3.8 (Evaporation of water in a wetted-wall column )1 Water is being evaporated into a counter-current stream of air in a wetted-wall column, 30mm in diameter. Estimate the evaporative flux of water at a point in the column where the water temperature is 305K and the mole fraction of water vapour in the bulk air is 0.0098. The following data and information are supplied: air rate (dry basis) =1kg/min; water rate =0.2kg/min; air temperature at the location =38C; air viscosity ( at 38C)= 1.85105lb/fts; total pressure =1atm. Vapour pressure of water at the given temperature can be obtained from Antoine equation (see Problem 2.2). The gas-phase mass transfer coefficient can be calculated using the Gilliland and Sherwood correlation given by (note that it resembles the Dittus-Boelter equation for heat transfer) Sh=0.023(Re)0.8(Sc)0.33