Temperature simulation of the heating segment of large bright annealing muffle furnaces

A three-dimensional simulation model was built to investigate the temperature field of the heating segment of a bright annealing muffle furnace. Based on the actual structure of the muffle furnace as well as the annealing speed and heating curves of steel strips, the equivalent heat flux was proposed in this model to characterize heat exchanges between the protection gas and steel strips in the muffle furnace. Then the combustion model for the transport and reaction of gaseous components, the radiation heat transfer model and the k-ε two-equation turbulence model for turbulent flow in the muffle furnace were adopted respectively. The SIMPLE method was used to solve the model. Simulation results by the model are consistent with the measured temperature values of characteristic points in an SUS304 stainless steel strip during the bright annealing process. The temperature, velocity and flow fields in the muffle furnace were obtained by this model. It is shown that the distribution of temperature on the muffle tube surface is relatively even, and only the zone of the burner has a higher temperature. The muffle tube is approximately uniformly heated since the combustion gases flow along the muffle tube spirally. With the injection quantity (inlet velocity) increasing, the temperature in the muffle furnace rises gradually; however, when the injection quantity is above a limit, the temperature in the muffle furnace begins to drop.