Sammendrag
Slug liquid holdup and frequency for gas-liquid flows in horizontal and upward low-inclination annuli are investigated. The annulus consists of an outer pipe of 99 mm inside diameter and an inner pipe of 50 mm outside diameter. Two annulus configurations are studied, namely, concentric and fully eccentric with the inner pipe at the bottom of the outer pipe. The test fluids are water and Exxsol D60 as the liquid phases and sulphur hexafluoride (SF6) as the gas phase. The slug characteristics are obtained from time-traces of the cross-sectional average liquid holdup from broad-beam gamma densitometers. Results show that the eccentricity of the annulus has limited effect on the slug liquid holdup and slug frequency. For a given superficial liquid velocity, the slug frequency has a parabolic profile as function of the mixture velocity with a minimum value at UM ≈ 3 m/s. Once UM is greater than 3 m/s, the slug frequency sharply increases. Experimental results are compared with predictions calculated using existing correlations and models developed for full pipe systems in the literature. These models fail to capture the slug characteristics in annulus configurations. One of the existing models for predictions of slug liquid holdup has been modified in this paper to account for the effect of the annulus geometry. In addition, the paper documents a new correlation development for slug frequency using the Taylor bubble (or translational velocity) and the slug liquid holdup in an annulus geometry. The proposed models, for both slug liquid holdup and frequency, perform better than the existing models in literature when tested against experimentally obtained annulus flow data.
Vis fullstendig beskrivelse
