Direct current arc furnaces see considerable use in modern industrial melting and smelting
processes. Pyrometallurgical applications for this type of furnace are wide-ranging, and
include commodities such as Ferrochrome, Ferronickel, Cobalt, Zinc, Magnesium, Titanium
Dioxide, Platinum-group metals1, and others.
Central to the operation of such furnaces is the direct current plasma arc, a sustained high
temperature jet of ionised gas which is formed between the end of one or more graphite
electrodes and the bath of molten process material below. Passage of electric current through
the arc inputs energy and maintains the high temperatures necessary for ionisation via ohmic
heating. This is balanced by various mechanisms of energy loss from the arc, including
volumetric radiation and convection to the molten bath surface below. Much of this energy is
delivered to a localised area directly beneath the arc, making it a very efficient means of
heating the process material.
Flow of plasma in the arc column is driven strongly by electromagnetic Lorentz forces
resulting from the constriction of the conduction channel in the vicinity of the electrode. This
constriction causes the arc to draw in gas from the surroundings and accelerate it away from
the electrode surface, toward the molten bath below (the Maecker effect2).
Much research has been conducted in the area of numerical modelling of arc phenomena,
starting with Szekely and co-workers3 and becoming increasingly more sophisticated with the
advent of better software, property data, and increased computing capability. However, the
majority of arc modelling efforts concentrate on steady-state, axisymmetric systems. While
valuable from an engineering standpoint these models are not able to describe any transient
behaviour exhibited by the arc, or any evolution of the shape and structure of the arc which
breaks the symmetry imposed by the model. Both of these aspects are important for a deeper
understanding of direct current plasma arc behaviour
