Experimental and Theoretical Study of Evaporation of a Volatile Liquid Lens on an Immiscible Liquid Surface

The evaporation of a hexane lens on a distilled water surface was experimentally and theoretically studied. The formation of the hexane lens was recorded by a high-speed camera from the side to observe the variations of the contact diameters and contact angles. The experimental results showed that the shape variation of the hexane lens experienced the spreading stage and the evaporation stage. The spreading stage lasted for about 6% of the lens lifetime. For most time of the evaporation stage, the square of the lens contact radius decreased linearly with time, while the contact angle remained almost unchanged. During the final rapid evaporation stage (about 2% of the lens lifetime), the shape of the hexane lens changed and the lens shrank rapidly until it disappeared. A theoretical model based on diffusion-controlled evaporation under the constant contact angle mode was developed to describe the evaporation of the hexane lens on the water surface. In terms of geometry, the model assumes that a lens is composed of upper and lower spherical caps, and the apparent contact angle is defined based on the intersection of the two caps. The results calculated using the model were found to be in good agreement with the experimental data. Finally, the effects of initial lens volume, water temperature, and water surface deformation on lens evaporation were discussed through calculations. The results showed that increase in the water temperature and deformation of the water surface accelerated the evaporation process.