Film boiling from a downward-facing curved surface in saturated and subcooled water

Film boiling from a downward-facing curved surface in saturated and 5 K, 10 K, and 14 K subcooled water was investigated experimentally. Local and surface average Nusselt number correlations developed for both saturation and subcooled conditions were within +/-10% of data. Surface rewetting in saturation boiling was hydrodynamically driven, but thermally driven in subcooled boiling. Consequently, surface rewetting in the former occurred earlier at higher q(min); the critical film thickness prior to rewetting, however, was higher than that at 10 K and 14 K subcooling, but lower than at 5 K subcooling. Surface rewetting occurred first at lowermost position, theta = 0 degrees, then sequentially at higher inclinations. For saturation boiling, the critical film thickness vas similar to 85 mu m and 180 mu m at theta = 0 degrees and 8.26 degrees, respectively. For subcooled boiling at theta = 0 degrees, the critical film thickness (similar to 50 mu m) was Smaller: it increased, however, with increased inclination and decreased subcooling, reaching similar to 175 mu m at theta = 8.26 degrees and 5 K subcooling.