Evaporation characteristics analysis of water film on a spherical solid particle

A theoretical study has been conducted to analyze the transient evaporation characteristics of water film on a spherical solid particle, with the water free surface exposed to air fluid. An analytical solution for transient heat transfer of a spherical solid/water bilayer structure with a combined sensible and latent heat transfer boundary condition at the water/air interface that is movable due to the water evaporation is derived based on the method of variable separation. The water film evaporation characteristics are analyzed for different air temperatures and solid particle materials. The results show that when water evaporation begins, the water surface temperature initially changes sharply, then more gently, and eventually stabilizes at the air wet-bulb temperature. The latent heat needed for the water evaporation may come from both the water film by heat conduction and the bulk air by heat convection, or from the latter only, depending on the magnitude of the air wet-bulb temperature relative to the initial water temperature. The water film transient evaporation characteristics are affected more by the heat capacity than by the thermal conductivity of the solid particle.