Visualization and measurements of two-phase flow in metallic ducts using neutrons as microscopic probes. 2. Measurements of some flow characteristics by image processing techniques

In order to apply the neutron radiography technique to fluid research, quantitative analyses of high-frame-rate neutron radiographs of air-water flows in a narrow rectangular duct were demonstrated by using image processing techniques. From the geometrical information of the images, the flow regime, bubble rising velocity, water-layer thickness, and interfacial area calculated by multiplying the interfacial length by the channel gap and size distribution of bubbles with diameter greater than 1 mm could be measured by the image processing technique. From the gray levels of the images, the spatial and temporal averaged void fractions and the void profile across the duct could also be measured by the image processing technique. It was clarified that the limited value of the measurable liquid-film thickness with the neutron radiography technique was calculated by an error analysis. It was shown quantitatively that the measurement error decreased by integrating the image temporally. (author)