MISSFINCH: Models for Steady Stratified Flow in CANDU Headers

Abstract

Many steady two-phase flow tests have been conducted in a Erge Scale Header (LASH) experimental facility to study the flow behaviour in a horizontal header. In these tests, a steam-water mixture is injected into the header through either one or two vertical turrets. These tests have shown that after the mixture jet impacts the bottom of the header, the phases separate even when the mixture contains a small amount of steam. The results of these tests are used to obtain a criterion for transition from bubbly to stratified flow pattern in the header. A physical mechanism for this transition is proposed. A previous model developed at AECL to predict the collapsed water level distribution along the header with two-phase injection into a single turret is generalized to that for two-phase injection into two turrets. In these models, which are called MISSFINCH (for Models for njection and Steady Stratified Flow IN WDU Header), the water-level profile along the header is predicted using conseriation equations in one spatial dimension for the water phase only. Steam flow is assumed to affect the water flow only through the pressure difference between the headers. This pressure difference determines the feeder water flowrates which are assumed to be all equal. In agreement with the collapsed water level profile deduced from the LASH tests, MISSFINCH predicts that the water level is low near the injection axis and undergoes an extensive hydraulic jump e., level rise) downstream of the axis. (The phenomenon of hydraulic jump was also observed in air-water flow visualization tests conducted in a small scale transparent header/feeder facility at Sheridan Park Engineering Laboratories.) It is shown that, after the two-phase jet impact with the bottom of the header, the collapsed water level undergoes a hydraulic jump for all steam and water flowrates of interest and for all header geometries.