Apple slices $4mm$ thick are exposed to sulphur fumes from top in a

sulphuring house before drying. If the Biot number for mass transfer is higher than $40,$

and the surface concentration of $S{O}_2$ is $0\mathrm{.}1$molS$\frac{O_2}{m^3},$ determine how long it will take

for the concentration on the non$-$exposed surface of the apple slice to increase by $5\%$

of the initial concentration difference using both the analytical solution and Heisler

charts. Assume zero initial concentration of $S{O}_2$ in the apple, negligible mass transfer

through the sides of the apples, and a diffusion coefficient of $S{O}_2$ in the apple of $1{10}^{-9}$

$\frac{m^2}{s}.$