Problem Sheet $2-$ Diffusion Through a Varying Cross$-$sectional Area

$2\mathrm{.}1$ Derive an expression for the flux of A through non$-$diffusing $B$ in a tapered conduit with a circular cross$-$section as shown in the figure.

Ans:

$N_{A1}=\frac{D_{AB}ck}{r_1^2[\frac{1}{r_1}-\frac{1}{r_2}]}ln[\frac{c-c_{A2}}{c-c_{A1}}]$