Numerical Investigation on the temperature uniformity of mill rolls and the energy efficiency during heating in the resistance furnace

Abstract

Revealing the heat transfer characteristics and evaluating the efficiency of the forced convection resistance furnace are crucial for energy saving in the steel industry. A three-dimensional transient numerical model was established for the multi-roll simultaneous heating process, validated by experimental data from a mill roll factory. The simulation results indicated that the narrow channel formed by the adjacent three rolls induces stable boundary layers, resulting in poorer convective heat transfer and the formation of cold valleys. In contrast, hot ridges are formed on the rest surfaces due to continuous boundary layer disruption. A multidimensional multi-metric evaluation system was developed to comprehensively assess the temperature distributions of the roll barrel surfaces. Based on this, the effects of roll spacing d_r, layout, and fan speed ω on roll surface temperature uniformity and process efficiency have been examined. At d_r = 250 mm, the temperature non-uniformity of the three rolls decreased by 12 %, 14 %, and 22 %, respectively. When ω is increased to 2000 rpm, the overall temperature non-uniformity of the three rolls decreased by only about 14 %. Increasing fan speed improves temperature uniformity but decreases energy efficiency. A balance index of roll surface temperature uniformity and energy efficiency was proposed as a decision criterion for this trade-off. At ω = 1600 rpm, the balance index is reached maximum value, with a total temperature uniformity improvement of 5.1 % and a 7 % reduction in energy efficiency. The layout position of rolls more significantly impacts the temperature uniformity. In the optimized case, rolls 1 and 2 were placed above, thereby the temperature non-uniformity reduced by 48 % and 67 %, far exceeding the reduction caused by the increase in roll spacing and fan speed. Meanwhile, the temperature non-uniformity of roll 3 is increased by only 10 %. Overall, the total temperature uniformity of the optimized case increased by 39.7 %, while the energy efficiency and thermal efficiency decreased by only 7 % and 0.34 %, respectively.