Modeling transient and hysteretic hygrothermal processes in wood using the hybrid mixture theory

摘要

Porous materials used in constructions and many other daily activities tend to have a strong affinity towards external fluids, especially moist air, which accumulates in the porous media leading to physical and mechanical effects. For wood based materials, moisture transport dynamics is a function of relative humidity, temperature and sorption history. Coupling of these three parameters has not been fully captured in many of the existing numerical models, which usually make use of the classical forms of Fick's and Fourier's laws. A thermodynamic approach based on the hybrid mixture theory is therefore used in this work to provide a system of consistent coupled equations that incorporate multi-component processes of: Fickian-like diffusion of vapor, Darcy-like seepage of gas and Fourier-like heat transport. The sorption process is driven by the difference in chemical potential between the bound water and local vapor in the material, and governed by sorption isotherms implemented along with Frandsen's hysteresis model. The result is a thermodynamically consistent model, which is implicitly capable of modeling inherent hygrothermal properties including the heat of sorption. Numerical examples are implemented in a finite element method framework to describe the performance of the model in simulating moisture and heat transport dynamics in a wood section.