In Drying, water is removed from the grain by evaporation in two phases.
In first phase, only water on the surface of the grain or very close to the surface evaporates.
The rate of drying, depends on
- Surface area of the grain
- Air temperature,
- Speed of the current of air passing over the grain
- Relative humidity or wetness of the air.
The drying rate during the first phase will be increased by the increasing the grain surface area by splitting the grain and scoring them.
During the second phase, the drying rate depends on:
– Type of grain,
– Thickness of the grain,
– Temperature of the grain,
– Water content of the grain,
If moisture is removed from the grain surface quickly, the drying rate is independent of the level of humidity in the air. It depends on the rate at which water reaches the surface of the grain.
If drying is very fast during the early period, the surface may dry quickly, which results in producing a hard layer which will slow down the rise of the water to the surface, resulting in hardening.
APIT process dryers have the function like distribute the temperature level by level to the grain and remove the moisture from grain to avoid the case of hardening in the process.