Visualization and measurements of two-phase flows in metallic ducts using neutrons as microscopic probes. 1. Time-resolved neutron radiography and its limited time-resolution

Experiments on visualization of high-speed fluid phenomena in metallic ducts were conducted by three kinds of time-resolved neutron radiography techniques. In the direct film method with a pulsed neutron beam, frozen neutron radiographs of air-water flows in a rectangular duct were obtained successfully. The high-frame-rate neutron radiography with pulsed and steady neutron beams allowed visualization of boiling water two-phase flow in a tube at the recording speed of 500 frames/s and air-water flows in a rectangular duct at up to 1000 frames/s, respectively. The quality of the images obtained from the time-resolved neutron radiography was sufficient for observation of the fluid behavior. The limit of the time-resolution was clarified based on the sensitivity and light-decay constant of the converter and the measurement error of neutrons calculated by statistical analysis. (author)