Energy analysis of droplet jumping induced by multi-droplet coalescence: The influences of droplet number and droplet location

Self-propelled droplet jumping phenomenon during condensation on superhydrophobic surfaces has various engineering applications such as heat transfer enhancement, hotspot cooling and anti-icing/frosting. Since most of the droplet jumping phenomena are induced by multi-droplet rather than two-droplet coalescence, understanding the influences of droplet number and multi-droplet location on the droplet jumping is essential. In this work, droplet jumping induced by multi-droplet coalescence was simulated using the volume of fluid (VOF) method with various coalesced droplet number and locations considered. The simulations showed visualized droplet morphology evolutions during the droplet jumping processes. The changes of several energies, such as surface energy, kinetic energy and jumping energy, were also discussed with the energy conversion efficiencies calculated. The results show that increasing the coalesced droplet number is advantageous for surface energy releasing and the energy conversion efficiency from the surface energy to the jumping energy also increases with increasing coalesced droplet number. Coalescence of droplets with more concentrated location distribution has weaker oscillation during the jumping process, along with less oscillatory kinetic energy, indicating that concentrated droplet distribution is conductive to increase the energy conversion efficiency from the surface energy to the jumping energy. (C) 2018 Elsevier Ltd. All rights reserved.