Separate-effect experiments and modeling for two-phase flow under geometric restrictions

Abstract

While significant efforts have been made to investigate two-phase flows in vertical upward channels, limited work has been performed to study the effects stemming from geometric configurations on two-phase flow transport, such as flow restrictions and change in flow orientation. This presents significant shortcomings in the application of predictive models to practical systems, including nuclear power reactors. It has been well observed that geometric restrictions (e.g., elbows, spacer-grid, and inlet configurations) and change in flow orientation (e.g., upward-to-horizontal, horizontal-to-downward) can cause significant effects on the hydrodynamics of two-phase flow. In view of these, high-resolution separate-effect experiments have been performed to establish a two-phase flow database that is accurate, extensive and good enough for multi-phase CFD codes development, to develop predictive models accounting for geometric effects, and to improve the performance of nuclear reactor system analysis codes. Recent studies on the effects of the vertical-upward and vertical-downward 90-degree elbows, spacer grid, inlet configurations, and change in flow orientation are summarized. Some of the major two-phase flow phenomena investigated in the present study include flow regime transition, pressure loss, two-phase flow parameters, flow development, and interfacial drag. To demonstrate the functionality of the newly developed models, the one-dimensional steady-state one-group interfacial area transport equation is employed to predict two-phase flow transport under geometric effects.