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The present study deals with the experiments for the gas-liquid two-phase flow inside an acrylic Venturi tube using a high-speed video camera. Some interesting phenomena on the bubble dynamics are observed in the tube. First, the volume and surface oscillations of two interacting bubbles are observed in converging section of the tube when one bubble enters the throat. The volume oscillation of the bubble that enters the throat is caused by the detachment of the tip of the downstream surface of the bubble. The pressure wave irradiated from the bubble that enters the throat induces the volume and surface oscillations of the bubble that remains at the converging section. The parametric excitation is the reason for the surface oscillations. Second, the bubble deformations at the throat in a Venturi or a converging tube are investigated. The experiments show that two kinds of liquid jets are formed on the bubble surface; one is a forward jet that develops from the upstream surface to the downstream surface and the other is a counter jet in which the direction of the jet is opposite to the forward jet. It is shown that the counter jet occurs only when the distance between two bubbles in the throat is sufficiently short. The interactions between two bubbles cause the counter jet. It is also shown that the velocity of the forward jet becomes faster when the bubble is pinched off more upstream in the converging section. Finally, the propagations of the pressure waves are measured with pressure transducers. The impulsive pressure associated with the collapse of cavitation bubble cloud is measured when a bubble enters the throat of the tube. Also, the propagation speed of pressure waves is evaluated with the cross-correlation function. The results show that the propagation speed and damping of the pressure waves are dependent on the number density of bubbles at the downstream part in the tube.

JSME rules for fitness for service have flaw acceptance rules for cast austenitic stainless steel (CASS) pipes. They allow applying two-parameter and elastic-plastic fracture mechanics methods using Z-factor. However they do not clearly describe whether limit load method is applicable for the case of no or low thermal aging condition. The authors performed tensile fracture tests using flat plate specimens with a surface flaw and confirmed that limit load method is applicable in the conditions of no thermal aging and even fully saturated thermal aging with high ferrite number. Also the plate with a shallow flaw ruptured at the critical stress defined by nominal stress at rupture-flaw depth curve in the code case which was determined by the similar flat plate tests of stainless steel or nickel alloy specimens. These results will be reflected to the revision of the code.

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