Theoretical analysis of water film evaporation characteristics on an adiabatic solid wall

• Transient evaporation characteristics of water film exposed to moist air is studied.
• Analytical solution describing water film heat conduction and evaporation characteristics is given.
• Water surface temperature drops sharply and then more slowly until it reaches air wet-bulb temperature.
• Latent heat needed for water evaporation comes mainly from water film and then from air fluid.

A theoretical study was conducted to analyze the transient evaporation characteristics of water film attaching to an adiabatic solid wall, with its other surface exposed to moist air. An analytical solution for the heat conduction in water film with a combined sensible and latent heat transfer boundary condition at the water/air interface was provided, and the effects of water film thickness, water/air convective heat transfer coefficient, and air temperature on water film evaporation characteristics was investigated. The results show that when the water evaporation starts, the water surface temperature drops instantly, as time goes on, the water surface temperature declines continuously until it reaches the air wet-bulb temperature. The latent heat needed for the water evaporation comes mainly from the water film by heat conduction at the initial stage, but more from the air fluid by heat convection afterward, and entirely from the air fluid when the water temperature attains to the air wet-bulb temperature.