Development of Prediction Technology of Two-Phase Flow Dynamics Under Earthquake Acceleration: (17) Effect of Structure Vibration on a Rising Single Bubble

Abstract

Earthquake is one of the most serious phenomena for safety of a nuclear reactor in Japan. Structural safety of nuclear reactors has been studied and nuclear reactors were contracted with structural safety for a big earthquake. However, it is not enough for safe operation of nuclear reactors because thermal-fluid safety is not confirmed under the earthquake. For instance, behavior of gas-liquid two-phase flow is unknown under the earthquake conditions. Especially, fluctuation of void fraction is an important factor for the safe operation of the nuclear reactor. In the previous work, fluctuation of void fraction in bubbly flow was studied experimentally and numerically. In case of the earthquake, the fluctuation is not only the flow rate, but also body force on the two-phase flow and shear stress through the pipe wall. Interactions of gas and liquid through their interface also act on the behavior of the two-phase flow. The fluctuation of the void fraction is not clear for such complicated situation under the earthquake. Our study has investigated the behavior of gas-liquid two-phase flow experimentally and numerically. In this paper effects of vibration on bubbly flow in the components and construct experimental database for validation and performs visualization experiments of a rising single bubble in a rectangular water tank on which sinusoidal vibration was applied. In this paper, results of visualized experiment evaluated by the visualization techniques, including positions of a bubble, a shape of the bubble and the bubble tilt angle were shown. In the results, bubble behavior were affected by the table oscillation. The bubble tilt angle is also almost same value of the bubble movement angle. It is implied that higher table oscillation frequency than 20 Hz quite weakly affects on fluctuation of bubble tilt angle frequency.