Characterization of multiphase flow through Venturi nozzle using gamma-ray tomography

Abstract

Venturi-based differential pressure flow meters have proven to be robust and well suited to measure the flowrate of multiphase flow in combination with other measurement techniques. However, important challenges remain in order to reduce the effect of flow regime dependent measurement uncertainties from non-homogeneous flow.Understanding the complexities of multiphase flow through a Venturi is critical, not only for the Venturi flow measurement but also for the potential implications it might have on adjacent measurements affected by the constriction-induced flow perturbations.In this study, we examine the evolution of multiphase flow through a vertically oriented Venturi situated downstream of a T-bend, with a particular emphasis on the effects this might have on associated measurements within a multiphase metering context. Using Gamma-ray tomography, we conducted measurements at the inlet, throat, outlet, and downstream of the Venturi across a wide range of flow rates and Gas Volume Fractions (GVFs). We evaluated gas fraction (GF), slip, and cross-sectional distribution, quantified using measures of asymmetry and annularity.Our findings suggest that deviations between GF and GVF, relative slip velocity, annularity, and asymmetry are generally less at the outlet and downstream of the Venturi compared to the inlet and throat. Notably, annularity exhibits a greater impact than asymmetry on the estimation of bulk fractions from cord measurements.Overall, the study suggests that there may be more favorable conditions for measurements that require a homogeneous mix and less difference between GF and GVF at the outlet or a short distance downstream of the Venturi. However, despite the inlet results showing larger deviations due to inhomogeneous flow compared to the outlet and downstream, these results demonstrate a more predictable pattern in line with predictive models, offering potential benefits for the application of corrective models.