Promoting advances in understanding water vapor sorption in wood: relegating popular models and misconceptions

Abstract

Water vapor sorption is a fundamental characteristic of wood as a building material. Apart from empirical prediction, models are often used to interpret the time-dependent process of water vapor uptake (sorption kinetics) and equilibrium states of water in wood (sorption isotherms). This paper summarizes our recent investigations into measurement methods and popular models that are widely used for interpreting these physical phenomena. Commonly used criteria for determining equilibrium moisture content with the dynamic vapor sorption technique yield much larger errors than previously thought. A more rigorous equilibrium criterion and a method to reduce data acquisition time are proposed. Evaluation of the parallel exponential kinetics model with improved data and multi-exponential decay analysis indicates that this model is unable to characterize the full sorption kinetic response following a step change in relative humidity. Fitting of common sorption isotherm models to high-quality equilibrium data for wood gives model predicted physical quantities such as monolayer capacity and enthalpy of sorption that are far from agreement with independently measured data. Thus, these models are not valid for water vapor sorption in wood. New theoretical models are needed that correctly describe the physical phenomena.

Citation

Glass, Samuel V.; Zelinka, Samuel L.; Boardman, Charles R.; Thybring, Emil Engelund. 2023. Promoting advances in understanding water vapor sorption in wood: relegating popular models and misconceptions. In H. Johra (Ed.), NSB 2023 - Book of Technical Papers: 13th Nordic Symposium on Building Physics (Vol. 13). [239] Department of the BuiltEnvironment, Aalborg University. https://doi.org/10.54337/aau541615744.