Effect of grooves on nucleate boiling heat transfer from downward facing hemispherical surface

Abstract

The external reactor vessel cooling (ERVC) is the key method to ensuring the success of in-vessel retention (IVR), which is one strategy of the Generation III+ advanced light water nuclear reactor to address severe accidents. The heat removal ability of ERVC is limited by the critical heat flux (CHF) on the outer surface of the lower head. In this paper, a heating system with the liquid metal as the intermediate heat medium in the scaled vessel was used to investigate the boiling heat transfer. A three-dimensional (3D) hemispherical grooved surface on scaled vessel was proposed and its steady boiling performance was investigated in saturated water. Consequently, the liquid metal temperature exceeded 430 °C when the heating power was 185 kW and the boiling crisis occurred, and the CHF increased from 967.4 to 2030.2 kW/m2 when the orientation increased from 5° to 85°. Compared with the 3D plain surface, the CHF enhancement was higher than 102%. The CHF enhancement could attribute to the increase of heat transfer area and the improvement of the wettability. If the grooves on the reactor vessel could be manufactured by 3D printing in the future, the grooved surface will be a promising structure for ERVC.