The nature of boiling during rewetting of surfaces at temperatures exceeding the thermodynamic limit for water superheat

• Published in: Journal of fluid mechanics Vol. 895
• Main Authors: Gomez, C. F., van der Geld, C. W. M., Kuerten, J. G. M., Liew, R., Bsibsi, M., van Esch, B. P. M.
• Format: Journal Article
• Language: English
• Published: Cambridge Cambridge University Press 25.07.2020
• Subjects: Boiling; Bubbles; Heat; High temperature; Hydraulic jets; Impingement; Jet impingement; Mechanical properties; Quenching; Stagnation; Superheating; Surface temperature; Temperature; Water; Water temperature; Wetting
• ISSN: 0022-1120; 1469-7645
• DOI: 10.1017/jfm.2020.232

Rewetting is the establishment of water–surface contact that occurs during quenching of high temperature surfaces by water jet impingement. Rewetting is an unexpectedly complex phenomenon that has been reported to occur at surface temperatures significantly higher than the superheating limit of water. The presence of intermittently wet and dry episodes, and in particular the occurrence of so-called explosive boiling, is one of the theories to explain the contact of water with high temperature surfaces. However, there is a lack of experimental data in the literature to prove the presence of explosive boiling and intermittent wetting due to the small duration and scale of the rewetting phenomenon. In this study, recordings of the jet stagnation zone during rewetting are provided at a frame rate of 81 kfps. The high-speed recordings show a flashing regime consisting of intermittent (dry) bubble-rich and (wet) bubble-free periods at frequencies up to 40 kHz when the rewetted surface temperature exceeds the water superheat limit. As far as the authors know, these are the first direct observations of intermittent dry–wet periods occurring in the jet stagnation zone during quenching by water jet impingement. The dependency of the flashing frequency on initial surface temperature is quantified. A correlation between the size of the rewetting patch and the flashing frequency is found. Finally, a hypothesis to explain the role of water subcooling in maintaining the water–surface contact at surface temperatures well above the superheating limit of water is presented.