Heat, Air, and Moisture Transfer Model in Porous Building Materials with Consideration of Hygric Non-equilibrium Between Liquid Water and Vapor

The paper presents a model for drying building materials or masonry walls. The mixture approach was used to model transport phenomena in a porous medium. Therefore, effective properties were used instead of modeling the exact microstructure. The model considered three phases, i.e., solid material (matrix), liquid water, and humid air (a mixture of vapor and dry air). Liquid water capillary and diffusive vapor and air transfer were accounted for. Thermal equilibrium between all phases (the same temperature of all components) was assumed. However, the hygric non-equilibrium between the liquid water and vapor was considered. Hence, moisture phase transition with a finite rate could be modeled. The model was implemented in the commercial software ANSYS Fluent by using advanced customization user interfaces, i.e., User-Defined Function (UDF), Scalar (UDS), and Memory (UDM), which allowed extending the capability of the software to phenomena models that are not available in the software. The model was tested and subsequently validated against the experiment. The experimental stand was explicitly designed for comparing simulations with measurements. The experiment was conducted in forced convection conditions at the surface of the damp material. The validation shows limited agreement of the model predictions with the measurements.