Influence of sorption hysteresis on moisture transport in wood

The independent domain theory is used to analyze the influence of sorption hysteresis on the behavior of wood exposed to environmental conditions. Due to hysteresis, sorption history of wood has an impact on its performance under varying moisture conditions. An integrated Preisach-Mayergoyz (IPM) approach that is phenomenologically sound and insightful while mathematically and computationally straightforward to implement is applied, where the parameters of the IPM space are determined from experiments. The implementation of the IPM approach in a heat and moisture transport model is validated based on independent measurements of dynamic vapor sorption in spruce wood. The transport model, including sorption hysteresis, is further used to simulate the response of a wood beam to weekly humidity variations and hourly climatic humidity and temperature variations. The analysis shows that hysteresis of wood is strongly dependent on the magnitude of moisture changes. As moisture penetrates the material faster in longitudinal than in radial direction, due to a lower vapor resistance factor, the effect of hysteresis is more pronounced deeper into the wood in longitudinal than transversal directions. Furthermore, the simulations imply that errors in moisture content of more than 20 % (or 30 %) can be made when using the main adsorption curve (or main desorption curve) instead of the hysteresis model for wood sorption behavior. Sorption hysteresis must thus be accounted for in heat and mass transport models to assess moisture-related damage risks such as mold growth, rot or moisture-induced cracking, and the IPM approach offers such an appropriate avenue.