An experimental study is conducted by use of a 6-in.-inner-diameter (ID) facility to investigate characteristics of three-phase stratified wavy flow in horizontal pipelines. The experiments are conducted under low-liquid-loading condition, which is very commonly observed in wet-gas pipelines. The analyzed flow characteristics include wave pattern, liquid holdup, water holdup, pressure gradient, and wetted-wall fraction.
The experimental range covers superficial-gas-velocity (vSg) values of 8 to 23 m/s, superficial-liquid-velocity (vSL) values of 1 to 2 cm/s, and inlet-liquid-stream water-cut values of 0 to 100%. Differential-pressure transmitters, a quick-closing valve and pigging system, and a high-speed camera are used to acquire the data. The trends of the data with respect to input parameters are investigated. The performances of commonly used models are compared with liquid-holdup, pressure-gradient, and water-holdup experimental results.
The observed wave patterns include stratified smooth and stratified wavy with 2D waves, 3D waves, roll waves, and atomization flow. The transitions between the flow patterns vary as a function of water cut. The trends of pressure gradient, liquid holdup, and water holdup with respect to vSg, vSL, and water cut are observed, and interpretations on the basis of physics are provided. The predictions of a transient multiphase-simulation software; the Tulsa University Fluid Flow Projects (TUFFP) unified model (Zhang et al. 2003), version 2012; Beggs and Brill (1973); Taitel and Dukler (1976); and Xiao et al. (1990) are compared with the acquired experimental data. The results from the transient multiphase-simulation software, Taitel and Dukler (1976), and Xiao et al. (1990) are in good agreement with experimental liquid-holdup and pressure-gradient data, but the three-phase water-holdup trends are not predicted well. The complicated nature of liquid/liquid interactions in three-phase low-liquid-loading flow causes greater uncertainties in predictions.
The number of experimental three-phase data, especially with larger pipe diameters, is very limited. This paper provides comprehensive data for three-phase stratified flow for a 6-in.-ID pipe. In addition, the prediction performance of the commonly used predictive tools in the industry is provided.
Low-liquid-loading flow is a flow condition wherein the liquid-flow rate is very small compared with the gas-flow rate. It is widely encountered in wet-gas and gas/condensate pipelines. Even though the pipeline is fed with single-phase gas, the condensation of the heavier components of the gas phase, along with traces of water, results in three-phase flow. The presence of these liquids in the pipeline, although in very small amounts, can significantly influence flow characteristics such as pressure gradient and liquid holdup. Therefore, understanding of the flow characteristics of low-liquid-loading gas/oil/water flow is of great importance in transportation of wet gases.