Determination of the thermal conductivity of wood by the hot plate method: The influence of morphological properties of fir wood (Abies alba Mill.) to the contact thermal resistance

Abstract

Thermal conductivity is frequently determined by the hot plate method. The influence of the anatomical and morphological properties of fir wood (Abies alba Mill.) was studied on the hot plate method and the mechanical treatment on the contact thermal resistance of the surface was addressed. It was confirmed that there is a contact thermal resistance between the surface of a specimen and the smoother metal plate of an experimental device. It amounted to 3.04×10^-3 m²K W^-1 in the direction of wood fibres and, similarly, 2.96×10^-3 m²K W^-1 in the transverse direction. A negligible contact thermal resistance – maximal 9% of the contact thermal resistance between the wood specimen and the metal plate – was determined at the contact of two wood surfaces. It is ascribed to the better fit of two wood surfaces compared to the fit of the wood surface with a smoother metal one. Irreversible morphological changes were determined in the real surface layers of mechanically treated test specimens. Abbot curves of real bearing profiles were additionally prepared, where the equality of longitudinal and transverse wood surfaces, as well as a sigmoid increase of bearing surface towards the inner wood tissue of test specimens was confirmed. The inverse proportional relation between the contact thermal resistance and the contact surface of wood was ascertained. The thermal conductivity of the combined and reintegrated composite of solid wood was invariable.