Two-phase flow structure of an air-water, bubbly, upward, cocurrent flow in a large diameter pipe, 20cm, was investigated experimentally. Local flow parameters such as void fraction, bubble velocity, bubble diameter and inter facial area concentration were measured using a dual fiber optic probe.
A well calibrated air-water testing loop was used to conduct the present experimental work. A computerized data acquisition system was used to analyze the probe output signals and so measuring the different flow parameters.
The local time-averaged bubble diameter was measured using a direct averaging method and Uga's statistical method. The interfacial area concentration was measured using two methods; the bubble diameter-based method and the direct method proposed by Kataoka et al. (1985).
Results of the present tests were compared with available data obtained for flow in small diameter pipes under the same flow conditions. Also, selected existing correlations based on data from small diameter pipe flows were applied to the present data to check their applicability to flows in large diameter pipes.
The results indicated the following under the same flow conditions, the local void fractions were in good agreement with those of Stankovic (1992) obtained using the same experimental setup. The bubble diameter results obtained using the direct average method and Uga's statistical method were in good agreement. The present work showed that the bubble diameter was generally insensitive to changing the flow rate. Unlike the small diameter pipes results, the present work showed an increase in bubble diameter near the wall.
Local Interfacial Area Concentration (IAC) results obtained using the two measuring methods were in good agreement. The IAC values measured in the present work were higher than those obtained in small diameter pipes under the same flow conditions. Also, the existing IAC correlations underestimated the area-averaged values significantly, particularly at low air flow rates.