Mapping of impact and heat transfer regimes of water drops impinging on a polished surface

Abstract

Still and high-speed photographic techniques were used to record the impact behavior of water droplets on a hot aluminum surface. Drop velocity and surface temperature were two important parameters governing both the impact behavior and ensuing heat transfer. Droplet Weber numbers of 20, 60 and 220 identified three major classes of impact behavior, while surface temperatures ranging from 280 to 100°C were used to define heat transfer regimes corresponding to film boiling, transition boiling, nucleate boiling, and film evaporation. Temperatures corresponding to the critical heat flux and the Leidenfrost point showed little sensitivity to both droplet velocity and impact frequency. The photographic results and heat transfer measurements were used to construct droplet impact regime maps which identify the various boiling regimes for each of the three Weber numbers. These maps serve as a new useful foundation for understanding droplet impact behavior as well as future analytical or numerical modeling of droplet and spray heat transfer.