Thermal conductivity and diffusivity of wood

Transient simultaneous measurements of thermal conductivity and diffusivity of Swedish wood have been performed with the plane source technique on ove n-dry hardwood (birch) samples at room temperature and at 100 degrees C. Th e influences of temperature, density, porosity and anisotropy on thermal co nduction were investigated. The measurements were done in longitudinal (par allel to the grain) and transverse (intermediate between radial and tangent ial) directions. As the temperature increased from 20 to 100 degrees C, the thermal conductivity of each sample increased slightly for both longitudin al and transverse directions. The effect of density and porosity on the the rmal conductivity may be related to the presence of other scattering mechan isms such as voids and cell boundaries. It seems that the dominant mechanis m of heat transfer across the cell lumina in these types of wood is the hea t conduction through the voids. An attempt was made to explain the behaviou r of the effective thermal conductivity by adopting a model based on the ra tio between heat conduction in parallel and serial layers of gas, liquid, a nd solid phases.