A comprehensive evaluation of axial gas permeability in wood using XCT imaging

The permeation of fluid through wood is a crucial aspect of the drying and modification of this material. The accurate measurement of wood permeability and the analysis of the effects of microstructure on permeability are very challenging. The present study generated visual representations of the three-dimensional pore structures of wood specimens using X-ray computed tomography combined with image processing. In addition, axial seepage in wood samples was simulated based on seepage theory and structural information and microscopic gas flows were calculated to evaluate the macroscopic permeability of the wood. Finally, the simulation results were verified by comparison with experimental data and a detailed investigation of the effects of microstructure on permeability was performed. The porosity, average aperture, local connectivity ratio and fractal dimension of larch wood were evaluated based on the mesoscale resolution capacity of the tomography system and determined to be 0.638, 28.37, 0.67 and 1.779 µm, respectively. The average simulated axial gas permeability value of 5.256 µm² was in the range of previously reported values (2.595–6.398 µm²). The permeability of the earlywood (6.555 µm²) was found to be significantly higher than that of the latewood (3.959 µm²). The accuracy of such simulations was determined to be affected by the wood properties, simulation method and testing equipment. Porosity, average aperture, and local connectivity ratio were the primary factors affecting permeability and these parameters were all positively correlated with permeability (with R² values of 0.879, 0.814 and 0.721 respectively). The relationship between fractal dimension and permeability was unclear and requires further study.