Thermophysical Properties of Beech Wood in the Range from Room Temperature to 900 °C

Wood is a structural material of biological origin that undergoes thermal degradation when exposed to high temperatures. Additionally, wood shows an anisotropic behavior in terms of thermal expansion and thermal conductivity along and across fiber direction. This work reports thermophysical measurements of beech wood from room temperature up to 900 degrees C. The wooden material was investigated in different states: moist, dry, charred and during pyrolysis. A push-rod dilatometer was used to measure thermal expansion, from which temperature dependent density was derived. Specific heat was determined by differential scanning calorimetry. A laser flash apparatus was applied to measure thermal diffusivity. Thermal conductivity was calculated from thermal diffusivity, specific heat, and density. The measurements of thermal expansion and thermal diffusivity were performed along and across fiber direction to consider the anisotropic behavior of wooden material. The results of the thermophysical properties are reported from room temperature to 200 degrees C for the beech wood, during pyrolysis, and up to 900 degrees C for the charred material. It was found that thermal expansion of beech wood across fiber direction is greater than along fiber direction in the order of a magnitude. In contrast, thermal expansion of charred material is rather independent on fiber direction. Thermal conductivity of beech wood along fiber direction was found to be approx. 2 to 3 times higher than across fiber direction. In the case of the charred material the relative difference is smaller.