Progress of two-phase flow research is divided into four stages. These periods are 1948-1959, 1960-1970, 1971-1979 and 1980-1989. In this, the fourth report, the development of research of flow configuration of slug flow and two-phase critical flow conducted in the second period are described. The initiation and development of researches of the fluctuation of static pressure and pressure drop in slug flow is introduced. Also, the development of theoretical analysis of the two-phase critical flow is discussed.

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A closed-loop analysis of phase distribution is presented. This analysis is based on the use of a two-fluid model. It is shown that the treatment of the turbulence distribution in the continuous phase is crucial if accurate predictions are to be made. A K-κ model is used to model turbulence in this study. Finally, recommendations are made as to how the state-of-the-art can be advanced.

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Heat-transfer coefficients in gas-liquid-solid three-phase flows in a 50.8mm i. d. vertical tube were measured in relation to flow patterns such as bubble, slug and penetrant flows. The gas velocity, slurry flow velocity and solid concentration were changed. The heat-transfer coefficients in the bubble and slug flow regime decreased with an increase in slurry flow velocity at low slurry flow velocity, while increased in the penetrant flow regime. The solid concentration greatly influenced the heat-transfer coefficients in all flow regimes, and the maximum value existed at a certain solid concentration.

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In order to elucidate hydrodynamic characteristics of gas slugs in gas-liquid-solid three-phase upward flows the measurements of film thickness around slugs, rise velocity and lengths of gas and liquid slugs were conducted. For the measurements of these values a new optical fiber probe, which could be used even in the high solid concentration, was developed. It was found that both the film thickness and rise velocity of slugs were almost constant, independently of particle size and solid concentration. On the other hand, the length of gas slugs had a maximum value at a certain solid concentration, but that of liquid slugs monotonously became longer with an increase in the solid concentration.

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A flatplate-type obstacle, which simulates a grid-type spacer in a nuclear reactor, is set in an air-water cocurrent stratified flow to investigate liquid film breakdown occurring near the obstacle. We made detailed visual observations and measurments of the velocity profile of the air flow and the axial distributions of liquid film thickness and static pressure near the obstacle. Experimental parameters were the inclination of the rectangular duct, the configuration of the obstacle, i. e., with and without a projection and a hole, which is bored in order to delay the onset of dry patch formation near the obstacle and the gap between the plate and the lower-wall surface. The results show that the plate itself does not promote dry patch formation but the projection, even if it is in contact with the wall surface at only one point, has a strong effect on the liquid film breakdown. In general the film breakdown occurs in front of the projection in a wide range of flow conditions due to the leading edge down-wash of the stream and due also to the rejection of water by gravitational force in the case of the upward flow in the inclined duct. By setting a hole in or in front of the projection the occurrence of the dry patch formation is delayed.

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