A circular tube coated with naphthalene on inside surface. Tube has ID of $20$ mm and length of $1\mathrm{.}1$ m$.$ Fresh air enters the tube at a velocity of $0\mathrm{.}8$ m$/$s$.$ Calculate the concentration of naphthalene in air, C $10=2\mathrm{.}8*10^-5$ kmal$/$m$^3.$ Density of air $1\mathrm{.}1$kg $/($m $^3)$ viscosity of air $1\mathrm{.}9*10^-3$ Ns $/($m $^2)*$ l diffusion coefficient of naphthalene in air D AB $=0\mathrm{.}7*10^-5$ m$^2/5$