Hydrodynamics and heat transport during the vertical coalescence of multiple drops impacting successively onto a hot wall

•Numerical predictions generally agree well with experimental data.•A wide heat flux peak can be observed during the spreading phase.•A wavy fluid flow causes several rings of high heat flux at the drop footprint.•Successive drop impact during the spreading phase enhances heat transfer. In this work, hydrodynamics and heat transport during the vertical coalescence of multiple drops impacting successively onto a hot wall are studied numerically and experimentally. The numerical model uses the volume of fluid method within the OpenFOAM library and takes evaporation into account. The significant heat transfer at the three-phase contact line is considered in a subgrid model. FC-72 is used as working fluid in a pure, saturated vapor atmosphere at ambient pressure. For the case of a drop chain of low impact frequency, numerical results are compared with experimental data. In particular, temperature and heat flux fields at the drop footprint as well as drop shape are compared between experiments and simulations. During the impingement of the second drop, several rings of high heat flux are observed in experiment and predicted by simulations, and the physical reasons of their appearance are elucidated by the analysis of simulated velocity and temperature fields. Furthermore, the impact of a drop chain consisting of five drops impacting at a high frequency is studied numerically. The drop chain configuration enhances both spreading and heat transport compared to the case of a single drop impact with a five-fold volume.