Visualization of thermal flow phenomena and application to measurement

The visualization of phenomena is indispensable for scientific research, and neutron radiography utilizes the interaction of neutrons and atomic nuclei. The absorption coefficient of neutrons changes according to the structure of atomic nuclei, namely, it is different among isotopes even if in a same element. Neutrons transmit easily through most metals, but are absorbed in hydrides, boron, plastics, cadmium, gadolinium and so on. Recently, high neutron flux has become to be obtained, and one of the useful visualizing and measuring methods which positively use neutrons as the probe is being developed. Its application to thermal flow phenomena is one example. For the visualizing and measuring technology for thermal flow phenomena, the no contact, three-dimensional measurement possessing high spatial and temporal resolution is required. Also metallic vessels are frequently necessary. Neutron radiography can realize these objectives. The present state of the technical development of neutron radiography is described. As its application to the visualization and measurement of thermal flow phenomena in pipes, the measurement of flow mode and void fraction, and the high speed photographing of thermal flow phenomena in pipes, the application to the bubble columns in gas-liquid system, the jet in solid-liquid system, the flow in gas-solid system and high pressure three-phase flow, and the application to porous media are reported. (K.I.)