Abstract:
It has long been thought that the evaporation rate from mesoporous
materials during the constant drying rate period (CDRP) is
equal to that of a free-water surface, due to the presence of a liquid
film covering the surface of the material. In this article we review
several early articles and demonstrate that the experimental scrutiny
this hypothesis has received is insufficient. Further, we report
a set of evaporative drying experiments on eight building materials
whose results also do not confirm such hypothesis. Indeed, the drying
rate during the CDRP is not equal either among the tested materials
or between these and the free-water surfaces. To explain the
differences in drying rate, we have looked at the influence of surface
texture and porosity. We have concluded that surface texture, which
could increase the effective surface area of the materials, did not
have a relevant effect on the CDRP drying rate. However, we have
found a good correlation between the CDRP drying rate and capillary
porosity. This is consistent with the hypothesis that drying
occurs at the pore level during the CDRP. Further, it contradicts
the suggestion that there is a film of water covering the surface of
the materials during this period.
