APPLICATION OF HIGH-FRAME-RATE NEUTRON RADIOGRAPHY WITH A STEADY THERMAL-NEUTRON BEAM TO 2-PHASE FLOW MEASUREMENTS IN A METALLIC RECTANGULAR DUCT

To apply the neutron radiography (NRG) technique to fluid research, hi gh-frame-rate NRG with a steady thermal neutron beam was developed by gathering up-to-date technologies for neutron sources, scintillators, high-speed videos, and image intensifiers. This imaging system has man y advantages such as a long recording time, high-frame-rate (up to 100 0 frame/s) imaging, and no need for a triggering signal. Visualization of air-water two-phase flow in a metallic rectangular duct was achiev ed at the recording speeds of 250, 500, and 1000 frame/s. The qualitie s of those consecutive images were good enough to observe the flow mec hanism and to measure the flow characteristics. It was demonstrated th at some characteristics of two-phase flow could be measured by using t he current imaging system. To quantify geometric information from NRG images, measurements of flow regime, rising velocity of bubbles and wa ve height, interfacial length, and interfacial area in annular flow we re performed by using the image processing technique. To quantify atte nuation characteristics of neutrons in materials, measurements of aver age void fraction and void profile were conducted. It was confirmed th at this new technique may have significant advantages in both visualiz ing and measuring high-speed fluid phenomena when the ordinary methods such as the optical method and X-ray radiography cannot be applied.