A steam injector (SI) is a simple, compact and passive pump and also acts as a high-performance direct-contact compact heater. This provides SI to apply as a direct-contact feed-water heater that heats up feed-water by using extracted steam from the turbine. To develop high performance compact feed-water heater, it is necessary to quantify the characteristics between physical properties of the flow field. We carried out the analysis and visualization study. The analysis was conducted by using CFD code embedded separate two-phase flow models and confirmed that the steam has a high-performance direct-contact heater that was suitable for compact feed-water heater. To visualize the water jet behavior inside the SI, we used the Dynamic PIV system. The Dynamic PIV system consists of the high-speed camera and lasers. In this study, 384×180 pixel resolution with 30 000 fps camera is used to visualize the flow. For the illumination CW green laser with 300 mW is applied. To view inside the SI, relay lens system is set at the SI wall. Very high speed water jet during the starting up of SI had been clearly visualized with 30 000 fps. The wave velocity on the water jet had been analyzed using PIV technique. The instability of the water jet is also detected.
