Flow pattern identification for two-phase flow in a U-bend and its contiguous straight tubes
Flow pattern identification for two-phase flow in a U-bend and its contiguous straight tubes
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U 型弯管及其相邻直管内两相流的流型识别
DOI：
10.1016/j.expthermflusci.2017.12.024
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发表时间：
2018-05-01
影响因子：
3.2
通讯作者：
Liu, Furen
中科院分区：
文献类型：
--
作者：
Ma, Xiaoxu;Tian, Maocheng;Liu, Furen
弯曲通道内的气液两相流动广泛存在于各种换热器和输送管道中。流体的流动和传热特性与流型密切相关。本文对压力为0.1MPa、温度为25 ℃的U形弯管及其相邻直管中空气-水两相流的流型进行了实验研究，提出了一种新的流型识别方法。采用流场显示技术沿着、功率谱密度（PSD）分析和多尺度熵（MSE）分析相结合的方法对压降时间序列进行了研究。该弯曲具有16 mm的内径和100 mm的曲率半径，并且其以向下或向上的布置安装。空气和水的表观速度分别设定为0.17-16.58 m/s和0.10-2.03 m/s。根据采集的流动图像、压降时间序列和PSD分布，识别出五种流型。提出了两种流动方向的流型图。在较低的表观气速和表观液速下，得到了两种独特的流型：向下流动时的分层塞流和向上流动时的不稳定流。结合PSD的偏度和MSE的速率，使我们能够客观地识别U形弯曲单元中的流动模式，这有助于识别其他非透明弯曲通道中的流动模式。
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.