Boiling crisis is a consequence of thermal runaway in the substrate due to degradation of nucleate boiling heat transfer

Chaotic bubble interactions during vigorous boiling have foiled attempts at an accurate mechanistic understanding of this important industrial transport process. Prediction of the boiling crisis (dryout) that occurs due to the spontaneous merger of bubbles into an insulating vapor film at critical heat flux remains an unsolved challenge. This work diagnoses the dryout process using synchronized high-resolution spatiotemporal heat flux and phase data, obtained via through-substrate infrared and visual inspection. We examine prevailing theories for the boiling crisis and provide evidence to rule out all but one. The boiling crisis is found to be a consequence of a peak in the nucleate boiling curve, past which the degradation of boiling heat transfer and concomitant increase in superheat are caused by replacement of the thermally efficient contact line region with the inefficient vapor-covered region for the surface-fluid combination studied. This results in substrate thermal runaway and dryout. Rather than seeking a separate dryout trigger mechanism, nucleate boiling models must instead inherently capture this peak. The heat flux partitioning employed demonstrates that critical heat flux can indeed be predicted by capturing this peak. A generalized framework is suggested for predicting the boiling curve as part of a multidimensional surface, a boiling manifold.