Local coefficients and average coefficients. There is a small cylindrical bed of $60$ cm long, packed with naphthalene spheres $($A$)$ of $0\mathrm{.}2$ cm in diameter, as illustrated in Figure $.$ The specific bed area of the packed spheres is approximately of $25$ cm$2$ for each cm$3$ of bed volume and is represented by a$.$ To this bed feeds air $($B$)$ pure and dry at $1$ atm and $75\backslash$deg C$,$ at a superficial speed of $2$ m$/$s$.$ steam pressure of naphthalene at air temperature is $5$ mm Hg$.$ The mass transfer coefficient average in the bed is $6\mathrm{.}81$x$10-2$ cm$/$s$.$ It can be assumed that the naphthalene spheres do not change its size.

Calculate the molar flux of naphthalene at the outlet of the bed