The permeability of wood to liquid, a transport property that is necessary for accurate modeling of industrial processes such as drying and impregnation, should be measured by using experimental conditions that recreate the transient behavior of those processes. Previous works have used more standardized steady-state methods for measuring unsaturated water permeability of wood. The results of these studies are inconsistent with other experimental data, probably due to the difficulty in achieving uniform unsaturated conditions within the wood samples.
This study employed transient flow of water through wood to calculate the unsaturated permeability. Southern pine specimens were initially saturated with water. A low-speed centrifuge was then used to force the water to flow out of the porous wood cell structure while minimizing evaporative drying. Periodically, the moisture distribution within each sample was measured with a scanning gamma-ray densitometer. When water movement ceased, the steady-state moisture distribution was used to define the capillary properties of the wood. Using the data as the solution to the governing equation, the unsaturated permeability was back-calculated. The results demonstrate the trend that unsaturated wood permeability is relatively large at much lower saturation levels than previously reported, therefore capillary transport of liquid through wood can significantly affect industrial processes. The quantitative value of the findings, however, is marginal due to this technique's requirement for differentiation of data that is widely scattered by wood's inherent inhomogeniety.