TWO-PHASE FLOW PHENOMENA IN A HORIZONTAL PIPE WITH A SUDDEN CONTRACTION: EFFECTS OF CONTRACTION RATIO ON FILM BEHAVIOUR

Experimental studies were conducted on the behaviour of water films in a horizontal pipe with a sudden contraction to achieve a fundamental understanding of the film mechanisms of annular flow using high-speed video imaging analysis. The sudden contraction area ratios A C = (d 2 /d 1 ) 2 = 0.36 and 0.64, where d 1 is the inlet pipe diameter (50 mm) and d 2 is the contracted pipe diameter were examined. The experiments were carried out for various values of superficial gas and liquid velocities. The superficial gas velocity after mixing (j G1 ) ranged from 18.02 to 24.41 m/s (the calculated velocity from the cross-sectional at the sudden contraction was j G2 = 27.98–67.39 m/s) and the superficial liquid velocity (j L1 ) ranged from 8.62×10 -2 to 1.23×10 -1 m/s (j L2 = 1.35×10 -1 –3.42×10 -1 m/s). Four flow regimes were observed after the sudden contraction, namely, huge-wave (HW), two-dimensional disturbance wave (DW 1 ) which is formed perpendicularly to a pipe axis having a distinct coherence, three-dimensional disturbance wave (DW 2 ) which is formed obliquely to the pipe axis, and bow wave (DW 3 ) which is transitional wave to “Misty wave” from DW 2 . The disturbance wave occurrence frequencies were studied under various conditions of flow rate combination of air and water. DW 2 occurs over wide range of the superficial gas and liquid velocities. As the superficial gas velocity and the superficial liquid velocity increase, two-dimensional disturbance waves change into three-dimensional ones. The wave occurrence frequencies in the pipe with the sudden contraction ratio A C = 0.36 were mostly higher than those in the pipe with A C = 0.64.