$[60$ Marks

A solid material with the mass of $20kg(4kg$ water$)$ is going to be dried until the humidity of $2\%$ dry humidity as shown in the Figure. Q$1.$If the amount of mass of solid per surface of the dryer is $10k\frac{g}{m^2}$ and rate of drying at the critical humidity is $900k\frac{g}{m^2}.h.$

Figure Q$1$: Drying curve of a solid

i$)$ Determine the time of constant rate drying time, $h.$

$[8$ Marks$]$

ii$)$ Calculate the falling rate drying time, $S.$

$[8$ Marks$]$

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

$[4$ Marks$]$