Visualization of fluid phenomena using a high frame-rate neutron radiography with a steady thermal neutron beam

Experiments on visualization of fluid phenomena in a metallic vessel were conducted using a high-speed video camera with a steady thermal neutron beam. The Japan Research Reactor 3M, whose flux at the imaging plate is 1.5 × 10⁸ n/cm² s, of Japan Atomic Energy Research Institute was used as a neutron source. The imaging system for high frame-rate neutron radiography with the steady thermal neutron beam consisted of a high sensitivity scintillator, ⁶LiF/ZnS:Ag, an image intensifier whose gain was a factor of 100 000 at the maximum, and a high-speed video which could record phenomena at 1000 frames/s for 14 min by using an ordinary VHS tape with the recording time of 120 min at the normal speed. Visualization of air-water two-phase flows in a rectangular duct with 2.4 mm gap and 40 mm width were successfully performed with the steady thermal neutron beam and this imaging system at frame rates up to 1000 frames/s. The shapes and the behavior of bubbles and liquid films were clearly observed. The rising velocities of slug bubbles and the flow regimes could be also measured. It was clarified that this new technique may have significant advantages both in visualizing and measuring high-speed phenomena when the visible light is not applicable. © 1994.