Mechanism and Modeling of Rewetting Initiation of Hot Dry Surface in Saturated and Subcooled Film Boiling

Abstract

The behavior of rewetting on a high superheated and dry surface, focusing on rewetting temperature just as collapse of saturated and subcooled film boiling was investigated experimentally and analytically. Saturated and subcooled pool film-boiling experiments were conducted by using a Silicon wafer with 20 mm length, 20 mm width and 0.5 mm thickness and pure water at atmospheric condition. Saturated and subcooled impingement jet experiments were also preformed. Then, the model analysis of rewetting initiation of a hot dry surface in saturated and subcooled film boiling was constructed by using hydrodynamics instability on liquid-vapor interface (Rayleigh-Taylor instability) and a heat conduction model (rewetting model under a falling film). Some physical parameters on Rayleigh-Taylor instability, for example released period of bubble from vapor film on a heater, generated volume rate of vapor and so on, were estimated by using Two-Phase Boundary Layer theory of saturated and subcooled film boiling. The present analytical results also showed that as the liquid subcooling was high, MHF temperature was higher. Namely, the predictions agreed with the present experimental results and Dhir-Purohit’s correlation. In addition, the present model of MHF temperature was developed by taking into account the dependence on thermal conductivity of wall of the MHF-temperature.