Modeling and simulation of heat transfer in loaded heat treatment furnaces

The simulation of heat transfer in heat treatment furnace is of great importance for the prediction and control of the ultimate microstructure and properties of workpieces. In this paper simplified models based on numerical simulation and analytical methods are proposed to calculate the radiation, convection and conduction heat transfer in heat treatment processes. View factors between the furnace and workpieces, especially among workpieces. are calculated by evaluating exposed surface areas. Therefore the radiation between the furnace and load, and that, between adjacent workpieces is presented. Workpieces are classified into lumped capacitance and massive objects. In the latter case, the conduction heat transfer models in different shapes of workpieces are given. Natural and forced convections under common load patterns are solved by analytical algorithms. Other thermal terms such as gross heat input, heat storage in the furnace, heat storage in load, heat loss from the walls and opening, shell cooling, etc. are included in the furnace model. The heat transfer models are integrated with furnace model to simulate the heat treatment processes of workpieces in furnace, and then to improve heat treatment quality and efficiency by the optimization of workpiece loading and the thermal schedule. These models can be applied to different batch furnaces, such as direct gas-fired furnaces, indirect gas-fired furnaces and electric furnaces. Two cases studies are given to validate the models. The relevant program has been put into industrial application.