Abstract Based on the fluid volume approach, a transient numerical model for the condensation heat transfer and flow features in a microchannel is proposed. The flow condensation of R32 in a circular microtube with 0.1 mm diameter was studied. Four typical flow patterns, annular, injection flow, slug flow and bubbly flow are simulated along a two-dimension calculational domain successively. The numerical mode is verified by the experiments from the literature. The numerical results discern that the increase of mass flux, wall temperature and saturation temperature affect the detachment point of vapor slug further toward the outlet with higher occurrence frequency, which can be attributed to the higher Weber number and Capillary number of tail vapor core respectively. The local heat flux and wall shear stress will decrease along the flow direction overall, and tend to be constant in the single phase liquid area. However, there exit some rebounds and oscillations of the local heat flux and wall shear stress during injection and slug flow. The transient oscillations of wall shear stress can induce fluctuations and even waves in the annular flow upstream, which can be concluded as “surface tension force affecting upstream”, is proposed based on the minimum potential energy theory. This mechanism could be a supplement for the traditional theory of “flow pattern transition at high mass flux being induced by fluctuations which grow up while flowing downstream”.

中文翻译：

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微管内 R32 冷凝过程中流动模式的数值模拟及其对热通量的影响

摘要 基于流体体积法，提出了微通道内冷凝传热和流动特征的瞬态数值模型。研究了 R32 在直径为 0.1 mm 的圆形微管中的流动冷凝。沿二维计算域依次模拟了环形、注入流、段塞流和气泡流四种典型流型。通过文献中的实验验证了数值模式。数值结果表明，随着质量通量、壁温和饱和温度的增加，蒸汽段塞的脱离点进一步向发生频率更高的出口方向影响，这分别归因于尾气核的韦伯数和毛细管数较高。局部热通量和壁面剪应力将沿整体流动方向减小，并在单相液体区域趋于恒定。然而，在注入和段塞流过程中，局部热通量和壁面剪应力存在一些反弹和振荡。基于最小势能理论提出壁面剪应力的瞬态振荡会在环流上游引起波动甚至波浪，可以将其归结为“影响上游的表面张力”。这种机制可以作为传统理论的补充，即“大质量通量下流型转变是由向下游流动时长大的波动引起的”。在注入和段塞流过程中，局部热通量和壁面剪切应力会出现一些反弹和振荡。基于最小势能理论提出壁面剪应力的瞬态振荡会在环流上游引起波动甚至波浪，可以将其归结为“影响上游的表面张力”。这种机制可以作为传统理论的补充，即“大质量通量下流型转变是由向下游流动时长大的波动引起的”。在注入和段塞流过程中，局部热通量和壁面剪切应力会出现一些反弹和振荡。基于最小势能理论提出壁面剪应力的瞬态振荡会在环流上游引起波动甚至波浪，可以将其归结为“影响上游的表面张力”。这种机制可以作为传统理论的补充，即“大质量通量下流型转变是由向下游流动时长大的波动引起的”。