| Summary: | The work described in this thesis was aimed at obtaining and interpreting a data set for fully developed upwards air-water annular flows. The experiments were carried out in a vertical 32 mm diameter tube which was about 600 diameters long. The experiments were conducted at three fixed outlet pressures of 2.4,3.6 and 3.8 bars, respectively. The ranges of dimensionless gas and liquid flowrates covered were: 0< V/G < 10; 0< V/G <10; 0<V/L < 1.8. These flowrates considerably extended the range of previous air water measurements, which were generally confined to V/G < 2.5 and V/L < 0.3, and have allowed the Roberts and Hewitt (1969) flow pattern map to be considerably modified. Pressure gradient measurements were made using a purged D. P. cell system while film flowrate measurements were made by extracting the film through a porous wall. Wall shear stress measurements using hot film probes were also made and a method of calibrating the probes using a two-phase annular flow was proposed. The film flowrate results (Figures 3.1 to 3.14) indicate that there is a limiting film flowrate below which no significant entrainment occurs. The most interesting of the experimental results obtained, however, was the existence of a maximum in the plot of pressure gradient versus gas flowrate. This maximum occurred at high liquid and gas flows and was distinct from previously reported maxima and minima associated with the slug-churn-annular flow transitions, as shown in Figure 4.6. It was found that the newly discovered maximum was identical to the pressure gradient phenomenon in steam-water flows called the hydraulic resistance crisis. The obtained film flowrate and pressure gradient data were compared with a number of empirical correlations. None of the tested correlations could predict the data to any extent. Relative deviations between the predicted results and the experimental data were as great as 1900% for film flowrate and 200% for pressure gradient. A proposed entrainment correlation predicts well air-water data obtained in tubes ranging in diameter from 6 mm to 125 mm. A new annular flow model is also proposed which attempts to account for the effect of droplet turbulence suppression as well as the effect of waves on the interfacial roughness.
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