Numerical and experimental results on copper electrolysis in homogeneous and inhomogeneous magnetic fields

Lorentz forces due to external magnetic fields are well known to force electrolyte flow and thereby to influence mass transport in electrochemical reactions. To achieve a quantitative understanding of this so called “MHD-effect” and maybe to tailor it, it is crucial to study the magneti-cally forced convection in as much detail as possible.
The present work aims to further clarify the role of magnetically forced convection during copper electrolysis in cuboid cells with vertical wall electrodes. Both, homogeneous and inhomogeneous magnetic fields of different directions are investigated. Substantial differences in the convection forced arise from the fact that only the rotational part of the Lorentz force drives additional convection [1]. In case of homogeneous magnetic fields, this results in characteristic horizontal counter-rotating flow in the top and the bottom region of the cells (see Fig. 1) [2]. Inhomogeneous magnetic fields characterized by a constant gradient in a certain direction give rise to simpler convection patterns as the Lorentz force possesses a natural rotational part. This way, tailored electrolyte stirring throughout the cell can easily begenerated.
The presentation will summarize recent results of numerical simulations combined with detailed experimental PIV measurements of the electrolyte flow. The influence of the forced convection on the limiting current, the vertical density stratification and the vertical distribution of the current density at the cathode will be discussed.
Acknowledgment: We are very grateful to C. Cierpka for contributing to the initial DP-PIV setup. This work was supported by Deutsche Forschungsgemeinschaft in frame of the collaborative research center SFB 609 "Electromagnetic flow control in metallurgy, crystal growth and electrochemistry"
References
[1] G. Mutschke, A. Bund, Electrochem. Comm. 10 (2008) 597-601.
[2] G. Mutschke, C. Cierpka, T. Weier, K. Eckert, S. Mühlenhoff, A. Bund, Trans. Electrochem. Soc. 13 (16) (2008) 9-13.