Steam Injector (SI) is a passive jet pump with a converging-diverging structure. SI operates without the electrical power source by direct contact condensation of a supersonic steam flow and a subcooled water jet in a mixing nozzle of converging section. Since SI has high heat-transfer performance and discharges water at high pressure, SI is expected to apply to the safety system that is able to condense steam efficiently and inject water into the reactor when severe-accident occurs in a nuclear power plant. The objective of the present study is to clarify the operating criteria and mechanisms of generating discharge pressure. For these objects, we performed experiments. Operating in various conditions about the inlet water and steam flow rate was performed. The pressure distributions along the flow direction and the discharge pressure were measured by changing the load on the exit of test section. In addition, the discharged flow at the diffuser was observed with a high-speed camera, and an electric resistance was measured in the discharged flow in order to estimate the void fraction. The inlet conditions which SI could operate were specified experimentally. It was found that significant pressure rise position was generated in the diffuser, and this position moved toward the upstream with increasing the discharge pressure. In addition, the void fraction estimated from electric resistance in the discharged flow decreases with increasing the discharge pressure. From the above, the relation between the generation mechanism of discharge pressure and the discharged flow structure is thereby discussed.
