The mechanism and prediction of critical heat flux in inverted geometries

Recent interest in a severe accident management scheme known as ʹIn-Yessel Retentionʹ has created the need to establish the coolability limits of large, inverted geometries. In this paper, full-scale simulations conducted at UCSBʹs ULPU facility are examined at the microscopic level. Because of the peculiar geometry, it has become possible to directly visualize the boiling transition phenomenon, and with the help of microthermocouples to quantitatively identify the mechanism of dryout. Altogether, a new boiling transition regime was identified, with a significant coupling between overall systems dynamics and the microphenomena. This leads the way to the a priori prediction of critical heat flux and factors that may influence it.