Study of heat transfer model and buried thermocouple test of bell-type annealing furnace based on thermal equilibrium

The bell-type annealing furnace is a key equipment in the cold rolling process, and the heat transfer process inside the furnace has a significant impact on the annealing process and product quality. At present, there are shortcomings in the calculation accuracy of model research based on heat transfer theory and practical experience. In addition, existing research has not fully considered the influence of gas flow distribution and corresponding heat transfer coefficient in each channel of multi tube steel coils on the temperature field. The aim of this study is to develop a more accurate heat transfer model for bell type annealing furnaces and verify its reliability. In this work, a heat transfer model for a bell jar furnace was established based on the thermal equilibrium method, and its accuracy was verified through industrial buried thermocouple tests. The results indicate that the heat transfer model has high accuracy due to considering the distribution of protective gas flow rate, convective heat transfer coefficient, and radial thermal conductivity of the steel coil. The average relative error of the cold spot temperature calculated by the model is less than 0.5%, and the hot spot temperature does not exceed 5%, which proves the accuracy and reliability of the model, especially for cold spot temperature. When the relative error of the cold spot temperature is within 2.5%, the accuracy of the coil is above 95%. This study provides an accurate heat transfer model for fitting the heat transfer process of bell type annealing furnaces.