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首页> 外文期刊>Experimental Thermal and Fluid Science: International Journal of Experimental Heat Transfer, Thermodynamics, and Fluid Mechanics >Flow pattern identification for two-phase flow in a U-bend and its contiguous straight tubes
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Flow pattern identification for two-phase flow in a U-bend and its contiguous straight tubes

机译：U形弯和其连续的直管中两相流动的流动图案识别

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摘要

Gas-liquid two-phase flow in curved channels is widely found in various heat exchangers and transport pipes. The fluid flow and heat transfer characteristics are closely related to flow patterns. This work experimentally investigated flow patterns for air-water flows in a U-bend and its contiguous straight tubes at a pressure of 0,1 MPa and a temperature of 25 degrees C, and proposed a new flow pattern identification method. A flow visualization technique along with frequency spectral (power spectral density, PSD) and chaos analysis (multi-scale entropy, MSE) of pressure drop time series were used. The bend had an inner diameter of 16 mm with curvature radius of 100 mm, and it was installed with either a downward or an upward arrangement. The superficial air and water velocities were set to the range of 0.17-16.58 m/s and 0.10-2.03 m/s, respectively. Five flow patterns were identified on the basis of captured flow images, pressure drop time series and PSD distributions. Flow pattern maps for both flow orientations were proposed. Two unique flow patterns (stratified-plug flow in downward flow and unstable flow in upward flow) were obtained under low superficial gas and liquid velocities. Combining the skewness of PSD and the rate of MSE enabled us to objectively identify flow patterns in the U-bend unit, which facilitates identification of flow patterns in other non-transparent curved channels.
机译：在各种热交换器和运输管中广泛地发现弯曲通道中的气液两相流。流体流动和传热特性与流动模式密切相关。这项工作实验研究了在U形弯和其连续的直管中的空气水流动模式，在0.1MPa的压力和25摄氏度的温度下，并提出了一种新的流动模式识别方法。使用流量可视化技术以及频谱（功率谱密度，PSD）和CHAOS分析（多尺度熵，MSE）的压降时间序列。弯曲的内径为16mm，曲率半径为100mm，其用向下或向上布置安装。浅表空气和水速度分别设定为0.17-16.58 m / s和0.10-2.03 m / s的范围。基于捕获的流动图像，压降时间序列和PSD分布来识别五个流动模式。提出了两个流向取向的流动模式图。在低浅表气体和液体速度下，获得了两个独特的流动图案（在向上流动下流动和向上流动的不稳定流动）。组合PSD的歪斜和MSE的速率使我们能够客观地识别U形弯单元中的流动模式，这有助于识别其他非透明弯曲通道中的流动模式。

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