Ammonia, NH3, in air is being absorbed into water within the enclosed tank shown in the figure below. The liquid and gas phases are both well mixed, and mass transfer occurs only at the exposed gas–liquid interface. The diameter of the cylindrical tank is 4 m, total liquid volume inside the tank is constant. The bulk gas pressure of ammonia is maintained at 0.02 atm, and the total gas pressure is constant at 1.0 atm. The system is isothermal at 208C. The inlet volumetric flow rate of water is 200 L/h and enters NH3 free. You may assume that Henry’s law, pAi ¼ HcAi describes the equilibrium distribution of NH3 between the gas and the liquid phases where H ¼ 0:02 atm/(kg mol/m3). The film mass-transfer coefficients are kG ¼ 1:25 kg mol/m2 h atm and kL ¼ 0:05 kg mol/m2 h (kg mol/m3). a. Determine the overall mass transfer coefficient, KG. b. Determine the partial pressure of NH3 at the gas–liquid interface, pAi. c. Determine WA the total molar rate of ammonia transfer. d. Develop a material balance for NH3; then determine cAi the concentration of NH3 in the outlet liquid stream.
Ammonia, NH3, in air is being absorbed into water
within the enclosed tank shown in the figure below. The liquid
and gas phases are both well mixed, and
only at the exposed gas–liquid interface. The diameter of the
cylindrical tank is 4 m, total liquid volume inside the tank is
constant. The bulk gas pressure of ammonia is maintained at
0.02 atm, and the total gas pressure is constant at 1.0 atm. The
system is isothermal at 208C. The inlet volumetric flow rate of
water is 200 L/h and enters NH3 free. You may assume that Henry’s law, pAi ¼ HcAi describes the equilibrium distribution
of NH3 between the gas and the liquid phases where
H ¼ 0:02 atm/(kg mol/m3). The film mass-transfer coefficients
are kG ¼ 1:25 kg mol/m2 h atm and kL ¼ 0:05 kg mol/m2 h
(kg mol/m3).
a. Determine the overall mass transfer coefficient, KG.
b. Determine the partial pressure of NH3 at the gas–liquid
interface, pAi.
c. Determine WA the total molar rate of ammonia transfer.
d. Develop a material balance for NH3; then determine cAi the
concentration of NH3 in the outlet liquid stream.
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