Effect of evaporation cooling on drying capillary active building materials

The relevance of evaporation cooling on drying capillary active building materials is investigated through numerical simulation and non-destructive measurements. The drying rate results to be strongly related to the so-called wet bulb temperature, i.e. the temperature reached inside the sample during the early drying phase. It is shown that the faster the process occurs, the lower is the wet bulb temperature. The experiments are carried out inside a climatic chamber under controlled atmospheric conditions (temperature and relative humidity), using calcium silicate samples. The drying rates are determined by weighting the samples during time, while the surface temperature is measured via infrared thermography. A mathematical model describing transient heat and moisture transfer is implemented with the software COMSOL for 3D-simulation, and afterward validated by comparison with the measured data. The numerical solution presents a satisfactory agreement with the experimental results. A sensitivity analysis is also performed for different input parameters including convective heat transfer coefficient and uncertainties in material properties. The validated model is then used for simulation of a set of drying cases by varying the sample thickness and boundary conditions. Hence, the water content distribution inside the samples is investigated by determining boundary conditions and sample dimensions, in which nearly uniform water content can be obtained. In fact, uniform distribution is a prerequisite for an experimental method, recently studied by the authors, that aims at determining the water retention curve of capillary active materials by means of drying tests.