Transient Surface Temperature Behavior in the Film Boiling Region

Abstract

An array of miniature thin-film thermometers was used to measure local, transient boiler-surface temperatures in the film-boiling region of saturated nitrogen. The data recordings were made at selected power levels throughout the region – including the condition of minimum heat flux – and are related to the conventional steady-state heat flux vs. excess temperature boiling behavior. The transient temperature signals illustrate features indicative of liquid impingement on the boiler surface. Additional experiments were performed to simulate liquid impingement on the same boiler surface and thermometer array, and the results substantially confirm the liquid-solid contact hypothesis. A computer-based data recording and processing system made possible both temperature and time expansions of the data for visual analyses. Progressive changes in the local, transient surface temperature characteristics with decreasing power levels – ultimately leading to the collapse of the vapor film at the minimum heat flux – a...