There are two periods of drying process. The first is
constant rate period at which the moisture is removed
at an even rate till the required critical moisture content
Mc. The second is falling rate period at which the rate
of moisture removal is decreased [16]. During first
period, the wet surface of the product behaves as a free
water surface and the period continues as long as water
is supplied to the surface. During second period, the
drying is characterized by subsurface evaporation
throughout till the equilibrium moisture content ME is
reached. Most of the drying actually takes place in the
falling rate period and involves the movement of
moisture in the material to the surface and continued
with the removal of the moisture from the surface.