Direct observation of rewetting failure mechanism at CHF under different subcooled flows

In this study, we visualized vertical upward flow boiling under different subcooling conditions to identify dry patch behaviors. Shadowgraph visualizations and total internal reflection images were synchronized to capture the bubble structure and dry patch behaviors. A 12-cm-long indium tin oxide film heater coated with 0.5-mm-thick sapphire was used for the experiments. Under all subcooling conditions, we observed a significant retardation of the rewetting momentum when large elongated bubbles and dry patches were generated. Before CHF triggering, the dry patch size reached its maximum value and rewetting was delayed, thereby leading to an increase in the dry patch lifetime. We also investigated the relationship between the maximum size and lifetime of irreversible dry patches under different subcooling conditions and determined the reason for the significant increase in the lifetime of the irreversible dry patch.