ABSTRACT
Wood is a hygroscopic, porous, anisotropic and nonhomogeneous material. After log sawing, the lumber contains liquid water in fiber cavities (capillary water) and bound water inside the fiber wall (hygroscopic water). Porosity refers to volume fraction of void space. This void space can be actual space filled with air or space filled with both water and air. Capillary-porous materials are sometimes defined as those having pore diameter less than 10-7m. Capillary porous materials were defined as those having a clearly recognizable pore space. In capillary porous material, transport of water is a more complex phenomena. In addition to molecular diffusion, water transport can be due to vapor diffusion, surface diffusion, Knudsen diffusion, capillary flow, and purely hydrodynamic flow. In hygroscopic materials, there is large amount of physically bound water and the material often shrinks during heating.
