Dynamics of Two-Phase Flows

ISBN Print: 0-8493-9925-4

CRITICAL FLASHING FLOW IN PIPES AND CRACKS

DOI: 10.1615/0-8493-9925-4.270
pages 571-602

Abstrakt

Critical flow occurs when, for a constant upstream stagnation state, the flow becomes independent of the pressure in the receiver. At critical flow, the downstream changes in pressure cannot propagate upstream beyond the location of the critical state unless the pressure there is exceeded. Critical flow has been studied extensively for the case of two-phase flashing fluids because of the importance of this phenomenon in the analysis of hypothetical accident sequences in nuclear reactor systems and many other industrial applications.
The present paper summarizes the results of an on-going study related to current issues in the nuclear applications. Leakage through pipe cracks is important as a potential means of detection and diagnosis of possible impending failure of the pressure envelope. In this case the modelling of the flow process becomes a key element in the "leak-before-break" philosophy. The work of Amos and Schrock (1985, 1983) included experiments using thin rectangular slits to simulate cracks and the development of a homogeneous non-equilibrium model. A simpler homogeneous equilibrium model (with subcooling correction) was later presented by Schrock, et al. (1986a) for actual cracks. A study of entrainment phenomena at the entrance of a break channel connected to an upstream stratified region was carried out by Schrock, et al.(1986b,1986c). Correlations were obtained for incipient entrainment and for quality entering the break following onset of entrainment. Recently Lee and Schrock (1988) have completed some improvements in Amos' model to represent data from an exceptionally wide range of experimental conditions (size of break channel and stagnation states in the liquid region).