Modeling of Radiation in Bar Bundles Using the Thermal Resistance Concept

Abstract

A method to obtain the effective thermal conductivity due to radiation heat transfer, which occurs in steel bar bundles during their heating associated with heat treatment, is presented. This problem is related to the determination of the thermal properties of a bar bundle, which is modeled as a porous medium with a granular structure. The thermal properties of the bundles are needed to optimize the heat treatment process. A methodology for radiation heat transfer modeling that uses radiation resistance is presented. Resistance is calculated from the radiosity balance for the surfaces that form the analyzed system. The geometry of the heat transfer area is defined using the elementary cell concept. The analysis of the phenomenon is performed within the temperature range from 200 to 700°C. The values of radiation resistance for three different unit cells are presented, as well as the values of the associated effective thermal conductivities due to radiation . The cell radiation resistance decreases sharply with temperature, with the values between 0.08 and for the temperature range studied. The coefficient increases with bar diameter, and for bar bundles of 10 and 40 mm, its maximal values are 1.21 and 4.34 , respectively. Finally, the values of radiation exchange factor for the medium were analyzed. decreases slightly with emissivity and bar diameter, ranging from 0.61 to 0.41.