Falling-film evaporation is an efficient heat-transfer technology. The average film thickness is an important factor that affects the heat-transfer performance. Based on the volume of fluid (VOF) algorithm

a computational fluid dynamics (CFD) model was established to describe the flow of a two-phase (air-water) falling film on a two-dimensional vertical channel. The effects of the film velocity

working medium

and co-current and counter-current gas on the liquid film thickness were investigated. The results show that the film thickness grows with the increasing film velocity. The gas-phase medium has little effect on the liquid-film thickness; however

the liquid medium has a great influence

and the film thickness increases with the liquid-film viscosity. The co-current gas flow has little effect on the film thickness in the entry and development regions. However

in the stable regions

the film thickness decreases with the increasing co-current gas velocity. The average film thickness decreases with the increase of the counter-current gas velocity. When the counter-current gas velocity reaches 2.5 m/s

the gas-velocity’s influence on the liquid-film thickness decreases.