Signal generation mechanisms, intracavity-gas thermal-diffusivity temperature dependence, and absolute infrared emissivity measurements in a thermal-wave resonant cavity

The operating thermal power transfer mechanisms in a thermal-wave resonant cavity were explored theoretically and experimentally. Both steady-state ac (thermal-wave) and dc temperature rise were considered, and conduction and radiation heat transfer modes were found to co-exist in the cavity. By introducing controlled variable offset dc resistive heating superposed on the fixed-amplitude thermal-wave oscillation, it was also found that the thermal-diffusivity values of the intracavity gas can vary sensitively as a function of the dc temperature rise within a thin boundary layer adjacent to the cavity thermal source (a metallic Cr–Ni alloy strip). This resulted in the measurement of the temperature dependence of the thermal diffusivity of air. Furthermore, the observed dominance of thermal-wave radiation power transfer in the phase channel of the thermal-wave signal at large cavity lengths allowed the measurement of the absolute infrared emissivity of the thin Cr–Ni strip source material: $ε=0.091±0.004.$