Experimental study of gas entrainment at free surface; Development of circulation and gas core of surface vortex

Ezure, Toshiki ; Kimura, Nobuyuki; Kobayashi, Jun ; Ito, Masami*; Kamide, Hideki 

A sodium cooled reactor has been investigated in the feasibility study of FBR cycle. In the study, a compact reactor vessel was designed, and the cover gas entrainment (GE) at the free surface is one of the significant issues. It is required to clarify the criterion of GE at free surface. GE at the free surface could be categorized into following three types, wave break, submerged flow, surface vortex. However, there was no clear quantitative evaluation method and criteria regarding the onset condition of GE by the surface vortex. In the present study, some experiments were performed focusing on the transient phenomena of GE by surface vortex. The relationship between circulation and length of gas core were measured by the particle image velocimetry and visualization. From the results of this study, the relationship between gas core length and probability of GE was clarified, and time-delay between the increase of circulation and the increase of gas core was found.