Transferts couplés chaleur/masse dans les matériaux de construction biosourcés : investigation expérimentale et théorique du non-équilibre local

Abstract : The growing interest in biosourced materials in the construction sector is confronted with difficulties in simulating their hygrothermal behavior. Insulating materials such as fiberboard concentrate all the difficulties because they are not very thermally conductive, very hygroscopic and very diffusive to water vapor. Consequently, in transient state, heat and mass coupling is exacerbated, and the phases of water are not in equilibrium locally.In order to highlight this second phenomenon, a new experimental device has been developed. It allows to subject a sample a few centimeters thick to a disturbance of relative humidity on its front face and then to simultaneously measure the evolution of relative humidity on its back face and its mass. In a situation of non-equilibrium, there is a phase shift between these two quantities that the classic coupled transfer formulation cannot predict. In order to obtain a correct prediction, a new formulation was used. It is based on the use of memory functions characterizing microscopic diffusion. In order to demonstrate the predictive capacity of the new formulation, these functions have been determined with gravimetric tests performed on very small samples using a magnetic suspension balance. In parallel, a rigorous analysis of the heat and mass coupling in these materials made it possible to highlight the impact of different macroscopic parameters on their characterization.The use of the new formulation fed by the identified memory functions and the various macroscopic parameters allows an excellent prediction of relative humidity and mass. This new formulation, experimentally validated, can now be used in energy simulation of the building.
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Arnaud Challansonnex. Transferts couplés chaleur/masse dans les matériaux de construction biosourcés : investigation expérimentale et théorique du non-équilibre local. Matériaux composites et construction. Université Paris-Saclay, 2019. Français. ⟨NNT : 2019SACLC022⟩. ⟨tel-02164432⟩

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