A theoretical model was derived for the steady state one-dimensional velocity distribution and two-dimensional temperature distributions in annular laminar liquid films falling down on the wall outside a vertical tube with heat and mass transferring from the interface to counter-current gas flow.Based on the model

liquid film thickness and interfacial heat flux could be predicted if shear stress was obtained.From the good agreement of experimental data and predicted values of the interfacial heat fluxes within the range of gas flow Reynolds number Reg<1200

the method of using interfacial friction factor to solve the model was reliable under laminar conditions of the two phases.The model simulation results revealed the non-linear characteristics of velocity and temperature distributions in the film.The sharp temperature gradient close to the gas-liquid interface indicated that it was an effective way to enhance heat and mass transfer by reducing film thickness.