A new method for measuring the thermal conductivity of small insulating samples

Abstract

Due to the limited size of samples prepared at the lab scale, characterizing the thermal properties of new materials may be problematic, and this makes it all the more difficult to optimize them. This statement especially applies to the development of innovative thermal (super)insulators. In this work, we demonstrate that the hot disk method, which might be preferred for such kinds of studies because of the low sample size it can allow in practice, is unable to provide realistic values of thermal conductivity in the case of insulators. A new method was thus developed, called Calibrated Tiny Hot Plate (CTHP). The corresponding heat transfers were modeled, and the two unknowns of the model were obtained by calibration with insulating samples whose thermal conductivity was precisely measured with a reference (guarded hot plate) method. We show that the CTHP is able to estimate conductivities within the range 0.014-0.2 W m-1 K-1 based on samples having thicknesses ranging from 3 to 9 mm and diameters as low as 15 mm. The accuracy was generally much better than 10%, which is a remarkable result for characterizing so small insulating materials.