Theoretical accuracy of anisotropic thermal conductivity determined by transient plane source method

The transient plane source (TPS) method could measure the in-plane thermal conductivity and through-plane thermal conductivity of anisotropic materials through one single test once the volumetric heat capacity is known. The practical thicknesses of the heating element and the insulation layer deviate from the plane source assumption and have an influence on the accuracy of the isotropic thermal conductivity of bulk specimen and film specimen determined experimentally. The theoretical accuracy of measured anisotropic thermal conductivities will also be affected by the practical sensor thickness. A numerical study is conducted to investigate the deviation of anisotropic thermal conductivity due to the non-compliance of the theoretical assumption of TPS method. The influence of the practical sensor thickness on the theoretical accuracy of different thermal conductivities and different anisotropic ratios is discussed. The simulation studies show that the deviation brought by the plane source assumption, i.e., with zero thickness, becomes significant for materials with high thermal conductivity (thermal diffusivity) and can be improved by employing sensor with larger radius.