Question

air-H2S mixture is flowing by a film of water that is flowing as a thin film down a vertical plate. H2S is being absorbed. P = 1.5 atm and T= 303K. K'c= 9.567*10^-4 m/s and pA (atm) = 609xA (liquid mole fraction). Na=-1.485 *10^-6 kg-mol/s*m^2.

a) Convert the gas-phase mass-transfer coefficient, kc ' , to k y ' and k G ' .

b) Based on the flux calculated above, calculate the liquid-phase mass-transfer

coefficient, kc ' , at this point in the tower.

c) Convert the liquid-phase mass-transfer coefficient, kc ' , to k x ' .

d) Calculate Ky’, Kx’ and the percent resistance offered by the gas and liquid phases.

e) Sketch both the concentration profiles (i.e., cA vs distance) and the mole-fraction

profiles (i.e., xA and yA vs distance) in the gas and liquid phases. Clearly indicate

values at the interface and bulk.

Again consider the falling film in TP 7.2-3, but assume negligible gas-phase mass

transfer (i.e., xA1 ≠2 × 10-5). What value of z (see Equation 7.3-22) corresponds to NA

= -1.485 × 10-6 kg-mole/s⋠m2? Assume the diffusion coefficient for water-H2S is DAB =

10-9 m2/s, the liquid has the properties of pure water, and the liquid film is

approximately 2 mm thick (see section 2.9C for more information on the velocity

profile in a following film). Calculate kcʹ in the gas and liquid phases at this z and at a

z half this value. Sketch both the concentration profiles and the mole-fraction profiles

in the gas and liquid phases. Again, clearly indicate values at the interface and bulk.