Fiber's hygromorphic effect on thermal conductivity of wooden fibrous insulation characterized by X-ray tomography

Fibrous-woods have very complex morphology and high heterogeneity, hence their properties are not well-known and need to be investigated, especially concerning microstructural changes due to hygro-thermal loads. The present, experimental and numerical work studies the microstructural hygro-thermal behavior of such material. The experimental procedure was performed on the microstructure level using the non-destructive method; X-ray tomography through a specifically developed processing protocol. The reconstructed volumes have a fine resolution of 7 µm/voxel. The volumetric analysis illustrated a representative elementary volume of 57 mm3. The geometrical microstructure properties (porosity, fiber diameter and pore, fiber orientation, etc.) were extracted from the 3D image analysis. Moreover, a successive X-ray scans of the same fibrous specimen solicited at different relative humidity levels were achieved. The evolution of both the average and the local fibers' diameters distribution properties as a function of the water content were examined. The material's porosity and its fibers' thicknesses show an explicit correlation with the water content. Also, heat transfer simulation of the 3D real insulation structure was evaluated using the energy balance equation. The effective thermal conductivity is computed as a function of the relative humidity. Interlink between the porosity and the thermal conductivity was established too. The results provide enhance our understand of the wood fiber insulation's behavior.