Drying of Liquid Water in Wood as Influenced by the Capillary Fiber Network

Abstract

A stochastic three-dimensional model for the behavior of liquid water in the capillary network formed by the fibers in solid wood has been developed and adapted to simulate drying of sapwood of softwood. In a cluster of interconnected, water-filled fibers, the free water menisci will retract during drying but stop at the tiny openings of bordered pits between fibers. As the drying process continues, the meniscus in the widest opening cannot withstand the capillary suction any more and retracts into the corresponding fiber, which is gradually emptied and the process is repeated. This introduces a stochastic element into the process and the behavior is studied using a Monte Carlo approach.

This new approach explains several observed features of wood drying that cannot be explained by traditional diffusion models. In addition, the relative permeability of both the gaseous and liquid phases is calculated as functions of water saturation. The model is finally extended by inclusion of film and corner flow.

Keywords:

• Film flow
• Kiln brown stain
• Percolation
• Relative permeability
• Wood drying