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Electro-osmotically induced convection at a permselective membrane
1Jacob Blaustein Institute for Desert Research, Ben-Gurion University of the Negev, Sede-Boqer Campus, 84990, Israel.
Summary
This study investigates ion exchange membrane electrodialysis, revealing that nonequilibrium electro-osmosis drives convection and overlimiting conductance. Experimental and numerical results support an electro-osmotic origin for this phenomenon.
Area of Science:
- Electrochemistry
- Fluid Dynamics
- Membrane Science
Background:
- Concentration polarization and nonequilibrium electro-osmosis are key phenomena in ion exchange electrodialysis.
- Understanding the origin of overlimiting conductance is crucial for optimizing membrane processes.
Purpose of the Study:
- To analyze convection induced by nonequilibrium electro-osmosis at ion exchange membranes.
- To investigate the stability of electrodiffusion and resulting flow regimes.
- To determine the primary cause of overlimiting conductance in ion exchange membranes.
Main Methods:
- Recapitulation of nonequilibrium electro-osmotic slip condition derivation.
- Linear stability analysis of quiescent electrodiffusion.
- Numerical calculations for nonlinear steady-state and time-dependent convection.
- Experimental validation with modified membranes.
Main Results:
- Instability analysis predicts nonlinear steady-state convection and oscillations.
- Numerical simulations show periodic and chaotic flow patterns.
- Experimental results favor an electro-osmotic origin for overlimiting conductance.
Conclusions:
- Nonequilibrium electro-osmosis is a significant driver of convection at ion exchange membranes.
- The observed overlimiting conductance is primarily attributed to electro-osmotic effects, not bulk electroconvection.