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Show A DYNAMIC THERMAL SYSTEM MODEL FOR A LOW INERTIA FURNACE H. Yoshino and R. Viskanta Heat Transfer Laboratory School of Mechanical Engineering Purdue University West Lafayette, Indiana 47907 ABSTRACT A dynamic thermal system model developed for a gas-fired, low-inertia, batch-type reheating furnace is discussed in this paper. The mathematical model of the furnace integrates the models for heat transfer within the enclosure with the model for the load. The transport processes occurring in the flat radiant heaters are not treated, but the radiation exchange between the load, the radiant heater surfaces, and the furnace refractories are analyzed using the radiosity method. The batch furnace operation is simulated using a dynamic thermal model. The scope and flexibility of the model is assessed by performing extensive parametric calculations using the furnace geometry, material properties and operating conditions as input variables of the model and predicting the thermal performance of the furnace. The various model parameters studied include the size and radiative properties of the load, thermophysical properties of the stock material and the flat radiant heater designs. INTRODUCTION Indirectly-fired radiant tube furnaces are widely used in metal heat-treating applications where the quality of the final heated product is a major concern [1]. In this type of furnace, the combustion of fuel and air takes place within the radiant tubes, and the high-temperature products of combustion are kept isolated from the stock material being heated. The energy released due to combustion is transferred to the radiant tube wall, and the heating of the stock material in the furnace is accomplished via radiative heat transfer from the heated walls of the radiant tubes and from other surfaces of the furnace enclosure. Furthermore, the furnace enclosure may be filled with an inert radiatively nonparticipating atmosphere, such as nitrogen or argon, to prevent the scaling or decarburization of the load during the heating process [1]. The primary objectives in the design and operation of any industrial furnace are to maximize production (i.e., heat transfer to the load due to combustion of the fuel) and to reduce pollutant emissions. However, attempts to maximize productivity m a y have adverse effects on the maximum heat transfer rate to the load and vice-versa. Therefore, it becomes necessary to optimize the furnace operation for best thermal performance, stock throughput and uniformity of heating. This can be accomplished by conducting numerical experiments using a thermal system model of the furnace. The physical/mathematical model of the furnace developed in this study provides for detailed simulations of the heat transfer processes occurring in the furnace, and uses design, operating conditions and materials properties of the furnace as inputs to examine their efforts on furnace operation. A detailed parametric analysis of the furnace is then performed to |