Effects of Pressure and Pipe Diameter on Gas-Liquid Two-Phase Flow Behavior in Pipelines

Abstract

Abstract The effects of pressure and pipe diameter on gas-liquid two-phase flow behaviors were investigated experimentally and theoretically for horizontal and slightly inclined pipelines. Experimental data of flow pattern, pressure drop and liquid holdup were acquired in the wide range of the gas and liquid flow rates in a large diameter (106.4 mm) pipe for different pressures (592 and 2060 kPa) and different inclination angles (0°, 1°, and 3°). To evaluate effects of the pipe diameter, our previous experimental data of low pressure (490 kPa) and small diameter (54.9 mm), were also used. Based on analysis of the experimental observations, a flow pattern map was developed for each pressure, pipe diameter, and inclination. Major phenomena identified in data analysis include: Pressure and pipe diameter clearly affect the flow pattern transition boundaries. The high pressure tends to shift the boundaries to the lower side of superficial gas velocity in the flow pattern maps. In the large-diameter-pipe experemints, stratified flow was observed at higher superficial liquid velocities than in small diameter. The gas flow rate and inclination angle showed influences on liquid holdup and pressure drop behavior. The average pressure did not show large influences on liquid holdup and pressure drop. Based on the experimental data, a mechanistic model was developed incorporating transition criteria for eight flow patterns, and individual flow models for estimating liquid holdup and pressure drop. The results predicted by the individual models demonstrated excellent agreements with the experimental data for each pressure and each inclination angle. Introduction Gas-liquid two-phase flow in pipes occurs in various major industrial fields including the petroleum, chemical, nuclear and geothermal industries. In the petroleum industry it occurs at production and transportation facilities for oil and gas, e.g. horizontal, inclined and vertical pipes of wellbores and flow lines. Accurate prediction of gas-liquid two-phase flow behaviors, such as flow pattern, pressure drop and liquid holdup, are crucial information for designing and operating multiphase flowlines and pipelines. The methods used to predict flow pattern, liquid holdup and pressure drop can be classified as empirical correlations and mechanistic models. Early predictive methods were based on empirical approaches developed to meet individual designing requirements. A new approach called mechanistic modeling emerged in the early 1980's. An important improvement in mechanistic models was the work for investigating the flow patterns and transition boundaries in steady-state gas-liquid two-phase flow done by Taitel and Dukler1, Taitel et al.2, Mishima and Ishii3, and Barnea et al.4–6 This opened the door for improved models for each of the flow patterns, including the possibility of linking the various models through unified flow pattern transition criteria. The first comprehensive mechanistic model was proposed by Xiao et al.7 They incorporated a flow pattern prediction model and separate models to calculate the flow variables, such as pressure drop and liquid holdup, for the individual flow patterns. More recently, comprehensive mechanistic models extending the Taitel and Barnea work have been presented for predicting flow pattern, pressure drop and liquid holdup by Ansari et al.8, Kaya et al.9, Gomez et al.10, and Petalas and Aziz11. Mechanistic models should be valid for all inclination angles, and evaluated with a large number of experimental data. However, some of the empirical correlations used in the models were derived on the basis of data acquired by small-scale facilities, and modeling efforts were concentrated on effects of the inclination angle on the flow pattern transition boundaries at low-pressure conditions, mostly less than 980 kPa, and small diameter pipelines as 2 inches. Little study of two-phase flow has been conducted in large-diameter pipes at pressure conditions higher than 1961 kPa (20 kgf/cm2). The objectives of this study were to experimentally and theoretically investigate the effects of pressure and pipe diameter on two-phase flow behaviors, and to develop a mechanistic model for predicting flow patterns, liquid holdups and pressure drops, and to valid the model for pressure and pipe diameter.