Quantification of Radiation‐Dominated Heat Transfer in High Temperature Nanoporous Ceramics

ABSTRACT Thermal radiation is a major mode of heat transfer in high temperature porous materials such as insulations, ceramic foams, and thermal barrier coatings. However, quantification of radiation heat transfer is not straightforward due to the complexity of measuring optical parameters, and the coupling with conduction heat transfer. In this work, high‐temperature laser flash analysis measurements with a coupled radiation‐conduction model were used to directly quantify thermal radiation in monolithic porous samples of ceramic nanoparticles. These samples had sub‐50 nm pores stable up to 1000°C, thus suppressing solid and gaseous conduction, while minimizing infrared scattering. A combination of the resulting low thermal conductivity (<0.5 W m −1 K −1 ) and high transmittance of the samples leads to radiation dominant heat transfer at high temperatures. The contribution of radiative heat transfer was quantified using the Planck number (conduction‐to‐radiation parameter). Above 500°C, radiation heat transfer became significant and at higher temperatures, the contribution was up to five times larger than conduction.