STRUCTURE OF BUBBLY FLOW THROUGH VENTURIS

The phase structure of vertical air-water mixture flows through venturis were investigated using area contraction ratios of 3.16 and 7.11 and with variations in angles of convergence and divergence. The flow conditions were predominantly of the bubbly type and covered a range of gas volume fraction at the throat between 0.2 and 0.6 for average mixture velocities of up 32 m/s. Resistivity probe signals indicating void fluctuations were analyzed to yield local void fraction, bubble velocity, bubble detection rate and probability density function of bubble sizes in the flow. Velocity ratios were also obtained to provide information on the overall behaviour of the two concurrent phases. The resistivity probe was shown to give reliable results for bubble flows in a wide range of speeds indicating velocity ratios up to 1.7 in the venturi throat. All flows tended toward a stable and well-mixed bubbly pattern downstream of the venturi exit following a sufficient length. The void and velocity profiles here always appeared to be characterized by a local maximum in the pipe centre, the local maximum close to the wall of some of the inlet flows being eliminated. Bubble coalescence was noted in the convergent passage whilst significant bubble fragmentation in the divergent passage was observed from the results. © 1979.