Q$\mathrm{.}2$

$[60$ Marks $]$

Drying is an application which widely use in industries to concentrate the solution and most of its application is in pharmaceutical companies for producing medicine with high purity. A solid material with the mass of $20kg(2\mathrm{.}5kg$ water$)$ is going to be dried until the humidity of $8\%$ wet humidity as shown in the Figure. Q$2.$ The critical humidity is at the time that mass of water become one third of of its initial amount. If the amount of mass of solid per surface of the dryer is $5k\frac{g}{m^2}$ and rate of drying at the critical humidity is $24k\frac{g}{m^2}.$ws$.$

Figure Q$2$: Drying curve of a solid

i$)$ Determine the time of constant rate drying time $($hours$)$

ii$)$ Calculate the falling rate drying time.

ii$)$ Compare the results of drying stages in term of time and rate.