The following drying curve indicates each phase of the drying

process.

Drying curve

Drying phases

Phase I $($A$)$: Preheating $($not shown on the graph$).$

Phase II $($B$-$C$)$: Constant rate. The drying rate is constant.

Phase III $($C$-$D$)$: First rate drop. The drying rate decreases.

Phase IV $($D$-$E$)$: Second rate drop. The drying rate becomes even slower.