RESEACH ON THE GENERATION MECHANISM OF BURNOUTNEAR THE FLOW OBSTRACTION IN BOILING TWO-PHASE FLOW WITHIN ANANNULAR CHANNEL

点击翻译按钮获取中文摘要

In order to clarify the mechanism of burnout occurrence near the obstacle, which simulate spacers of BWR, flow phenomena was carefully observed' by using a high-speed video and time varying wall temperatures were measured at many axially different locations. The results are summarized as follows.1.In relation to the occurrence of burnout, we carefully observed two-phase flow phenomena. The generation of dry-out of liquid film, which acts as a trigger of generation of burnout, is caused by the dry-out of base film between two disturbance waves at the location upstream of the spacer. On the other hand burnout is scarcely generated downstream of the spacer because wall temperature is always low and liquid film is easy to formed even if dry-out is occurred. This result means the importance of the behavior of disturbance wave.2.Based on the above mentioned results we detected the passing of the disturbance waves by the differential pressure fluctuation. It is again confirmed the close relation between the passing of disturbance wave and the generation of dry-out as well as the generation of burnout are. It is also noticed that in order to explain the frequent generation and disappearance of the dry patch we never forget the unsteadiness of the vapor-liquid two-phase flow. The spacer has important influence on the fluid and thermodynamic phenomena downstream of the spacer.3.We put two spacers at axially different locations and it was clarified that the shorter the spacer distance, the higher the critical heat flux. Because the large amplitude of film thickness due to disturbance waves was flattened by the spacer, time averaged film thickness became thick. And therefore dry-out generation rate became low.4.We proposed a theoretical flow model to explain the dry-out as well as the burnout occurrence. It is based on the disturbance wave flow and time fluctuate phenomena is taken into consideration.