INTERFACIAL INSTABILITIES IN ALUMINUM REDUCTION CELLS

This paper extends the analysis of Sneyd (1985) on interfacial instabi lities in aluminium reduction cells. The cell model consists of a plan e fluid layer of relatively low electrical conductivity, sandwiched be tween an upper rigid wall and lower fluid layer, both of high conducti vity. A steady current passes through the layers, and the magnetic fie ld is assumed to be a linear function of position. The principal new e ffects introduced are (i) a horizontal current component in the alumin ium; (ii) vertical magnetic field components, and vertical field gradi ents; (iii) an aluminium pool of finite depth; and (iv) uniform zeroth -order flow in the fluid layers, and mechanical dissipation. A dispers ion relation for small-amplitude waves is derived and discussed. The d estabilizing Kelvin-Helmholtz mechanism and electromagnetic forces com pete with gravity, surface tension and mechanical dissipation. Electro magnetic destabilization is likely to occur in practice at wavelengths of 1 m or more, and becomes more intense with decreasing layer depths . The most dangerous mechanism appears to be driven by vertical gradie nts of the horizontal field.