Liquid-solid contact measurements using a surface thermocouple temperature probe in atmospheric pool boiling water

Abstract

The objective of this investigation was to apply the technique of using a microthermocouple flushmounted at the boiling surface for the measurement of the local surface-temperature history in film and transition boiling on high temperature surfaces. From this measurement direct liquid-solid contact in film and transition boiling regimes was observed. In pool boiling of saturated, distilled, deionized water on an aluminum-coated copper surface, the time-averaged, local liquid-contact fraction increased with decreasing surface superheat. Average contact duration increased monotonieally with decreasing surface superheat, while frequency of liquid contact reached a maximum of ~ 50 contacts s −1 at a surface superheat of ~100 K and decreased gradually to 30 contacts s −1 near the critical heat flux. The liquid-solid contact duration distribution was dominated by short contacts < 4 ms for high surface superheats and shifted to long contacts > 4 ms at low surface superheats, passing through a relatively flat contact duration distribution at about 80 K. The results of this paper indicate that liquid-solid contacts may be the dominant mechanism for energy transfer in the transition boiling process.