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

摘要

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 highspeed 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 8.62x10~(-2) to 1.23x10~(-1) m/s (j_(L2) = 1.35x10~(-1) -3.42x10~(-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.