Wood is traditionally modeled as an orthotropic material, with direction dependent transport properties, in this way homogenizing the specific structure of wood: a cellular material with growth rings, consisting of early wood and late wood layers. In this paper we present a mesoscopic model for vapor transport in wood, where earlywood and latewood are modeled as distinct materials. The sorption and vapor transport properties for early- and latewood are determined using a unit cell model with constant cell geometry. These properties are used in two-dimensional calculations of vapor transport in a piece of wood consisting of several growth rings. The mesoscopic results are compared to measurement results and to macroscopic results using homogenized orthotropic transport properties. For vapor transport in radial and tangential direction the difference between meso- and macro modeling of wood is negligible, justifying the vapor transport modeling with homogenized orthotropic transport properties.

Presented at Thermal Performance of Exterior Envelopes of Whole Buildings X – December 2007

Units: SI