Influence of heat transfer on the estimation of water vapor diffusion coefficient in transient regime

Abstract

The use of bio-sourced materials for thermal insulation of buildings is growing mainly for environmental reasons. It has already been demonstrated that since these materials are highly hydrophilic, mass transfer may have significant influence on their temperature field. We first develop a heat and mass transfer model with a limited number of parameters and we use it to simulate the mass and temperature fields during a typical transient experiment dedicated to vapor diffusion coefficient estimation. Estimations made from these simulations with a simple mass transfer model show that the estimation error can be greater than 30 % in some cases. A sensitivity study shows that the vapor diffusion coefficient, the thermal conductivity and the external mass transfer coefficient can be estimated separately from a mass recording, with the coupled model. An experimental study carried out at 15°C, 25°C and 35°C on a wood fiber board confirms the results of the theoretical study. The deviation between the vapor diffusion coefficient estimated with and without taking into account the heat transfer was 13.3 % at 35°C. It is finally shown that the isosteric heat of sorption has no effect on the estimation of the diffusion coefficient.