Bubble dynamics and induced flow in a subcooled nucleate pool boiling with varying subcooled temperature

We experimentally investigate the dynamics of a vapor bubble and subsequent flow induced in a bulk liquid, generated by a subcooled nucleate pool boiling. We focus on the dependency of bubble lifetime (e.g., growth, departure, rise and collapse) on the subcooled temperature. While varying the subcooled temperature (Delta T-sub) as 2 - 15 degrees C, the temporal variation of bubble dynamics and liquid flow induced in its vicinity are measured simultaneously using the high-speed two-phase particle image velocimetry. In general, the bubble departure diameter and growth time tend to decay exponentially with increasing Delta T-sub, and it is possible to classify the regimes further. In a highly subcooled condition (Delta T-sub >= 8 degrees C), the bubble starts to shrink (condense) before departing from the wall, while it grows without shrinkage in a less subcooled condition (Delta T-sub < 8 degrees C). We modify and combine the existing bubble growth models to predict this phenomenon, which shows a good agreement with the measured data. When Delta T-sub < 8 degrees C, the departing bubble (2.5 - 3.1 mm in size) rises vertically with a significant deformation driven by the liquid inertia. However, the smaller bubble (1.5 - 2.2 mm) in a highly subcooled condition dissipates rapidly (much shorter lifetime) with a less deformation, owing to the enhanced condensation rate and surface tension. The rising velocity and aspect ratio of the bubble in a less subcooled condition fluctuate following the liquid flow induced by the bubble deformation. Counter-rotating vortical structure around a rising bubble develops larger for the less subcooled condition, which convects further from the wall than the cases of a highly subcooled condition. (C) 2021 Elsevier Ltd. All rights reserved.