POST-DRYOUT DISPERSED FLOW IN CIRCULAR BENDS

The effect of curvature on the post-dryout dispersed flow in 90-degree circular bends is investigated theoretically and experimentally. The theoretical study concentrates on two basic aspects of the flow, i.e. bulk vapor flow and droplet dynamics. The former is analyzed by solvin g the conservation equations of the vapor phase whereas the latter is studied by a Lagrangian droplet trajectory model considering both ther mal and turbulence effects. The experimental study deals with phase di stribution of the flow by measuring local liquid fraction with an impe dance probe. The results indicate that the curvature induced centrifug al force and the secondary flow significantly change the behavior of d roplet dynamics and phase distribution. Droplets in the vapor stream r eveal a general trend of centrifugal migration towards the outside of the bend and may even impinge directly on the wall. The effects of the secondary flow and turbulent dispersion are found to bring about a be tter circumferential transportation of liquid. Depending on the heat t ransfer condition, two different patterns of phase distribution are fo und. The first associated with film boiling is mainly dominated by pha se separation. The second connected with the rewetting phenomenon is g overned firstly by phase separation and then phase redistribution in t he form of liquid inward reversal.