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. Loc al and surface average Nusselt number correlations developed for both saturation and subcooled conditions were within +/-10% of data. Surfac e rewetting in saturation boiling was hydrodynamically driven, but the rmally driven in subcooled boiling. Consequently, surface rewetting in the former occurred earlier at higher q(min); the critical film thick ness prior to rewetting, however, was higher than that at 10 K and 14 K subcooling, but lower than at 5 K subcooling. Surface rewetting occu rred first at lowermost position, theta = 0 degrees, then sequentially at higher inclinations. For saturation boiling, the critical film thi ckness 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 incre ased, however, with increased inclination and decreased subcooling, re aching similar to 175 mu m at theta = 8.26 degrees and 5 K subcooling.