The study of post-dryout heat transfer has generated great interest because of its importance in determining maximum clad temperature in nuclear reactor loss-of-coolant accidents (LOCAs). An associated phenomenon, the deterioration of heat transfer in boiling, is significant to other industrial sectors. This book provides comprehensive coverage of post-dryout heat transfer, discussing such essential topics as post-dryout heat transfer in dispersed flow, interpretation and use of transient data in surface rewetting by reinstatement of flow or by reducing heat flux, rod bundles, two-phase flow occurrences in the post-dryout region, various methods for predicting ""inverted annular flow,"" and new experiments for measuring thermodynamic nonequilibrium with probes in the channel. The book also presents a basis for independent safety assessment of nuclear reactors and chemical plant systems where post-dryout heat transfer may occur. Post-Dryout Heat Transfer will be a useful reference for researchers and professionals in the nuclear and chemical production industries.

Conduction and single-phase convective heat transfer are well understood phenomena: analytical models [1] and empirical correlations [2] allow capturing the thermal behavior of plate-type fuels or heaters in contact with a single-phase coolant. On the other hand, transient boiling heat transfer is a scarcely studied and much less understood phenomenon. Although, earlier studies have shown that important features of the boiling curve (i.e. onset of nucleate boiling (ONB), nucleate boiling heat transfer coefficient, and critical heat flux (CHF)) in transient conditions. These parameters significantly differ from those at steady-state. The mechanisms by which these changes occur are not clear. Furthermore, some of the conclusions from different authors are quantitatively or qualitatively in disagreement with each other. This work studied transient pool boiling heat transfer phenomena under exponentially escalating heat fluxes on plate-type heaters, at the time scales of milliseconds typical of Reactivity Initiated Accidents (RIAs) in nuclear reactors. The investigation utilized state-of-the-art diagnostics such as Infrared (IR) thermometry and high-speed video (HSV), to gain insight into the physical phenomena and generate a database that could be used for development and validation of accurate models for transient boiling heat transfer. The tests with exponential power escalation periods ranging from 100 ms to 5 ms and subcoolings of OK (saturation), 25K and 75 K were conducted. The measured pre-ONB heat transfer coefficient agrees well with the theoretical predictions for transient conduction. The ONB and onset of significant void (OSV) temperature and heat flux were found to increase monotonically with decreasing period and increasing subcooling, as expected. The mechanistic ONB model of Hsu was able to predict the measured ONB temperature and heat flux. The transient pool boiling curves were measured up to fully developed nucleate boiling (FDNB). Generally two types of boiling curve were observed: with overshoot (OV) or without overshoot. Data show that, when an OV is present, the OV temperature increases monotonically with decreasing period and increasing subcooling. The present study clears the confusions (eg. the trend of ONB temperature and heat flux versus power period) in previous research, and sheds light to the mechanisms behind transient boiling heat transfer. This can ultimately reduce the uncertainty in both design and safety analyses of the research reactors especially under RIAs.