Droplet Behavior Analyses in the BWR Dryer and Separator

Abstract

Droplet behavior in the BWR dryer and separator was analyzed. The computer program HIJET-AFIMA was used to simulate the liquid droplet behavior in a dryer with four stage wave-type vanes. This program can describe movement of liquid droplets, as influenced by gas flow, and their deposition on the vane surface, considering drag force which is exerted on droplets. Close agreement between calculations and air-water tests was obtained for the wetness fraction at the exit of each vane stage. The calculated results under reactor conditions showed that larger droplets (30–600 μm in diameter) were concentrated in the first and second stages due to their larger inertia force. Smaller droplets (less than 30 μm in diameter) were able to pass through the flow channel without deposition on the vane surface. This was because the effect of the drag force was exerted more strongly on smaller droplets. As a result, wetness fraction at the exit was small and less than 0.1% when inlet wetness was 10%.The droplet behavior analyses in a separator showed that the deposition coefficient with swirl was much higher than that without swirl. Since the ratio of inertia force to drag one was almost the same everywhere in the separator, the difference in inlet quality had only a small effect on droplet deposition.