Analytical and Experimental Study of Condensation and Collapse of Steam Bubbles at High Jakob Number

Abrupt collapse of vapour bubbles at high Jakob number is the leading physical phenomenon of the simulated chugging sodium boiling regime occurring during unprotected loss of flow (ULOF) accident in Sodium Fast Reactor (SFR) low-void core designs. The ESFR-SMART Horizon 2020 project aims at a better understanding and simulation of chugging conditions. Therefore, the small-scale two-phase flow facility “CHUG” for the mock-up of sodium boiling using water as sodium simulant has been designed at Paul Scherrer Institut (PSI) and built at the Laboratory of Reactor Systems behaviour at EPF Lausanne. CHUG consists of an acrylic glass test section filled with water at ambient temperature and atmospheric pressure, where high-temperature steam is injected from the bottom in order to study the interaction be-tween vapour and liquid at high sub-cooling level. In this paper the experimental results obtained with CHUG facility are compared with the simulation of bubble collapse in sub-cooled liquid at high Jakob number performed with PSI’s in-house CFD tool PSI-BOIL. The three-dimensional bubble surface during formation and collapse at the orifice is obtained from high-speed imaging and compared to the results from PSI-BOIL simulation, where an interface tracking method based on third-order accurate CIP-CSL2 (Constrained Interpolation Profile – Conservative Semi-Lagrangian 2nd order) method is employed. The main features of inertia-driven bubble collapse are analysed and commented in both cases.