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首页> 外文期刊>International Journal of Heat and Mass Transfer >Air-water two-phase bubbly flow across 90° vertical elbows Part Ⅱ: Modeling
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Air-water two-phase bubbly flow across 90° vertical elbows Part Ⅱ: Modeling

机译：气水两相气泡流过90°垂直弯头第二部分：建模

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Following Part (I) of the current study, which presents the experimental results of the elbow effects on two-phase flow parameters in bubbly flow, Part (II) develops models and correlations to predict the evolution of these parameters across and downstream of 90 degrees vertical-upward and vertical-downward elbows. To quantify the length requires for the effects of the elbows to dissipate (or the dissipation length), the strength of elbows is defined as the variance of the local void fraction distribution. The axial development of the elbow-strength is modeled by an exponential function of the axial development length based on the experimental data. Then, the dissipation length of the elbow is determined by characterizing the evolution of the elbow-strength parameter. The elbow-strength parameter is also used to correlate the void-weighted bubble velocity and covariance terms in the interfacial area transport equation (IATE). The two-phase pressure drop across vertical elbows is modeled with a modified Lockhart-Martinelli correlation which considers the additional pressure drop induced by elbows. To evaluate the above developed models and correlations, they are implemented into the IATE applicable to the elbow-influenced region. The established IATE together with the available IATE of different flow orientations in straight channels are implemented to predict the interfacial area transport from the vertical upward to horizontal to vertical-downward two-phase flow across elbows. It is found that the interfacial area concentration predictions are in good agreement with the experimental data with an average absolute percent difference of +/- 6% throughout the test section. The individual contributions to the interfacial area concentration transport due to each source and sink term in the IATE are discussed, demonstratin that the models and correlations developed for the two-phase flow parameters in elbow regions are reliable. (C) 2018 Elsevier Ltd. All rights reserved.
机译：在当前研究的第一部分介绍了气泡对气泡流中两相流动参数影响的实验结果之后，第二部分建立了模型和相关性，以预测这些参数在90度内和下游的演变。垂直向上和垂直向下的肘部。为了量化长度，需要使肘部的影响消散（或耗散长度），将肘部的强度定义为局部空隙率分布的方差。基于实验数据，通过轴向展开长度的指数函数来建模肘强度的轴向展开。然后，通过表征肘强度参数的变化来确定肘的耗散长度。弯头强度参数还用于关联界面面积传输方程（IATE）中的空隙加权气泡速度和协方差项。竖向肘部的两相压降采用修正的Lockhart-Martinelli相关性建模，其中考虑了肘部引起的附加压降。为了评估上述开发的模型和相关性，将它们应用到适用于肘部影响区域的IATE中。已建立的IATE以及在直通道中不同流动方向的可用IATE一起用于预测跨肘部从垂直向上到水平到垂直向下的两相流的界面区域传输。发现界面区域浓度的预测与实验数据高度吻合，整个测试部分的平均绝对百分比差异为+/- 6％。讨论了IATE中每个源和汇项对界面面积浓度迁移的贡献，证明了为肘部区域的两相流参数建立的模型和相关性是可靠的。 （C）2018 Elsevier Ltd.保留所有权利。

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