Analysis of Multimodal Magnetohydrodynamic Instability at the Bath-Metal Interface in Aluminum Reduction Cells
摘要
This study experimentally investigates the magnetohydrodynamic instability of the bath-metal interface in aluminum reduction cells. A key finding is the instability of a single bichromatic interfacial mode that is characterized by independent longitudinal and transverse wavenumbers, in contrast to previously reported coupled modes, which coexist to become unstable. Interface positions determined from the measurement of anode voltage oscillations are analyzed using Fourier and Hilbert-Huang transforms. Analysis of the reconstructed interface revealed both bichromatic and monochromatic modes. A close match is observed between the experimental mode frequencies and those predicted by the analytical relation reported in our earlier work. The frequencies of (3, 1), (1, 1), and (1, 0) modes come out to be 0.0332 s−1, 0.0780 s−1, and 0.00977 s−1, respectively, from the experiments and 0.0292 s−1, 0.0752 s−1, and 0.00803 s−1 from the analytical relations. Further investigation of interfacial oscillations revealed distinct instability characteristics under different perturbed conditions. The reduction in the height of the upper liquid by a maximum of 10 mm increases the oscillation frequency by a maximum of three times. An increase in oscillation frequency of bichromatic modes was also observed analytically. However, the local perturbation caused by the anode change resulted in the amplification of the low-frequency modes.