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An investigation of the gravity effects on pool boiling heat transfer via high-fidelity simulations

机译：通过高保真模拟对池沸腾热传递的重力影响研究

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Nucleate pool boiling simulations are carried out to study the effects of gravity on the dynamics of bubble formation, bubble departure, and the mutual bubble interactions. We focus on identifying the dominant trends associated with the flow and thermal behavior at different gravity levels using fixed values of wall superheat and liquid subcooling. This is accomplished by measuring the contributions to heat flux associated with turbulent flow resulting from the dynamics of bubble interaction. The time averaged fluctuations of velocity and temperature indicate that the wall heat flux conditioned by the wetted surface area - the liquid heat flux - provides a useful indication of high heat flux hot spots. Furthermore, despite substantial differences in the dynamics of large scale bubbles at different gravity levels, the average heat flux in the liquid region is found to be dominated by the sliding and merger type events associated with small scale bubbles over a wide range of gravity levels. This significance of near-wall, small scale bubble dynamics is reflected in the transition of vorticity structures from hairpin type vortices in the near-wall region to vortex ring patterns away from the wall. While the maximum value of average turbulent fluctuations occurs away from the wall for earth normal gravity, the near-wall peak is only slightly lower and is similar in magnitude to that in the case of low gravity. These observations reveal the significance of small scale dynamics in affecting the heat transfer which was previously thought to be dominated by large scale bubbles, particularly at low gravity levels.
机译：进行核心池沸腾模拟，以研究重力对泡沫形成，泡沫偏离和相互泡沫相互作用的动态的影响。我们专注于使用固定的壁过热和液体过冷的固定值来识别与不同重力水平的流动和热行为相关的主导趋势。这是通过测量与由气泡相互作用的动态产生的湍流相关的热通量的贡献来实现的。速度和温度的平均波动的平均波动表明由湿润的表面积调节的壁热通量 - 液体热通量 - 提供高热通量热点的有用指示。此外，尽管在不同重力水平的大规模气泡的动态中存在显着差异，但是发现液体区域中的平均热通量被发现由与小型重力水平的小规模气泡相关联的滑动和合并类型事件来支配。这种近壁的这种意义，小规模气泡动力学反映在靠近壁区域中的发夹式涡流的涡旋结构的转变中，以远离墙壁的涡旋环图案。虽然平均湍流波动的最大值远离墙壁以​​获得地球正常重力，但近壁峰值仅略低，并且在低重力的情况下，幅度相似。这些观察结果揭示了小规模动力学在影响以前认为以大规模气泡主导的传热，特别是在低重力水平下的显着性。

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