MAPPING OF IMPACT AND HEAT-TRANSFER REGIMES OF WATER DROPS IMPINGING ON A POLISHED SURFACE

Still and high-speed photographic techniques were used to record the i mpact behavior of water droplets on a hot aluminum surface. Drop veloc ity and surface temperature were two important parameters governing bo th the impact behavior and ensuing heat transfer. Droplet Weber number s of 20, 60 and 220 identified three major classes of impact behavior, while surface temperatures ranging from 280 to 100 degrees C were use d to define heat transfer regimes corresponding to film boiling transi tion boiling, nucleate boiling, and film evaporation. Temperatures cor responding 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 const ruct droplet impact regime maps which identify the various boiling reg imes for each of the three Weber numbers. These maps serve as a new us eful foundation for understanding droplet impact behavior as well as f uture analytical or numerical modeling of droplet and spray heat trans fer. Copyright (C) 1996 Elsevier Science Ltd.