A study on gas-liquid two-phase flow metering: Identification of flow dynamics that influence the performance of CMFs

Abstract

Metering on gas-liquid two-phase flow is challenging even though the Coriolis Mass Flowmeters (CMFs) outperform most of other flow measurement technologies owing to their ability to directly measure the fluid mass flowrates. This is due to complexity of the dynamics of the gas-liquid two-phase flow. Thus, Coriolis Mass Flowmeters have been undergoing modifications to improve their accuracy on measuring complex flows but still the variation of error due to bubble entrainment and the mechanisms responsible of these errors remain less understood. Hence there is a strong need to conduct further characterization on the performance of CMFs on measurement on gas-liquid two-phase flow.This study aims to analyse the performance of a U-shape CMF on metering gas-liquid two-phase flow via both CFD simulation and experimental measurements. For simulation, a two-way coupling of Fluid-Structure Interaction was used to minimize the inaccuracy in simulation results. It has the ability to count on influences of fluid forces on the tube deformation and the reaction of the oscillating-fluid conveying tube to the overall dynamics of the system.The results show that at low nominal flowrates (NFRs), the flow/phases separation occurs and dominates the previously identified factors of errors such as bubble theory effect/friction damping effect and cause positive errors. The error associated with bubble theory effect or friction damping is negative i.e. the CMFs under-estimate the mass flowrates of the mixture. Our study, however, found negative errors only at high nominal mass flowrates. In addition, it is to be noted also that even though the theoretically predicted error due to mixture compressibility in some literatures could be positive, it is important to carry out further experimental and computational studies for analysis. In this study, it is observed that the oscillations of separated fluid phases amplify the amplitude of tube oscillation and hence leading to distortion of the displacements of the CMF tube. This could lead to up to 14.9% of positive error in CMFs’ measurements at the low nominal mass flowrates.It is believed that these results can serve as baselines for future studies on corrections and compensations of CMFs’ errors on measurement on gas entraining fluid flow encountered in fuel bunkering and LNG metering processes.