Film behaviour of vertical gas-liquid flow in a large diameter pipe

Gas-liquid flow commonly occurs in oil and gas production and processing system. Large diameter vertical pipes can reduce pressure drops and so minimize operating costs. However, there is a need for research on two-phase flow in large diameter pipes to provide confidence to designers of equipments such as deep water risers. In this study a number of experimental campaigns were carried out to measure pressure drop, liquid film thickness and wall shear in 127mm vertical pipe. Total pressure drop were studied systematically through a data bank of 600 experimental runs. Magnitude and directional wall shear stress measurements have been made selectively using commercial non-directional probes and directional hot films. The latter were produced at Nottingham University during this study. Experimental data on liquid film characteristics were obtained by measuring total pressure drop, wall shear stress and film thickness simultaneously. In addition, the data were supported by some high speed video images through a visualization campaign. The pressure drop profile (time-averaged total pressure drop as a function of gas flow rate) introduced is visibly different from that for smaller pipes as it does not show a clear minima in the chum-annular transition region and not in both bubble-slug and slug-chum region. No completely unidirectional upward flow has been observed in the range of the conditions studied from the results of directional wall shear stress measurement which provided information on both time-varying and time-averaged wall shear stress. A condition of zero wall shear stress not reached. However, there was a minimum observed in the plot of mean wall shear stress against dimensionless gas velocity. This minimum occurred at the same dimensionless velocity for the present data at those from small diameter pipes. The change in the direction of the liquid film also supported by the measurements of local film thickness and high speed video images which have shown waves move both upward and downward and not purely in axial direction