Visualization and measurement of gas-liquid two-phase flow by neutron radiography

In order to design/improve gas-liquid two-phase flow equipment or to construct numerical analysis model of gas-liquid two-phase flow, it is required to understand flow behavior, since the performance strongly depends on interface structure in gas-liquid two-phase flow. However, it is difficult to visualize flow behaviors in metallic equipment. Neutron radiography is more effective for visualization of gas-liquid two-phase flows in a metallic vessel than X-ray radiography, because attenuation coefficient is low for most metals and is high for hydrogen. From neutron radiographs, it is possible to visualize only liquid behaviors and to measure 2D void fraction distributions quantitatively via some image processing methods. Moreover, 3D void fraction can be obtained by CT method. In this paper, the principle of neutron radiography is explained, and some application examples by a real-time neutron radiography facility in research reactor JRR-3M of Japan Atomic Energy Agency are shown. (author)