Thermal conductivity of the cell wall of wood predicted by inverse analysis of 3D homogenization

Abstract

This work proposes an accurate prediction of the directional thermal conductivity of wood at the cell wall scale. To that purpose, the strategy combines the physical characterization at the macroscopic scale, the description of the cellular morphology, homogenization calculations and an inverse analysis. The first step consisted in measuring the macroscopic thermal conductivity using the Transient Plane Source (TPS) method in the three material directions of spruce and poplar. The values range from 0.10 to 0.31 Wm−1K−1 depending on direction and species. The 3D morphology was acquired by micro-tomography and subsequently processed to generate a digital representation of the cellular structure. This representation is the input geometry in an homogenization procedure. Based on the results of this algorithm, the measurements of the solid fraction and the macroscopic values, we are able to determine the microscopic thermal conductivity of the cell wall λ0s, which is impossible to measure directly. λ0s was also found to be anisotropic with respective values of 0.6 and 1.0 Wm−1K−1 in the transverse plane and the longitudinal direction.