Local heat transfer and phase change phenomena during single drop impingement on a hot surface

Heat and mass transfer at a droplet impinging on a hot wall is investigated experimentally and numerically. The experiments are conducted with refrigerant FC-72 within a saturated vapour atmosphere. The droplet dynamics and the heater temperature very close to the solid-fluid interface are captured with high spatial and temporal resolution. The boundary conditions for the numerical simulations are chosen according to the experiments. The simulation accounts for the complex two-phase flow including evaporative mass transfer. Special attention is given to the local heat and mass transfer close to the moving three-phase contact line. Numerical and experimental results are compared to give insight into the basic heat transport mechanisms occurring during drop impact and to quantify their relevance for the overall heat transfer. It turns out that convective heat transfer is dominant during the initial stage of the impact corresponding to the droplet spreading, while at the final stage of the impact, corresponding to evaporation of a sessile droplet, a considerable part of the total heat transfer occurs in the direct vicinity of the three-phase contact line.