Evaporation Characteristics of Two Interacting Moving Droplets

The droplet evaporation in sprays and clouds is largely influenced by the interacting surrounding droplets. This study presents a numerical investigation on the evaporation dynamics of two inline interacting droplets in a high-temperature vapor domain using ANSYS Fluent. Several methods are available to solve the multiphase flow problems with phase change, including level set, phase field, volume of fluid (VOF), and hybrid techniques. In the present study, the multiphase model equations are solved in the framework of the VOF method, which is a well-established and robust solver for multiphase flows with excellent volume conservation properties. The Lee model is used to handle the evaporative phase change at the interface. The droplet spacing, sizes, and arrangement pattern of differently sized droplets are the key parameters varied to explore their effects on the evaporation rate, droplet velocities, and inter-droplet distance. For equal-sized droplets, the evaporation of the trailing droplet slows down due to the low-temperature buffer layer of the droplet vapors generated by the evaporation of the leading droplet; the effects decrease as the initial spacing is increased. For two droplets at center-to-center distances of 2do and 6do, the evaporation of the trailing droplets reduces by 20.8% and 7%, respectively. Decreasing the size of the trailing droplet increases its evaporation rate since the smaller droplet experiences more temperature gradients as it escapes out of the influence of the leading drop buffer layer. For a smaller to larger droplet diameter ratio of 0.9, the evaporation rate of the trailing droplet is reduced by ~26% than expected. However, for the diameter ratio of 0.5, this reduction is only 12.5%. Regarding the arrangement pattern of different-sized droplets, the overall evaporation rate is lower when the bigger droplet follows the smaller one. The fact is attributed to close interaction followed by the coalescence of the bigger droplet with the leading smaller droplet, resulting in a single bigger droplet.