Mass Transport

Air containing an undesired substance A is to be treated in a wetted-wall column, as shown in Fig.. The air inside the column contains A at a partial pressure pA= 20 Pa. The air is well mixed right up to the water-air interface. The water film has a thickness of 0.07 cm and flows with an average water velocity of 3 cm/s. The flow in the water-film is laminar and transport into the film is by diffusion only. The column diameter is 10 cm and its length is 20 cm. The diffusion coefficient of A in water is 1.8 109 m2/s and the solubility of A in water is 6.2 Pa m3/mol.

(a) Calculate the concentration of A at the liquid side of the gas- liquid interface. (b) Use an adequate Sherwood correlation to calculate the mass transfer coefficient for the transfer of A from the gas to the bulk of the water film. (c) Calculate the concentration of the water leaving the column.

Tip/ Use mass balanse: in - out = accumilation

Gas out PA Liquid in CA0=0 Gas in PAO Liquid ot CA1