| Summary: | During heat treatment of rectangular steel sections, a heated charge in the form of regularly arranged packages is placed in a furnace. The article presents a model of a complex heat transfer in such a package using the thermo-electric analogy. The model considers the following types of heat transfer: conduction in section walls, conduction and natural convection within gas, heat radiation between the walls of a section, as well as contact conduction between the adjacent sections. The results of our own experimental research were used for calculations of heat resistance applying to natural convection and contact conduction. We assumed that the material of sections was low-carbon steel and the gas was air. The result of the calculations of the presented model is total thermal resistance <i>R<sub>to</sub></i>. The calculations were performed for the temperature range 20–700 °C for four geometrical cases. Due to the variability of conditions for contact heat conduction, we assumed that total thermal resistance for a given charge is contained within a value range between <i>R</i><sub><i>to</i>-min</sub> and <i>R</i><sub><i>to</i>-max</sub>. We established that the value of <i>R<sub>to</sub></i> depends significantly on the section’s geometry. The larger the section sizes, the greater the changes of <i>R<sub>to</sub></i>. The minimal and maximal values of <i>R<sub>to</sub></i> for all packages were 0.0051 (m<sup>2</sup>·K)/W and 0.0238 (m<sup>2</sup>·K)/W, respectively. The correctness of model calculations was verified with the use of experimental data.
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