In slug flow modelling, the shear stress between the slug body and the pipe wall is one of the critical parameters to define the frictional pressure drop. Experiments were carried out in a 50.8-mm ID horizontal flow loop to identify the trend of the wall shear stress within the slug body for liquid viscosities of 0.51 Pa·s and 0.96 Pa·s. A new setup allowed accurate assignment of the signals from the Constant Temperature Anemometry (CTA) to the corresponding positions in the slug body. Experimental evidence shows that arrival of the slug fronts do not indicate an immediate increase in the wall shear stress at the bottom of the pipe.


Slug flow is a commonly encountered gas/liquid two-phase flow pattern in pipelines. In slug flow modelling, the shear stress between the slug body and the pipe wall is one of the important parameters for the estimation of frictional pressure drop. In many of previous modelling studies such as Dukler and Hubbard (1), constant wall shear stress values are predicted, and applied to develop and validate models. A more adequate wall shear stress measurement is required to investigate the possible effect of wall shear stress changes within the slug body. Additionally, the observation contributes to the analysis of eddy length in the mixing region, Nicholson et al. (2).

In production system design, it is crucial to predict the slug characteristics correctly based on fluid properties and operational conditions. In predicting flow features, viscosity appears as an intrinsic variable in almost all slug flow models. These models are developed for low viscosity fluids. However, two-phase slug flow can exhibit significantly different behaviour for higher viscosity oils as reported by Gokcal et al (3), (4), Kora et al. (5), Brito et al. (6) and Kim (7).

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