Measurements of flow characteristics and interfacial evolution in the evaporative thin film region of aqueous solutions under reduced pressure.

In this paper, the internal flow characteristics and interfacial profile evolution of the thin liquid film region of aqueous solutions of ethanol and hexanol, which were compared with those of deionized water, were observed by employing a nanoparticle image velocimetry technique during evaporation under reduced pressure. It was observed that for both solutions, the film thickness shows two stages of decrease with time. The critical thicknesses that represent the transition of these two stages were then obtained. The change in critical thickness of the aqueous solution of ethanol is more sensitive to the low-pressure condition, while the aqueous solution of hexanol is less affected by the low pressures. The depinning time, critical thickness, and film thickness decline rate of these liquids showed an approximately exponential relationship with the absolute pressure. Finally, correlations between the logarithmic values of the relevant parameters and the absolute pressure were obtained.