Ammonia, $N{H}_3,$ is being selectively removed from an air $-N{H}_3$

mixture by absorption into water. In this steady$-$state process,

ammonia is transferred by molecular diffusion through a stagnant

gas layer $5mm$ thick and then through a stagnant water layer $0\mathrm{.}1mm$

thick. The concentration of ammonia at the outer boundary of the

gas layer is $3\mathrm{.}42$mol$\%$ and the concentration at the lower boundary

of the water layer is essentially zero.

The temperature of the system is $288K,$ and the total pressure is $1$

atm. The diffusivity of ammonia in air under these conditions is

$0\mathrm{.}215c\frac{m^2}{s}$ and in liquid water is $1\mathrm{.}77{10}^{-5}c\frac{m^2}{s}.$ Neglecting water

evaporation, determine the rate of diffusion of ammonia, in $k\frac{g}{m^2}-h.$

Assume that the gas and liquid are in equilibrium at the interface.

The equilibrium data for ammonia over very dilute aqueous solution

at $288K$ and $1$atm can be represented by $($Welty et al$.,1984)$

$y_A=0\mathrm{.}121+0\mathrm{.}013ln{x}_A$

Hint: At steady state, the ammonia rate of diffusion through the gas

layer must equal the rate of diffusion through the liquid layer.