This paper experimentally studies the influence of two-phase flow behavior on the operating limits of steam injector (SI). SI is the passive jet pump with a converging-diverging structure. SI operates without the electrical power and discharges water at high pressure. However, in regard to the operating limits of SI, it is unclear which takes into account the discharged flow structure. In this paper, the pressure distributions along the flow direction and the discharge pressure were measured by changing the inlet steam pressure and the load on the exit of the test section. Furthermore, the discharged flow at the diffuser was observed with a high-speed camera. As a result, a boundary was observed in the discharged flow at which the flow structure changed. The area from the throat to this boundary is considered as a two-phase region which steam did not condense completely in the mixing nozzle remained. This boundary moved upstream as the load on the exit increased, and a significant pressure rise occurred at the position where the boundary was reached. In addition, white propagations towards the downstream direction were observed. This propagation is considered as pressure wave propagation. The propagating speed was estimated using image processing. Assuming that the pressure wave propagates at sonic speed, the void fraction at the discharged flow was estimated by the existing model. Based on the above, the influence of the two-phase flow (in the discharged flow structure) on the operating characteristics of SI is discussed. measurements of the temperature and velocity distributions in the mixing nozzle, and the study on the heat transfer characteristics were also conducted (Iwaki, et al., 1994(Iwaki, et al., , 2002(Iwaki, et al., , 2004. On the other hand, our group has quantified the interfacial behavior of the water jet with the help of high-resolution observations in the mixing nozzle, and the correlation between the interfacial behavior and the transfer characteristics of heat and momentum. It was implied that there was an existing possibility for the presence of the gas-liquid, and a two-phase flow region in the discharged flow (Abe, et al., 2014). Hence, SI is said to be a passive jet pump as well as a highly efficient heat exchanger without a power supply although it has a simple and compact structure. Figure 2 shows an example of the application of SI into the safety system in a nuclear power station (Ohmori, et al., 2007). The cooling water is located at the upper part of the building. The injection of the cooling water into the core or the cooling pool is achieved without the use an electric power supply by installing the SI into the passive core injection system (PCIS) and the passive containment cooling system (PCCS). At this stage, SI is not yet to be installed in the existing power plant, while the IC and the RCIC are already in practical use since the detailed phenomena of SI, such as the operating characteristics, and the influence of flow behavior with the heat transfer on the operating ...
Steam injector (SI) is a passive jet pump with a converging-diverging structure. A SI operates without an electrical power source by direct contact condensation of a supersonic steam flow and a subcooled water jet in a mixing section. Furthermore, there are advantages that a SI has high heat-transfer performance and discharges water at high pressure. Therefore a SI is expected to apply to the safety system that is able to condense steam efficiently and inject water into a core reactor when severe-accident occurs in a nuclear power plant. However it is not cleared about the operating range of a SI which is taken account of the discharged flow structure. The objective of the present study is to reveal the influence of two-phase flow behavior on operating limits of a SI. The test section of the SI is made by transparent material to observe flow structure in it. The pressure distributions along the flow direction and the discharge pressure were measured by changing the inlet steam pressure and a load on exit of the SI. At the same time, the discharged flow at the diffuser was observed with a high speed camera. From the observation results, it was confirmed that a boundary which the flow structure changed in the discharged flow. The area from the throat to this boundary is seemed a two-phase region that steam which has not been condensed completely in the mixing nozzle remains. It was found that this boundary moved to upstream as the load on the exit increased and significant pressure rise occurred at the position the boundary reached. Additionally white propagations toward downstream were observed. This propagation is seemed a pressure wave propagation. The velocity of the propagation was estimated by image processing. Assuming a pressure wave propagates at sonic speed, void fraction at the discharged flow was estimated by existing homogenized model. From the above, the influence of two-phase flow in discharged flow on the operating limits of the SI is discussed.
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