On the conservation of mass and energy in hygrothermal numerical simulation with COMSOL Multiphysics

In this paper, two different forms of the non-linear PDE-system for heat and mass transfer in porous materials and their implementation with COMSOL Multiphysics are considered. The φ-based form presents the relative humidity as system variable and leads in general to non-conservative solutions. The u-based form uses the water content as variable and is conservative. This study aims to select the most appropriated form for the implementation of the heat and mass transfer problem in COMSOL Multiphysics, comparing the quality of the numerical solutions and the solver performances. As first test-example, the simulation of a one-dimensional porous layer with a moisture flux imposed on one of the boundaries is presented.As second example, the moisture redistribution inside a partially saturated layer is simulated.