Prediction of mass transfer coefficients in closed channels, estimate the gas-phase mass transfer coefficients for water vapor evaporating into air at 2 atm and 25°C, and a mass flow rate of 1570 lb_m/hr, in the systems that follow. Take D_AB = 0.130 cm²/s. 

(a) A 6-in. i.d. vertical pipe with a falling film of water on the wall. Use the following correlation¹ for gases in a wetted-wall column: Sh_loc = 0.023 Re^0.83Sc^0.44 (Re > 2000)

(b) A 6-in.-diameter packed bed of water-saturated spheres, with a = 100ft^–1.