Phase identification of single microdroplet impacting a hot surface

Fundamental understanding of the physics of droplet impingement is essential in order to design an efficient spray cooling system. While there is extensive literature on single macrodroplet impingement, the results do not apply to spray cooling since the droplets in a spray are microscopic. In the present study, the impact of single microdroplets on a heated surface was experimentally investigated for a broad range of liquids, impact Re and We numbers, and for $60<T<250^{\circ }C$. It was found that the heat transfer regimes were independent of the impact velocity. A properly scaled phase diagram was developed to identify the heat transfer regime of a microdroplet’s impact given the impact conditions. An analytical model was proposed using the conservation laws to estimate the droplet lifetime on the hot surface in the film evaporation regime.