Modelling of the behaviour of free water in sapwood during drying

A stochastic, computer based, three-dimensional model for the behaviour of water in a capillary network has been developed and adapted to simulate drying of sapwood of softwood. Some basic morphological properties of the fibres and the fibre network are included in the model. Mathematical experiments have been performed with the model according to a Monte Carlo procedure. It has been found that such a model is able to predict several features observed in reality. This includes "gradient free'' drying in the initial half of the process, followed by a phase with receding moisture fronts and further rapid initial development of a dry shell at the wood surface. The connection to percolation theory is pointed out. The results suggest that the new approach gives a more correct description of the sapwood drying process than a traditional, purely diffusion based model. It is obvious that the same approach can be used for other processes also, such as the uptake of water or liquid.