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首页> 外文期刊>International Journal of Heat and Mass Transfer >Flow regimes during condensation from superheated vapor
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Flow regimes during condensation from superheated vapor

机译：过热蒸汽冷凝过程中的流态

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摘要

Two-phase flow during condensation in smooth horizontal round tubes of R245fa, R1233zd(E), R1234ze (E), R134a, R32 from superheated vapor is visualized and presented in this paper. Flow regimes under different mass fluxes, heat fluxes, saturation pressures, specific enthalpies and tube sizes (1, 4, 6 mm) are identified. The paper describes to the flow regime transitions according to the visualizations. The driving force behind the annular-stratified flow transition is identified to be the force balance between shear, gravity and surface tension. The mechanism that dictates the annular-intermittent flow transition is the comparison between wave-height and the tube size. The slip ratio, which generates the Kelvin-Helmholtz instability, is considered to be the reason of transition from stratified-wavy to the fully-stratified flow. The more complicated scenarios where characteristics of different flow regimes coexist are detailed and methods for simplification are provided. The results are also compared to two different flow regime maps. The flow regime map that does not consider the non-equilibrium effects does not provide information beyond bulk quality 1 and 0. Additionally, it does not capture the annular entrance during condensation either. The flow regime map with non-equilibrium taken into account addresses issues above while having its own defects. For instance, it is highly empirical and some transition lines do not properly reflect experimental observations. A more mechanistic flow regime map is recommended. (C) 2018 Elsevier Ltd. All rights reserved.
机译：可视化并介绍了在R245fa，R1233zd（E），R1234ze（E），R134a，R32的光滑水平圆管中冷凝时的两相流，它们来自过热蒸汽。确定了不同质量通量，热通量，饱和压力，比焓和管尺寸（1、4、6 mm）下的流态。本文根据可视化描述了流态转换。环形分层流动过渡背后的驱动力被确定为剪切力，重力和表面张力之间的力平衡。决定环形间歇流动过渡的机制是波高和管尺寸之间的比较。产生开尔文-亥姆霍兹不稳定性的滑移率被认为是从分层波浪状过渡到完全分层流动的原因。详细介绍了不同流态特征共存的更复杂场景，并提供了简化方法。还将结果与两个不同的流态图进行比较。不考虑非平衡效应的流态图不会提供超过散装质量1和0的信息。此外，它在冷凝过程中也不会捕获环形入口。考虑了非平衡的流态图解决了上述问题，同时也有其自身的缺陷。例如，它是高度经验的，某些过渡线不能正确反映实验观察结果。建议使用更机械的流动状态图。 （C）2018 Elsevier Ltd.保留所有权利。

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