Pressure transient and two-phase swelling due to a small top break

Abstract A sudden small break in the top of a pressure vessel filled partially with pressurized liquid and partially with vapor will result in a blowdown, which is a function of liquid flashing in the vessel, and liquid entrainment in the exiting flow. This behaviour is of interest in conjunction with, e.g., light water reactors. A review of different liquid entrainment mechanisms, blowdown experiments of another investigator and own experiments indicate that swelling of the flashing mixture and resulting oscillations of the interface are key parameters in defining the exit flow rate, pressure, and mass transient. Therefore, a new analytical model is proposed here, which describes these quantities. The model stresses the dynamics of the vapor-liquid interface. It predicts successfully the vessel pressure, mass, and interface level transients of our experiments, and the few data which are presently available from only one other author.