Characteristic functions for the drying of non-hygroscopic porous slab with a constant body temperature

This paper deals with the isothermal drying process for slabs of non-hygroscopic porous material. First, the falling rate period is divided into the regular regime and the penetration period. Then the mass transfer equation involving a moving boundary is analyzed for both periods. In the regular regime, the relation between a modified flux parameter and a modified mean moisture content is characteristic of the dependence of moisture diffusivity on moisture content. On the other hand, in the penetration period, the relation between the flux parameter and the mean moisture content is not affected by the dependence of the diffusivity on the moisture content. These characteristic functions generalize the drying-rate curves, which differ with drying conditions. By using these functions, it may be possible to predict drying rate curves under any drying condition from a measured curve.