Accuracy of the Thermal Diffusivity Estimation of Layered Materials

When respecting the basic principles of the flash method the thermal diffusivity of one layer of a two-layered composite can be determined analyzing the experimental temperature rise vs. time data. Unlike measuring homogeneous materials a measurement of the thermal diffusivity (even though having an ideal two-layered composite with zero thermal contact resistance) has to be viewed as the dependent measurement because the estimation depends on other relevant physical properties that enter into calculation. The paper presents how the accuracy of the thermal diffusivity estimation depends on the variation of the thermal diffusivity of the second layer, on the density and on the heat capacity as a function of the geometry of the sample. Qualitative similar error propagations caused by variation of the thermal diffusivity as well as by the density and the heat capacity variations are obtained. In spite of the fact, that influence of the thermal diffusivity variation to the accuracy of the estimation of the supplementary thermal diffusivity is larger, the influence of the density and of the heat capacity is significant, too.