Sub-channel flow regime maps in vertical rod bundles with spacer grids
Sub-channel flow regime maps in vertical rod bundles with spacer grids
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DOI：
10.1016/j.ijheatmasstransfer.2018.01.133
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发表时间：
2018-07
影响因子：
5.2
通讯作者：
Quanyao Ren;Wenxiong Zhou;S. Du;Zhong-chun Li;L. Pan
中科院分区：
文献类型：
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作者：
Quanyao Ren;Wenxiong Zhou;S. Du;Zhong-chun Li;L. Pan
基于棒束流态图的热工参数准确预测对核反应堆的安全运行具有重要意义。通过空气-水两相流实验，研究了5 × 5杆束剖面的子通道流态（SCFR）图，该剖面采用了两种不同的间隔网格，包括简化间隔网格（SSG）和混合叶片间隔网格（MVSG）。为了获得杆束中客观的SCFR图，研制了一种子通道阻抗空隙率计，用于测量子通道中的时间序列空隙率。基于训练样本和选取的13个时间序列孔隙率特征值，采用随机森林聚类算法客观识别子通道流态。特征值包括平均值、标准差值、样本熵值和10个比例值。通过这种方法，在四个不同的位置用不同的间隔网格得到目标子通道流态图。不同的scfr有不同的特征。对于同一截面上不同子通道的SCFR过渡，由于套管的影响，几乎都首先在内子通道发生。间隔栅的耗散长度大于19.5L/D。在间隔栅影响区域，从帽泡到帽湍流的过渡首先发生在间隔栅下游19.5L/ d角子通道，低液速先发生在6.8L/ d处，高液速先发生在6.8L/ d处。隔离栅对SCFR转捩的影响程度取决于液体和气体的表面流速，以及当前流动条件下隔离栅的结构。只有Liu和Hibiki的模型适用于子通道从气泡流到帽状气泡流的过渡。因此，对于其他子通道流型的过渡，应该建立新的过渡模型或相关性。
The accurate prediction of thermal-hydraulic parameters is based on the flow regime maps for rod bundle, which is important for the safety of nuclear reactor. An air-water two phase flow experiment has been performed to study the sub-channel flow regime (SCFR) maps in 5 × 5 rod bundles section with two distinct spacer grids, including simplified spacer grid (SSG) and mixing vane spacer grid (MVSG). To obtain the objective SCFR maps in rod bundles, a sub-channel impedance void meter is newly developed to measure the time series void fraction in sub-channels. Besides, the random forest clustering algorithm has been adopted to identify the sub-channel flow regimes objectively based on a training sample and 13 selected feature values of time series void fraction. The feature values include mean value, standard deviation value, sample entropy value and 10 proportion values. In this way, the objective sub-channel flow regime maps are obtained at four different locations with different spacer grids. Distinct features have been observed for different SCFRs. As for the SCFR transitions in different sub-channels over the same cross-section, almost all of them arise in the inner sub-channel firstly for the effect of casing tube. Moreover, the dissipation length of spacer grid is larger than 19.5L/D. In the influencing region of spacer grid, the transition from cap bubbly to cap turbulent flow occurs in the corner sub-channel at 19.5L/Ddownstream of spacer grid firstly and then at 6.8L/Dfor low liquid velocity, while firstly occurs at 6.8L/Dfor high liquid velocity. The magnitude of the spacer grid effect on SCFR transition depends on the superficial liquid and gas velocity, as well as the structure of spacer grid for current flow conditions. Only Liu and Hibiki’s model is applicable for the transition from bubbly to cap bubbly flow in sub-channel. Therefore, new transition models or correlations should be developed for other sub-channel flow regime transitions.