A comprehensive model for transient moisture transport in wood below the fiber saturation point: Physical background, implementation and experimental validation

During the last three decades the macroscopic formulation of moisture transport in wood below the fiber saturation point has motivated many research efforts. From experiments the difference in steady-state and transient transport processes is well known, but it could not be explained in a fully physically motivated manner. In this article, we aim at enhancing the current understanding and improving the mathematical description of the moisture transport process in wood. For this purpose, we first present the microstructure of wood and then describe the physical background of steady-state and transient transport processes in wood, based on which we finally derive a suitable mathematical model. For a correct macroscopic description of transient transport processes, three coupled differential equations have to be solved in parallel, which is done using the finite element method. A comparison of model predictions for the sorption behavior of wood specimens with corresponding experimentally derived values yields very promising results and confirms the suitability of the assumptions underlying the model.