Consider an evaporation pond. A Feed water containing solute A enters the open p
ID: 528200 • Letter: C
Question
Consider an evaporation pond. A Feed water containing solute A enters the open pond, and exits at the same rate. Solute A transfers from the feed water in the open pond to the surrounding air which is essentially free of the solute. At these conditions, the individual liquid-film mass-transfer coefficient, k_L, is 5 times 10^-4 kgmol/(m^2 s (kgmol/m^3)) the individual gas-film mass-transfer coefficient, k_G is 0.01 kg mol/(m^2 s atm). The concentrations are in the Henry's law region where p_Ai = H_cAi with H = 10 atm/(kgmol/m^3). (a) Using two-film theory, calculate the the overall coefficient in the liquid phase, K_L? (b) What is the percent resistance to mass transfer in the liquid film?Explanation / Answer
Given, kL = 5 * 10-4 kgmole/(m2 s (kgmole/m3))
kG = 0.01 kgmole/(m2 s atm)
m = Henry's constant = 10 atm/(kgmole/m3)
(a) Overall coefficient in the liquid phase 1/KL = 1/kL + 1/(m.kG)
= 1/(5 * 10-4) + 1/(10 * 0.01)
= 2000 + 10
= 2010
Therefore, KL = 1/2010
= 4.975 * 10-4 kgmole/(m2 s (kgmole/m3))
(b) Percent resistance to mass transfer in the liquid film = (Resistance in liquid film / Total resistance in both the films) * 100 %
= (1/kL / 1/KL) * 100 %
= 1/(5 * 10-4) / 1/(4.975 * 10-4) * 100 %
= 2000 / 2010.05 * 100 %
= 99.5 %