Study on Visualization and Void-fraction Measurement of Boiling Two-Phase Flow by Using Neutron Radiography

本研究的目的是研究窄通道沸腾两相流的流动特性（流态和空隙率），作为热-水力研究的第一步。利用稳定中子束的中子射线照相技术，观察了窄矩形通道中过冷沸腾两相流动，并测量了空隙率。1998年度，建立了中子射线照相实验的可移动热工测试回路，并对流道内过冷沸腾的流动状态和空隙率进行了观测。实验采用日本原子能研究所的JRR-3M反应堆作为中子源，高帧率中子射线照相系统作为成像系统。将实验结果与已有的相关性进行比较，发现测量误差的评价是非常重要的。为此，在1999财年，研究了空隙率的测量方法，并对测量误差进行了评估。更多的是通过在1998财年相同的流道中插入聚苯乙烯片来模拟沸腾两相流。通过图像处理系统对高帧率成像系统拍摄的图像进行处理，通过Σ-scaling方法获得测试截面与聚苯乙烯片材的等效空隙率。然后，通过实测和理论等效空隙率的比较，评估了瞬时空隙率和时间平均空隙率的测量误差。在2000财年，采用1999财年开发和验证的方法，获得了窄矩形通道内沸腾两相流的瞬时和时间平均空隙率分布，并对其流动特性进行了研究。通过对数据的分析，得到了窄矩形通道内沸腾两相流在临界热流密度条件下的流动形式、过冷沸腾区空隙率分布的详细结构等方面的有用信息。少

The purpose of this study is to investigate flow characteristics (flow regime and void fraction) as a first step of thermal-hydraulic research on boiling two-phase flow in narrow channels. Using neutron radiography with a steady neutron beam, subcooled-boiling two-phase flow in a narrow rectangular channel is visualized and the void fraction is measured.In FY1998, a movable thermal-hydraulic test loop for neutron radiography experiment was set up and the observation of flow regimes and the void fraction was measured for subcooled-boiling in the flow channel. The experiment was performed using the JRR-3M reactor of Japan Atomic Energy Research Institute as a neutron source and the high-frame-rate neutron radiography system as a imaging system. Comparing the experimental results with existing correlations, it turned out that the evaluation of measurement error was very important. For this, in FY1999, the method for void fraction measurement was examined and the measurement error was eval … More uated by inserting a polystyrene sheet in the same flow channel as used in FY1998 to simulate the boiling two-phase flow. Images taken by the high-frame-rate imaging system were processed by an image processing system and the equivalent void fractions of the test section with the polystyrene sheet were obtained by the Σ-scaling method. Then the measurement errors were evaluated for instantaneous and time-averaged void fractions by comparing the measured and theoretical equivalent void fractions. In FY2000, instantaneous and time-averaged void fraction profiles were obtained for boiling two-phase flow in a narrow rectangular channel by using the same method as developed and verified in FY1999, and the flow characteristics were investigated. By analyzing the data, useful information was obtained on the flow regimes near critical heat flux conditions, detailed structure of void fraction distribution in the subcooled-boiling region, and so forth, for boiling two-phase flow in a narrow rectangular channel. Less