Experimental study of liquid-carrying by swirling flow in a U-shaped tube

In natural gas pipelines, temperature and pressure vary along the line, leading to liquid condensation in undulating sections of the pipelines. This phenomenon has a significant impact on the gas transportation efficiency and safety. In this study, an experimental investigation on liquid-carrying by a swirling flow in an undulating pipeline was carried out. As the condensate liquid would usually accumulate in the pipeline, a U-shaped tube with a diameter of 0.025 m was used to simulate a low-lying part. The effect of swirl on flow patterns in the Ushaped tube was observed using a high-speed camera and processed with image processing technology. Five flow patterns, namely stratified, stratified wave, slug, plug and annular flow, were observed in the U-shaped tube under gas superficial velocities ranging from 0.17 to 14.15 m/s, and with the height of liquid accumulation ranging from 15 to 125 mm. Compared to a non-swirling flow, the swirling flow was observed to increase the liquid-carrying capacity; which however, was a function of the flow pattern. The liquid-carrying capacity of the swirling flow for different flow patterns in the order of highest to lowest was: annular, slug, plug, stratified wave and stratified flow. The initial liquid volume and inlet gas velocity also influenced the liquid-carrying efficiency of the swirling flow. With an increasing gas flow rate, the fluctuation of gas-liquid interface increased, and the liquid-carrying efficiency also increased. Furthermore, Swirling flow reduced the critical gas velocity needed to carry the liquid phase by 14.14% compared to a non-swirling flow.