Impact of Leidenfrost Drops on Spherical Targets

The impact of Leidenfrost drops on planar surfaces has been an on-going topic of research. However, the impingement of these drops on spherical targets is less understood despite its important implications for petroleum processing such as in fluid catalytic cracking. In this work, an experimental system was designed to heat metallic targets beyond the Leidenfrost temperature for drop impingement studies. Water drops with Weber numbers ranging from 10 to 45 were impinged on planar and spherical targets with temperatures from 160 °C to 220 °C. Impinging drops covered a larger surface area on a spherical compared to a planar surface. In addition, it was observed that the Leidenfrost temperature depended on the ratio of the drop diameter to the spherical target diameter. For Weber numbers from 10 to 15, drops were observed to rebound off the target. At Weber numbers from 15 to 30, liquid hole formation was observed and analyzed. For greater Weber numbers and temperatures, liquid toroids developed. The toroidal drop dynamics were measured with high speed photography and these results were compared with existing models for planar surfaces. The toroids broke up into a discrete number of smaller drops as a result of a Plateau-Rayleigh instability.