Characterization of the thermal properties of millimeter-sized insulating materials

The work deals with the thermal characterization of low conductivity millimeter-sized samples. Regarding the increasing of the technical problems when the sample sizes decrease and become millimetric, an analytical solution obtained from the fin model and adapted from previous work is developed to estimate the thermal diffusivity and a modified Biot number by least-squares method. Then separated calorimetric and density measurements enable the calculation of the thermal conductivity. During experiment, the sample is heated from one side for a few seconds. An infrared thermography is used to measure the temperature field of the sample surface. At first, the method is tested with polycarbonate and balsa samples, which thermal properties are well-known. Then, the thermal diffusivity and conductivity of the hemp shiv are estimated, which values are of the same order of magnitude as those encountered in the literature for cellulosic materials of same density. If the estimation of the thermal diffusivity of the samples is in good agreement with a low uncertainty, the uncertainty on the thermal conductivity is about 10% due to the difficulty to consider the heat exchange coefficient when the tested material becomes a better insulator. Nevertheless, this method seems relevant to characterize millimeter samples of low thermal conductivity.