Development of evaluation system for flashing erosion

Liquid droplet impingement erosion (LDI) is defined as an erosion phenomenon caused by high-speed droplet attack in a wet steam flow, and sometimes observed in a steam piping system of a power plant. In our previous researches, we have developed an LDI evaluation system to evaluate the thinning shape due to LDI on a steam piping within a practically acceptable time. However, present system is not applicable to LDI on a hot-water piping due to flashing phenomena (flashing erosion) because it is difficult to calculate the flashing flow due to sudden phase change and critical flow rate evaluation models needed for LDI evaluation system are not verified in wet steam region. Therefore, in this study, we tried to develop a new flow calculation code for flashing flow and to verify the critical flow rate evaluation models in wet steam region. For flashing flow simulation, based on a present CFD code, pre-conditioning method was adopted to achieve the stable calculation of the water region, and extended look-up table including from low-pressure water to high-pressure dry steam was incorporated. Finally, a new CFD code water-steam flow was developed. Several benchmark tests were conducted and those results show this new code can reproduce the flashing phenomena and is applicable from the very low-speed flow to supersonic flow. Then, HEM model for critical mass flow rate was verified with flashing and wet steam experiments and CFD calculations, and incorporated into LDI evaluation system to extend applicable region of the evaluation system into flashing erosion. (author)