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Development and validation of a guarded comparative axial furnace system for high-temperature thermal conductivity characterization of engineering materials
Walid M. Shewakh, Zainab Hussain, Majed H. Moosa and Abdulrahman Mohammed Albar

Thermal conductivity remains a defining parameter in the design of heat transfer equipment, yet measuring it accurately at elevated temperatures is still difficult. This paper reports the characterization and validation of a guarded comparative axial furnace system designed for operation up to 1200 °C; in the present study it is characterized and validated over the range 100 °C to 800 °C. The apparatus couples silicon carbide heating elements, programmable logic controllers (PLCs), and calibrated K-type thermocouples to a reference-bar stack that provides an independent determination of the heat flux through the specimen. Six common engineering materials were tested: copper, aluminum, low-carbon steel, soda-lime glass, pine wood, and glass wool. For the metallic specimens, thermal conductivity decreased monotonically with temperature, consistent with increased phonon-phonon scattering and, for steel, with the combined contribution of electron-phonon scattering and the gradual loss of magnetic order approaching the Curie temperature. Copper decreased from 403 W/(m·K) at 100 °C to 350 W/(m·K) at 800 °C. Steel fell by 57 % over the same range, most of the decline occurring below the Curie point. An effective metal-metal contact resistance, estimated from the same measurements rather than measured independently, falls by 60–75 % between 200 °C and 800 °C and follows the Cooper-Mikic-Yovanovich correlation to within about 10 %; the four-sensor stack cannot isolate a single interface, so this is reported as a correlation-based estimate with an experimental consistency check. For air layers between steel specimens, an effective conductivity was reported that combines conduction, convection, and radiation; at 800 °C across a 40 mm layer, radiation contributes more than convection. Finite element simulations in ANSYS, run with an independent CMY contact-resistance input, agreed with the experimental temperatures within a mean deviation of 3.2 K (RMSE 3.7 K). The results offer practical design guidance for multi-layer thermal systems and confirm the reliability of the guarded comparative axial method at high temperature.

Keywords: Thermal conductivity; Steady-state measurement; Guarded comparative axial method; Thermal contact resistance; Radiation in enclosures; High-temperature characterization