学术论文

On the Relation between Nucleation Site Density and Critical Heat Flux of Pool Boiling




作者: Ke Wang, Shengjie Gong, Bofeng Bai & Weimin Ma
发表/完成日期: 2017-08-24
期刊名称: Heat Transfer Engineering
期卷: DOI: http://dx.doi.org/10.1080/01457632.2017.1369836
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论文简介
It is traditionally accepted that the critical heat flux (CHF) decreases with increasing nucleation site density (NSD). However, such a CHF-NSD relation was no longer observed in the BETA-B experiment performed on nano-film heaters; instead the increase of NSD resulted in a gain in CHF. To address this seeming contradiction in the relation between critical heat flux and nucleation site density, the present work employed probabilistic analysis to reveal the different tendencies. A concept of effective NSD was proposed, which concerns the active nucleation sites appear within a bubble lifetime, and the resulting bubbles have the chance of direct interaction. We assumed that the boiling crisis on a heater surface is mainly induced by two mechanisms: dry spot expanding in isolated bubble regime for low-NSD surface, coalescence of dry spots under multiple bubbles in fully developed nucleate boiling regime for high-NSD surface, or a combination of the two in the transition regime for medium-NSD surface. Accordingly, we estimated the critical heat flux of each boiling regime at which the boiling crisis occurs. The result indicated that there is a threshold of nucleation site density below which the increase of NSD is contributing to CHF enhancement, while the trend is inverted beyond the threshold.