Electrode placement effects on Joule heating and thermal uniformity in an AC zinc-smelting furnace

The steady electrothermal behavior of AC zinc-smelting furnaces is governed by current redistribution and Joule-heat localization, which directly affect bath-temperature uniformity and refractory thermal loading. A three-dimensional one-way coupled electromagnetic-thermal-flow model was developed for the stable heating stage of an industrial AC zinc-smelting furnace. The three-phase electromagnetic field was solved using a frequency-domain eddy-current formulation, and the cycle-averaged Joule heat was transferred to the thermal-flow model as a volumetric heat source. Current concentrated near the electrode surfaces and tips, forming localized heating zones that drove recirculation in the molten bath. Electrode immersion depth controlled the vertical matching between heat release and bath circulation, whereas pitch-circle diameter governed the horizontal overlap among the three heating zones. Across the twenty-five combined configurations, the temperature nonuniformity coefficient ranged from approximately 0.09% to 0.24%, and the high-temperature-zone volume fraction ranged from approximately 14% to 40%. Increasing immersion depth generally improved temperature uniformity but reduced high-temperature coverage, whereas increasing pitch-circle diameter enlarged the effective heating region. Considering the average temperature, temperature nonuniformity, and high-temperature coverage, immersion depths of 100-300 mm and pitch-circle diameters of 2400-2800 mm provided a favorable relative range; 200-300 mm was preferred when temperature uniformity was prioritized. For a representative configuration, the electromagnetic-to-buoyancy force ratio was 0.016, indicating that the Lorentz force modified local flow but had limited influence on the global temperature trends under the investigated stable-heating condition.