AJK2011-08001 INVESTIGATION OF ROD VIBRATIONS IN DROPLET TWO-PHASE FLOWS

ABSTRACT Flow-induced vibrations are important problems in nuclear power plants from the view point of reactor safety. In the investigations of these vibrations especially those induced by two-phase flows, a numerical simulation plays a significant role, so it is necessary to obtain the experimental datasets that can validate the results of the numerical simulation. This paper deals with the experimental data of one-end-supported rod vibration, and focuses on the differences between the rod vibrations induced by single-phase air flows and those induced by droplet two-phase flows. In the experiments, the displacement of the non-supported end of the test rod was visualized by the high speed camera with high spatial and temporal resolutions, namely 9.5 µm and 500 µsec. Using an image analyzing software, the rod vibration displacements were measured by the motion tracking method. The curved surface of the rod was observed by another high speed camera and the relationship between the rod vibrations and the wet condition on the surface of the rod was investigated. In addition, the vibrations measured by the strain gages and those by the high speed camera were compared to discuss the differences in these two ways of the measurements

Measurements of liquid film and droplets of annular two-phase flow on a rod-bundle geometry with spacer

Measurements have been conducted to simultaneously consider both liquid films and droplets of the annular flow on a 3 × 3 simulating BWR fuel rod-bundle test-section with spacers. The optical system of a high speed camera and a tele-microscope was used to record the backlight images at the gap between a corner rod and a side rod of the bundle at high time and space resolutions. The data obtained from the liquid film showed that the mean film thickness, wave height, power spectral density, and wave velocity at the corner rod are larger than those at the side rod, and that the influences of the spacer are different in the cases of low and high gas superficial velocities. Simultaneously, the data containing size and spatial distributions as well as the axial velocity distribution of liquid droplets were obtained. In the case of lower gas flow rates, the spacer generates not only a large number of small droplets but also big droplets whose size exceeds the maximum droplet diameter at upstream. At further downstream, the spatial distribution of the droplets indicates an asymmetry characteristic, which emphasizes the contribution of the droplet impingement mechanism to the entrainment phenomena. Moreover, a close-up observation at right up- and downstreams of the spacer was conducted to describe the interactions between the two-phase flow and this structure. By using these new experimental arrangements, the interaction mechanisms among the wavy liquid film, droplets and spacer were discussed

Viscoelastic fluid behaviors around a rising bubble via a new method of mesh deformation tracking

The deformation of a hydrogen microbubble line and/or mesh in a viscoelastic fluid around a rising bubble was tracked from the original static position in order to discuss the mechanism of the typical phenomena such as the negative wake or the cusp shape. This new experimental method is essentially important because of the hysteresis-dependent nature of the viscoelastic fluid. This new method makes this study distinctive from a number of conventional studies of viscoelastic fluids focusing on the non-Newtonian properties and/or the instantaneous flow field. According to our experimental results, the flow mechanism responsible for the negative wake or cusp shape was attributed to the accumulation and release of the shear strain energy. Some residual displacements were observed after the bubble rising, which were almost completely reproduced as the internal dissipations in a Maxwell model modified with a non-linear spring