Influences of Subcooling on Burnout of Horizontal Cylindrical Heaters

The peak pool boiling heat flux is observed on horizontal cylindrical heaters in acetone, Freon-113, methanol, and isopropanol over ranges of subcooling from zero to 130° C. Photographs, and the data themselves, revealed that there are three distinct burnout mechanisms at different levels of subcooling. Three interpretive models provide the basis for accurate correlations of the present data, and data from the literature, in each of the three regimes. Burnout is dictated by condensation on the walls of the vapor jets and columns at low subcooling. In the intermediate regime, burnout is limited by natural convection, which becomes very effective as vapor near the heater reduces boundary layer resistance. Burnout in the highsubcooling regime is independent of the layer of subcooling, and is limited by the process of molecular effusion.