Flow rate measurements of slug flow by pressure differences of a venturi tube with a swirler

Abstract

When the elongated bubbles and liquid slugs of slug flow alternately flow through a throttling element, the strong random fluctuations of pressure difference leads to low accuracy of online measurement of gas-liquid flow rates. In this paper, slug flow is converted into an annular flow before entering a venturi tube using a swirler, and the pressure fluctuation amplitude of the gas-liquid two-phase flow is greatly reduced, and the linear correlation between the pressure difference and the gas-liquid flow rates is more significant. The effects of gas-liquid flow rates on the axial pressure difference ΔPs across the swirler, the radial pressure difference ΔPr on a cross-section downstream of the swirler and the axial pressure difference ΔPo of the venturi tube were studied under the condition of 40%–82% gas volume fraction. The square root of the pressure difference increases linearly with the liquid/gas flow rate, and the empirical correlations between the square root of the pressure differences and the gas-liquid flow rates are established. By combining the empirical correlations in pairs, three flow rates measurement models of slug flow based on double pressure differences are established. When ΔPo and ΔPs are used as the measurement parameters of flow rates, the relative errors of liquid-phase flow rate and gas-phase flow rate are below ±2% and ±15%, respectively. When ΔPo and ΔPr are used as the measurement parameters of flow rates, the relative errors of liquid-phase flow rate and gas-phase flow rate are below ±3% and ±15%, respectively. It provides high-precision, low-cost and non-radioactive two-phase flow measurement technology for oil-gas gathering and transportation.