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 w ere conducted using a high-speed video camera with a steady thermal ne utron beam. The Japan Research Reactor 3M, whose flux at the imaging p late is 1.5 X 10(8) n/cm(2) s, of Japan Atomic Energy Research Institu te was used as a neutron source. The imaging system for high frame-rat e neutron radiography with the steady thermal neutron beam consisted o f a high sensitivity scintillator, (LiF)-Li-6/ZnS:Ag, an image intensi fier whose gain was a factor of 100000 at the maximum, and a high-spee d video which could record phenomena at 1000 frames/s for 14 min by us ing an ordinary VHS tape with the recording time of 120 min at the nor mal 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 rate s up to 1000 frames/s. The shapes and the behavior of bubbles and liqu id films were clearly observed. The rising velocities of slug bubbles and the flow regimes could be also measured. It was clarified that thi s new technique may have significant advantages both in visualizing an d measuring high-speed phenomena when the visible light is not applica ble.