Two-Phase Flow Phenomena in a Horizontal Pipe With a Sudden Contraction: Effects of Contraction Ratio on Film Behaviour

Abstract

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 AC = (d2 /d1) 2 = 0.36 and 0.64, where d1 is the inlet pipe diameter (50 mm) and d2 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 (jG1) ranged from 18.02 to 24.41 m/s (the calculated velocity from the crosssectional at the sudden contraction was jG2 = 27.98-67.39 m/s) and the superficial liquid velocity (jL1) ranged from 8.62×10 -2 to 1.23×10 -1 m/s (jL2 = 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 (DW1) which is formed perpendicularly to a pipe axis having a distinct coherence, three-dimensional disturbance wave (DW2) which is formed obliquely to the pipe axis, and bow wave (DW3) which is transitional wave to "Misty wave" from DW2. The disturbance wave occurrence frequencies were studied under various conditions of flow rate combination of air and water. DW2 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 AC = 0.36 were mostly higher than those in the pipe with AC = 0.64.