Assessment of Coriolis meters as instrumentation for gas void fraction measurement in air–liquid multiphase flow in a pipeline riser system

Measurement of void fraction in gas-liquid flow systems is important in determining pumping requirements, designing downstream facilities and in detecting off-design problems such as cavitation and flashing during operation. Hence, it is key that this parameter is known in real time during oil & gas production and other process operation. As a result, the use of clamp-on flow meters which operate on the Coriolis principle are useful for such purposes as they instantaneously measure the flow’s density which can change depending on the gas fraction in the flowing mixture. In this study, we demonstrate the use of Coriolis mass flow meters in instantaneously measuring the void fraction in a multiphase mixture flowing in a 2-inch pipeline riser system at Cranfield University, UK. A Coriolis meter was installed on the vertical section of the facility. A set of experiments were conducted at fixed liquid superficial velocities of 0.25 and 1 m/s and air flow rates of 6-100 Sm3/h (corresponding to 0.39–3 m/s). The instantaneous densities of the mixtures were recorded at 100 Hz acquisition frequency. These were then used to estimate the gas void fraction at the vertical section using the homogenous model for the mixture density. Also, a well-calibrated 16 by 16 wire mesh sensor (WMS) fitted at the same vertical location to validate the gas void fraction measurements of the Coriolis flow meter. It was found that the Coriolis flow meter presented excellent agreement with the WMS for void fraction measurement at high gas flow rates. We observed that the agreement coincided with conditions that exhibit core-peaking void fraction distributions, i.e., at conditions that are not bubbly flow. Hence, it may be concluded that the Coriolis flow meter can be used with some confidence in industrial application at these condition