Static Beds of Porous Solids
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The drying curve obtained when the particles that compose the bed are them-selves porous.
STATIC BEDS OF POROUS SOLIDS
The
drying curve obtained when the particles that compose the bed are them-selves
porous is shown in Figure 7.5. It differs from the curve obtained with
nonporous materials in that the constant rate period is shorter. The rate of
drying may be higher and is almost independent of particle size. The critical
moisture content is a function of both pore size and particle size. During the
first falling rate period, the rate of drying falls steeply because, it is
thought, of the drying of the surface granules. The second falling rate period
is influenced by the diffusion of moisture from within the particles.
FIGURE 7.5 Drying curves for a tablet granulation
dried in a tray drier (A) moisture content versus time and (B) drying rate
versus moisture content.
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