"Even though electrochemically induced magnetohydrodynamic (MHD) convection is a straightforward inexpensive method for moving fluids in confined spaces as for example during electrodeposition, stripping voltammetry, or in microfluidics, efficient quantitative models only recently have begun to appear. This is traced to complex mathematics that have prevented development of analytical expressions, e.g., for mass-transfer limited currents in analogy to the well-known Levich equation for the rotating electrode. Thus, related literature expressions remain mainly phenomenological concerning particular cell geometries or applications. Here, using such reports as points of departure, we validate a computationally rigorous description of the magnetoelectrochemical problem and define the relative significance of all system parameters. For this we use a three-dimension transient numerical simulation and establish that the full problem is adequately described by the conservation of momentum (modified Navier-Stokes equation), conservation of mass, and conservation of species (Fick's second law augmented with convection). These three equations are coupled by the Faradaic current given as a function of the flux of the redox active species to the working electrode. Computations are performed in the regime of milli and microelectrodes ranging from 250 µm in diameter to 16 mm, both with and without a magnetic field. Millielectrodes without a magnetic field generate diffusion-controlled voltammograms, and with the magnetic field vector parallel to the electrode surface, generate sigmoidal-shaped steady-state voltammograms. The Lorentz force was applied to the whole solution, but migrational current was ignored, so only in the presence of a concentration gradient was the Lorentz force applied. This region is in the near field of the working electrode and renders the placement of the counter electrode unimportant. The limiting current generated captures most of the experimental observations"--Abstract, page iv.
Isaac, Kakkattukuzhy M.
Nisbett, J. Keith
Mechanical and Aerospace Engineering
M.S. in Mechanical Engineering
National Science Foundation (U.S.)
Missouri University of Science and Technology
vii, 29 pages
© 2012 Cajon Gonzales, All rights reserved.
Thesis - Open Access
Magnetohydrodynamics -- Mathematical models
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Gonzales, Cajon, "A three-dimensional transient simulation of an electrochemical magnetohydrodynamics cell with micro and millielectrode: A unified reconciliation of theory and experiment" (2012). Masters Theses. 4143.