Parametric estimation of thermoradiative properties of materials based on harmonic excitation

Abstract

A simple device for the measurement of emissivity, thermal conductivity, and diffusivity of opaque materials is described. The measurement method is based on the use of a harmonic excitation of a material sample plate. The front surface of the sample is heated periodically and its temperature is measured using a thermocouple. The sample back surface temperature is obtained by infrared thermography. Half of the sample back surface is covered by a black paint of known emissivity used as a reference to compute the sample surface directional emissivity. Thermal conductivity and diffusivity are simultaneously identified from both real and imaginary parts of experimental and theoretical heat transfer functions. Results are presented for a thermally thick sample of PVC, where the sample thickness is greater than the thermal diffusion length. The identified thermophysical properties are in agreement with literature values and reproducible results are obtained. Moreover, some limitations of the method are considered. First, the black paint layer influence on the heat transfer cannot be neglected in all the frequency ranges of measurement. Secondly, an accurate estimation of the thermal conductivity cannot be obtained without an exact knowledge of the heat transfer coefficient.