Theoretical and Numerical Studies of Liquid Lens Evaporation with Coupled Fields

Abstract

The evaporation of the liquid lens on an immiscible liquid is widely adopted in many industrial and scientific applications, so it is crucial to predict the evaporation rate and lifetime of the liquid lens. During the evaporation, the internal thermocapillary flow, external natural convection, and interfacial evaporative cooling are coupled together and affect the evaporation characteristics greatly. In this paper, the slow and fast evaporation with coupled fields are studied by theoretical analysis and numerical simulation, respectively. It is found that the evaporative cooling can always inhibit the liquid lens evaporation, while the thermocapillary flow and natural convection can enhance the liquid lens evaporation. The total evaporation rate is determined by the competence between the interfacial evaporative flux and upper surface of the liquid lens. With the increasing liquid lens volume, the total evaporation rate will generally increase for fast evaporation, while for slow evaporation that only considers the evaporative cooling effect, the total evaporation rate may decrease at a low tangential angle ratio. The evaporation of the liquid lens follows the constant contact angle mode, the transient variation of volume satisfies the “2/3 law”, independent of evaporative cooling, thermocapillary flow, and natural convection, and it is analogous to the sessile droplet evaporation in constant contact angle mode. These findings can provide guidance for the wide application of liquid lens evaporation.