ABSTRACT
Any action on the external conditions of the solid will
influence the drying rate. The main action would be the
change in air velocity. This variable must be carefully
controlled. The falling drying rate period begins when the
constant drying rate period has finished and the so-called
critical moisture content is reached. The transition between
periods is not abrupt. The falling drying rate period is
divided into two steps. During the first step, a part of the
surface of the solid cannot be maintained water-saturated,
thus the drying rate decreases slowly. During the second
step, the whole evaporating surface is unsaturated and the
evaporation front moves inside the product. Then, the dry-
ing rate is controlled by the internal movement of water
and the influence of external variables (e.g., shape and air
velocity) diminishes. Inside the solid, a moisture gradient
develops. Nevertheless, the average water content is
usually considered for kinetic purposes.
