Keywords:Precursory cooling, Rewetting, Heat transfer
A rewetting phenomenon by liquid film propagation is one of key factors to evaluate peak cladding temperature and dryout duration after the occurrence of the post-boiling transition.The AESJ (2003) proposed the empirical correlation to predict the rewetting velocity in the anticipated operational occurrence conditions, which was recently applied to the evaluation of fuel rod surface temperature during an anticipated transient without scram for the safety review on the Japanese new regulation. Our previous studies have indicated the propagation velocity of the rewetting front is significantly affected by the heat transfer in the dried region immediately before the rewetting front, which is defined as precursory cooling (PC). The mechanism of the PC is still not clarified because of insufficient related studies. Therefore, this study visually investigates liquid film front behavior on a single heater pin surface with air-water flow at atmospheric pressure. Results showed oscillatory formation of dry patches in the liquid film in the vicinity of the rewetting front. This oscillation continued until the heated rod was completely cooled.