The purpose of this study is to observe an air-water flow in a narrow rectangular duct and to measure the void fraction and the interfacial area by applying an image processing technique. Video images of a two-phase flow were taken either by an optical method or by a neutron radiography technique. Flow regimes were determined by observing the video images.
Observed flow regimes were slug, froth and annular flows. Since the transition of flow regimes occurred rather gradually, the boundary between them was expressed with a band. Data of void fraction obtained with the image processing technique were compared to those obtained with the conventional conductance probe technique. The agreement was good and the results were well-reproduced by the drift flux correlation. A strong correlation was observed between the interfacial area concentration and the void fraction.