Modeling of moisture diffusion and heat transfer during softening in wood densification

Mechanical densification of wood involves compressing the wood in radial direction using heat, water and steam to produce a higher density surface exhibiting better mechanical properties. The densified wood is an environmentally friendly product that presents new opportunities for the wood products industry. Wood surface densification involves both soaking and heating. The objective of this study is to present a two-dimensional model of moisture diffusion and heat transfer during softening process in order to understand and control the degree of surface densification. The governing equations for diffusion process and heat transfer are solved numerically at non-steady state conditions. Experimental data was also collected on Aspen and Balsam fir specimens to determine the moisture profile. The model predicts suitably the moisture content and temperature in the soaking process. The results showed that the surface to be softened could be heated to a temperature of 80~90 C in 3~5 minutes with an average moisture content of 25 percent in the surface layer.