Thermoelectroconvection near charge-selective surfaces

Area of Science:

• Electrochemistry
• Fluid Dynamics
• Surface Science

Background:

• Charge-selective surfaces, such as permselective membranes and electrodes, are crucial in various electrochemical systems.
• Joule heating effects near these surfaces can lead to complex phenomena, including instabilities.
• Previous theoretical models may not fully capture the interplay between electrical fields, fluid flow, and thermal effects.

Purpose of the Study:

• To theoretically investigate a novel instability driven by Joule heating near charge-selective surfaces.
• To analyze the conditions under which Joule heating can destabilize or stabilize the system.
• To elucidate the physical mechanism of this thermal instability and compare it with existing theories.

Main Methods:

• Utilizing a theoretical model based on the Rubinstein-Zaltzman approach.
• Deriving a simple relation for marginal stability curves.
• Conducting numerical investigations of both linear and nonlinear instabilities.
• Comparing theoretical predictions with experimental data.

Main Results:

• Joule heating can either destabilize or stabilize the steady state, depending on the orientation of the space charge region relative to gravity.
• A long-wave thermal instability replaces the short-wave Rubinstein-Zaltzman instability in destabilizing cases.
• The thermal instability mechanism arises from non-uniform electrical conductivity in the electrolyte, differing from Rayleigh-Bénard convection.
• Good qualitative agreement was found between analytical predictions and numerical simulations.

Conclusions:

• A new Joule heating-induced thermal instability near charge-selective surfaces has been identified and characterized.
• The orientation of the space charge region relative to gravity is a critical factor in determining stability.
• The findings offer a potential explanation for discrepancies between previous theoretical models and experimental observations.