Influence of flow turbulence on the evaporation rate of a suspended droplet in a hot air flow

The evaporation process of a suspended droplet was examined for several kinds of drops of paraffin hydrocarbons, distilled water, and ethanol in a hot, turbulent air flow. As the turbulence intensity increases, the evaporation rate constant increases for all materials because the Kolmogorov microscale becomes smaller and it breaks the concentration boundary layer of the droplet. When the boundary layer thickness of vapor concentration around a droplet is thin, the droplet evaporation is accelerated as the mass transfer rate of vapor is increased by the flow turbulence, due to the steep gradient of concentration. The vaporization Damkohler number advocated by Gokalp and colleagues is not suitable to estimate the influence of turbulence on the evaporation rate at the condition where intense evaporation occurs.