| Abstract: | This paper details experiments and analyses regarding the phenomenon of liquid discharge into a gaseous atmosphere from the bottom of a vessel with an unvented, upper gas space. The primary goal is the development of a simple model that predicts the rate of liquid discharge under the prevailing unvented condition. A literature survey of previous work on this phenomenon yielded only simple experiments and analyses that were limited in scope. Experiments were subsequently undertaken with an air-water system, using a larger volume and a wide range of drain line diameters. In addition to flowrate data, visual information was acquired regarding the physical mechanism possibly governing the prevalent flow regimes. The governing physical mechanism is identified as the stability of a gas-liquid interface, perturbed by buoyancy, at the drain line entrance. G.I. Taylor's fundamental analysis of interfacial stability lead to the determination of criteria for flow regime transition among the three prevalent flow regimes, corresponding to so-called small, medium, and large diameters. Also, analysis of the growth of interfacial instabilities lead to the application of flooding models for drainage rates within each regime. The models for moderate and large diameters were then compared against data, which confirmed their success in predicting discharge rates under the unvented condition.The motivation for this effort, besides the basic scientific significance of studying such a fundamental phenomenon, was its numerous applications, one of which is commercial nuclear reactor systems. Specifically, the phenomenon prevails in liquid coolant discharge from a PWR pressurizer, with an unvented steam volume, into a steam atmosphere existing in the adjoining hot coolant leg. Such a phenomenon could occur as part of a transient, or severe accident, scenario, entailing saturated conditions and steam production in the normally subcooled primary heat transport loop. The developed model was implemented in the Modular Accident Analysis Program (MAAP), a computer code designed to predict reactor system behavior in response to postulated off-normal conditions, including severe accident scenarios. |
