Abstract In heat exchangers employing flow boiling, e.g., boiling water reactors and industrial boilers, the heat transfer mechanism will transition from nucleate boiling to forced convective evaporation as the flow pattern transition from bubbly to annular flow at relatively high steam quality. Such thermal transition is called suppression of nucleate boiling (SNB). The occurrence of SNB affects the local heat transfer coefficient, the stability of liquid film, as well as the characteristics of entrained liquid droplets in the gas core. Despite its importance, there has been hitherto few direct measurements of the SNB conditions. Furthermore, the existing prediction approaches of SNB are only approximate, since they are based on extrapolation of empirical heat transfer correlations valid for nucleate boiling and forced convective evaporation regimes, rather than SNB mechanism. The objective of this study is to, experimentally and theoretically, fill the gap in understanding SNB phenomenon, using a modern set of diagnostics and a semi-empirical modeling approach. We leveraged synchronized infrared thermometry and an electrical conductance-based liquid film thickness sensor to investigate the details of the SNB phenomenon with high spatial and temporal resolutions. Such advanced diagnostics measure two crucial boundary conditions for SNB, i.e., the distribution of the temperature and heat flux on the heated wall, as well as the thickness of the liquid film. Such direct measurement revealed a clear dependency of SNB heat flux and wall superheat on both steam quality and mass flux. The experimental database has informed a more accurate semi-empirical model for predicting the SNB condition.

中文翻译：

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抑制向上两相环形流中的核沸腾：使用现代诊断方法的直接测量

摘要 在采用流动沸腾的换热器中，例如沸水反应器和工业锅炉，随着流型从气泡流转变为环流，蒸汽质量较高，传热机制将从核沸腾转变为强制对流蒸发。这种热转变称为抑制核沸腾 (SNB)。SNB的发生影响局部传热系数、液膜稳定性以及气核中夹带液滴的特性。尽管它很重要，但迄今为止很少有对 SNB 条件的直接测量。此外，SNB 现有的预测方法只是近似的，因为它们基于对核沸腾和强制对流蒸发机制有效的经验传热相关性的外推，而不是 SNB 机制。本研究的目的是使用现代诊断方法和半经验建模方法，从实验和理论上填补理解 SNB 现象的空白。我们利用同步红外测温仪和基于电导的液膜厚度传感器来研究具有高空间和时间分辨率的 SNB 现象的细节。这种先进的诊断测量 SNB 的两个关键边界条件，即加热壁上的温度和热通量分布，以及液膜的厚度。这种直接测量揭示了 SNB 热通量和壁面过热度对蒸汽质量和质量通量的明显依赖性。实验数据库为预测 SNB 状况提供了更准确的半经验模型。