In this work, an X-ray system consisting of six cameras was used to obtain instantaneous cross-sectional phase distribution of gas-liquid flow in annuli. The horizontal annulus test section, made of PVC, consisted of an outer pipe of 99 mm inside diameter and an inner pipe of 50 mm outside diameter using two different configurations, namely, concentric and fully eccentric (with the inner pipe at the bottom of the outer pipe). The test fluids used in this investigation were water and a low viscosity oil (Exxsol D60) as the liquid phases and sulphur hexafluoride (SF6) as the gas phase. Results reveal that flows in the presence of a fully eccentric annulus have a more consistent behaviour in terms of phase distribution. Three-dimensional flow structures were reconstructed based on the instantaneous cross-sectional phase distribution. This offers insight into the Taylor bubble nose and tail shape as well as the evolution of the liquid film.


The flow of gas and liquid in annulus pipes is commonly encountered in several industrial applications, e.g. horizontal wells, oil well drilling, and heat exchangers. Yet, it has not been as thoroughly studied as multiphase flows in conventional pipelines. An annulus pipe configuration is defined as two coaxial pipes where the inner pipe can be located at any position relative to the outer pipe, i.e. from concentric (both pipe centre-lines matching) to fully eccentric where the inner pipe is in contact with the outer pipe. The fluids flow between the inside wall of the outer pipe and the outside wall of the inner pipe. They can adopt different configurations (flow regimes) which depend on the flow velocity, the physical properties of the fluids, and the characteristics of the pipe system. In general, three main flow regimes are observed: separated, intermittent, and dispersed flow.

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