Experimental results of the countercurrent flow limit of steam and water in an upright 90° elbow are presented. Subcooled water (ΔT_sub<6°C) was introduced into the vertical leg and saturated steam into the horizontal leg of the elbow at atmospheric pressure.
Flooding inception was identified with the formation of a water-slug in the horizontal section. At low water flow rates, a hydraulic jump was observed in the horizontal section and slugging started from the crest of the jump. At higher water flow rates no hydraulic jump was seen and slugging started from the end of the horizontal pipe.
Three flow regimes were observed: (1) a regime characterized by a countercurrent flow of steam and water; (2) a regime characterized by a partial or complete carryover of injected water from the vertical leg of the elbow; and (3) a regime characterized by an unsteady water column in the vertical leg on top of a countercurrent steam-water region with no water carryover.
The present observations and results are compared with those of previous work.