Evaporation of methanol droplet on the Teflon surface under different air velocities

An experiment on the evaporating methanol droplet under different horizontal air velocities on Teflon substrate is presented. The droplet shape evolution was investigated using optical techniques (camera) of DSA100 apparatus. The controlled air velocity is at temperature of 22 °C (ambient and initial droplet). The contact angle, the base line were recorded and the volume time evolution is deduced. It was observed that there were three distinct stages for all air velocities: the constant contact angle stage (CA), the constant contact based line “diameter” stage (CD) corresponding to pinned triple line stage and the transition stage (TS) between CA and CD. In the three stages, the evaporation rate increases with the air velocity increase. And the resulting droplet lifetime is reduced by such increasing of the air velocity. In all different air velocities, it was found that among the three stages, the evaporation rate of the CA stage was largest, the evaporation rate of the CD stage is the least and the evaporation rate of the transition stage is the middle. And the evaporation rate is depended on the energy balance between the latent heat and the sensible heat.

► We analyze sessile droplet evaporation under imposed air flow.
► We examine the droplet volume time evolution change on non-wetting surface.
► Three different evaporation stages were identified.
► Increasing air flow intensity modifies flow boundary layer and droplet sizes interaction.
► The evaporation induces droplet cooling modifying the flow interface (liquid–gas) exchange.