Simulation of Magnetohydrodynamic Multiphase Flow Phenomena and Interface Fluctuation in Aluminum Electrolytic Cell with
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in industrial process for the production of primary aluminum. In this process, alumina powder is dissolved into a thin layer of bath floating over a shallow layer of metal. A direct current is applied via a busbar to a block of carbon anodes and passes through the shallow layers of bath and of metal into a carbon cathode, where they are collected by an iron collector bar. Because of the electrochemical reaction, the alumina powder is reduced QIANG WANG, Ph.D. Candidate, and BAOKUAN LI and NAIXIANG FENG, Professors, are with the School of Materials and Metallurgy, Northeastern University, Wenhua Road 3-11, Heping District, Shenyang 110819, People’s Republic of China. Contact e-mail: [email protected] ZHU HE, Associate Professor, is with the Key Laboratory for Ferrous Metallurgy and Resources Utilization, Ministry of Education, Wuhan University of Science and Technology, Wuhan 430081, People’s Republic of China. Manuscript submitted July 13, 2013. Article published online December 3, 2013. 272—VOLUME 45B, FEBRUARY 2014
at the bath/metal interface to form aluminum droplets that add to the pool of metal at the base of the cell.[1,2] A great amount of electrical energy is consumed during the Hall-He´roult process. Unfortunately, a considerable part of the electrical energy is converted into the joule heat because of the very low electric conductivity of bath. Therefore, it is of importance for the smelter to keep the thickness of the bath layer [the so-called anode-cathode distance (ACD)] as small as technologically possible.[3] However, one of the main obstacles to the ACD decreasing of the cell is that the bath/metal interface turns unstable with respect to its oscillating motion if the ACD is decreased below a certain threshold value.[4] When the fluctuation of the bath/metal interface grows, the metal may touch the bottom of the anode. This creates a short circuit of the cell since most resistance is bypassed. Because of the short circuit, the joule heat in the cell decreases and the cell temperature drops which would at last affect the efficiency of the electrochemical reaction. For the avoidance of short circuit, the ACD is kept at an METALLURGICAL AND MATERIALS TRANSACTIONS B
enough value in the usual operations of the electrolytic process which goes against the energy saving. The fluctuation of bath/metal interface is closely related to the melt flow. EMF and gas bubbles are the main factors among those affecting the melt flow. Magnetic field is created within and around the cell by the cell current. The interaction of magnetic field with the cell current gives rise to EMF. In addition, because of the electrochemical reaction, the carbon monoxide (CO) and the carbon dioxide (CO2) are produced at the bottom of the anode.[5] Over the years, significant improvements and changes in the structure of cells have occurred for the sake of ACD decreasing. A new type of cell, called drained cell, was considered to own potential to enhance the interface stability once. Many significant researches have been done on the use of drained
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