Correct Use of the Guarded-Hot-Plate Method for Thermal Conductivity Measurements on Solids

The guarded-hot-plate (GHP) method is a method used world-wide for the determination of the thermal conductivity of solid materials, especially low-conducting insulation materials, based on the direct application of Fourier's law. It is an absolute method, which means that no reference material is needed, though regular performance checks using reference materials are highly encouraged. All measured quantities are traceable to SI-units. Applying the GHP method in accordance with existing standards, relative uncertainties in the determined values of the thermal conductivity below 2.5% are achievable. This work describes the basic theory of the measurement and is focused on difficulties and possible stumbling blocks in daily measuring practice and laboratory routine when applying the GHP method on specimens which are not or only partly covered by standards. The work explains in which cases the definition of a thermal conductivity value is not possible for a specimen and only system-related values as the thermal resistance can be attributed to a specimen. The aim of this work is to improve the measuring quality of GHP measurements for the determination of the thermal conductivity in daily laboratory operation.