X-ray CT-scanning of wood during drying

Abstract: Moisture flux in wood during drying was studied using a medical CT scanner. A special device was built that enables performance of nondestructive measurements without removing the test piece during the whole drying process. This work is mostly experimental and some of the conclusions are: The drying process is separated into three phases: Capillary phase, transition phase and diffusion phase. During the capillary phase the free water in sapwood flows towards the surface under the influence of capillary forces. No free water flux from sapwood to heartwood is observed during the capillary phase. On the other hand, moisture transportation from regions with low concentration to regions with high concentration is observed. The evaporative plane recedes slowly into the wood as the drying proceeds. The average MC in the sapwood at the transition phase is about 50% and is called irreducible saturation (IS). During the final phase, the drying of wood is diffusion-controlled. The analytical part shows that a mass and heat transfer model can predict the drying rate. Integrating these results in a receding-plane model is a promising method and calls for future research. The development of control strategies based on this knowledge is perhaps the key area of focus for the future.