Computational and experimental investigations on the evaporation of single and multiple elongated droplets

Abstract

Although droplet evaporation has been studied extensively, the focus is mostly limited to single spherical drops rather than elongated or multiple droplets, which is extensively encountered in a wide range of applications. The present study provides, for the first time, an experimental investigation on the evaporation of high aspect ratio elongated droplets. In addition, a fully coupled model is developed and validated against the experimental observations. The model is extended to provide a fully coupled analysis of adjacent droplets. The model considers all instabilities in both liquid and gas phases. The results indicate that the dynamics of droplet evaporation dramatically changes with droplet size, shape, and distance between adjacent droplets. Therefore, a non-dimensional pitch distance (L/D) is introduced to investigate the velocity fields in the droplets and gas domains as well as the temperature map at the interface of the droplets. While previous studies stated that the side droplets have higher evaporation rates compared to their central counterparts, and depending on the strength of natural convection their evaporation rate may exceed a single droplet, it is revealed in this study that besides the effect of natural convection, the evaporation rate of the high aspect ratio elongated side droplets becomes larger than that of a single one in the absence of Marangoni flow. Also in the presence of Marangoni flow, the side elongated droplets possess evaporation rates smaller than their central counterpart, and the evaporation rate of both central and side droplets becomes smaller than a single droplet.