Study of gas-liquid upward annular flow through a contraction

Abstract

Transient response of two-phase flow is important in many analyses of nuclear reactor accident scenarios. In the present work, we study the response of vertical annular flow to a sudden or gradual pipe contraction. The three component fields of gas-liquid annular flow, namely, the liquid film, the entrained liquid droplets and the gas core, show different behaviour as they pass through an area change section because of their very different inertias. Pressure variation through the contraction is a result of the integrated effect of these responses. In order to throw light on these, pressure profiles along the upstream and downstream sections of the contraction have been measured in air-water flow through a vertical converging pipe section for diameter ratios of 1.5 and 2.0 and for half-cone angles of 8°, 15° and 90°. The gas-droplet field interaction has been studied using computational fluid dynamics simulations while the gas-film flow interaction has been studied using an analytical model for film flow. These studies highlight the role of droplet inertia as the principal contributor to the pressure change in the contraction. A semi-empirical model has been developed for the pressure loss coefficient in the contraction.