Example:

Graphical Integration in Falling$-$Rate Drying Period

A batch of wet solid whose drying$-$rate curve is represented by Fig. $9\mathrm{.}5-1$b is to be dried from a free moisture content of $x_1=0\mathrm{.}38kg{H}_2\frac{O}{k}g$ dry solid to $x_2=0\mathrm{.}04kgH{H}_2\frac{O}{k}g$ dry solid. The weight of the dry solid is $L_S=399kg$ dry solid and $A=18\mathrm{.}85m^2$ of top drying surface. Calculate the time of drying. Note that $\frac{L_S}{A}=\frac{399}{18\mathrm{.}85}=21\mathrm{.}5k\frac{g}{m^2}.$