Characterization of slug initiation for horizontal air-water two-phase flow

Two-phase gas-liquid slug flow is the prevailing flow regime in many processes in the petroleum and chemical industries. This flow regime is the result of the growth of wavelike instabilities at the gas liquid interface. The main characteristic of slug flow is the presence of liquid slugs that span the entire pipe diameter separated by gas bubbles. The rear end of these gas pockets can exhibit a staircase shape (also known as plug flow) or a hydraulic jump that reaches the top of the pipe when the flow rate is increased. In this paper, an experimental investigation of the statistical properties of slug flow is presented for flow initiation. A gas-liquid circuit made of acrylic tubes with a 26 mm ID was used to make these measurements. The test facility was composed of two sections: the first corresponded to a downward flow of 3 degree inclination where the prevalent flow regime was stratified flow, and the second was a horizontal section where the prevalent flow regime was slug flow. Resistive sensors located at three different positions in the horizontal section were used to acquire the liquid holdup, and the time series were processed and analyzed. Statistics for slug initiation position, slug and bubble lengths, bubble velocity, slug and unit-cell frequencies are presented. Further, the length and probability of occurrence of the bubble tail were also analyzed in the cases where the bubbles exhibited a staircase shape. Ultimately, data are provided for the validation and development of mathematical models and numerical codes for the simulation of two-phase slug flow. (C) 2017 Elsevier Inc. All rights reserved.